ISSN : 2250-0081 (Print) ISSN : 2250-009X (Online)

INDIA Wish you a Very Happy & Prosperous New Year 2020 Journal Vol. 10, No. 1 - January 2021 (Half Yearly Journal)

Happy New Year 2020

Senior dignitaries during Inauguration of International Colloquium on 21 November 2019 at New Delhi Mr. S.K.G. Rahate, Addl. Secretary, Govt. of India, Ministry of Power (in the middle) (to his right) Mr. I.S. Jha, Hon’ble Member, CERC & President CIGRE-India; Mr. Prakash S. Mhaske, Chairperson, Central Electricity Authority & Ex Officio Secretary to Govt. of India and Mr. K. Sreekant, Chairman & Managing Director, POWERGRID. (to his left) Mr. V.K. Kanjlia, Secretary, CIGRE-India; Dr. Konstantin, Honorary Member, CIGRE Paris and Former Chairperson of CIGRE Study Committee on Overhead Lines and Mr. P.P. Wahi, Director, CIGRE-India

Join CIGRE The World Forum for Electric Power System India Governing Body of CIGRE-India A. Governing Council (2020 - 22) President CIGRE-India Vice Presidents, CIGRE-India

I.S. Jha Seema Gupta U.K. Bhattacharya Renuka Gera Praveer Sinha Manish Agrawal Anil Saboo Member, CERC Director, Powergrid Director, NTPC Director, BHEL MD, Tata Power CEO, Sterlite Power President, IEEMA Transmission

Chairman Tech. Jt. Chairman Tech. Member Secretary Director CIGRE-India CIGRE-India CIGRE-India CIGRE-India

R.P. Sasmal N.N. Misra Sunil Misra A.K. Dinkar A.K. Bhatnagar Former Dir. Powergrid Former Dir. NTPC Director General, IEEMA Secretary, CBIP Director, CBIP

B. Technical Council of CIGRE - India (2020 - 22)

Seema Gupta K.V.S. Baba Subir Sen Anil Kumar Arora B.B. Chauhan R.K. Tyagi Director, Powergrid CMD, POSOCO ED, Powergrid ED, Powergrid Former MD, GETCO ED, Powergrid Chairperson CIGRE Chairman CIGRE Chairman CIGRE Chairman CIGRE Chairman CIGRE Chairman CIGRE NSC A2 NSC C2 NSC C1 NSC B4 NSC C4 NSC A3

B.N. De Bhomick Anish Anand Debasis De, S.C. Saxena Dr. B.P. Muni S.S. Misra Former ED, Powergrid ED, Powergrid ED, NLDC, POSOCO SGM, POSOCO GM, BHEL GM, NTPC Chairman CIGRE Chairman CIGRE Chairman CIGRE Chairman CIGRE Chairman CIGRE Chairman CIGRE NSC C3 NSC B2 NSC D2 NSC C5 NSC D1 NSC C6

Subhas Thakur D.K. Chaturvedi Y. B. K. Reddy Nihar Raj Lalit Sharma Santanu Sen AGM, NTPC Former GM, NTPC AGM, SECI VP, Adani Ltd. COO, KEI DGM, CESC Ltd. Chairman CIGRE Chairman CIGRE Co-Chairman CIGRE Chairman CIGRE Chairman CIGRE Co-Chairman CIGRE NSC B5 NSC A1 NSC C6 NSC B3 NSC B1 NSC C1 CIGRE India Journal Volume 10, No. 1 January 2021 CONTENTS Page No Editor’s Note 2 Articles • Open Line Test Application in Uhvdc for Condition Monitoring of Insulation Health of Ultra High Voltage Equipments – Tuhin Suvra Das and Vinita Kumari 3 • Significance of Quality & Quantity of Gravel for Safe Designing of Grounding (Earthing) System of Substations – Dr. Rajesh Kumar Arora 11 • Condition Monitoring of GIS Surge Arresters – M. Mohana Rao, Archana L and Mritunjay Kumar 18 • Project GPTL – Sandip Maity and Abshan Farooq 24 • Utility Roadmap for System strength aspects for Reliability, Stability and Flexibility of RE Rich Modern Power Grid– Indian grid context – B.P. Soni and N.M. Sheth 28

Activity of the Society 45 Series of International Tutorial (Virtual) Organize by CIGRE-India in the Recent Past 56 CIGRE Members from India in 2021 62 Technical Data 74 News 76

Editorial Advisory Board • Dr. Konstantin O. Papailiou, CEO, PFISTERER Holding • I.S. Jha, President, CIGRE-India & Hon’ble Member, AG and Chairman of CIGRE SC B2 on Overhead Lines CERC • Ivan De Mesmaeker, Swedan, Former Chairman CIGRE SC B5 on Protection & Automation • R.P. Sasmal, Former Director, POWERGRID & Chairman Tech, CIGRE-India Editor • N.N. Misra, Former Director (Opn.), NTPC & Vice-Chairman • A.K. Dinkar, Secretary, CIGRE India & Secretary, CBIP (Tech.) CIGRE-India Associate Editor • A.K. Gupta, Director, NTPC, & Vice President, CIGRE- • Vishan Dutt, Chief Manager, CIGRE India & CBIP India All communications to be addressed to: • Prof. S.C. Srivastava, Deptt. of Elect. Engg. IIT, Kanpur The Secretary & Treasurer • Philippe Adam, Secretary General, CIGRE HQ, Paris CIGRE India • Amitabh Mathur, Former Director, BHEL CBIP Building, Malcha Marg Chanakyapuri, New Delhi - 110021 • Dr. Mohinder S. Sachdev, University of Saskatchewan, Canada

Disclaimer : The statements and opinions expressed in this journal are that of the individual authors only and not necessarily those of CIGRE-India.

Subscription Information 2021/ (2 issues) Institutional subscription (Print & Online) : Rs. 900/US$75 Institutional subscription (Online only) : Rs. 600/US$50 Institutional subscription (Print only) : Rs. 600/US$50 Subscription for 10 Years (Print Only) : Rs. 5,000 Subscription for 10 Years (Online) : Rs. 5,000 Subscription for 10 Years (Print & Online) : Rs. 8,000 Editor’s NOTE CIGRE the International Council on Large Electric Systems founded in 1921, is leading worldwide Organization on Electric Power Systems, covering technical, economic, environmental, organisational and regulatory aspects. It deals with all the main themes of electricity. CIGRE is the unique worldwide organization of its kind - 14,000 equivalent members in around 90 countries. CIGRE is focused on practical technical applications. The main aim of CIGRE is to facilitate and develop the exchange of engineering knowledge and information, between engineering personnel and technical specialists in all countries as regards generation and high voltage transmission of electricity. CIGRE achieves its objective through the 16 Study Committees, each consisting of about 30 members from different countries. India is representing in all the 16 Study Committee of CIGRE. Besides National Committees in about 60 Countries CIGRE has also constituted its regional chapters in the world. The chapter created for Asia is named as CIGRE-AORC (Asia Oceans Regional Council). CIGRE-AORC is a forum for sharing experience and knowledge regarding pertinent technical issues particularly those affecting power systems in the Asia-Oceana Region. The countries from Asia Oceana Region, who are associated with the forum are Australia, China, Cambodia, Gulf Cooperative Council, Hong Kong, India, Indonesia, Iran, Jordan, Japan, Korea, Malaysia, New Zealand, Taiwan and Thailand. It is a matter of great honour for India that CIGRE AORC has been chaired by India during 2016-2018. Dr. Subir Sen, ED, POWERGRID was Chairman and Shri P.P. Wahi, Secretary of CIGRE AORC for two year during 2016-18. It is a matter of pride that CIGRE (India) has been in the administrative Council of CIGRE since 1970 and got seat in Steering Committee in 2018. CIGRE India functions as the National Committee, for CIGRE HQ (Paris). The CIGRE (India) coordinates interest of Indian members; organises National Study Committee (NSC) meetings. It recommends appropriate persons for CIGRE Study Committees. The National representatives are instrumental in providing feed back to CIGRE Study Committees at Paris. The aims and objectives for which the committee, i.e., CIGRE (India), is constituted, is to implement and promote objectives of the International Council on Large Electric Systems (CIGRE) and accelerate its activities, which include the interchange of technical knowledge and information between all countries in the general fields of electricity generation transmission at high voltage and distribution etc. All-out efforts are being made to increase the CIGRE membership and activities in India. CIGRE India has regularly been making efforts to invite various CIGRE study committees and their working groups to hold their meeting in India. We in the recent past have already hosted SC D2 on Information and telecommunication in 2013; SC B4 on HVDC - in 2015 and SC B1 on HV Insulated cables in 2017 in India. In the Year 2019 we have hosted four Study Committees SC A1 on Rotating Electrical Machines in Sept. 2019 & SC A2; SC B2 & SC D1 on Transformers, Overhead Lines and Materials & test techniques respectively in Nov. 2019. This is done with the aim to provide opportunities to professional to exchange & share views / knowledge with international experts. We have already got approval from CIGRE to host Study Committee SC A3 on high voltage equipment’s and B5 on Power System Protection in 2021 and 2023 respectively. There was excellent participation from India in CIGRE session 2018 at Paris. Total 22 papers were presented and more than 150 officers from India including CEOs & Sr. Officers from various PSUs, State Electricity Corporation and various Regulatory Commissions participated in CIGRE session 2018 besides six exhibitors. For CIGRE Session 2020, CIGRE India received 240 Abstract for consideration. Out of the 45 Abstracts were recommended to CIGRE HQ for their consideration, 37 abstracts were accepted. The Covid 2019 affected organisation of CIGRE session 2020, virtual session was organised by CIGRE, where these were 107 participants from India. In this present COVID-19 situation where skill enhancement and training of professional is emerged as an important aspect and a challenge, CIGRE- India held series of virtual Tutorials/ Workshops/ Webinars on the subject relevant to 16 CIGRE Study Committees, to further promote CIGRE in India and involve additional professional including New Generation / Young professionals with CIGRE. The reports of the virtual tutorials is included in this issue of journal. The Membership of CIGRE from India is also on the rise and in the year 2018 we achieved membership count to 827 Nos. and the same was maintained for 2019. For 2020 total 800 members were registered as CIGRE Member from India. We are bringing out this Journal on half yearly basis. The last issue was published in the month of July 2020. This issue covers the informative and useful technical articles and statistical data on the subject. I am thankful to the Governing Council and the Technical Committee of CIGRE-India for their valuable time and guidance, but for which, it would not have been possible to achieve the above significant progress, appreciated by CIGRE HQ Paris. I am also thankful to all the senior experts from India and abroad and also to one and all who have supported in the past to realize the goal set forth for CIGRE India and expect the similar support in future too.

A.K. Dinkar Secretary & Treasurer CIGRE India

Volume 10 v No. 1 v January 2021 2 Open Line Test Application in Uhvdc for Condition Monitoring of Insulation Health of Ultra High Voltage Equipments

Tuhin Suvra Das Vinita Kumari Powergrid Corporation of India Ltd. ABSTRACT Open Line Test is used in Ultra High Voltage DC Transmissionsystem to test the voltage insulation capability of a line or a converter after an extended period of de-energization or after recovering from insulation faults. It is done in order to avoid converter startup towards a solid ground fault. OLT can be done on the internal dc pole bus in each station/converter or in the dc line. To perform OLT, converteris deblockedin open circuit condition and the dc voltage is increased to the desired reference level at a predefined ramp rate. DC voltage reference level and the voltage ramp rate are operator selectable. For any kind of persisting insulation fault, the converter fails to build up the dc voltage across the pole to neutral. To understand the behavior of HVDC system during OLT, modeling and simulation for following converter configurations have been done (a) Converter is connected to DC bus without DC filter and without DC line. (b) Converter is connected to DC line with DC filter. The simulation results thus obtained have been compared with the actual OLT operation results.This paper analyses the application of the results of the Open Line Test as an effective tool for condition monitoring of the insulation health of HVDC equipments. Keywords: Open Line Test, HVDC, Insulation Health monitoring of UHVDC equipments

1. Introduction There is very few information available in literatureregarding Open Line Test is used in Ultra High Voltage DC Open Line Test. As mathematical expression for DC Transmission system to test the voltage insulation voltage across the opened dc line in Open Line Test is capability of a line or a converter after an extended period complex and is not only the function of thyristor firing of de-energization or after recovering frominsulation angle (alpha) but also of the equivalent circuit parameters faults. To perform OLT, converter is deblocked in open i.e., equivalent resistance, inductance and capacitance. circuit condition and the dc voltage is increased to With the variation of line capacitance and inductancethe the desired reference level at a predefined ramp rate. peak to peak DC voltage ripple also varies.The dielectric The phenomenon can be described as the charging of loss accounts for the power losses in Open Line Test the capacitance of the various dc voltage equipments mode. The loss varies with the line length, weather, through the reactance and resistance of the line. The pollution and other factors. charging capacitances are the snubber circuit, valve HVDC converter characteristics in Open Line Test mode support insulators, pole bushing,arrester insulators, bus is different from that of normal power flow operation post insulators, pole smoothing reactor post insulator, mode.For power flow operation mode,the dc current must dc voltage divider and line insulators. The charging be in continuous conduction mode and the DC voltage currents of the capacitances are limited by the pole across the pole to neutral can be inverted by varying smoothing reactor, valve reactors, transformer leakage the thyristor firing angle.The thyristor firing angle control reactance and dc line reactance. The low value of series between 0 to 90 degree and 90 to 180 degree operates resistance provides damping of LC oscillations. The the converter as rectifier and inverter respectively. This high value of parallel resistance across each non ideal inversion of dc voltage is valid for continuous current capacitancesincurspower losses. conduction mode. But in case of Open Line Test the dc

3 Volume 10 v No. 1 v January 2021 Equivalent circuit model has been taken tion 1(converter is connected to DC line from the configuration of ±800kV NEA- with DC filter).The equivalent circuit para- Agra multi-terminal HVDC system. meters can be modelledas :

In the configuration shown above OLT is being performed at rectifier converterof Sta-

= (1)

푑푐푦푎푟푑 푙푖푛푒 푓푎푢푙푡 푅푒푞 푅푒푞 (very‖푅 low푒푞 value‖푅 in case of fault) (2)

푓푎푢푙푡 푅푒푞 ≈ 푅= 4 ( 60°) 3 3 (3) 휋 푝표푙푒 √ 푉푑푐 = ∗2푉푑(푖표 ∗ 퐶표푠 푎푙푝ℎ푎 − ) (4)

푉Th푑e푖표 capacitances푉퐿퐿 ∗ √ ∗shown푇푟푎푛 in푠푓 the표푟푚 fig푒푟 1푟 푎are푡푖표 the∗ 푡 푎푝 푐ℎ푎value푛푔푒푟 푟 by푎푡 푖 controlling표 the tap changer posi- equivalent capacitances of the insulators in tion. In case of persisting insulation fault, dc yard as well as in dc line. Similarly the the across the capacitance reduces to a resistances shown in fig1 are the equivalent very low value which forces the controller to shunt resistance across each non-ideal capa- reduce푅푒 푞 the thyristor firing angle to a very citance. The resistance can be calculated low value tobuild the dc voltage. Voltage reactance and dc line reactance. The low normal power flow operation mode.For value of series resistance provides damping power flow operation mode,the dc current from the dielectric loss or tan delta val- difference between the theoretically calcu- of LC oscillations. The high value of parallel must be in continuous conduction mode and resistance across each non ideal capacitan- the DC voltage across the pole to neutral can ue.The theoretical equation (3) used to cal- lated voltage and the actual voltage enforces cesincurspower losses. be inverted by varying the thyristor firing angle.The thyristor firing angle control be- culate the dc voltage in controller is a func- the controller to operate Open Line Test pro- There is very few information available in tween 0 to 90 degree and 90 to 180 degree literatureregarding Open Line Test. As ma- operates the converter as rectifier and inver- tion of the thyristor firing angle and tection. The plot of dc voltage with respect thematical expression for DC voltage across 4 ter respectively. This inversionCIGRE of dc voltage India Journal the opened dc line in Open Line Test is is valid for continuous current conduction no load dc voltage . in equation (4) to cos( 60°) helps to understand the complex and is not only the function of thy- mode. But in case of Open Line Test the dc 푎푙푝ℎ푎 ristor firing angle (alpha) but also of the voltage across the pole to neutralvoltage across cannot the pole beto neutral inverted cannot be calculatedis the line voltage to line and the voltage actual of퐿voltage퐿 the enforcesac bus. the In behavior of Open Line Test. equivalent circuit parameters i.e., equivalent inverted by varying the thyristor firing an- 푉푑푖표 푉 푎푙푝ℎ푎 − byresistance, varying inductance the and thyristorcapacitance.W ithfiring angle, as the dc current controllerOpen Line to operate Test Open mode Line the Test controller protection. The keeps plot gle, as the dc current remains in disconti- o the variation of line capacitance and induc- remains in discontinuous conductionnuous conduction mode. mode. The The polaritypolarity of the of dc voltage with respect to Cos(alpha – 60 ) helps to tancethe peak to peak DC voltage ripple also of the dc voltage is decided dcby voltage the isgrounding decided by the groundof theing of understandthe no load the dc behavior voltage of Open Line constant Test. to a set varies.The dielectric loss accounts for the valve anode or cathode. DC voltagethe valve is anode positive or cathode. for DC anode voltage is power losses in Open Line Test mode. The grounding of lower most valve positiveand negativefor anode grounding for cathode of lower most Fig2. : Theoretical relation between loss varies with the line length, weather, pol- valve and negative for cathode grounding of 푉푑푖표 lution and other factors. grounding of upper most valve.upper So most in valve. Open So in Line Open Line Test Test ( 60°) and during nor- mode,HVDC converter the converter characteristics operates in Open asmode, a therectifier converter operatesfor any as afiring rectifier angleLine Test between mode is different 0 to180 from that degree. of for any firing angle between 0 to180 degree. mal power flow operation 퐶표푠 푎푙푝ℎ푎 − 푉푑푐푝표푙푒 2.2. EquivalentEquivalent Circuit Model Circuit of Open M Lineodel Test of Open Line Test

Fig. 2 : Theoretical relation between Cos (alpha – 60o) and Vdcpole during normal power flow operation The rectifier station valves are designed to take more Fig3.:Theoreticalrelation voltage than inverter station. Hence, the no load voltage of inverter station is less than the rectifier station. The Fig1.F :ig. Equivalent 1 : Equivalent Impedance model Impedance of Open Line Test model (Rectifier of ConverterOpen Lineof Station Test 1 is con- tween and during normal nected to DC(Rectifier line with DC Converter filter) of Station 1 is connected to theoretically calculated dc pole voltage follows a cosine DC line with DC filter) relation with alpha.The dc pole voltage doesn’t depend power flow operation 푉푑푐푝표푙푒 푎푙푝ℎ푎 Equivalent circuit model has been taken from the on any other circuit parameter as per the Fig 3. In Fig Equivalent circuit model has been taken tion 1(converter is4 & connected Fig. 5, the to DCtheoretically line calculated dc pole voltage configurationfrom the configuration of ±800kV of NEA-Agra ±800kV NEA multi-terminal- with DCHVDC filter).The equivalent circuit para- system. can be plotted with the actual one from the operational Agra multi-terminal HVDC system. meters can be modelexperienceledas : of Open Line Test operation. In the configuration shown above OLT is being performed atIn rectifier the configuration converterof shown Station above 1 (converter OLT is is connected to DCbeing line performed with DC at filter).The rectifier converter equivalentof Sta- circuit parameters Fig3.:Theoreticalrelation can be modelledas : tween and during normal = (1) ...(1) The rectifier station valves are designed to tagepower doesn’t flow operationdepend on any other circuit pa- 푅푒푞 푅푒푞푑푐푦(푎very푟푑 ‖푅 low푒푞푙 푖value푛푒 ‖푅푓 in푎푢푙 푡case of fault) ...(2) 푝표푙푒 (2) take more voltage than inverter station. rameter푉 푑as푐 per the푎 fig3.푙푝ℎ푎In fig 4 & fig 5,the 푓푎푢푙푡 푅푒푞 ≈ 푅= 4 ( 60°) ...(3) 3 3 (3) 휋 Hence,the no load voltage of inverter station theoretically calculated dc pole voltage can 푝표푙푒 √ 푉푑푐 = ∗2푉푑(푖표 ∗ 퐶표푠 푎푙푝ℎ푎 − ) is less (4) than the rectifier station. The theoreti- be plotted with the actual one from the oper-

푉Th푑e푖표 capacitances푉퐿퐿 ∗ √ ∗shown푇푟푎푛 in푠푓 the표푟푚 fig푒푟 1푟 푎are푡푖표 the∗ 푡 푎푝 푐ℎ푎푛value푔푒푟 푟 by푎...(4)푡 푖 controlling표 cally the tap calculated changer pos i-dc pole voltage follows a ational experience of Open Line Test opera- Fig. 3 : Theoretical relation between Vdc and alpha during equivalent capacitances of the insulators in tion. In case of persisting insulation fault, pole The capacitances shown in the Fig. 1 are the equivalent cosine relationnormal with power alpha. flow operationThe dc pole vol- tion. capacitancesdc yard as well ofas the in dc insulators line. Similarly in dc the yard asthe well as across in the capacitance reduces to a resistances shown in fig1 are the equivalent very low value which forces the controller to dc line. Similarly the resistances shown in Fig.푅푒 푞1 are theshunt equivalent resistance acrossshunt each resistance non-ideal across capa- eachreduce non-ideal the thyristor The firing rectifier angle to a station very valves are designed to tage doesn’t depend on any other circuit pa- capacitance.citance. The resistanceThe resistance can be can calculated be calculated low from value the tobuild the dc voltage. Voltage dielectricfrom the loss dielectric or tan loss delta or value.The tan delta va theoreticall- difference equation between take the theoretically more voltage calcu- than inverter station. rameter as per the fig3.In fig 4 & fig 5,the (3)ue. Theused theoretical to calculate equation the (3) dc used voltage to cal- in controllerlated voltage is a and theHence,t actual voltagehe no enforces load voltage of inverter station theoretically calculated dc pole voltage can functionculate the of dc the voltage thyristor in co firingntroller angle is a fun alphac- andthe no controller load dc to operate Open Line Test pro- tion of the thyristor firing angle and tection. The plot of dc voltage with respect voltage Vdio VLL in equation (4) is the line to line voltage of is less than the rectifier station. The theoreti- be plotted with the actual one from the oper- theno loadac bus. dc voltage In Open Line. Testin equation mode (4)the controllerto cos (keeps 60°) helps to understand the 푎푙푝ℎ푎 cally calculated dc pole voltage follows a ational experience of Open Line Test opera- theis the no line load to dc line voltage voltage ofVdio퐿퐿 the constantac bus. In to a setbehavior value of by Open Line Test. 푉푑푖표 푉 푎푙푝ℎ푎 − controllingOpen Line the Test tap mode changer the controller position. keeps In case of persisting cosine relation with alpha.The dc pole vol- tion. insulationthe no load fault,dc voltage the Reg across constant the to a capacitance set reduces to a very low value which forces the controller to reduce 푉푑푖표 Fig2. : Theoretical relation between the thyristor firing angle to a very low value tobuild( the 60°) Fandig. 4 : Theoreticalduring noandr- actualrelation between Vdc and pole dc voltage. Voltage difference between the theoreticallymal power Fig4. flow : Theoretical operationalpha for rectifier and during actual OLTrelation be- Fig5. : Theoretical and actual relation be- 퐶표푠 푎푙푝ℎ푎 − 푉푑푐푝표푙푒 tween and for rectifier dur- tween ( 60°) and for Volume 10 v No. 1 v January 2021 ing OLT rectifier during OLT 푉푑푐푝표푙푒 푎푙푝ℎ푎 퐶표푠 푎푙푝ℎ푎 − 푉푑푐푝표푙푒

Fig4 and fig5 have been plotted with the ac- to . The ( 60°) follows tual data sets taken from an OLT operation a cosine curve for different dc voltages. 푉푑푐푝표푙푒 퐶표푠 푎푙푝ℎ푎 − performed on converter of station1(+ve pole) of ±800kV NEA-Agra multi-terminal The deviation of actual curve from the theo- HVDC Fig4. : projectTheoretical as perand the actual configurationrelation be- reticFig5.al : one Theoretical in fig5 shows and actual the nonlinearity relation be- showntween in fig1. and for rectifier dur- betweentween ( ( 6060°)° )and . Tofor ing OLT understandrectifier during the OLT behavior of the Open Line 푝표푙푒 퐶표푠 푎푙푝ℎ푎 − 푉푑푐푝푝표표푙푒푙푒 Fig4. shows푉푑푐 the deviation푎푙푝ℎ푎 of actual dc pole Test the퐶 practical표푠 푎푙푝ℎ 푎data− is required푉 푑for푐 differ- voltageFig4 and fromfig5 have the been theoretically plotted with calculated the ac- entto configuration. The s which( is not feasible60°) follows from one.tual dataThe dcsets pole taken voltage from varies an OLT linearly operation with commerciala cosine curve point for different of view. dc voltages.So electrical 푉푑푐푝표푙푒 퐶표푠 푎푙푝ℎ푎 − alpha.performed The linearon converter relationship of ofstation dc voltage1(+ve modelling is necessary for better under- withpole) alphaof ± 800kVcan be NEAbetter- Ainterpretedgra multi- terminalby plot- stanThed deviationing of the of basic actual Open curve Line from Test the circ theuito- tingHVDC project( as per60° ) the with configuration respect configurationretical one ins. fig5 shows the nonlinearity between ( 60°)and . To shown in퐶표 fig1.푠 푎푙 푝 ℎ푎 − understand the behavior of the Open Line 퐶표푠 푎푙푝ℎ푎 − 푉푑푐푝표푙푒 Fig4. shows the deviation of actual dc pole Test the practical data is required for differ- voltage from the theoretically calculated ent configurations which is not feasible from one. The dc pole voltage varies linearly with commercial point of view. So electrical alpha. The linear relationship of dc voltage modelling is necessary for better under- with alpha can be better interpreted by plot- standing of the basic Open Line Test circuit ting ( 60°) with respect configurations. 퐶표푠 푎푙푝ℎ푎 − Fig3.:Theoreticalrelation tween and during normal power flow operation 푉푑푐푝표푙푒 푎푙푝ℎ푎

3. Modelling of Open Line To run the electrical model a closed loop control system is required, which can be The rectifier station valves are designed to tageTest doesn’t Configuration depend on any other o fcircuit pa- done with the help of control system replica take more voltage than inverter station. rameterHvDC as per System: the fig3.In fig 4 & fig 5,the with RTDS simulation.But to design in Hence,the no load voltage of inverter station theoretically calculated dc pole voltage can MATLAB Simulink platform or in any kind is less than the rectifier station. The theoreti- OLTbe canplotted be performed with the actual for the one following from the ci oper- r- of offline simulation platform it is required cally calculated dc pole voltage follows a cuitational configurations: experience of Open Line Test opera- to design the controller in the respective cosine relation with alpha.The dc pole vol- tion.Open Line Test Application in Uhvdc for Condition Monitoringplatform. of Insulation The Health controller of Ultra High has Voltage to beEquipment sames as 5 (a) Converter is connected to DC bus Tothe run main the electrical controller model used a closed in real loop HVDC control systemsys- without DC filter and without DC line. is required, which can be done with the help of control systemtem. The replica controller with RTDS shown simulation.But in fig6 used to design for (b) Converter is connected to DC bus with inOpen MATLAB Line Simulink Test has platform been replicatedor in any kind from of offline the DC filter and without DC line. simulation platform it is required to design the controller incontroller the respective used platform. by ABBThe controller for the has ±800kVto be same (c) Converter is connected to DC line with asNEA the -mainAgra controller multi-terminal used in real HVDC HVDC project. system. The DC filter. controller shown in Fig. 6 used for Open Line Test has been replicated from the controller used by ABB for the (d) Converter is connected to DC line ±800kV NEA-Agra multi-terminal HVDC project. without DC filter Fig. 5 : Theoretical and actual relation between Cos (alpha – 60o) and Vdc for rectifier during OLT Fig4. : Theoretical and actualrelation be- AnFig5. equivalent : Theoretical electrical and pole model actual can relation be de- be- tween and for rectifier dur- Fig.tween 4 and Fig.( 5 have been60 plotted°) and with the actual datafor signedsets taken in any from of an the OLT simulationplatform operation performed ons converterlike ing OLT 푝표푙푒 EMTDC/ofrectifier station1(+vePSCAD, during pole) RSCAOLT of ±800kV D,HYPERSIM NEA-Agra multi-terminal,푝 표푙푒 푉푑푐 푎푙푝ℎ푎 HVDC project퐶표푠 as푎 푙per푝ℎ 푎the− configuration shown푉푑푐 in Fig. 1. MATLAB SIMULINK etc. All the simula- Fig4 and fig5 have been plotted with the ac- Figto 4. shows the. The deviation (of actual dc pole60° voltage) follows from tion platformshave their own advantages. tual data sets taken from an OLT operation thea cos theoreticallyine curve calculated for different one. dcThe voltages. dc pole voltage Mostvaries 푉of푑 linearly푐them푝표푙푒 withuse alpha.their퐶표푠 patentThe푎푙푝 linearℎ푎 solving− relationship tech- of dc performed on converter of station1(+ve voltage with alpha can be better interpreted by plotting Fig. 6 : Closed and Open Loop control strategy for Open niqueCosThe (alpha ordeviation solver – 60o) with forof actual respect simulation curve to Vdc results.from. The the Cos The the(alpha o- pole) of ±800kV NEA-Agra multi-terminal pole Fig6. :Closed andLine TestOpen of a Loop rectifier control strate- – 60o) follows a cosine curve for different dc voltages. HVDC project as per the configuration basicretic controlal one and in fig electrical5 shows blocks the nonlinearity are the 3.2gy forClosed Open LoopLine TestControl of a rectifierModel in MATLAB IEEE/IECThebetween deviation standard of (actual blocks. curve 60from The°) theand parameter theoretical of one. To in Simulink shown in fig1. Fig. 5 shows the nonlinearity between Cos(alpha – 60o) theandunderstand blocks Vdc can. To the beunderstand changed behavior the to ofbehavior customize the Open of the the LineOpen The basic controller shown in fig 7 is a negative feedback pole 퐶표푠 푎푙푝ℎ푎 − 푉푑푐푝표푙푒 loop using a comparator, PI controller and the HVDC Fig4. shows the deviation of actual dc pole model.LineTest Test the thepractical practical data data is isrequired required forfor differentdiffer- configurations which is not feasible from commercial equivalent electrical model. The PI controller is designed voltage from the theoretically calculated pointent configurationof view. So electricals which modelling is not feasibleis necessary from for to have a faster response so that the simulation time to reach steady state is less. The open loop electrical model one. The dc pole voltage varies linearly with 3.2bettercommercialClosed understanding pointLoop of the of basicControl view. Open So Line electricalModel Test circuit in MATLAB Simulink configurations. with an alpha regulator can be used to check the behavior alpha. The linear relationship of dc voltage modelling is necessary for better under- of the system for different values of alpha. with alpha can be better interpreted by plot- The3. basicModelling controller o shownf Open in Lfigine 7 Tisest a ne g- time to reach steady state is less. The open stanCdoningf igurationof the basic Openof HVDC Line Sy Teststem circuit ting ( 60°) with respect ative feedback loop using a comparator, PI loop electrical model with an alpha regulator OLTconfiguration can be performeds. for the following circuit controllerconfigurations: and the HVDC equivalent elec- can be used to check the behavior of the sys- 퐶표푠 푎푙푝ℎ푎 − trical(a) Convertermodel. The is connected PI controller to DC isbus designed without DC to filter tem for different values of alpha. have aand faster without response DC line. so that the simulation (b) Converter is connected to DC bus with DC filter and without DC line. Fig7.F :ig. Closed 7 : loopClosed control loop model control in MATLAB model Simulink in MATLAB Simulink

(c) Converter is connected to DC line with DC filter. TheThe Vdc_ref Vdc_ref input isinput given isby givenusing a ramp by usinging. a Theramp forward function biased voltage and is increased (d) Converter is connected to DC line without DC filter functiona ramp and rate a ramp is rate used is used to to build build upup the slowlydc voltage. by regulating An alpha to get the re- thelimiter dc voltage. is used An alpha in limiterthe controlleris used in toquired maintain dc pole voltage. the alpha The subsystem con- An equivalent electrical model can be designed in any of thebetween controller toa maintain given the maximum alpha between and sistsminimum of the electrical value.The modelling of the AC the simulationplatforms like EMTDC/PSCAD, RSCAD, apositive given maximum phase and minimumvoltage value across.The anodesource, Converterto cathode transformer of aand Converter HYPERSIM, MATLAB SIMULINK etc. All the simulation positive phase voltage across anode to ca- subsystem with the DC filter and line equiv- thodevalve of ais valve required is required for for forward forward bia biasing.s- alent The parameter forward shown biased in fig8. platformshave their own advantages. Most of them use voltage is increased slowly by regulating alpha to get their patent solving technique or solver for simulation the required dc pole voltage. The subsystem consists results. The basic control and electrical blocks are the of the electrical modelling of the AC source,Converter IEEE/IEC standard blocks. The parameter of the blocks transformer and Converter subsystem with the DC filter can be changed to customize the model. and line equivalent parameter shown in Fig 8.

Volume 10 v No. 1 v January 2021

Fig8. : HVDC Subsystem Module model in MATLAB Simulink

Fig7. : Closed loop control model in MATLAB Simulink

The Vdc_ref input is given by using a ramp ing. The forward biased voltage is increased function and a ramp rate is used to build up slowly by regulating alpha to get the re- the dc voltage. An alpha limiter is used in quired dc pole voltage. The subsystem con- the controller to maintain the alpha between sists of the electrical modelling of the AC a given maximum and minimum value.The source,Converter transformer and Converter positive phase voltage across anode to ca- subsystem with the DC filter and line equiv- 6 thode of a valve is required for forward CIGREbias- India Journalalent parameter shown in fig8.

Fig. 8 : HVDC Subsystem Module model in MATLAB Simulink

Fig8. : HVDC Subsystem Module model in MATLAB Simulink

Fig9.Fig. 9 :: Converter Subsystem Subsystem model model in MATLAB in MATLAB Simulink with S DCimulink filter, DC with yard DC and DCfilter, line DCequivalent yard modeland DC line The controlequivalent pulse generation model scheme is the Equidistance The DC yard components consists of smoothing and Phase Control (EPC) by using the phase voltages. In blocking reactor, bus post insulator, dc voltage divider practicalThe scenario control there pulse is a Phase generation Locked scheme Loop (PLL) is the and otherinsulator, supporting dc voltageinsulator. divider The insulators and other can su p- to change the pulse generation depending upon the be modelled as an equivalent capacitance of parallel frequencyEquidistance of AC bus voltages. Phase ControlIn the simulation, (EPC) byac bususing connectedporting insulators insulator. with an The equivalent insulators resistance can be voltagesthe and phase frequencies voltages. have been In kept practical constant scenario which across themodelled capacitance. as an equivalent capacitance of is a valid approximation for the steady state condition. there is a Phase Locked Loop (PLL) to Similarlyp arallelthe dc connectedline can be insulatorsmodelled like with the an dc equivyard a- Each converterchange valvethe pulse consists generation of an equivalent depending thyristor, up on component.lent resistanceThe dielectric across loss the coefficient capacitance. tan delta a valve reactor, connected in series with another valve is the measuring index for insulation resistance. The and an theequivalent frequency snubber of ACcapacitance bus voltages. and resistance In the si- loss coefficient varies with ageing, weather, pollution Similarly the dc line can be modelled like across mulatthe valve.ion , ac bus voltages and frequencies and other factors. The string insulators connected have been kept constant which is a valid ap- the dc yard component. The dielectric loss coefficient tan delta is the measuring index Volumeproximation 10 v No. 1 v for January the steady 2021 state condition. for insulation resistance. The loss coefficient Each converter valve consists of an equiva- varies with ageing, weather, pollution and lent thyristor, a valve reactor, connected in other factors. The string insulators con- series with another valve and an equivalent nected between conductor and tower pro- snubber capacitance and resistance across vides the insulation. The equivalent capacit- the valve. ance is the series and parallel combination of the insulation capacitance. The equivalent The DC yard components consists of resistance is calculated from dielectric loss smoothing and blocking reactor, bus post in actual circuit. sin t + alpha + Leq di Vceq(t) = 0 , 6 dt (5) π Where푉푚 ∗ i =� ωcurrent through inductor� − L∗eq − sin t + alpha + Leq di Vceq(t) = 0 , 6 dt (5) Vceq(t)=volπ tage across capacitance Ceq Where푉푚 ∗ i =� ωcurrent through inductor� − L∗eq − Vm=maximum phase voltage Vceq(t)=voltage across capacitance Ceq =fundamental frequency of the AC voltage Open Line Test Application in Uhvdc for ConditionVm=maximum Monitoring phase of voltageInsulation Health of Ultra High Voltage Equipmenttors.s 7 The charging currents of the capacit- 휔The operation of rectifier under open cir- ances are limited by the pole smoothing between conductor and tower provides the insulation.=fundamental frequencyofcuit the condition equivalent of the canAC bevoltagecircuit described capacitances as simulta-. The chargingreactor, valve reactors, transformer leakage The equivalent capacitance is the series and parallel capacitances(Ceq)neous charging and consists discharging of thetors. snubberof Thethe charging circuit, reactance curvalverents of and the dc capaci line t- reactance which has The operation of rectifier under open cir- combination of the insulation capacitance. The휔 equivalent supportequivalent insulators, circuit capacitances pole bushing,. Theances arrester char areg- insulators, limited been by bus the shown pole as smoothing Leq. resistance is calculated from dielectric losscuit in condition actual canposting be describedinsulators, capacitances as pole (Ceq)simult smoothing a- consists reactor reactor, of thepost valve insulator, reactors, dctransformer leakage circuit. neous charging voltagesnubber and discharging divider circuit, and valveof line the insulators. support insulators,reactance The charging and dc currents line During reactance charging which and has discharging operation equivalent circuit capacitances. The charg- ofpole the bushing, capacitances arrester are insulators limited, been bybus the shown post pole as smoothing Leq.the 2nd order Capacitor Voltage equation ing capacitances(Ceq) consists of the reactor,insulators valve, pole reactors, smoothing transformer reactor post leakage in- reactancecan be written as snubber circuit, valve support insulators, During charging and discharging operation sulator, dc voltage divider and line insula- pole bushing, arresterand dc insulators line reactance, bus post which hasthe been 2nd shownorder Capacitor as Leq. Voltage equation insulators, pole smoothingDuring charging reactor andpost2 discharging in- canoperation be written the as 2nd ( )order sulator, dc voltage divider and line insulVceqa- (t) + 2 + 2 ( ) Capacitor Voltage equation2 can be written as 푑 2 푑푉푐푒푞 푡 2 (=) cos( + + /6) Vceq(t) + 2 휏 ∗+휔푛 2∗ ( ) 휔푛 ∗ 푉푐푒푞 푡 2 푑푡 푑푡 푑 = 2 푑푉푐푒푞 푡cos휔푛( ∗+푉푚 ∗ 휔 +∗ /6)휔 푡 푎푙푝ℎ푎 휋 (6) 휏 ∗ 휔푛 ∗ 휔푛 ∗ 푉푐푒푞 푡 푑푡 푑푡 ...(6) 휔푛 ∗ 푉푚 ∗ 휔 ∗ 휔푡 푎푙푝ℎ푎 휋 2 1 (6) Where time constant, = and natural frequency of oscillation, = Where time constant, and natural frequency Fig.10 : DC filter equivalent model in MATLAB 퐿푒푞 Fig10.:: DC filter equivalent model in MATLAB SIMULINKwithSIMULINKwith eequivalentquivalent electricalelectrical param parame-e- SIMULINKwith equivalent electrical parameters 휏 푅푒푞 2 1 휔푛 �퐿푒푞 ∗퐶푒푞 tersters Where time constantEquation, = (6) canand benatural solved frequency analytical of lyoscillation. , = The DC filter is modelled on the basis of parameters of oscillation,퐿푒푞 The DC filter is modelled on the basis of of speedspeed and and increases increases the the computational computational휏 bu bu푅r-푒r-푞 휔푛 퐿푒푞 ∗퐶푒푞 used in the electrical model of ±800kV NEA-AgraEquation multi- (6) can beThe solved current analytical throughly the. capacitor can be expressed as � parameters used in the electrical model model of of den.den.ToTo achieve achieve the the simulation simulationEquation response response (6) can be solved analytically. terminal HVDC system replica.This DC filter model ±800kV NEA-Agra multi-terminal HVDC HVDC nearlynearly The equal equal current to to the the through actual actualThe response, response, the current capacitor aann through can be the expressed capacitor as can be expressed as usedsystemsystem inreplica the. Thissimulation DC filter modeldecreases used inin the simulationequivalentequivalent model model speed can can be be used used to to representrepresent andthe simulationincreases decreases the computational the simulation burden.To the DC achieve filter with anthe equivalent RLC circuit. sin + (0) the simulation decreases the simulation the DC filter with an equivalent RLC circuit. 6 simulation response nearly equal to the actual response, ( ) = 휋 cos( )(7) 푉푚 ∗ �푎푙푝 ℎ푎 �−푉푐푒푞 an3.3 equivalent Mathematical model can Mode be usedl-l- to represent the DC sin + (0) −ξ∗휔푛 ∗푡 ...(7) ( ) = 6 휔푛 ∗퐿푒푞 cos( ) filter with an equivalent RLC circuit. 푖푐 푡 휋 1 2 ∗ 푒 (7) ∗ 휔푛 ∗ 푡 ling of Converter in OpenOpen 푉푚 ∗ �푎damping푙푝 ℎ푎 �−푉 ratio푐푒푞 = (8) −2ξ∗휔푛 ∗푡 3.2 Mathematical Modelling of Converter푖푐 in푡 Open 휔푛 ∗퐿푒푞 ∗ 푒 퐿푒∗푞 휔푛 ∗ 푡 Circuit Condition damping1 2 ratio ...(8) damping ratio = (8) ∗푅 퐶푒푞 Circuit Condition 2 ξ � whereR=퐿푒 푞resistance of line where R = resistance of line ξ ∗푅 �퐶푒푞 whereR= resistance of line

Fig11.: Schematic diagram of 12 pulse bridge ac to dc converter in open loop condition Fig11Fig..: 11Schematic : Schematic diagram diagramof 12 pulse of bridge 12 pulse ac to dc bridge converter ac into open dc loop condition converter in open loop condition written as In this circuit, while the first valve is fired In this circuit, while the first valve is firedwritten at ωt as = alpha, Fig12. : Voltage across the valves in first leg theatIn ω thisKVLt= circuit, equation, thewhile KVL the can equationfirst valvebe canwritten is firedbe as Fig. 12 : Voltage across the valves in first leg at ωt= , the KVL equation can be 푎푙푝ℎ푎 di From Fig. 13 and Fig. 14, it can be observed that during , sin t + alpha + Leq Vceq(t) = 0 (5) 푎푙푝ℎ푎 6 dt OLT there is a high amount of current ripple which is π ...(5) 푉푚 ∗ �ω � − ∗ − caused due to fast charging and discharging of circuit WhereWhere i i = = currentcurrent through inductor LLeqeq capacitances. Hence it is not recommended to per VceqVceq(t)(t)= vol = voltagetage across across capacitance capacitance Ceq Ceq form OLT for a long time duration.Typically the time for staying in OLT may be less than 30 minutes. Also the Vm = maximum phase voltage Vm=maximum phase voltage successive OLT should be performed after a gap of atleast 2 hours. = fundamental frequency of the AC voltage =fundamental frequency of the AC voltage Fig13. : Current through 12 valves The𝜔 operation of rectifier under open circuit condition can be described as simultaneous charging and dischargingtors. The charging currents of the capacit- 휔The operation of rectifier under open cir- ances are limited by the pole smoothing cuit condition can be described as simulta- reactor, valve reactors, transformer leakage neous charging and discharging of the reactance and dc line reactance which has equivalent circuit capacitances. The charg- been shown as Leq. v v ing capacitances(Ceq) consists of the Volume 10 No. 1 January 2021 snubber circuit, valve support insulators, During charging and discharging operation pole bushing, arrester insulators, bus post the 2nd order Capacitor Voltage equation insulators, pole smoothing reactor post in- can be written as sulator, dc voltage divider and line insula- Fig14. : Current through valve T1 and voltage across valve T1 2 ( ) Vceq(t) + 2 + 2 ( ) 2 From fig13 and fig14, it can be observed form OLT for a long time dura- 푑 = 2 푑푉푐푒푞 푡cos( + + /6) 휏 ∗ 휔푛 ∗ 휔푛 ∗that푉 푐 during푒푞 푡 OLT there is a high amount of tion.Typically the time for staying in OLT 푑푡 푑푡 current ripple which is caused due to fast may be less than 30 minutes. Also the suc- 휔푛 ∗ 푉푚 ∗ 휔 ∗ 휔푡 charging푎푙푝ℎ푎 and 휋discharging of circuit capacit- cessive OLT should be performed after a (6) ances. Hence it is not recommended to per gap of atleast 2 hours.

2 1 Where time constant, = and natural frequency of oscillation, = 퐿푒푞 휏 푅푒푞 휔푛 퐿푒푞 ∗퐶푒푞 Equation (6) can be solved analytically. �

The current through the capacitor can be expressed as

sin + (0) 6 ( ) = 휋 cos( )(7) 푉푚 ∗ �푎푙푝 ℎ푎 �−푉푐푒푞 −ξ∗휔푛 ∗푡 휔푛 ∗퐿푒푞 푖푐 푡 1 2 ∗ 푒 ∗ 휔푛 ∗ 푡 damping ratio = (8) 2 퐿푒푞 ξ ∗푅 �퐶푒푞 whereR= resistance of line 4. Simulation of OLT Con- Vdc_ref of 400kV, 600kV and 800kV is given. figurations 4. Simulation of OLT Con- Vdc_refThe simulation of 400kV, results 600kV thus and obtained 800kV for is given. Closed loop simulation has been done three reference voltages has been shown in figurations fig 15, fig 16 and fig17 respectively. The for following configurations of OLT op- The simulation results thus obtained for TFR data from an actual OLT operation is Closederation :loop simulation has been done three reference voltages has been shown in shown in fig 18. forCase following 1 :Converter configurations is connected of OLT to o DCp- fig 15, fig 16 and fig17 respectively. The TFR data from an actual OLT operation is erationline with : DC filter shown in fig 18. 8 CIGRE India Journal Case 1 :Converter is connected to DC . Fig12. : Voltage across the valves in first leg line with DC filter Fig12. : Voltage across the valves in first leg .

Fig15Fig.. : Closed15 : Closedloop simulation loop ofsimulation rectifier(+ve of pole) rectifier(+ve with circuit configuration pole) with 3 (c). DC Volta- Fig15gecommand=400kVcircuit. :Closed configuration loop simulation 3 of(c). rectifier(+ve DC Voltagecommand pole) with circuit configuration = 400 kV 3 (c). DC Volta- gecommand=400kV Fig13. :: CurrentFig. throughthrough 13 : Current 12 12 valves valves through 12 valves

FigF16ig... ::Closed 16 : Closedloop simulation loop ofofsimulation rectifier(+verectifier(+ve of pole)pole) rectifier(+ve withwith circuitcircuit configurationconfiguration pole) with 3 3 (c). (c). DC DC Voltage Voltage command=600kVcircuit configuration 3 (c). DC Voltage command = 600 kV command=600kV

Fig14. :F Currentig. 14 :through Current valve through T1 and valve voltage T1 andacross voltage valve T1 Fig14. : Current throughacross valve T1 valve and T1voltage across valve T1

4. Simulation of OLT Configurations From fig13 and fig14, it can be observed form OLT for a long time dura- Closed loop simulation has been done for following thatFrom during fig13 OLT and there fig14, is it a can high be amount observed of tion.formTypically OLT the for time a for long staying time in OLT dur a- configurationscurrentthat during ripple OLT which of there OLT is is caused aoperation high due amount to : fast of maytion. beTypically less than the 30 timeminutes. for stayingAlso the in su OLTc- Casechargingcurrent 1 ripple and:Converter discharging which isis causedconnectedof circuit due capaci to to fast t-DC linecessive withmay DCbe OLT less filter shouldthan 30 beminutes. performed Also aftheter su a c- Vdc_refances.charging Hence andof 400kV,itdischarging is not recommended 600kV of circuit and to 800kVcapaci per t- is given.gapcessive ofOLT should atleast be performed 2 hours. after a ances. Hence it is not recommended to per gap of atleast 2 hours. FigF17ig.. :Closed 17 : Closedloop simulation loop ofsimulation rectifier(+ve ofpole) rectifier(+ve with circuit configuration pole) with 3 (c). DC Voltage The simulation results thus obtained for three reference command=800kV voltages has been shown in fig 15, fig 16 and fig17 circuit configuration 3 (c). DC Voltage command=800kV Fig17. :Closed loop simulation of rectifier(+ve pole) with circuit configuration 3 (c). DC Voltage respectively. The TFR data from an actual OLT operation command=800kV is shown in Fig 18.

Fig18. :Three sets of data (S1,S2,S3) for different reference voltages of 400 kV, 600kV, 800kV during Open Line Test operation of +ve pole at rectifier station1.

Case 2:Converter is connected to DC bus Simulation result is shown in fig 19 and ac- Fig18. F:Threeig 18 :sets Three of data sets (S1,S2,S3) of data (S1, for differentS2, S3)without referencefor different DC filter voltage andreference withouts of 400 DC voltages kV,line. 600kV, of 800kVtual TFR data for OLT performed at –ve 400during kV, Open600 kV, Line 800 Test kV operation during Open of +ve Line pole Testat rectifier operation station of1 .+ve pole at rectifier stationpole 1. of rectifier station 2is shown in fig 20. Vdc_ref=-800kV is given

Volume 10 v No. 1Case v January 2:Converter 2021 is connected to DC bus Simulation result is shown in fig 19 and ac- without DC filter and without DC line. tual TFR data for OLT performed at –ve pole of rectifier station 2is shown in fig 20. Vdc_ref=-800kV is given

Open Line Test Application in Uhvdc for Condition Monitoring of Insulation Health of Ultra High Voltage Equipments 9

Case 2:Converter is connected to DC bus without DC Simulation result is shown in Fig. 19 and actual TFR filter and without DC line. data for OLT performed at –ve pole of rectifier station 2is shown in Fig. 20. Vdc_ref=-800kV is given

Fig19. : Closed loop simulation of (–vepole) of Station 2 with circuit configuration 3 (a). DC Fig19. : Closed loop simulation of (–vepole) of Station 2 with circuit configuration 3 (a). DC FVoltageig. 19 : Closed command= loop simulation-800kV of (–vepole) of Station 2 with circuit configuration 3(a). DC Voltage command = -800 kV Voltage command=-800kV

Fig.Fig20 20 : Negative. : Negative pole of Station pole of 2 with Station circuit 2 configuration with circuit 3(a). configuration DC Voltage command 3 (a). = DC 800 VoltagekV com- Fig20. : Nmand=800kVegative polewithout of considering Stationwithout 2 the consideringwith sign. circuit the sign. configuration 3 (a). DC Voltage com- 5. Rmand=800kVesults andwithout Discussions considering the sign. connected insulators between conductor and tower In both the cases,5. itResults can be seen and that Discussionsalpha required increases.So the equivalent IR value decreases. As the to build5. Resultsup the reference and dc voltages Discussions is almost same equivalent IR decreases for a long line, the loss increases in the simulationIn result both as the well cases, as it in can the be actual seen thatOLT alphaduring openduring line OLT.test. It This is evident small from DC powerfig16 that is athe dielectric loss is very less in case of a circuit configuration operationresult.Thisrequired validates to build theup theaccuracy reference of dc the volta g- measure of the dielectric losses incurred in simulationIn both model. the cases, it can be seen that alpha whereduring the converter OLT. is This only connected small DC to powerdc bus.The is a es is almost same in the simulation result asequivalent the IR invaluesulation is typically of the between HVDC 10MΩ circuit to equi 100MΩp- In additionrequired to Vdc to and build alpha up values, the reference the TFR data dc obtained voltag- measure of the dielectric losses incurred in well as in the actual OLT operationre-for a circuitments configuration during OLT where operation. converter is connected to fromes actual is almost OLT operation same in(Fig. the 18 simulation & Fig. 20) shows result the as dc busthe without insulation line and ofdc filter. the The HVDC different circuit equivalent equip- DC power during sult.ThisOLT. This validates small DC the power accuracy is a measure of the simu- well as in the actual OLT operationre- IR valuesmentsThe have duringdielectric been usedOLT loss in operation. isthe inversely simulation proportional for different of the dielectric losseslation model.incurred in the insulation of the configurations. HVDCsult.This circuit equipments validates duringthe accuracy OLT operation. of the simu- to the IR value. As the line length increases As seen from the results of actual OLT operation in In addition to Vdc and alpha values, the Thethe dielectric number of loss parallel is inversely connected proportional insulators The lationdielectric model. loss is inversely proportional to the IR Fig. 18, for constant IR the losses vary significantly for value. As the line TFRlength data increases obtained the from number actual of parallel OLT oper a-differentto thedcbetween pole IR value. voltages. conductor As The the and theoretically line tower length increases. calculated increasesSo In additiontion to(fig Vdc 18 & and fig alpha 20)shows values, the DC the power thethe number equivalent of parallel IR value connected decreases. As insulat the ors TFR data obtained from actual OLT opera- between conductor and tower increases.So tion(fig 18 & fig 20)shows the DC power the equivalentVolume IR 10 value v No. de1 vcreases. January As 2021 the equivalent IR decreases for a long line, the equivalent IR values have been used in the loss increases during open line test. It is evi- simulation for different configurations. dent from fig16 that the dielectric loss is very less in case of a circuit configuration As seen from the results of actual OLT op- where10 the converter is only connected to dc eration in fig 18,for constantCIGRE IR the losses India Journal bus.The equivalent IR value is typically be- vary significantly for different dc pole vol- tweenlosses 10MΩ with to 100MΩ respect for a circuit to conf differenti- tages .dc The pole theoretically voltages calculated for losses with respect to different dc pole voltages for gurationdifferent where equivalentconverter is connected insulation to dc resistance (IR) is shown bus without line and dc filter. The different different equivalent insulation resistance in Fig. 21. (IR) is shown in fig21.

Fig. 23 : Vdcpole with respect to alpha in degree during OLT Fig22. : Fig21. : Theoretical( dielectric loss60 with respect°)with to dc pole voltage respect during Open Line to Test for dif- for different Reg : Theoretical dielectric loss with respect to dc pole Fig23. : with respect to alpha in ferentFig. equivalent 21 resistance (1) dc pole voltage,voltage during Open Line duri Test forng different OLT equivalent for Conclusion 퐶The표 losses푠 푎during푙푝 Openℎ푎 Line−푅푒 푞Testresistance indicates Reg ((1) 60°) increases due to reduc- degree during푝 표OLT푙푒 for different the insulation health of the line. Any degra- tion in equivalent IR for a specific dc pole The losses during푉푑 Open푐 Line Test indicates the insulation different The losses. during Open Line Test퐶표푠 indicates푎푙푝ℎ푎 − the insulation dation in IR increases the losses.푝표 The푙푒 lowest voltage. Similarly the can be plotted health of the line. Any degradation in IR increases the health of the푉 line.푑푐 Any degradation in IR increases the IR value is more significant in case of with respect to dc voltage for different IR losses. The condition monitoring of insulation health푅푒푞 is losses. The lowest IR value is more significant푎푙 푝inℎ푎 case of 푅equivalent푒푞 resistance across the capacitor. values shown in fig23. During annual main- of utmost importance to the Ultra High Voltage system 6. ConclusionTheequivalent equivalent IR resistance is less than the acrossIR value thetenance capacitor. of the HVDC The substationequivalent, OLT can where the failure of even one insulator can cause a ofIR the is weakestless than insulator the. There IR value must be aof thebe weakest performed forinsulator. different configurations There prolonged outage of the concerned pole. During the The lossesparametermust during be to show a parameter the Openvariation of I RtoLine value. show Testtheand the variation characteristic indicates of graphs IR canvalue. be plotted maintenanceprevious shutdown one. I f when to the build system up is healthy the i.e., same dc InIn this this case case thyristor thyristorfiringfiring angle alpha can angleto trackalpha down canthe rate be of changeused of equivas a- free from any insulation fault, OLT can be performed the insulationbean used important as anhealth important factor facto ofr to detecttothe detect the line. lentthe Any IR variation value.The degr signature of a-IR. curve The obtained forvoltage differentreduction configurations.The of alph plota valuebetween is alphaobserved, variationCos(alpha of IR. The– 60 o() is further60°) is plotted for afor circuit different configuration equivalent where converter is and Vdcpole obtained from the TFR can be treated as a further plotted for different equivalent IR isolated from dc line is very important. o dation in IR with increases respect퐶표 푠to푎 푙 Vdc푝ℎthe푎 −pole losses.in Fig. 22. TheThe Cos cond(alphai- – 60 ) signatureit clearly curve forindicate the insulations thehealth degradationof the HVDC of with respect to in fig 22. The increases due to reduction in equivalent IR for a specific circuit components.Signature curve of OLT performed tion monitoring of푝표 푙푒 insulation health is of insulation. The results from different dc pole voltage.푉푑푐 Similarly the alpha can be plotted with during subsequent maintenance shutdowns can be utmost importancerespect to dc voltageto the for Ultra different High IR values Voltage shown in Fig. comparedconfiguration with the previouss can one. be If used to build toup theidentify same the 23. During annual maintenance of the HVDC substation, dc voltagereduction of alpha value is observed, it clearly system whereOLT can the be failureperformed of for even different one configurations insula- and indicatesdegraded the insulationdegradation of zone. insulation. If the The reduction results in the characteristic graphs can be plotted to track down from different configurations can be used to identify tor can causethe rate a ofprolonged change of equivalent outage IR of value.The the co signaturen- thethe degraded IR value insulation obtained zone. If the from reduction the Openin the Line cerned pole.curve obtainedDuring for a circuitthe configuration maintenance where converter IRT valueest isobtained less from than the Open the Line threshold Test is less than value, a is isolated from dc line is very important. the threshold value, a preventive action can be taken shutdown when the system is healthy i.e., bypreventive replacing the actionfaulty insulator. can be The taken faulty insulatorsby replacing can be detected by IR test. Thus, using the results of free from any insulation fault,OLT can be Openthe faultyLine Test,insulation insulator. failure The canfaulty be anticipatedinsulators can performed for different configurations.The wellbe in detected advance and by hence IR preventive test. Thus, action canusing be the taken.Thus,OLTproves to be an effective tool for the plot between and obtained conditionresults monitoring of Open of insulation Line Test health,insulation of the HVDC failure equipments. from the TFR can be treated as푝 표a푙 푒signature can be anticipated well in advance and 푎푙푝ℎ푎 푉푑푐 Rhenceeferences preventive action can be curve for the insulation health of the HVDC [1] ABB controller used in ±800kV NEA-Agra multi- circuit components.Signature curve of OLT taken.terminalThus, HVDCOLT projectproves to be an effective performed during subsequent maintenance [2]tool HVDC for Control the System condition Functional Descriptionfor monitoring of Fig 22 : Cos(alpha (– 60o) with respect to )dc pole voltage, ±800kV NEA-Agra multiterminal HVDC by ABB Fig22. Vdc: during OLT for different60° Regwith. respect to shutdowns can bepole compared with the [3]insulation RTDS ReplicaFig health23 training. :of manual:±800kVthe HVDC with equipments.NEA-Agra respect to alpha in dc pole voltage, during OLT for multi-terminaldegree HVDC during OLT for different 퐶표푠 푎푙푝ℎ푎 − [4] HVDC Transmission :Power Conversion푝표푙푒 Applications different . 푉푑푐 푉푑푐푝표푙푒 in Power Systems by Chan Ki Kim, Vijay K.Sood, Gil-Soo Jang, Seong-Joo Lim and Seok-Jin Lee 푅푒푞 References6. Conclusion:푅 푒푞 Volume 10 v No. 1 v January 2021 [3] RTDS Replica training manual:±800kV [1]ABB controllerThe losses used during in Open±800kV Line NEA Test- indicates previous one. If to build up the same dc NEA-Agra multi-terminal HVDC Agra multithe-terminal insulation HVDC health project of the line. Any degra- voltagereduction of alpha value is observed, dation in IR increases the losses. The cond[4]i- HVDCit Transmission clearly indicate :Powers the Conversion degradation of [2] HVDC Control System Functional De- tion monitoring of insulation health is ofApplications insulation. in Power The System resultss by Chan from Ki different scriptionfor ±800kV NEA-Agra multiter- utmost importance to the Ultra High VoltageKim, Vijayconfiguration K.Sood, Gils can-Soo be Jang, used Seong to identify- the minal HVDC by ABB system where the failure of even one insula-Joo Lim anddegraded Seok- insulationJin Lee zone. If the reduction in tor can cause a prolonged outage of the con- the IR value obtained from the Open Line cerned pole.During the maintenance Test is less than the threshold value, a shutdown when the system is healthy i.e., preventive action can be taken by replacing free from any insulation fault,OLT can be the faulty insulator. The faulty insulators can performed for different configurations.The be detected by IR test. Thus, using the plot between and obtained results of Open Line Test,insulation failure from the TFR can be treated as a signature can be anticipated well in advance and 푎푙푝ℎ푎 푉푑푐푝표푙푒 curve for the insulation health of the HVDC hence preventive action can be circuit components.Signature curve of OLT taken.Thus,OLTproves to be an effective performed during subsequent maintenance tool for the condition monitoring of shutdowns can be compared with the insulation health of the HVDC equipments.

References: [3] RTDS Replica training manual:±800kV [1]ABB controller used in ±800kV NEA- NEA-Agra multi-terminal HVDC Agra multi-terminal HVDC project [4] HVDC Transmission :Power Conversion [2] HVDC Control System Functional De- Applications in Power Systems by Chan Ki scriptionfor ±800kV NEA-Agra multiter- Kim, Vijay K.Sood, Gil-Soo Jang, Seong- minal HVDC by ABB Joo Lim and Seok-Jin Lee Table 6 Impact of Gravel Height on Derating Factor

Fig.12 Impact of Resistivity of Gravel on Safe Potentials

Significance of Quality & Quantity of Gravel for Safe Designing of Grounding (Earthing) System of Substations

Dr. Rajesh Kumar Arora Delhi Transco Ltd (DTL), Delhi, India

Abstract An electrical sub-station is an assemblage of electrical components including busbars, switchgear, power transformers, auxiliaries etc. These components are connected in a definite sequence such that a circuit can be switched off during normal operation by manual command and also automatically during abnormal conditions such as short-circuit. Sub-station are integral parts of a power system and form important links between the generating station, transmission systems, distribution systems and the load points. The main objective of grounding electrical systems is to provide a suitably low resistance path for the discharge of fault current which ultimately provide safety to working personnel and costly installed equipments in the substation. The flow of heavy fault current results in rise of potential in the vicinity of point /area of fault (ground fault) with respect to remote ground. There is need to ensure that the ground potential rise, and touch and step voltages are within permissible limits. This paper provides an overview of significance of quality and quantity of gravel in the substation in accurate designing of grounding system. Keywords : Electrical Shock, Grounding (Earthing), Step and Touch Potential, Gravel (Surface Material)

1. Introduction 6. The grounding system provides a reference The grounding system in a substation is very crucial potential for electronic circuits and helps reduce electrical noise for electronic, instrumentation and for a few reasons, all of which are related to either the protection of people and equipment and/or the optimal communication systems operation of the electrical system. These include: 1. The grounding system provides a low resistance return path for earth faults within the substation, which protects both personnel and equipment 2. For earth faults occurred in far away generation sources, a low resistance grounding grid relative to remote earth prevents dangerous ground potential rises (GPR) 3. The grounding system provides a low resistance path for voltage transients such as lightning and surges / over voltages in the system 4. Equipotential bonding of conductive objects (e.g. metallic equipments, buildings, piping etc) to Fig.Fig. 1 Air1 : InsulatAir Insulateded Substation Substation with with Gravel Gravel Surface Surface the grounding system prevents the presence of dangerous voltages between objects (and earth). 2. Accidental circuit equivalents 5. Equipotential bonding helps prevent building up The following notations are used for the accidental circuit of electrostatic charge and discharge within the equivalent shown in Figure 2: substation, which can cause sparks with enough Ib is the body current (body is part of the accidental energy to ignite flammable atmospheres circuit) in A

11 Volume 10 v No. 1 v January 2021 Fig. 2 Flow of Current through the Working Staff during Fault

Fig.3 Different Resistances of Circuit for Touch Voltage

12 CIGRE India Journal

RA is the total effective resistance of the accidental The Thevenin voltage VTh is the voltage between circuit in Ω terminals H and F when the person is not present. The Fig. 1 Air Insulated Substation with Gravel Surface Thevenin impedance ZTh is the impedance of the system VA is the total effective voltage of the accidental circuit (touch or step voltage) in V as seen from points H and F with voltage sources of the system short circuited. Fig.4 TheveThe currentnin Equivalent Ib, through of the Circuit body of figure 3 of a person coming in contact with H and F is given by

= -----Equation (1) 푽푻+풉 ...Equation (1) 풃 Figure푰 5 shows풁 the푻풉 fault푹푩 current If being discharged to the ground by the grounding system of the substation. The current,For Ib, touch flows voltagefrom one accidental foot F1 through circuit the body of the person to the other..... foot,Equation F2. Terminals (2) F1 and F2 are = Fig. 2 FlowF ig.of Current2 : Flow through of Current the through Working the Staff Working during Fault the areas on the surface of the earth that are in contact with the two푹 풇feet, respectively. The Thevenin theorem Staff during Fault � allows풛 us푻풉 to representퟐ this two-terminal (F1, F2) network The tolerable body current, Ib, above, is used to define And for the step voltage accidental circuit in Figure 6. The Thevenin voltage VTh is the voltage the tolerable total effective voltage of the accidental circuit between terminals ...... F1 and Equation F2 when the (3) person is not (touch or step voltage) i.e. the tolerable total effective = present . The Thevenin impedance ZTh is the impedance voltage of the accidental circuit is that voltage that will of the system푻풉 ퟐ푹 as풇 ween from the terminals F1 and F2 with cause the flow of a body current, I ,, equal to the tolerable 풛 b the voltage sources of the system short circuited. body current, Ib. For touch voltage accidental circuit Figure 2 shows the fault current If being discharged to

the ground by the grounding system of the substation zTh = Rf ⁄ 2) ...Equation (2) and a person touching a grounded metallic structure at H. And for the step voltage accidental circuit Various impedances in the circuit are shown in Figure 3 . Terminal H is a point in the system at the same potential zTh = 2Rf ...Equation (3) as the grid into which the fault current flows and terminal F is the small area on the surface of the earth that is in

contact with the person’s two feet. The current, Ib, flows from H through the body of the person to the ground at F the Thevenin theorem allows us to represent this tow terminal (H,F) network of Figure 3 by the circuit shown in Figure 4.

Fig. F5 ig. Fig.Different 5 5 : Different Different Resistances Resistances Resistances of Circuitof Circuitof Circuit for for Step Stepfor VoltageStep Voltage Voltage

Fig.3 Different Resistances of Circuit for Touch Voltage Fig.3Fig. Different 3 : Different Resistance Resistancess of Circuit of Circuit for Touchfor Touch Voltage Voltage

Fig.6 Thevenin Equivalent of Circuit of figure 5 Fig.6F Thevenig. 6 : Theveninin Equivalent Equivalent of Circuit of Circuit of figure of figure5 5

For= ...... the Equationpurpose (4) of circuit analysis, the human foot is 흆 = ...... usually Equation represented (4) as a conducting metallic disc and 푹풇 ퟒ풃 흆 Wherethe contact ρ = Resistivity resistance of the of soilshoes, socks, etc., is neglected. 풇 ퟒ풃 Where푹 For ρ touch= Resistivity voltage accidental of the soilcircuit Fig.4Fig. Theve 4 : Theveninnin Equivalent Equivalent of Circuit of Circuit of figure of figure3 3 Traditionally, the metallic disc representing the foot is For touch voltage accidental circuit Fig.4 Thevenin Equivalent of Circuit of figure 3 ZTh= 1.5ρ ...... Equation (5)

Z For step voltage accidental(5) circuit = -----Equation (1) Th= 1.5ρ ...... Equation Volume푻+풉 10 v No. 1 v January 2021 푽 For step voltage accidental circuit =풃 -----Equation (1) 풁+푻풉 푹푩 푰 푽푻풉 풃 For touch voltage accidental circuit 푰 풁푻풉 푹푩 ..... Equation (2) For touch= voltage accidental circuit 푹풇 .....� Equation (2) 풛푻풉 ퟐ And= for the step voltage accidental circuit 푹풇 � 풛푻풉 ퟐ ...... Equation (3) And for =the step voltage accidental circuit 푻풉 ퟐ푹풇 풛= ...... Equation (3)

풛푻풉 ퟐ푹풇

Fig. 5 Different Resistances of Circuit for Step Voltage

Significance of Quality & Quantity of Gravel for Safe Designing of Grounding is the maximum (Earthing) fault System clearing of Substationtime (s) s 13 Fig.6 Thevenin Equivalent of Circuit of figure 5 taken as a circular plate with a radius of 0.08m. With only slight approximation, equations for ZTh can be obtained in ...Equation (13) numerical from and expressed in terms of as follows: ...... Equation (13) WhereWhere Cs is the is surfacethe surface layer layer derating derating factor = ...... Equation (4) ...Equation (4) ρ isis thethe soil soil resistivity resistivity (Ω.m) (Ω.m) 흆 is the resistivity of the surface layer material (Ω.m) Where ρ =풇 Resistivityퟒ풃 of the soil P is the resistivity of the surface layer material 푹 s is the thickness of the surface layer (m) Where ρ = Resistivity of the soil (Ω.m) For touch voltage accidental circuit

hs is the thickness of the surface layer (m) ZForTh = touch1.5 ρ voltage accidental...Equation circuit (5) For step voltage accidental circuit 3. Purpose of Gravel (Surface ZTh= 1.5ρ ...... Equation (5) Z= 6.0 ρ ...Equation (6) Material) in Switchyard ZTh= 6.0Th ρ ------Equation (6) There are various benefits of using Stones/Gravel over The permissibleFor step total voltage equivalent accidental voltage (i.e., tolerablecircuit The permissible total equivalent voltage (i.e., tolerablethe touch PCC and(Plain step Cement Concrete) in Switchyard. touch and step voltage), using above Equations are voltage), using above Equations are 1. Gravel Increases Resistance between Our Foot Etouch = IB (RB+1.5 ρ) ...Equation (7) & Ground. EEtouch = IB = (R IBB (R+1.5+6.0 ρ )ρ) ...... Equation...Equation (7) (8) step B Substation Switchyard is already grounded by earth mats The equations 7 and 8 shall be changed into equation Estep = IB (RB+6.0 ρ) ...... Equation (8) to provide a very low resistance path to the fault current 9 &10 and 11&12 respectively if we are using surface to flow to the ground. But, the Stones or Gravels are used The equations 7 and 8 shall be changed into equation 9 &10 and 11&12 material with resistivity ρs. in the Switchyard to decrease the Foot Surface Area. Therespectively maximum if wetolerable are using voltages surface for material step and with touch resistivity When ρs. the touch surface area decreases the resistance scenarios can be calculated empirically from IEEE Std increases. SectionThe maximum 8.3 for body tolerable weights voltages of 50 forkg stepand 70and kg: touch scenarios can be calculated empirically from IEEE Std Section 8.3 for body weightsSo, the ofmain 50kg purpose of filling Switchyard with Stones/ and 70kg: Gravels is to provide an extra layer of high resistance and act as an insulator between our foot and the ...Equation (9) ground...... (9) EquationThus, Fig.7gravels Impact in Switchyard of Resistivity increases of Gravel theon Safe resistance Potentials (70 kg) between our foot and ground. ...Equation (10) 2. Gravels Prevent the Accumulation of Rain Water -----Equation (10) in Switchyard

Stones/Gravels prevent the accumulation of water over ...Equation (11) the PCC surface in Switchyard and even if some water accumulates over some part of PCC due to the non- ...... Equation (11) uniform (not fully plain) surface then Gravel provides some breaks over the surface of the water. It makes the current non-continuous through our body and finally, it increases the resistance. ...Equation (12) ...... EquationFinally, (12) the rainwater can drop faster and it doesn’t make any mud inside the Substation. It protects the moisture Where E is the touch voltage limit (V) touch content evaporation and keeps the ground wet.

Estep is the step voltage limit (V) Where is the touch voltage limit (V) 3. Gravel Increases Tolerable Step Potential & is the surface layer derating factor Touch Potential is the step voltage limit (V) ρs is the soil resistivity (Ω.m) Step and Touch potentials increase during Short circuit is the surface layer derating factor t is the maximum fault clearing time (s) current. Gravel/Stones in Switchyard is provided to s is the soil resistivity (Ω.m) increase the tower footing resistance & helps in improving The choice of body weight (50kg or 70kg) depends tolerable step potential and touch potential when on the expected weight of the personnel at the site. operators work on Switchyard in the Substation. Typically, where women are expected to be on site, the conservative option is to choose 50kg. 4. Stone Prevents Vegetation & Growth of Small Weeds, Plants inside the Switchyard: This derating factor can be approximated by an empirical formula as per IEEE Std 80 Equation 13: Vegetation is already prevented by PCC in the switchyard.

Volume 10 v No. 1 v January 2021 is the maximum fault clearing time (s)

...... Equation (13) 14 CIGRE India JournalWhere is the surface layer derating factor is the soil resistivity (Ω.m) But, if we don’t fill with gravels then after some days/ 4. Impact is the resistivity of ofQualit the surface ylayer and material Quantit (Ω.m) y months/years, some soils & water will accumulate in is the thickness of the surface layer (m) of Gravel (Surface Material) on many parts on the Switchyard and grass will also grow. Grounding (Earthing) Design Thus, Gravels prevents the growth of grass & other small It is very interesting to understand the impact of resistivity plants inside the Switchyard and Substation remains (quality) of gravel (surface layer material) & height of nice & clean. gravel (quantity) on different parameters of design of earthing (grounding) system. 5. Prevents the Entry of Animals & Wildlife: The entry of animals likes Rats, Snakes, Lizards, etc. First of all , to analyze the impact of gravel resistivity on are also prevented to some extent by spreading Gravels safe step and touch potential for 70 kg body weight refer over the Switchyard surface. Table 1 along with Figure 7 below. is the maximum fault clearing time (s) 6. Improves Yard Working Condition Gravels also improve the working condition in the Switchyard of a Substation. 7. Protect from Fire when Oil Spillage Takes Place ...... Equation (13) In Substation, Power Transformers & Shut Reactors are filledWhere with oil as a cooling is the and surface insulating layer medium. derating factor Oil leakage may takes place during operation or when F ig. Fig.7 7 : Impact Impact of of Resistivity Resistivity of of Gravel Gravel on Safe PotentialsPotentials (70 (70 kg) kg) changing the oil is in thethe transformer. soil resistivity The spillage (Ω.m) oil which Further to analyze the impact of gravel resistivity on safe can catch fire is dangerous to the switchyard operation. is the resistivity of the surface layerstep and material touch potential (Ω.m) for 50 kg body weight refer Table So, Stones/Gravel is provided to protect from fire when 2 along with Figure 8. oil spillage takes is place. the thickness of the surface layer (m) Table 1 : Impact of Gravel Resistivity on Safe Potentials (70 kg)

Further to analyze the impact of gravel resistivity on safe step and touch potential for 50 kg body weight refer table 2 along with figure 8 below.

Table 2 Impact of Gravel Resistivity on Safe Potentials (50 kg) Table 2 : Impact of Gravel Resistivity on Safe Potentials (50 kg)

Volume 10 v No. 1 v January 2021

Fig.7 Impact of Resistivity of Gravel on Safe Potentials (70 kg)

Fig.8 Impact of Resistivity of Gravel on Safe Potentials (50 kg)

From above it can be seen that with the increase in the resistivity of the gravel the safe potentials (step and touch potential) also increase.

Next ,to analyze the impact of height of gravel on safe step and touch potential for 70 kg body weight refer table 3 along with figure 9 below.

Further to analyze the impact of gravel resistivity on safe step and touch potential for 50 kg body weight refer table 2 along with figure 8 below.

Table 2 Impact of Gravel Resistivity on Safe Potentials (50 kg)

Table 3 Impact of Gravel Height on Safe Potentials (70 kg)

Significance of Quality & Quantity of Gravel for Safe Designing of Grounding (Earthing) System of Substations 15

Table 4 Impact of Gravel Height on Safe Potentials (50 kg)

Fig.8Fig. Impact 8 : Impact of Resistivity of Resistivity of Gravel of on Gravel Safe Potentials on Safe Potentials(50 kg) F ig. Fig.9 9 : Impact Impact of of Height Height of of Gravel Gravel on onSafe Safe Potentials Potentials (70 kg)(70 kg)

From above it can be seen that with the (50increase kg) in the resistivity of the Now to analyze the impact of height of gravel on safe step and touch gravel Fromthe safe above potentials it (stepcan andbe touchseen potential) that with also increase.the increase in the potential for 50 kg body weight refer table 4 along with figure 10 below.

Next ,toresistivity analyze the of impact the gravelof height the of gravel safe onpotentials safe step and (step touch and touch potentialpotential) for 70 kg bodyalso weight increase. refer table 3 along with figure 9 below. Next, to analyze the impact of height of gravel on safe step and touch potential for 70 kg body weight refer Table 3 along with Figure 9. Now to analyze the impact of height of gravel on safe step and touch potential for 50 kg body weight refer Table 4 alongTable with 3 Figure Impact 10. of Gravel Height on F ig. Fig.10 Safe 10 : ImpactImpact Potentials of Height of of Gravel Gravel (70 on on Safekg) Safe Potentials Potentials (50 (50 kg) kg) : Impact of Gravel HeightFrom on above Safe it canPotentials be seen that (70 with kg) the increase in the height of the gravel Table 3 the safe potentials (step and touch potential) also increase.

It is very interesting to analyze the impact resistivity of gravel on derating factor refer table 5 along with figure 11 below.

Table 4 Impact of Gravel Height on Safe Potentials (50 kg)

Table 4 : Impact of Gravel Height on Safe Potentials (50 kg)

Volume 10 v No. 1 v January 2021

Fig.9 Impact of Height of Gravel on Safe Potentials (70 kg)

Now to analyze the impact of height of gravel on safe step and touch potential for 50 kg body weight refer table 4 along with figure 10 below.

Fig.10 Impact of Height of Gravel on Safe Potentials (50 kg)

From above it can be seen that with the increase in the height of the gravel the safe potentials (step and touch potential) also increase.

It is very interesting to analyze the impact resistivity of gravel on derating factor refer table 5 along with figure 11 below.

Table 6 Impact of Gravel Height on Derating Factor

Table 5 Impact of Resistivity of Gravel on Derating Factor 16 CIGRE India Journal

From above it can be seen that with the increase in the height of the gravel the safe potentials (step and touch potential) also increase. It is very interesting to analyze the impact resistivity of gravel on derating factor refer Table 5 along with Figure 11 below.

F Fig.12ig.12 Impact: Impact of ofResistivity Resistivity of Gravel of Gravel on Safe on PotentialsSafe Potentials

From above it can be seen that with the increase in the height of the gravel the derating factor also increases which further increase the safe potentials. 5. CONCLUSION Fig.11 Impact of Resistivity of Gravel on Derating Factor Fig. 11 : Impact of Resistivity of Gravel on Derating Factor The voltage drop in the soil surrounding the grounding system can present hazards i.e. Step and touch voltage From above it can be seen that with the increase in the resistivity of the gravelFrom (ratio above of gravel it can to soil be resistivity) seen that the deratingwith the factor increase decreases. in the for personnel standing in the vicinity of the grounding resistivity of the gravel (ratio of gravel to soil resistivity) Further to analyze the impact height of gravel on derating factor refer table system. Adequate designing of grounding system will 6the along derating with figure factor 12 belo decreases.w. help in mitigating or eliminating electric shocks, fire and Further to analyze the impact height of gravel on derating damage to equipments. factor refer Table 6 along with Figure 12 below. Table 5 Impact of Resistivity of Gravel on Derating Factor Table 5 : Impact of Resistivity of Gravel on Derating Factor

Table 6 Impact of Gravel Height on Derating Factor Table 6 : Impact of Gravel Height on Derating Factor

Volume 10 v No. 1 v January 2021

Fig.11 Impact of Resistivity of Gravel on Derating Factor

From above it can be seen that with the increase in the resistivity of the gravel (ratio of gravel to soil resistivity) the derating factor decreases.

Further to analyze the impact height of gravel on derating factor refer table 6 along with figure 12 below.

Fig.12 Impact of Resistivity of Gravel on Safe Potentials

Significance of Quality & Quantity of Gravel for Safe Designing of Grounding (Earthing) System of Substations 17

Role of quality (resistivity) and quantity (height) of gravel Authors Biographical Detail in the switchyard play important role in deciding the Dr. RAJESH KUMAR ARORA obtained the B. Tech. safe potential (tolerable potentials i.e. touch and step & Master of Engineering (ME) degrees in Electrical potentials). Engineering from Delhi College of Engineering, REFERENCES University of Delhi, India in 1999 and 2003 respectively. He completed his PhD in grounding system design from [1] IEEE Std. 80-2013, IEEE Guide for Safety in AC UPES, Dehradun. He is also certified Energy Manager Substation Grounding and Auditor. He has worked in 400 kV and 220 kV [2] I.S.3043-2018- Code of Practice for Earthing. Substation for more than 14 years in Delhi Transco [3] Manual on,” Earthing of A C Power Systems,” Limited (DTL). He has also worked as Deputy Director Publication No 339, C.B.I.P. New Delhi. (Transmission and Distribution) in Delhi Electricity Regulatory Commission (DERC) for 03 years and 06 [4] IEC 60479 - Effect of Electric Current on Human months. He has also given his contribution in the OS Being and Livestock department of DTL for more than 2 years and rendered his services in the SLDC of Delhi Transco Limited (DTL) also. Presently he is working in D&E (Design and Engineering) department of DTL. His research interests include high voltage technology, grounding system, protection system, computer application and power distribution automation.

Volume 10 v No. 1 v January 2021 Condition Monitoring of GIS Surge Arresters

M. Mohana Rao Archana L Mritunjay Kumar BHEL Corp. R&D, Hyderabad, India Abstract Leakage current measurement plays an important role in determining the healthiness of high voltage insulation of a power apparatus. The accurate and real time measurement of leakage current enables the utilities to access the healthiness of the gas insulated surge arrester. This paper describes about the design, development, calibration and testing of a novel non-contact type passive leakage current sensor, which can be used for monitoring of gas insulated surge arresters. Metal enclosed gas insulated surge arrester is one of the important components of Gas Insulated Substation (GIS). These arresters are installed to protect various electrical equipment in the GIS against over voltages. While in service high-energy stresses may lead to degradation and damage of surge arresters. To establish capabilities of the developed sensor with optimized design parameters, laboratory measurements of leakage current on 420 kV and 145 kV GIS surge arrester prototypes have been carried out and reported in the paper. Third harmonic content of surge arrester leakage current has been estimated in-line with IEC requirement to assess the healthiness of the surge arrester. Finally, resistive component has been extracted from leakage current of a 145kV GIS surge arrester under laboratory conditions. Keywords – Diagnostics, gas insulated surge arrester, GIS, leakage current, resistive component. I. Introduction has only little change. The increase of the resistive Gas-insulated metal oxide arresters provide protection component would lead to heating up of the arrester, which for gas insulated substation modules against operational may finally cause damage to the arrester. Therefore, over voltages, lightning and switching surges. The the resistive component of leakage current is of great gas insulated surge arrester with excellent protection importance in GIS arresters and should be monitored characteristics would decrease the overvoltage level continuously. Sometimes, absorption of moisture by applied on the power apparatus, hence helps to reduce ZnO blocks result to increase in resistive component their insulation levels and improve reliability. Surge significantly [4]-[5]. It is also important to note that the arrester is a vital component of substation and in case resistive component of leakage current reflects the third of its failure, offer limited protection to the substation harmonic current and hence it is of great importance in equipment against over voltages. Under these conditions, GIS arresters. In view of above, measurement of third over voltages lead disruptive discharges may result to harmonic leakage current of gas insulated metal oxide failures in substation equipment. Hence, to avoid surge surge arrester under operating voltage is one of widely arrester failures, it is necessary to monitor healthiness used techniques to evaluate degradation level of the of the surge arrester regularly. Measurement of resistive surge arrester [6]-[8]. leakage current and third harmonic leakage current In the recent years, various leakage current measurement of gas insulated metal oxide surge arresters under systems for high voltage power equipment, have been operating voltage are widely used techniques to evaluate developed and are available in the market. In the degradation level of the surge arrester [1]-[3]. available systems, the ground connection of the electrical The total leakage current of surge arrester (SA) is the device is disconnected and suitable impedance in the sum of capacitive and resistive current components. form of a resistor or a capacitance is introduced. The Under normal working conditions, the leakage current voltage that appears across this impedance is taken as a is mainly contributed by capacitive current component measure of the leakage current [1]. A typical conventional and resistive current component is only a small part of it. setup for measurement of leakage current is given in Due to aging of non-linear SA blocks, the resistive current Fig. 1. In this system, there is a provision for leakage increases substantially. However, the leakage current current measurement (LCM) as required during service

Volume 10 v No. 1 v January 2021 18 Condition Monitoring of GIS Surge Arresters

M. Mohana Rao Archana L Mritunjay Kumar BHEL Corp. R&D BHEL Corp. R&D BHEL Corp. R&D Hyderabad, India Hyderabad, India Hyderabad, India [email protected] [email protected] [email protected]

Abstract—Leakage current measurement plays an important of leakage current is of great importance in GIS arresters role in determining the healthiness of high voltage insulation of a and should be monitored continuously. Sometimes, power apparatus. The accurate and real time measurement of absorption of moisture by ZnO blocks result to increase in leakage current enables the utilities to access the healthiness of the resistive component significantly [4]-[5]. It is also important gas insulated surge arrester. This paper describes about the design, to note that the resistive component of leakage current development, calibration and testing of a novel non-contact type passive leakage current sensor, which can be used for monitoring reflects the third harmonic current and hence it is of great of gas insulated surge arresters. Metal enclosed gas insulated surge importance in GIS arresters. In view of above, measurement arrester is one of the important components of Gas Insulated of third harmonic leakage current of gas insulated metal Substation (GIS). These arresters are installed to protect various oxide surge arrester under operating voltage is one of widely electrical equipment in the GIS against over voltages. While in used techniques to evaluate degradation level of the surge service high-energy stresses may lead to degradation and damage arrester [6]-[8]. of surge arresters. To establish capabilities of the developed sensor In the recent years, various leakage current measurement with optimized design parameters, laboratory measurements of systems for high voltage power equipment, have been leakage current on 420 kV and 145 kV GIS surge arrester developed and are available in the market. In the available prototypes have been carried out and reported in the paper. Third harmonic content of surge arrester leakage current has been systems, the ground connection of the electrical device is estimated in-line with IEC requirement to assess the healthiness of disconnected and suitable impedance in the form of a the surge arrester. Finally, resistive component has been extracted resistor or a capacitance is introduced. The voltage that from leakage current of a 145kV GIS surge arrester under appears across this impedance is taken as a measure of the laboratory conditions. leakage current [1]. A typical conventional setup for measurement of leakage current is given in Fig. 1. In this Keywords— Diagnostics, gas insulated surge arrester, GIS, system, there is a provision for leakage currentCondition measurement Monitoring of GIS Surge Arresters 19 leakage current, resistive component. (LCM) as required during service to analyze healthiness of equipmentto analyze healthiness [1]-[3]. However, of equipment this [1]-[3]. method However, has its this own II. LEAKAGE CURRENT SENSOR DESIGN I. INTRODUCTION limitationsmethod has and its drawbacks own limitations. In case and the drawbacks. connection In with case the The leakage current from the high voltage insulation the connection with the impedance is disconnected or Gas-insulated metal oxide arresters provide protection impedance is disconnected or else there is an over voltage depends mainly on the capacitance of the insulation and whichelse there appear is acrossan over the voltage impedance, which the appear measurement across circuit the the applied voltage. Mathematically, if the capacitance of for gas insulated substation modules against operational impedance, the measurement circuit experiences high experiences high voltage that can damage the circuit and is the insulation is C and the applied voltage to the insulation over voltages, lightning and switching surges. The gas voltage that can damage the circuit and is also unsafe also unsafe to the operating personnel. In such cases, a is V, then the capacitive impedance Z of the insulating insulated surge arrester with excellent protection to the operating personnel. In such cases, a protection protection circuit and also an isolation circuit are employed material would be 1/ωC. Thus, the leakage current I, characteristics would decrease the overvoltage level applied circuit and also an isolation circuit are employed to on the power apparatus, hence helps to reduce their to minimize the effect of the over voltage. However, such shall be VωC. This condition is valid assuming that the minimize the effect of the over voltage. However, such resistive impedance of the insulation is much more than insulation levels and improve reliability. Surge arrester is a protection/isolationprotection/isolation circuit circuit is isalways always not notreliable reliable,, and furtherand vital component of substation and in case of its failure, offer increases the cost. It is also important that most of the the capacitive impedance and thus the total leakage further increases the cost. It is also important that most of current is primarily the capacitive leakage current. limited protection to the substation equipment against over equipmentthe equipment manufactures manufactures usually usually may may not not recommend recommend the voltages. Under these conditions, over voltages lead disconnectionthe disconnection of the of equipment the equipment ground ground connecti connection.on. Thus, based on the capacitance value of the insulation, disruptive discharges may result to failures in substation the corresponding leakage current can range from few equipment. Hence, to avoid surge arrester failures, it is micro amps to few milli amps. Hence a sensitive sensor necessary to monitor healthiness of the surge arrester must be designed to work in this range. Further, to regularly. Measurement of resistive leakage current and maintain a non-contact type approach, the sensor should third harmonic leakage current of gas insulated metal oxide be designed to form a closed loop around current carrying surge arresters under operating voltage are widely used conductor and produce an output voltage proportional techniques to evaluate degradation level of the surge arrester to the current flowing in the conductor. The typical sensor construction is as shown in Fig. 2. Theoretically, [1]-[3]. measurement of magnetic flux produced by the leakage The total leakage current of surge arrester (SA) is the current carrying conductor gives a direct measurement of sum of capacitive and resistive current components. Under the leakage current. The produced magnetic flux is linked normal working conditions, the leakage current is mainly to the sensor coil and can be measured in terms of the contributed by capacitive current component and resistive sensor coil output voltage. In practice, it is desirable that current component is only a small part of it. Due to aging of this voltage shall be large enough to be measured easily non-linear SA blocks, the resistive current increases and accurately. The sensors output signal amplitude is substantially. However, the leakage current has only little increased optimally by designing suitable number of change. The increase of the resistive component would lead turns, cross section of the sensor core and choosing to heating up of the arrester, which may finally cause core material with required magnetic properties. The B-H damage to the arrester. Therefore, the resistive component FigFig.. 1: 1 :Conventional Conventional LeakageLeakage Current MeasurementMeasurement Set-upSet-up characteristic of the core material used is such that, even

In the present paper, a non-contact type leakage current for very low current (leakage current) the output from the

sensor has been developed, which can be directly integrated sensor is at substantial level with linear characteristics. with the HV device, using suitable adapters. Using the Since the current to be measured with the sensor is of developed leakage current sensor, the ground connection micro ampere range, special magnetic core material was used. Further, it is necessary to observe the operation of the HV device is maintained through the sensor, thereby eliminating the drawbacks of the conventional system limits in the hysteresis and saturation curves with the as mentioned above. The output of the sensor can be purpose to avoid non-linearity problems. More clearly, the integrated with an online monitoring system to assess the operation region has been selected optimally to obtain a linear ratio between the voltage V and the leakage healthiness of the insulation on continuous basis. In this current, I in the current sensor operation. To further paper detailed analysis of the developed sensor to monitor enhance the output voltage from the sensor, a power surge arresters has been presented. frequency filter with RC combination can be integrated In this paper, an experimental investigation of GIS with the sensor. The filter rejects any high frequency (HF) surge arrester monitoring as per IEC 60099-5 standard noises associated with the leakage current and thereby is discussed. For leakage current measurements, a increasing the output signal strength of the sensor. The non-contact type current sensor designed in the study, sensor design as explained above ensures that the is installed at the insulated ground terminal of GIS sensor is fully passive and does not require any input surge arrester. Optimization of sensor design and its voltage for its operation. This enables a low cost solution suitability for measurement of leakage current for present for sensor manufacturing and its subsequent utilization application are discussed in detail in the paper. The for various online monitoring applications. The typical leakage current has been measured for 145 kV and 420 design parameters of a leakage current sensor for power kV gas insulated surge arrester modules developed in equipment monitoring applications are: the study. The resistive current component was extracted • Core : Special magnetic core material with high from leakage current data measured from the 145 kV gas permeability insulated surge arrester. • Core Inner Diameter (ID) : 40 mm

Volume 10 v No. 1 v January 2021 In the present paper, a non-contact type leakage current operation limits in the hysteresis and saturation curves with sensor has been developed, which can be directly integrated the purpose to avoid non-linearity problems. More clearly, with the HV device, using suitable adapters. Using the the operation region has been selected optimally to obtain a developed leakage current sensor, the ground connection of linear ratio between the voltage V and the leakage current, I the HV device is maintained through the sensor, thereby in the current sensor operation. To further enhance the eliminating the drawbacks of the conventional system as output voltage from the sensor, a power frequency filter mentioned above. The output of the sensor can be integrated with RC combination can be integrated with the sensor. The with an online monitoring system to assess the healthiness filter rejects any high frequency (HF) noises associated with of the insulation on continuous basis. In this paper detailed the leakage current and thereby increasing the output signal analysis of the developed sensor to monitor surge arresters strength of the sensor. The sensor design as explained above has been presented. ensures that the sensor is fully passive and does not require any input voltage for its operation. This enables a low cost In this paper, an experimental investigation of GIS surge solution for sensor manufacturing and its subsequent arrester monitoring as per IEC 60099-5 standard is discussed. utilization for various online monitoring applications. The For leakage current measurements, a non-contact type typical design parameters of a leakage current sensor for current sensor designed in the study, is installed at the power equipment monitoring applications are: insulated ground terminal of GIS surge arrester.

Optimization of sensor design and its suitability for  Core : Special magnetic core material with high measurement of leakage current for present application are 20 CIGRE India Journal permeability discussed in detail in the paper. The leakage current has been  measured for 145 kV and 420 kV gas insulated surge arrester • Core Core Outer Inner Diameter Diameter (OD) (ID) : 40mm : 65 mm current ranging from few tens of micro-amperes to tens modules developed in the study. The resistive current • Core Core Height Outer Diameter (OD) : 65mm : 30 mm of kilo-amperes. The characteristic of the surge arrester  component was extracted from leakage current data • Gauge Core of Heightwinding wire : 30mm : 30 SWG can be divided into three regions, low current region,  Gauge of winding wire : 30SWG measured from the 145 kV gas insulated surge arrester. • No. of turns : 400 operating region and high current region. The high  No. of turns : 400 current region relates to protective characteristic of the • No. of layers : 2 II. LEAKAGE CURRENT SENSOR DESIGN No. of layers : 2 arrester when the current due to over voltage has flown These parameters are the optimized values after through the arrester. In the continuous operating voltage The leakage current from the high voltage insulation evaluatingThese parameters sensor aredesigns the opt withimized different values ID, OD,after numberevaluating of region (up to rated voltage of the arrester), the ZnO depends mainly on the capacitance of the insulation and the turnssensor and designs number with of differentlayers. The ID, above OD, number design parametersof turns and surge arrester can be modeled as a non-linear resistor applied voltage. Mathematically, if the capacitance of the notnumber only giveof layers us the. The best above electrical design output parameters which can not drive only with a linear capacitive element in parallel. Increase in insulation is C and the applied voltage to the insulation is V, thegive data us theacquisition best electrical module output of the which associated can drive monitoring the data the resistive leakage current, in general, increases the then the capacitive impedance Z of the insulating material system,acquisition but module also ensures of the associated that the monitoringsensors are syst smallem, butin power losses and hence, increases the temperature of would be 1/ωC. Thus, the leakage current I, shall be VωC. size.also ensuresSmall sensorthat the issensors more are portable small in and size also. Small requires sensor the arrester. The resistive leakage current, at certain is more portable and also requires less core material which This condition is valid assuming that the resistive less core material which results in reduction of cost of instants, exceed a critical limit, where the accumulated theresults sensor. in reduction A typical of sensor cost of development the sensor. A typicalmade in sensor the impedance of the insulation is much more than the energy in the ZnO-blocks exceeds the energy capability studydevelopment is shown made in Fig in 2. the Equivalent study is electrical shown in circuit Fig is 2. capacitive impedance and thus the total leakage current is of the arrester. This may lead to abrupt failure of the primarily the capacitive leakage current. alsoEquivalent shown elect in Fig.rical 2. circuit is also shown in Fig. 2. arrester. The total leakage current (It) of the arrester is

the vector sum of a capacitive component (Ic), and the Thus, based on the capacitance value of the insulation, resistive leakage current component (Ir). the corresponding leakage current can range from few micro amps to few milli amps. Hence a sensitive sensor must be The leakage current of the surge arrester is in the range designed to work in this range. Further, to maintain a non- of tens of microamperes to few milliamps based on the contact type approach, the sensor should be designed to applied voltage of the arrester. The sensor employed for form a closed loop around current carrying conductor and the measurement was a non-contact type, Rogowski coil produce an output voltage proportional to the current based sensor which forms a closed loop around leakage flowing in the conductor. The typical sensor construction is current carrying conductor and gives an output voltage as shown in Fig. 2. Theoretically, measurement of magnetic proportional to the current flowing in the conductor. The flux produced by the leakage current carrying conductor laboratory setup for measurement of leakage current of gives a direct measurement of the leakage current. The 145 kV GIS surge arrester is shown in Figure 3(a). The produced magnetic flux is linked to the sensor coil and can experimental set-up consists of a gas insulated transformer be measured in terms of the sensor coil output voltage. In that energizes a gas insulated surge arrester through a practice, it is desirable that this voltage shall be large Fig. 2 : Typical Leakage Current Sensor developed in study gas insulated bus duct comprises of grounded enclosure enough to be measured easily and accurately. The sensors Fig 2: Typical Leakage Current Sensor developed in study with a central conductor. 145 kV GIS surge arrester is output signal amplitude is increased optimally by designing III. Voltage-Current suitable number of turns, cross section of the sensor core ChIII VaracteristicsOLTAGE-CURRENT CHARACTERISTICS of Gas OF GAS excited with voltage up to continuous operating voltage to INSULATED SURGE ARRESTER establish V-I characteristics. Gas insulated test transformer and choosing core material with required magnetic Insulated Surge Arrester properties. The B-H characteristic of the core material used The surge arrester is one of the critical components of the is rated for 325 kV(rms), 1 A and filled at a gas pressure The surge arrester is one of the critical components is such that, even for very low current (leakage current) the gas insulated substation, as it is extensively used in both of 3.5 bar(g). The system is partial discharge (PD) free of the gas insulated substation, as it is extensively output from the sensor is at substantial level with linear transmission and distribution networks to limit over voltages. for its rated voltage. For measuring leakage current, the characteristics. Since the current to be measured with the usedIn view in of both above, transmission IEC 60099-5 and covers distribution the various networksdiagnostic designed leakage current sensor was clamped on to the sensor is of micro ampere range, special magnetic core tomethods limit over and voltages. indicators In view for of revealing above, IEC the 60099-5 possible insulated ground terminal of the arrester. The test results material was used. Further, it is necessary to observe the coversdeterioration the various or failure diagnostic of the insulating methods properties and indicators of surge are shown in Table 1. Accuracy of this measurement for revealing the possible deterioration or failure of the of leakage current is confirmed by comparing current insulating properties of surge arresters. According to the levels with the data measured using digital earth leakage standards, most common and reliable diagnostic method clamp-on meter Model No. DCM 300E of resolution in is measurement of the arrester’s total leakage current the order of 1 µA (refer Table 1). From the results, it is and isolating its resistive component [9]. This component evident that current levels are within 5% difference and is an indicator of the arrester’s condition, as deterioration signifies accuracy of the developed portable CT sensor. or damage of arrester blocks lead to an increase of the The laboratory setup for measurement of leakage current resistive leakage current. From the various research from 420 kV GIS surge arrester is further shown in Fig. works published it is known that the change in third 3(b). The experimental set-up consists of a gas filled test harmonic component of leakage current of the surge transformer that energizes a gas insulated surge arrester arrester faithfully represents the change in resistive through a gas insulated bus duct comprises of grounded component of the leakage current. Some of the important enclosure with a central conductor and two epoxy methods are leakage current measurements, infrared insulators that support the conductor. A test transformer imaging, acoustic partial discharge measurements etc. is rated for 1000 kV (rms) and is partial discharge (PD) The surge arrester shows an excellent non linearity for free for rated voltage.

Volume 10 v No. 1 v January 2021 arresters.arresters. According According to to the the standards, standards, most most common common and and through a a gas gas insulated insulated bu bus s duct duct comprises comprises of of grounded grounded reliablereliable diagnostic diagnostic method method is ismeasurement measurement of of the the arrester’sarrester’s enclosure withwith aa central central conductor conductor and and two two epoxy epoxy insulators insulators totaltotal leakage leakage current current and and isolating isolating its its resistive resistive component component that support support the the conductorconductor. . A A test test transformer transformer is ratedis rated for for [9]. [9] This. This component component is is an an indicator indicator of of the the arrester’s arrester’s 1000 kVkV (rms)(rms) and and is is partial partial discharge discharge (PD) (PD) free free for forrated rated Condition Monitoring of GIS Surge Arresters 21 condition,condition, as detas deteriorationerioration or ordamage damage of of arrester arrester blocks blocks leadlead voltage. to an increase of the resistive leakage current. From the to an increase of the resistive leakage current. From the : Leakage current sensor data for 420kV GIS various research works published it is known that the change Table 2 various research works published it is known that the change Surge Arrester in third harmonic component of leakage current of the surge in third harmonic component of leakage current of the surge arrester faithfully represents the change in resistive Applied Leakage Leakage current arrester faithfully represents the change in resistive component of the leakage current. Some of the important Voltage (kV) current meter sensor output component of the leakage current. Some of the important Table 2: Leakage current sensor data for 420kV GIS Surge steps of 10 to 20 kV) has been applied to the 420 kV surge methods are leakage current measurements, infrared Table 2: Leakage currentreading sensor (mA) data for 420kVvoltage, GIS mV Surge steps of 10 to 20 kV) has been applied to the 420 kV surge methods are leakage current measurements, infrared Arrester arrester and the test results obtained are as shown in Table 2. imaging, acoustic partial discharge measurements etc. The Arrester20 0.136 0.42 Accuracyarrester and ofthe thistest results measurement obtained are of as leakage shown in current Table 2 is. imaging, acoustic partial discharge measurements etc. The Applied Voltage Leakage Leakage current Accuracy of this measurement of leakage current is surge arrester shows an excellent non linearity for current Applied40 Voltage Leakage0.260 Leakage0.84 current confirmed by comparing current levels with the data (kV) current meter sensor output confirmed by comparing current levels with the data surge arrester shows an excellent non linearity for current (kV) current meter sensor output measured using digital earth leakage clamp-on meter Model ranging from few tens of micro-amperes to tens of kilo- 60 reading0.390 (mA) voltage ,1.24 mV measured using digital earth leakage clamp-on meter Model ranging from few tens of micro-amperes to tens of kilo- reading (mA) voltage , mV No. DCM 300E of resolution in the order of 1 µA. From the amperes. The characteristic of the surge arrester can be 20 80 0.1360.550 0.42 1.63 No. DCM 300E of resolution in the order of 1 µA. From the 20 0.136 0.42 results, it was evident that current levels are within 2.0% amperes.divided The into characteristic three regions, of low the current surge region, arrester operating can be 40 0.260 0.84 differenceresults, it wasin the evident operating that region current and levels signifies are within accuracy 2.0% of 40 100 0.2600.607 0.84 1.90 dividedregion into and three high regions, current regio low n current. The high region, current operating region 60 0.390 1.24 thedifference developed in the sensor. operating Fig. 4 region shows andthe V signifies-I characteristics accuracy of 60 0.390 1.24 80 120 0.5500.716 1.63 2.20 the 145developed kV and sensor. 420 kV Fig. gas 4 insulated shows the surge V-I arresters.characteristics For 420 of regionrelates and to high protective current characteristic region. The of thehigh arrester current when region the 80 0.550 1.63 100 140 0.6070.847 1.90 2.66 kVthe 145 surge kV arrester, and 420 beyondkV gas insulated 390 kV, surge characteristics arresters. For become 420 relatescurrent to protectivedue to over characteristicvoltage has flown of thethrough arrester the arrester. when the In 100 0.607 1.90 kV surge arrester, beyond 390 kV, characteristics become 120 160 0.7161.000 2.20 2.90 non-linear and reference voltage is found to be close to 438 currentthe continuousdue to over operating voltage hasvoltage flown region through (up tothe rated arrester. voltage In 140120 0.8470.716 2.662.20 kV.non -linearSimilarly, and reference for 145 kVvoltage surge is arrester, found to beyond be close 130 to 438 kV, the ofcontinuous the arrester), operating the ZnO voltage surge arresterregion (upcan tobe rated modeled voltage as a 160140 180 1.0000.8471.075 2.902.66 3.10 characteristicskV. Similarly, become for 145 nonkV - surgelinear arrester, and reference beyond voltage 130 kV, is 160 1.000 2.90 characteristics become non-linear and reference voltage is non-linear resistor with a linear capacitive element in (a) 145 kV 180 200 1.0751.181 3.10 3.38 found to be close to 145kV (rms). of the arrester), the ZnO surge arrester can be modeled as a (a). 145 kV found to be close to 145kV (rms). parallel. Increase in the resistive leakage current, in general, 200180 1.1811.075 3.383.10 non-linear resistor with a linear capacitive element in 200 220 1.1811.274 3.38 3.65 (a). 145 kV 220 1.274 3.65 IV EXPERIMENTAL REALIZATION OF GIS SURGE ARRESTER increases the power losses and hence, increases the 220 1.274 3.65 parallel. Increase in the resistive leakage current, in general, 240 240 1.3901.390 4.00 4.00 IV EXPERIMENTALDIAGNOSTIC REALIZATION METHODS OF GIS SURGE ARRESTER temperature of the arrester. The resistive leakage current, at 240 1.390 4.00 DIAGNOSTIC METHODS increases the power losses and hence, increases the 250 250 1.4321.432 4.20 4.20 The GIS arrester was developed with ZnO elements stack certain instants, exceed a critical limit, where the * where250 x= leakage current1.432 in mA and 4.20y = sensor output in The GIS arrester was developed with ZnO elements stack temperature of the arrester. The resistive leakage current, at * where x= leakage current in mA and y = sensor output in mV; and the number of elements is based on its rated voltage. For accumulated energy in the ZnO-blocks exceeds the energy mV* where; y= 2.5824*xx= leakage + current0.4213 in mA and y = sensor output in and the number of elements is based on its rated voltage. For certain instants, exceed a critical limit, where the y= 2.5824*x + 0.4213 calculating the resistive leakage current and to assess the capability of the arrester. This may lead to abrupt failure of mV; y= 2.5824*x + 0.4213 calculating the resistive leakage current and to assess the accumulated energy in the ZnO-blocks exceeds the energy condition of the arrester an in-direct determination of the the arrester. The total leakage current (It) of the arrester is the conditionresistive component of the arrester has an been in -direct carried determination out by means of the of capability of the arrester. This may lead to abrupt failure of resistive component has been carried out by means of vector sum of a capacitive component (Ic), and the resistive leakage current measurement. the arrester. The total leakage current (It) of the arrester is the leakage current measurement. leakage current component (Ir). A. Determination of the resistive component from leakage vector sum of a capacitive component (Ic), and the resistive currentA. Determination measurement of the resistive component from leakage The leakage current of the surge arrester is in the range of current measurement leakage current component (Ir). A power frequency filter (50Hz filter) was designed and tens of microamperes to few milliamps based on the applied (b) 420 kV A power frequency filter (50Hz filter) was designed and (b). 420 kV integrated with the sensor, as described earlier. Similarly, a voltageThe leakage of thecurrent arrester. of the Thesurge sensor arrester employed is in the rangefor theof Fig. 3 : Experimental Set-up for Measurement of Leakage thirdintegrated harmonic with the filter sensor (150Hz, as described) was alsoearlier designed. Similarly for, a tensmeasurement of microamperes was ato non few-contact milliamps type, based Rogowski on the coil applied based Fig. 3 Experimental Set-upCurrent for Measurement of Leakage thirdmeasurement harmonic of third filter harmonic (150Hz) componentwas also of designed the leakage for Current (b). 420 kV measurementcurrent. These of filters third reject harmonic the highcomponent frequency of the noises leakage and voltagesensor of which the forarrester.ms a closedThe sensor loop around employed leakage for current the Table 1 : Measurement of Leakage current of Fig. 3 Experimental Set-up for Measurement of Leakage onlycurrent. allow These the filters leakage reject current the high of frequency 50Hz and noises 150 and Hz measurementcarrying conductor was a non and-contact gives an type, output Rogowski voltage proportional coil based Surge arrester only allow the leakage current of 50Hz and 150 Hz Current frequencies respectively to pass through them, as required for sensorto the which current for flowingms a closed in the conductor. loop around The leakagelaboratory current setup monitoringfrequencies ofrespectively the surge arrester.to pass through 145 kV them,GIS surge as required arrester for is Table Applied1. Measurement Measurement of Leakage current% deviationof Surge arrester monitoring of the surge arrester. 145 kV GIS surge arrester is carryingfor measurement conductor and of leakagegives an current output ofvoltage 145 kV proportional GIS surge (a) 145(a). 145kV kV energized with various voltage levels and the leakage current voltage, through non- of current energized with various voltage levels and the leakage current to thearrester current is flowing shown inin Figurethe conductor. 3(a). The The experimental laboratory setsetup-up (a). 145 kV sensor output was measured and analyzed. The kV contact type measurement correspondingsensor output plot was of the measured third harmonic and analyzed.content of The the for consists measurement of a gas of insulatedleakage transformer current of 145that kVenergizes GIS surge a gas Table 1. Measurement of Leakage current of Surge arrester corresponding plot of the third harmonic content of the Applied MeasurementCT sensor, milli through% deviation Clamp-on of leakage current is shown in Fig 5. By using fundamental insulated surge arrester through a gas insulated bus duct Amp Meter leakage current is shown in Fig 5. By using fundamental arrester is shown in Figure 3(a). The experimental set-up voltage, through non- current measurement component and third harmonic component of current, total comprises of grounded enclosure with a central conductor. leakagecomponent current and thirdhas been harmonic calculated. component From of the current, figure, total it is consists of a gas insulated transformer that energizes a gas kV 5.0 contact0.0249 type CT through+5.0 Clamp-on leakage current has been calculated. From the figure, it is insulated145 kV surge GIS arrester surge arrester through is exciteda gas insulatedwith voltage bus up duct to Applied Measurement % deviation of seen that third harmonic component increases continuously continuous operating voltage to establish V-I characteristics. 30.0 sensor,0.1624 milli Amp Meter+4.5 andseen the that rate third of increase harmonic is componentpredominant increases at higher continuouslyvoltages. At comprises of grounded enclosure with a central conductor. voltage, through non- current measurement and the rate of increase is predominant at higher voltages. At Gas insulated test transformer is rated for 325 kV(rms), 1 A 5.040.0 0.25530.0249 +2.55+5.0 lower applied voltages (from 5kV to 20kV) the resistive 145 kV GIS surge arrester is excited with voltage up to kV contact type CT through Clamp-on componentlower applied of voltages the arrester (from leakage 5kV to 20kV) current the would resistive be and filled at a gas pressure of 3.5 bar(g). The system is 3050.0.0 sensor,0.28720.1624 milli Amp Meter+0.97 +4.5 negligiblecomponent as of compared the arrester to the leakage capacitive current leakage would current. be continuous operating voltage to establish V-I characteristics. negligible as compared to the capacitive leakage current. partial discharge (PD) free for its rated voltage. For 4060.0.0 0.2553 +3.46+2.55 Thus the total leakage current at these voltages can be taken Gas insulated test transformer is rated for 325 kV(rms), 1 A 5.0 0.33990.0249 +5.0 Thus the total leakage current at these voltages can be taken measuring leakage current, the designed leakage current 50.0 0.2872 +0.97 as purely capacitive current. So the average value of the and filled at a gas pressure of 3.5 bar(g). The system is 3070.0.0 0.39110.1624 +2.70 +4.5 capacitanceas purely capacitive of the ZnO current. block Sofo the the arrester average was value calculated of the sensor was clamped on to the insulated ground terminal of 60.0 0.3399 +3.46 capacitance of the ZnO block of the arrester was calculated partial discharge (PD) free for its rated voltage. For 4080.0.0 0.44920.2553 -0.48 +2.55 to be close to 480pF. The capacitance of the ZnO block is the arrester. The test results are shown in Table 1. Accuracy 70.0 0.3911 +2.70 alsoto be got close verified to 480pF. through The experimentation capacitance of onthe limited ZnO blocknumber is measuringof this measurement leakage current, of leakagethe designed current leakageis confirmed current by 5090.0.0 0.51150.2872 -1.69 +0.97 also got verified through experimentation on limited number 80.0 0.4492 -0.48 (b) 420 kV of blocks. Assuming that the capacitance of the arrester ZnO sensorcomparing was clamped current on levels to the with insulated the data ground measur terminaled using of 60100.0.0 0.56240.3399 -1.32 +3.46 (b). 420 kV blockof blocks. would Assuming remain more that theor lesscapacitance the same of at the all artherester voltage ZnOs 90.0 0.5115 -1.69 Fig F ig. 4 4 : : Leakage Leakage current current calibration calibration (b). 420 curve curvekV for for gas insulatedinsulated block would remain more or less the same at all the voltages the digitalarrester. earth The leakage test results clamp are-on shownmeter Modelin Table No. 1. DCM Accuracy 300E Fig 4: Leakage current calibration curve for gas insulated (5kV to 120kV) and any abrupt change in the total leakage 17000..00 0.56240.3911 -1.32+2.70 surge arrester surge arrester current(5kV to at 120kV) higher appliedand any voltages abrupt changecan be inattributed the total mostly leakage to of thisof resolution measurement in the order of leakage of 1 µA current (refer Table is confirmed 1). From the by surge arrester current at higher applied voltages can be attributed mostly to 80.0 0.4492 -0.48 The leakage current of the surge arrester is in the range of the resistive component of the leakage current. comparingresults, it current is evident levels that with current the data levels measur are withined using 5% The leakage current of the surge arrester is in the range of the resistive component of the leakage current. 90.0 0.5115 -1.69 tens of microamperes to few milliamps depending on the Using this concept, the capacitive current component (I ) digitaldifference earth leakage and signifies clamp accuracy-on meter of Model the developed No. DCM portable 300E tens of microamperesVolume to few 10 milliamps v No. 1 dependingv January on 2021 the c 100.0 0.5624 -1.32 applied voltage of the arrester. The sensor forms a closed fromUsing 30 kVthis toco ncept 120 , kV the iscapacitive estimated current. Knowing component the total (Ic) CT sensor. The laboratory setup for measurement of leakage applied voltage of the arrester. The sensor forms a closed of resolution in the order of 1 µA (refer Table 1). From the loop around the insulated ground terminal and gives an fromleakage 30 current kV to (refer 120 Table kV is 2) estimated the resistive. Knowing component the of total the current from 420 kV GIS surge arrester is further shown in loopoutput around voltage the proportional insulated ground to the terminal current flowing and gives to the an leakage current (refer Table 2) the resistive component of the results, it is evident that current levels are within 5% output voltage proportional to the current flowing to the leakage current was calculated by assuming that the Fig. 3(b). The experimental set-up consists of a gas filled test ground which is primarily the leakage current. Voltage (in capacitiveleakage current and resistive was calculated current components by assuming differ thatin phase the difference and signifies accuracy of the developed portable ground which is primarily the leakage current. Voltage (in capacitive and resistive current components differ in phase CT transformersensor. The laboratory that energizes setup a for gas measurement insulated surge of leakagearrester current from 420 kV GIS surge arrester is further shown in Fig. 3(b). The experimental set-up consists of a gas filled test transformer that energizes a gas insulated surge arrester 22 CIGRE India Journal

The leakage current of the surge arrester is in the range current.by 90°. SoThe the results average are shown value in ofTable the 3.capacitance Here, the resistive of the conclude that the third harmonic component of leakage of tens of microamperes to few milliamps depending on ZnOleakage block current of the is arrester calculated was by calculated considering to nonbe -closeuniform to current of the GIS surge arrester faithfully represents the the applied voltage of the arrester. The sensor forms a 480pF.voltage The factors capacitance as 0% and of -the8% ZnO (highest block value is also obtained got healthiness of the surge arrester. through voltage distribution studies across blocks). The closed loop around the insulated ground terminal and verified through experimentation on limited number of One of the most widely used techniques for extracting the gives an output voltage proportional to the current flowing blocks. Assuming that the capacitance of the arrester resistive leakage current for the purpose of condition to the ground which is primarily the leakage current. ZnO block would remain more or less the same at all monitoring of surge arrester is the compensation technique. Voltage (in steps of 10 to 20 kV) has been applied to bythe 90°. voltages The results (5kV areto 120kV)shown in and Table any 3. abrupt Here, tchangehe resistive in Inconclude the compensation that the thirdtechnique harmonic, for measurement component of of leakage the the 420 kV surge arrester and the test results obtained leakagethe total current leakage is currentcalculated at higher by considering applied voltages non-uniform can resistivecurrent leakage of the current GIS surge, the arresterapplied voltage faithfully is not represents required the are as shown in Table 2. Accuracy of this measurement voltagebe attributed factors mostly as 0% to and the -resistive8% (highest component value obtained of the tohealthiness be monitored. of the This surge technique arrester. is most suitable for on-site through voltage distribution studies across blocks). The conditions. The method is based on the conditioning of the of leakage current is confirmed by comparing current leakage current. One of the most widely used techniques for extracting the total leakage current waveform to get its resistive levels with the data measured using digital earth leakage resistive leakage current for the purpose of condition clamp-on meter Model No. DCM 300E of resolution in component. Authors developed a system with necessary softwaremonitoring module of surge to calculate arrester the is resistthe compensationive component technique. of the the order of 1 µA. From the results, it was evident that leakageIn the current compensation of the technique GIS surge, for arrester measurement using above of the current levels are within 2.0% difference in the operating compensationresistive leakage technique current [9,] .the Results applied obtained voltage in isthe not present required region and signifies accuracy of the developed sensor. studyto be are mo comparednitored. This with techniqueresistive leakage is most currents suitable extracted for on- site Fig. 4 shows the V-I characteristics of the 145 kV and Fig. 5. Variation of third harmonic component of leakage fromcondition leakages. The current method data is using based compensation on the conditioning technique. of the 420 kV gas insulated surge arresters. For 420 kV surge current with respect to applied voltage. Fromtotal the leakage available current data , it waveform is evident to that get the its proposed resistive arrester, beyond 390 kV, characteristics become non- estimationcomponent. of resistiveAuthors leakage developed current a systemfrom leakage with current necessary Table 3. Calculation of Leakage Current components using linear and reference voltage is found to be close to 438 measurementsoftware module is accurate to calculate enough the to resist monitorive component healthiness of of the indirect method. kV. Similarly, for 145 kV surge arrester, beyond 130 kV, GISleakage surge arrester. current of the GIS surge arrester using above characteristics become non-linear and reference voltage compensation technique [9]. Results obtained in the present is found to be close to 145kV (rms). Voltage, Ic, p.u. Ir, p.u. Ic, p.u. Ir, p.u. CONCLUSIONstudy are compared with resistive leakage currents extracted Fig.Fig. 5. 5Variation : Variation of of third harmonic harmonic component component of ofleakage leakage from leakage current data using compensation technique. IV. Experimental realization of kV current(0% nonwith- respect(0% non to applied- (-8% voltage non- (-8% current with respectlinearity to appliedlinearity voltage. linearity non- From The the leakage available current data , measurement it is evident can that be the used proposed for GIS surge arrester diagnostic Using this concept, the capacitive current component monitoringestimation healthinessof resistive ofleakage surge current arresters, from insulators leakage andcurrent Table 3. Calculationvoltage of Leakagevoltage Currentvoltage components linearity using methods (I ) from 30 kV to 120 kV is estimated. Knowing the total variousmeasurement other electricalis accurate power enough apparatus. to monitor The healthiness insulation of indirectc method.factor) factor) factor) voltage The GIS arrester was developed with ZnO elements leakage current (refer Table 2) the resistive componentfactor) failureGIS surge of an arrester. electrical device is always unintentional and causes a flow of either leakage current or short circuit stack and the number of elements is based on its rated of the30 leakage.0 0.1508 current was0.0603 calculated 0.1387 by assuming 0.0844 that the capacitive40.0 0.2011 and resistive 0.1573 current components0.1850 0.1760 differ in current.CONCLUSION The leakage current, however, flows continuously voltage. For calculating the resistive leakage current Voltage, Ic, p.u. Ir, p.u. Ic, p.u. Ir, p.u. unlike short circuit current, with its magnitude being related phase50 .0by 90°.0.2513 The results0.1390 are shown0.2312 in Table 0.17043. Here, and to assess the condition of the arrester an in-direct kV (0% non- (0% non - (-8% non- (-8% to the condition of the insulation. The leakage current sensor 60.0 0.3016 0.1568 0.2774 0.1963 The leakage current measurement can be used for determination of the resistive component has been the resistivelinearity leakage currentlinearity is calculatedlinearity by consideringnon- as described in this paper is based on novel, compact and 70.0 0.3518 0.1708 0.3237 0.2195 monitoring healthiness of surge arresters, insulators and carried out by means of leakage current measurement. non-uniformvoltage voltage factorsvoltage as 0%voltage and -8% linearity(highest low cost design. The sensor design is optimized based on the 80.0 0.4021 0.2002 0.3699 0.2548 various other electrical power apparatus. The insulation A. Determination of the resistive component from leakage value obtainedfactor) through factor)voltage distributionfactor) studiesvoltage across type of power equipment and the leakage current levels to be .90.0 0.4524 0.2387 0.4162 0.2974 failure of an electrical device is always unintentional and current measurement blocks). The variation of the resistive leakage currentfactor) with monitored. The sensors output signal amplitude is increased respect30100.0 .0 to the0.1508 0.5026applied voltage0.06030.2523 is shown0.13870.4624 in Fig. 6. From0.32010.0844 the optimallycauses a by flow designing of either suitable leakage number current of or turns, short cross circuit A power frequency filter (50Hz filter) was designed and above40110.0 figures, .0 0.20110.5529 variation of0.15730.3024 third harmonic 0.18500.5087 component 0.37200.1760 and securrent.ction of The the sensor leakage core current, and choosing however, core flows material continuously with integrated with the sensor, as described earlier. Similarly, unlike short circuit current, with its magnitude being related the50 120resistive.0 .0 0.2513component0.6032 0.1390of0.3937 leakage current0.23120.5549 with0.45920.1704 applied required properties. More clearly, the sensitivity of the a third harmonic filter (150Hz) was also designed for to the condition of the insulation. The leakage current sensor voltage 60.0 are mostly0.3016 alike 0.1568and similar. 0.2774In other words,0.1963 we developed sensor as per its design is in the order of few measurement of third harmonic component of the as described in this paper is based on novel, compact and canvariation70 safely.0 of conclude the0.3518 resistive that leakage0.170 the third8 current harmonic0.3237 with respect component0.2195 to the micro-amperes for surge arrester monitoring. leakage current. These filters reject the high frequency low cost design. The sensor design is optimized based on the ofa pplied80leakage.0 voltage current0.4021 is shown of the 0.2002in GISFig. 6.surge From0.3699 arrester the above faithfully0.2548 figures, The leakage current measurements have been carried out noises and only allow the leakage current of 50Hz and type of power equipment and the leakage current levels to be representsvariation.90.0 of thethird0.4524 healthiness harmonic 0.2387 component of the surge and0.4162 the arrester. resistive 0.2974 on 145 kV and 420 kV GIS surge arrester prototypes and 150 Hz frequencies respectively to pass through them, as resultsmonitored. are The validated sensors with output the signal conventionally amplitude availableis increased required for monitoring of the surge arrester. 145 kV GIS 100.0 0.5026 0.2523 0.4624 0.3201 optimally by designing suitable number of turns, cross 110.0 0.5529 0.3024 0.5087 0.3720 current sensors. From the measurements, the variation of surge arrester is energized with various voltage levels thirdsection harmonic of the component sensor core and and the choosing resistive core component material of with 120.0 0.6032 0.3937 0.5549 0.4592 and the leakage current sensor output was measured and leakagerequired current propert withies applied. More voltage clearly, are t hefound sensitivity to be mostly of the analyzed. The corresponding plot of the third harmonic similardeveloped and alike. sensor The as extraction per its designof resistive is in component the order from of few content of the leakage current is shown in Fig 5. By using variation of the resistive leakage current with respect to the themicro total-amperes leakage currentfor surge is arresterfound to monitoring. be accurate enough with fundamental component and third harmonic component applied voltage is shown in Fig. 6. From the above figures, the method The leakage proposed current in the measure study. ments have been carried out of current, total leakage current has been calculated. variation of third harmonic component and the resistive on 145 kV and 420 kV GIS surge arrester prototypes and From the figure, it is seen that third harmonic component results are validatedACKNOWLEDGMENT with the conventionally available increases continuously and the rate of increase is currentAuthors sensors are thankful. From theto the measurements, Management ofthe BHEL variation for of predominant at higher voltages. At lower applied voltages theirthird permission harmonic to component publish the andwork. the resistive component of (from 5kV to 20kV) the resistive component of the arrester leakage current with applied voltage are found to be mostly leakage current would be negligible as compared to the similar and alike. The RextractionEFERENCES of resistive component from : Variation of resistive component of leakage capacitive leakage current. Thus the total leakage current Fig.F 6ig.. Variation 6 of resistive component of leakage current [1]the totalKuffel, leakage “High current Voltage is Engineering:found to be accurate Fundamentals”, enough 2e, with at these voltages can be taken as purely capacitive with respectcurrent to applied with respectvoltage. to applied voltage the methodElsevier Scienceproposed (reprint in the Technical study. Science & Engineering), 2005. component of leakage current with applied voltage are ACKNOWLEDGMENT mostly alike and similar. In other words, we can safely Volume 10 v No. 1 v January 2021 Authors are thankful to the Management of BHEL for their permission to publish the work.

REFERENCES Fig. 6. Variation of resistive component of leakage current [1] Kuffel, “High Voltage Engineering: Fundamentals”, 2e, with respect to applied voltage. Elsevier Science (reprint Technical Science & Engineering), 2005. component of leakage current with applied voltage are mostly alike and similar. In other words, we can safely Condition Monitoring of GIS Surge Arresters 23

Table 3 : Calculation of Leakage Current components by designing suitable number of turns, cross section of using indirect method. the sensor core and choosing core material with required properties. More clearly, the sensitivity of the developed Voltage, Ic, p.u. Ir, p.u. Ic, p.u. Ir, p.u. sensor as per its design is in the order of few micro- kV (0% non- (0% non (-8% (-8% amperes for surge arrester monitoring. linearity -linearity non- non- voltage voltage linearity linearity The leakage current measurements have been carried factor) factor) voltage voltage out on 145 kV and 420 kV GIS surge arrester prototypes factor) factor) and results are validated with the conventionally available 30.0 0.1508 0.0603 0.1387 0.0844 current sensors. From the measurements, the variation of 40.0 0.2011 0.1573 0.1850 0.1760 third harmonic component and the resistive component of 50.0 0.2513 0.1390 0.2312 0.1704 leakage current with applied voltage are found to be mostly similar and alike. The extraction of resistive component 60.0 0.3016 0.1568 0.2774 0.1963 from the total leakage current is found to be accurate 70.0 0.3518 0.1708 0.3237 0.2195 enough with the method proposed in the study. 80.0 0.4021 0.2002 0.3699 0.2548 Acknowledgment .90.0 0.4524 0.2387 0.4162 0.2974 Authors are thankful to the Management of BHEL for 100.0 0.5026 0.2523 0.4624 0.3201 their permission to publish the work. 110.0 0.5529 0.3024 0.5087 0.3720 120.0 0.6032 0.3937 0.5549 0.4592 References One of the most widely used techniques for extracting [1] Kuffel, “High Voltage Engineering: Fundamentals”, 2e, Elsevier Science (reprint Technical Science & the resistive leakage current for the purpose of condition Engineering), 2005. monitoring of surge arrester is the compensation technique. In the compensation technique, for [2] IEC60137-2008, Insulated bushings for alternating measurement of the resistive leakage current, the voltages above 1 000 V. applied voltage is not required to be monitored. This [3] Lundquist, L. Stenstrom, A. Schei and B. Hansen, technique is most suitable for on-site conditions. The “New method for measurement of the resistive leakage method is based on the conditioning of the total leakage currents of metal oxide surge arresters in service”, IEEE current waveform to get its resistive component. Authors Trans. Power Delivery, vol. 5, no.4, pp. 1811-1822, Oct. developed a system with necessary software module to 1990. calculate the resistive component of the leakage current [4] Tong Zhao, Qingmin Li and Jiali Qian, “Investigation on of the GIS surge arrester using above compensation digital algorithm for on-line monitoring and diagnostics technique [9]. Results obtained in the present study are of metal oxide surge arrester based on an accurate compared with resistive leakage currents extracted from model”, IEEE Transactions on Power Delivery, Vol. 20, leakage current data using compensation technique. No. 2, pp. 751 - 756, April 2005. From the available data, it is evident that the proposed [5] Surge arresters: Part 5: Selection and application estimation of resistive leakage current from leakage recommendations, International Electro-technical current measurement is accurate enough to monitor Commission (IEC): IEC 60099-5, 2000-2003. healthiness of GIS surge arrester. [6] Z. Abdul-Malek and Aulia Novizzon, “Metal Oxide Surge Arrester Degradation Monitoring using Third CONCLUSION Harmonic of the Resistive Leakage Current Component The leakage current measurement can be used for ass Indicator”, AUPEC, 14-17 December 2008, Sydney, monitoring healthiness of surge arresters, insulators and Dec 2008, pp. 1-5. various other electrical power apparatus. The insulation [7] Vegard Larsen and Kjetil Lien, “In-service testing and failure of an electrical device is always unintentional and diagnosis of gapless metal oxide surge arresters”, IX causes a flow of either leakage current or short circuit International Symposium on Lightning Protection, 26th current. The leakage current, however, flows continuously -30th November 2007, Foz do Iguacu, Brazil, unlike short circuit current, with its magnitude being [8] C.Karawita and M. R. Raghuveer, “Onsite MOSA related to the condition of the insulation. The leakage Condition assessment-A New Approach”, IEEE Trans. current sensor as described in this paper is based on Power Del., vol. 21, no. 3, pp. 1273-77, July 2006. novel, compact and low cost design. The sensor design [9] M. Mohana Rao and Mritunjay Kumar, “Experimental is optimized based on the type of power equipment evaluation of resistive leakage current in GIS surge and the leakage current levels to be monitored. The arresters”, International Journal of Power and Energy sensors output signal amplitude is increased optimally Systems, Vol. 36, No. 1, 2016.

Volume 10 v No. 1 v January 2021 Project GPTL

Sandip Maity Abshan Farooq Sterlite Power Transmission Ld. Abstract The Project Gurgaon Palwal Transmission Limited (GPTL), is designed and created to cater to the power requirements of the flourishing metropolis of Gurugram, Haryana, India. Gurugram, as we know, houses leading industrial and financial institutions, along with a thriving population, it often witnesses power-cuts, especially during summers. Since it is one of the growing and leading industrial and financial establishment in the North, GPTL Project has been designed to deliver over MW of power through three GIS establishments built across three different locations in Haryana, viz, Prithala, Kadarpur& Sohna Road.

I. INTRODUCTION land, along with the high cost of land was a major issue GPTL is a very crucial transmission project awarded, in which required that the stations be built with the smallest terms that the new (GIS) substations being built under footprint for economic reasons without compromising this project are a part of Inter-State Transmission System any technical standards. (ISTS). II. GIS SUBSTATION The project includes three new 400/220 kV GIS As explained in the introductory section that Gurgaon Substations in Palwal & Gurgaon districts. It also being a metropolis has major land availability issues. This II. GIS SUBSTATION includes an extension project in an existing 400/220 constraint, with respect to land, led to a solution which was an innovative layout, giving a remarkable reduction kV AIS Substation at Dhanonda (Haryana), which As explained in the introductory section that Gurgaon being a metropolis has major land comes under HVPNL (Haryana Vidyut Prasaran availabilityin footprint issues. Thismeeting constraint, all with the respect functionalities to land, led to a solution required. which was an Nigam Limited). In addition to this extension work at innovative layout, giving a remarkable reduction in footprint meeting all the functionalities required.The 400/220 kV GIS layout has the location of the Dhanonda, HVPNL Substation, a double circuit 400kV 400kV & 220 kV GIS installations at multiple levels transmission line too is under scope which connects The 400/220kV GIS layout has the location of the 400kV & 220kV GIS installations at multipleof the levels same of the samebuilding, building, with with 220kV 220kV line side equipmentline side placed equipment in the same the aforementioned substation and PGCIL Neemrana building,placed thereby in increasingthe same the power building, handled per unit thereby area. The layout increasing has the 400kV GISthe Substation (Rajasthan). with its Control & Protection system installed on the ground floor, which is further connected topower 500MVA handled400/220/33kV ICTsper and unit 420kV area. 125MVAr The Reactor layout placed justhas adjacent the to 400the The project scope also includes, a 400kV double circuit building.kV GIS This connectionwith its is Controlthrough Gas Insulated& Protection Bus (GIB) ducts, system thus eliminating installed SF6 to Oil Bushings for the Transformers and Reactor. The GIB ducts from 220kV side of transmission line, which runs from PGCIL Aligarh (U.P.) transformeron the isground routed from floor, inside the which building. Thisis further forms the bus connected ducts being routed to from 500 to (new) 400/220kV GIS Substation in Prithala (Palwal). groundMVA floor 400/220/33kV to the first floor of the ICTs building, and where 420 220kV kV GIS 125 is placed, MVAr alongside Reactor its From Prithala Substation, a 400kV double circuit line Contplacedrol & Protection just adjacent system. to the building. This connection is connects the second (new) 400/220kV GIS Substation at Kadarpur (Gurgaon). Further, from Kadarpur Substation, a 400kV double circuit line connects the third (new) 400/220kV GIS Substation at Sohna Road (Gurgaon). Furthermore, a double circuit 400kV line which connects PGCIL Manesar and PGCIL Gurgaon, is being LILOed at Sohna Road Substation. The paper describes a Gas Insulated sub-station (GIS) installation executed by Sterlite Power, India, which employs an unconventional approach towards a 400/220kV GIS installation. The project is situated near the large metropolis of Gurgaon in India, with availability of land being a major challenge as three 400/220kV GIS sub-stations had to be built relatively near to one another. Being so close to a major city, availability of Fig. 1 : 400 kV Gas Insulated Switchgear

Figure 1. Volume 10 v No. 1 v January 2021 24 400kV Gas Insulated Switchgear

Project GPTL 25 through Gas Insulated Bus (GIB) ducts, thus eliminating from inside the building. This forms the bus ducts being SF6 to Oil Bushings for the Transformers and Reactor. routed from ground floor to the first floor of the building, The GIB ducts from 220kV side of transformer is routed where 220kV GIS is placed, alongside its Control &

Figure 2.

400kV GIS BUILDING (GROUND FLOOR) LAYOUT Fig. 2 : 400 kV GIS Building (Ground Floor) Layout Figure 2.

400kV GIS BUILDING (GROUND FLOOR) LAYOUT

Fig. 3 : 220kV GIS Building (First Floor) Layout

Volume 10 v No. 1 v January 2021

Figure 3. 220kV GIS BUILDING (FIRST FLOOR) LAYOUT Figure 3. 220kV GIS BUILDING (FIRST FLOOR) LAYOUT

Figure 4. 220kV Gas Insulated Switchgear

This innovative layout also corresponds to elimination of 400kV gantry which is entirely made up of steel structure; hence benefitting in reducing the overall carbon footprint for the project. Stringing for the 220kV & 400kV circuits is done by erecting suitable steel structures along the length of the building. For both the voltage levels, viz. 400kV & 220kV, the jack bus is strung in two levels, one above the other, on either side of the building. Since the jack buses are placed just one above the other, phase segregation double tension string insulators are installed to insulate and establish necessary clearances between two circuits. The innovative layout of the building ensures that a control room with other facilities like, battery 26 room, AHU room and LT switchgearCIGRE India room Journal are accommodated in the same building.

Figure 5. 400kV Switchyard (View from Rooftop)

Protection system. Fig. 5 : 400kV Switchyard (View from Rooftop) Fig. 4 : 220kV Gas Insulated Switchgear two circuits. The innovative layout of the building ensures This innovative layoutFigure also4. corresponds to elimination of that a control room with other facilities like, battery room, 400kV gantry which is entirely made up of steel structure; AHU room and LT switchgear room are accommodated 220kV Gas Insulated Switchgear hence benefitting in reducing the overall carbon footprint in the same building.

for the project. Stringing for the 220kV & 400kV circuits Conventionally, GIS layout for a 400/220kV sub-station This innovative layoutis alsodone corresponds by erecting to elimination suitable ofsteel 400kV structures gantry which along is entirelythe of 2000MVA capacity would require about 15 acres of made up of steel structure;length hence of thebenefitting building. in reducing For both the overallthe voltage carbon footprintlevels, viz.for the land whereas the innovative layout described above project. Stringing for the 220kV & 400kV circuits is done by erecting suitable steel structures 400kV & 220kV, the jack bus is strung in two levels, one accommodates the whole station in approximately 3.8 along the length of theabove building. the For other, both onthe eithervoltage side levels, of viz. the 400kV building. & 220kV, Since the the jack bus is strung in two levels, one above the other, on either side of the building. Since the jack acres of land. This huge reduction in land by almost 75% jack buses are placed just one above the other, phase buses are placed just one above the other, phase segregation double tension string insulators has not only resulted in making the scheme economical are installed to insulatesegregation and establish double necessary tension clearances string insulators between two are circuits. installed The to execute but will also set a benchmark for the future to insulate and establish necessary clearances between innovative layout of the building ensures that a control room with other facilities like, battery installations and thus ensuring economic delivery of room, AHU room and LT switchgear room are accommodated in the same building.

Figure 5. 400kV Switchyard (View from Rooftop)

Figure 6. Fig. 6 : Line Side Equipment (Rooftop) Layout 220kV LINE SIDE EQUIPMENT (ROOFTOP) LAYOUT Volume 10 v No. 1 v January 2021 Conventionally, GIS layout for a 400/220kV sub-station of 2000MVA capacity would require about 15 acres of land whereas the innovative layout described above accommodates the whole station in approximately 3.8 acres of land. This huge reduction in land by almost 75% has not only resulted in making the scheme economical to execute but will also set a benchmark for the future installations and thus ensuring economic delivery of power.

III. TRANSMISSION TOWERS AND LINES

Facing some ROW (Right of Way) issues, the transmission towers are designed, manufactured, and erected for a span of 500 meters. Tower footing has been reduced drastically keeping in view the agricultural land. In purview of the innovative layout which is adopted in case of the newly constructed GIS substations, dead end towers have been designed as a double layered monopole, catering to four circuits, hence reducing the tower footprint and foundation size.

Project GPTL 27 power. Tower footing has been reduced drastically keeping in view the agricultural land. III. TRANSMISSION TOWERS AND LINES In purview of the innovative layout which is adopted in Facing some ROW (Right of Way) issues, the transmission case of the newly constructed GIS substations, dead towers are designed, manufactured, and erected for a end towers have been designed as a double layered span of 500 meters.

Fig. 7 : Monopole Fig. 8 : Monopole Figure 7. Figure 8. Monopole Monopole Figure 7. Figure 8. Monopole Monopole

Volume 10 v No. 1 v January 2021

B. P. Soni – I/C Superintending Engineer Corporate Engineering

Obtained Graduation in Electronics Engineering from Birla Vishwakarma Mahavidyalaya, Vallabh Vidyanagar (Gujarat) in 1989. He joined erstwhile Gujarat Electricity Board (GEB) in 1990.

Having total 30 years of experience in Power Generation & Transmission, he has worked in various fields e.g. Hydro and Thermal Power Plants, Operation & Maintenance of EHV Substations, Telecommunication, Protection and Automation, Substation Design and Equipment Engineering.

Presently, he is working as an In-Charge Superintending Engineer at Engineering Department, GETCO, Corporate office, Vadodara looking after all the engineering activities. A BVQI – TUV certified ISO auditor, he is a member of CIGRE and various Technical Committees of Electrotechnical Department of Bureau of Indian Standards (BIS). He was also a Technical Utility Roadmap for System StrengthCommittee Aspects Member of CBIP for for Substation Manual 2019

Reliability, Stability and Flexibility ofHe hasRE presented Rich Technical Modern Papers in various National & International conferences like GRIDTECH, Power Grid– Indian Grid SWITCHCON,Context CBIP & PowerLine events B. P. Soni – I/C Superintending Engineer Corporate Engineering N. M. Sheth – Executive Engineer, Corporate Engineering

Utility Roadmap for System strength aspects for Reliability, Stability and Flexibility of RE Rich Modern Power Grid– Indian grid context

B.P. SONI (I/C Superintending Engineer), N. M. SHETH (Executive Engineer)

GUJARAT B.P. ENSONIERGY TRANSMISSION CORPORATION Obt N.ained M. SGraduation HLIMITEDETH in Electrical Engineering from Saurashtra University Rajkot; and Qualification (I/C SuperintendingObtained Graduat Engineer)ion in Electronics Engineering (Executive from B Engineer)irla Vishwakarma Mahavidyalaya, Vallabh Vidyanagar (Gujarat) in 1989. He joined erstwhileof Certified Gujarat Project Electricity Man agementBoard (GEB) Associate in 1990. (Project Management Level-D, National Ranker) from Gujarat Energy Transmission CorporationInternational Limited Project Management Association (IPMA). Working in GETCO since 1994. Experience Introduction Having total 30 years of experience in Power Generationin the field of & Substation Transmission, Operation he has & workedMaintenance in various as well as Commissioning. Introduction 2022 that includes 100 GW Solar and 60GW wind from fields e.g. Hydro and Thermal Powercurrent 31 Plants, GW and Operation 37 GW level & respectively.Maintenance Share of of EHV Substations, RenewalRenewal energy’senergy’s rise rise and and increased increased role rolein meeting in meeting energy demandPresently has working brought in Engineeringwith it serious department and responsible for Design & Engineering of energy demand has Telecommunication,brought with it serious Protectionconcerns andRE Automation,in Indian powerControl, S systemubstation Protection, is @24% Design (Fig.1) Automation, and andEquipment shortly schemes Engineering. & Philosophies, Digital substation, Secondary concernsabout its impact about on its grid impact performance. on grid In performance.the initial stage Init the will beinitial @30% stage with of this RE planning. penetration It is also grid planned was toat have 40% shareengineering of clean energy as well sources as RE integration by 2030 due related domains. comfortableof RE penetration level grid andPresently, was very at comfortable stablehe is working because level asand of an inherent In-Charge supportive Superintending capabilities Engineer of conventionalat Engineering Department, to tremendous growth potential (Fig.1). synchronousvery stable because generation ofGETCO inherent. , But,Corporate supportive due tooffice, capabilities different Vadodara characteristics looking afterPresented and all the behaviour engineeringseveral technical of activities. RE, papersit greatly at various national and international conferences CIGRE, of conventional synchronous generation. But, due to impacts the power Asystem BVQI – steadyTUV certified as well ISO as auditor, dynamicAt henational performance is a member front,GRIDTECH many of and activitiesCI, CBIP,GRE thereby andPOWERLINE regarding various may steady jeopardize Technicaletc. onstate Relay Committees protection, of Substation Automation, Digital Substation different characteristicsElectrotechnical and behaviour of DepartmentRE, it greatly of aspects Bureau are of going and Indian REon. IntegrationRecently, Standards a pilotchallenges (BIS) project. He regardingrelated was matter. also a One Technical of the contributor from GETCO to review Draft impacts the power system steady as well as dynamic the reliability & stability by imposing lot of challengesFast if Responsenot dealtGrid Ancillary properly. code standardsServices (FRAS) and suggesting for improving some of the additional Technical requirement in context to performance and therebyCommittee may jeopardize Member the of reliability CBIP for Substationfrequency profile Manual and 2019 analysing operational aspects of RE integration challenges. Renewable& stability by energy imposing is thelot of area challenges of focus if not across dealt theancillary globe services as well without as in India. RE curtailment The wind for and175 solarGW properly. He has presented Technical PapersRE in scenario various with National the use & of International hydro power plant conf capabilityerences like GRIDTECH, generation is poised to grow significantly due to aggressiveMember plannin ofg distinguished by Government organization of India committees like; i) BIS Relay committee ETD 35, ii) 35 th Renewable energy is SWITCHCON,the area of focus CBIP across & PowerLine the globe eventsfeatures is implemented i.e. basically secondary & tertiary i.e.175GW renewables by 2022 that includes 100 GW Solar and 60GWRAC Committee wind from ERDA current, ii) Substation 31 GW and Automation Expert Group of CBIP and Cigre India iv) R&D as well as in India. The wind and solar generation is frequency response aspects (Fig 2). As an outcome 6% 37poised GW levelto grow respectively. significantlyN. M. due Share Sheth to aggressive of – RE Executive in planningIndian power Engineerimprovement system, Corporate consortiumisin @2Nos 4of% time(Fig.1) of Engineering frequencyNational and shortly Institute remain itin of willIEGC Wind be Energy (NIWE) @30%by Government with this planning.of India i.e.175GW It is also renewablesplanned to byhave band40% andshare 7% of decrement clean energy in frequency sources above by IEGC 2030 band due is achieved. to tremendous growth potential (Fig.1). 22

Obtained Graduation in Electrical Engineering from Saurashtra University Rajkot; and Qualification of Certified Project Management Associate (Project Management Level-D, National Ranker) from International Project Management Association (IPMA). Working in GETCO since 1994. Experience in the field of Substation Operation & Maintenance as well as Commissioning.

Presently working in Engineering department and responsible for Design & Engineering of Control, Protection, Automation, schemes & Philosophies, Digital substation, Secondary engineeringFig.1: PowerFig.1 as :well Power generation as generation RE integration scenario scenario related & & growth growth domain potential potentials.

At national front, manyPresented activities several regarding technical steady papers state at various aspects national are going and on. international Recently, a conferencespilot CIGRE, projectVolume regarding 10 v No. 1 v FGast RIDTECHJanuary Response 2021, CBIP, A POWERLINEncillary Services 28etc. on (FRAS) Relay protection,for improving Substation frequency Automation, profile andDigital Substation analysing operationaland aspects RE Integration of ancillary challenges services related without matter. RE curtailmentOne of the contributor for 175 GW from RE scenario GETCO to review Draft with the use of hydroGrid power code standards plant capability and suggesting features some is implem of theented additional i.e. basically Technical secondary requirement & in context to RE integration challenges. tertiary frequency response aspects (Fig 2). As an outcome 6% improvement in Nos of time frequency remain inMember IEGC band of distinguishedand 7% decrement organization in freque committeesncy above like;IEGC i) band BIS Relay is achieved committee. ETD 35, ii) 35 th RAC Committee ERDA, ii) Substation Automation Expert Group of CBIP and Cigre India iv) R&D consortium of National Institute of Wind Energy (NIWE)

22

Fig. 2: Role of Hydro in system balancing

2

Utility Roadmap for System strength aspects for Reliability, Stability and Flexibility of RE Rich Modern Power Grid– Indian grid context

B.P. SONI (I/C Superintending Engineer), N. M. SHETH (Executive Engineer) GUJARAT ENERGY TRANSMISSION CORPORATION LIMITED

Introduction

Renewal energy’s rise and increased role in meeting energy demand has brought with it serious concerns about its impact on grid performance. In the initial stage of RE penetration grid was at comfortable level and very stable because of inherent supportive capabilities of conventional synchronous generation. But, due to different characteristics and behaviour of RE, it greatly impacts the power system steady as well as dynamic performance and thereby may jeopardize the reliability & stability by imposing lot of challenges if not dealt properly. Renewable energy is the area of focus across the globe as well as in India. The wind and solar generation is poised to grow significantly due to aggressive planning by Government of India i.e.175GW renewables by 2022 that includes 100 GW Solar and 60GW wind from current 31 GW and 37 GW level respectively. Share of RE in Indian power system is @24% (Fig.1) and shortly it will be @30% with this planning. It is also planned to have 40% share of clean energy sources by 2030 due to tremendous growth potential (Fig.1).

Fig.1: Power generation scenario & growth potential At national front, many activities regarding steady state aspects are going on. Recently, a pilot project regarding Fast Response Ancillary Services (FRAS) for improving frequency profile and analysing operational aspects of ancillary services without RE curtailment for 175 GW RE scenario with the use of hydro power plant capability features is implemented i.e. basically secondary & tertiary frequency response aspects (Fig 2). As an outcome 6% improvement in Nos of time Utility Roadmap for System Strength Aspects for Reliability, Stability & Flexibility of RE Rich Modern Power Grid frequency remain in IEGC band and 7% decrement in frequency above IEGC band is achieved. 29

But, with planned development there will be impact on dynamic aspects also. Hence, now there is need to look into study of dynamic aspects of inertial, primary frequency response and also reactive power support.Fig. Paper 2: FRolefocusesig. 2 :of Role onHydro ofthese Hydro in aspects. insystem system balancingbalancing But, with1. Synchronousplanned development generation there will (SG) be impactVs Inverter on 5. based Fault generationride through capability(IBG) - Characteristics dynamic differenceaspects also. Hence, now there is need to2 6. Short circuit capability look into study of dynamic aspects of inertial, primary 7. Grid voltage support frequencyThere response is a fundamental and also reactive difference power support. between synchronous generation and inverter based Papergeneration focuses on (IBG)these (Fig.aspects.3). IBGs inherently do not have8. following Reactive characteristics. power support 1. Synchronous1. Inertia generation (SG) Vs Inverter based 9. Synchronization capability (Torque) generation2. Fre (IBG)quency - Characteristics response capability difference 10. Damping torque There is a 3.fundamental Frequency difference sensitive between mode synchronous 11. Harmonic voltage reduction etc. generation4. and Constant inverter basedvoltage generation source (IBG) (Fig.3). Recently many new capabilities are covered in Grid IBGs inherently5. Fault do notride have through following capability characteristics. code for technical requirements. Annexure-A depicts the 1. Inertia6. Short circuit capability potential difference between SG and IBG along with the 7. Grid voltage support 2. Frequency response capability feasibility of advanced capability. 8. Reactive power support 3. Frequency sensitive mode Some of the characteristics and behavioural differences 9. Synchronization capability (Torque) are elaborated in brief hereunder. 4. Constant10. voltageDamping source torque 11. Harmonic voltage reduction etc.

IBG SG

Fig.Fig.3: Characteristics3 : Characteristics Difference Difference between between SG SG and and IBG IBG Recently many new capabilities are covered in Grid code for technical requirements. Annexure-A depicts the potential difference between SG and IBG along with the feasibility of advanced v v capability. Volume 10 No. 1 January 2021 Some of the characteristics and behavioural differences are elaborated in brief hereunder. a) Rotating mass  IBGs do not have  Available reserve energy in IBG is limited and inertial response is not of significance inherently  Rating of electronic devices also limits for additional energy  To really use inertial response, a significant oversized IBG inverters are required b) Fault current contribution  Inverter predominantly lack inductive characteristics associated with rotating mass

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30 CIGRE India Journal

(a) Rotating mass stand short circuit of any kind without failure as it • IBGs do not have follows law of electrodynamics. • Available reserve energy in IBG is limited and • In case of IBGs, voltage phase angle cannot be inertial response is not of significance inherently detected when line voltage is very low as mag- • Rating of electronic devices also limits for addi- netic contactor loses excitation. However, new tional energy IBGs are available with this characteristic. • To really use inertial response, a significant over- (f) Reactive power support sized IBG inverters are required • During steady state (b) Fault current contribution (i) Rate P.F. of synchronous machine is 0.8 to • Inverter predominantly lack inductive character- 0.95, in case of IBG it is unity. istics associated with rotating mass (ii) Most of the IBGs are not desired to provide • Short circuit contribution by Synchronous gen- reactive support at full output voltage un- erator is due to law of constant flux in rotating less larger sized IBGs are designed. machine. • During transient condition • IBGs can contribute fault current slightly above 1 (i) Synchronous generator instantaneously/ p.u. unless specifically designed for over size. immediately provides reactive power out- (c) Constant voltage source put as an electrodynamic phenomenon. • In case of Synchronous generator (ii) In case of IBGs, due to detection time of (i) Internal induced voltage is independently controllers, it cannot be physically instanta- regulated from grid voltage. neous. (ii) Also it is higher than grid voltage. (iii) Additional reactive power can be supported (iii) This will cause increased current when grid by decreasing active power output within voltage sags. rated current range. • In case of IBGs this is limited to 1 p.u. due to This reveals that, steady state as well as dynamic control system behaviour unless designed over- behaviour of inverter based generation is quiet different. sized. Even, different type of machines behaves differently (d) Transmission level voltage support when exposed to transient condition. This has given rise to stability and reliability aspects. Apart from above, • Synchronous generators operate in AVR mode renewable generation is intermittent and highly variable where as IBGs operate in unity Power factor which challenges existing operational aspects also. mode means AQR mode. Looking to above challenges, a multidimensional • Thus voltage support cannot be expected unless conceptual approach to enhance the stability and designed for oversized. reliability of RE rich modern power system should (e) Fault ride through capabilities be adopted at state, region as well as national level • Synchronous generators are required to with- (Fig. 4).

FFig.ig. 4: :Multid Multidimensionalimensional Approach Approach 2. Improvement in technical requirement for grid connectivity as per new grid code Volume 10 v No.standard 1 v January 2021 For RE integration, Indian grid code standard 2013 is specifying some basic requirements like; i) Harmonic current injections limit: As per IEEE- 519 (2014) ii) DC current injection not greater than 0.5 % of the full rated output iii) Flicker limit: As per IEC 61000 Class A iv) Measurement of Harmonic, DC injection and flicker - Once in a year v) Dynamically varying Reactive power support - Power factor within the limits of +0.95 vi) Frequency: Operating range - 47.5 Hz to 52 Hz & Rated output range - 49.5 Hz to 50.5 Hz vii) LVRT Capability: V/Vn - 0.15 p.u. for 300ms & 0.85 p.u. for 3 sec But, with present planning and future scenario, these requirements are not sufficient as they do not address the aspects necessary to articulate IBG characteristics nearer to conventional generation for steady as well as dynamic operations and leading towards need for improvement in technical requirements. In Feb 2019, the grid code requirements are amended by hon’ble CEA including many of these technical aspects along with quantification of parameters as under.

These parameters are now the “Key reliability indices” as well as “Emerging tools” for further analysis, monitoring & considerations of system strength as well as operational aspects to enhance the grid strength by improving steady as well as dynamic performance of the grid.

5

Fig.4: Multidimensional Approach 2. Improvement in technical requirement for grid connectivity as per new grid code standard

ForUtility RE Roadmapintegration, for System Indian Strength grid code Aspects standard for Reliability, 2013 is Stability specifying & Flexibility some of basic RE Rich requirements Modern Power like; Grid 31 i) Harmonic current injections limit: As per IEEE- 519 (2014) 2. Improvementii) DC current in technical injection requirement not greater forthan grid 0.5 % of(vi) the Frequency: full rated Operating output range - 47.5 Hz to 52 Hz & connectivityiii) Flicker as limit per: newAs per grid IEC code 61000 standard Class A Rated output range - 49.5 Hz to 50.5 Hz For REiv) integration, Measurement Indian gridof Harmonic, code standard DC injection 2013 is and(vii) flicker LVRT - OnceCapability: in a yearV/Vn - 0.15 p.u. for 300ms & 0.85 specifyingv) someDynamically basic requirements varying Reactive like; power support - Powerp.u. for factor 3 sec within the limits of +0.95 (i) Harmonicvi) Freque currentncy: injections Operating limit: range As per - 47.5IEEE- Hz 519 to 52 HzBut, & withRated present output planning range -and 49.5 future Hz to scenario, 50.5 Hz these (2014)vii) LVRT Capability: V/Vn - 0.15 p.u. for 300ms &requirements 0.85 p.u. for are 3 sec not sufficient as they do not address (ii) DC current injection not greater than 0.5 % of the the aspects necessary to articulate IBG characteristics fullBut, rated with output present planning and future scenario, thesenearer requirements to conventional are generation not sufficient for steady as they as dowell not address the aspects necessary to articulateas dynamic IBG characteristics operations and nearer leading to towards conventional need for (iii) Flicker limit: As per IEC 61000 Class A generation for steady as well as dynamic operationsimprovement and leading in technical towards requirements. need for improvement (iv) Measurement of Harmonic, DC injection and flicker in technical requirements. In Feb 2019, the grid code requirements are amended by - Once in a year hon’ble CEA including many of these technical aspects (v) DynamicallyIn Feb 2019 varying, the gridReactive code power require supportments - Power are amendedalong with by quantificationhon’ble CEA of including parameters many as under. of these factortechnical within aspects the limits along of +0.95 with quantification of parameters as under.

TheseThese parameters parameters are now are the now“Key reliabilitythe “Key indices” reliability as indices3. Continuous” as well asanalysis “Emerging and monitoringtools” for further of new well asanalysis, “Emerging monitoring tools” for further & considerat analysis, monitoringions of system& strengthtechnical asparameters well as operational– Concept thereof aspects to 3.considerations Continuousenhance theof system analysisgrid strength strength and asby monitoring wellimproving as operational steady of new asToday, well technical as as dynamic grid parametersreliability performance indices – parametersConcept of the grid thereoflike. Angular aspects to enhance the grid strength by improving steady diff., Voltage Deviation Index, Violation of Available Today,as well as as dynamic grid reliability performance indices of the parameters grid. like AngularTransfer diff., Capacity Voltage etc. areDeviation being continuously Index, Violation monitored of Available Transfer Capacity etc. are being continuouslyat national moni leveltored (Fig. at national5). level (Fig.5). 5

Fig. 5: AngularFig. 5 Difference : Angular Difference,, Voltage Voltage Deviation Deviation IndexIndex, Violation, Violation of ATC of monitoring ATC monitorin & analysisg & analysis Now, it is proposed to monitor new grid code parameters also. This will definitely improve the increased concern to these aspects as well as their compliances.Volume On the 10 other v No. end 1 v Januarythere will 2021 be clear idea regarding grid support and ultimately the available system strength at any given time. For quantifying the grid performance at any given time, a system of metrics providing the details of percentage generation providing above technical support should be adopted at State, Region as well as National level. Also, minimum requirement of percentage generation providing above support for grid strength under various operating scenarios should be derived (based on simulation studies) and accordingly, it should be considered for system operational aspects e.g. for Parameter: Governor Response % Generation providing support at 20% RE is x machines and Minimum requirement for grid strength at 20% RE is a machines. Now, If x=a : Good operating condition, If x < a: More machines (having governor response) should be considered for operation If x>a: better operating condition (Similarly for other parameters, Fig 6).

Need action

Good Better

Fig. 6: Grid code parameter monitoring Today machines are running based on merit order dispatch and IBGs are must run. But, for RE rich future grid, if required, machines having better grid code compliance may also be required to be considered for operation irrespective of merit order dispatch to maintain minimum strength of the grid (highlighted part). With this vision, system operational aspects should also be replanned if necessary. Thus, these are the useful tools in planning of many power system aspects like; i. Frequency control reserve requirement

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32 CIGRE India Journal

Now, it is proposed to monitor new grid code parameters (ii) Ancillary services requirement also. This will definitely improve the increased concern (iii) Optimization of ramping requirement of conventional to these aspects as well as their compliances. On the generation other3. end Continuous there will be analysis clear idea and regarding monitoring grid support of new technical parameters – Concept thereof and ultimately the available system strength at any given (iv) Additional reactive support requirement etc. time.Today, as grid reliability indices parameters like Angularand help diff., to add Voltage to efficient Deviation and reliable Index system, Violation operation of For Availablequantifying Transfer the grid performanceCapacity etc at. areany beinggiven time,continuously in new moni generationtored mixat national scenario. level (Fig.5). a system of metrics providing the details of percentage 4. System strength aspects and related concerns generation providing above technical support should be System strength can be defined as an ability of power adopted at State, Region as well as National level. Also, system to produce and maintain control of sinusoidal minimum requirement of percentage generation providing 3 phase voltage waveforms which are the basis of AC above support for grid strength under various operating network. scenarios should be derived (based on simulation studies) and accordingly, it should be considered for It provides indication of network sensitivity to any sudden system operational aspects e.g. for Parameter: Governor changes in operating conditions such as variations in Response active and reactive power flows, status of the network elements and occurrence of fault induced disturbances. % Generation providing support at 20% RE is x machines It is a fundamental characteristics specific to each and connection point and will vary over a time as power flow Minimum requirement for grid strength at 20% RE is a and generation dispatch condition change. machines. Now, Thus, strength of the grid is an intrinsic characteristic If x=a : Good operating condition, of the local power system and reflects the sensitivity Fig. 5: Angular Difference, Voltage Deviation Index, Violation of ATC monitoring & analysis If x < a: More machines (having governor response) of power system variables to disturbances. It indicates inherent local system robustness. shouldNow, be consideredit is proposed for operation to monitor new grid code parameters also. This will definitely improve the If x>a:increased better operatingconcern tocondition these aspects(Similarly as for well other as theirIt is compliances. a measure of On the the stability other ofend power there electronic will be parameters, Fig. 6). interfaced control systems, synchronous generators, clear idea regarding grid support and ultimately thenetwork available dynamics system and strength protection at systems any given to assisttime. the Today machines are running based on merit order For quantifying the grid performance at any givenpower time, system a system rapidly of returning metrics toproviding steady-state the conditions details dispatch and IBGs are must run. But, for RE rich future following a disturbance. grid,of if percentage required, machines generation having providing better abovegrid code technical support should be adopted at State, Region complianceas well mayas Nationa also bel requiredlevel. Also, to be minimum considered requirement for Before of going percentage to further generation details, we needproviding to understand above operationsupport irrespective for grid of merit strength order dispatch under variousto maintain operating why there scenarios is a concern should for grid be strength. derived In (based this regard, on minimum strength of the grid (highlighted part). With types of generators and its behavioural impact is simulation studies) and accordingly, it should be highlighted.considered for system operational aspects e.g. this forvision, Parameter: system operational Governor aspectsResponse should also be replanned if necessary. Type of generation and its characteristics: % Generation providing support at 20% RE is x machines and Thus,Minimum these are requirement the useful tools for gridin planning strength of atmany 20% RE (a)is a Synchronous machines. Now, generation power system aspects like; If x=a : Good operating condition, (i) It has its own source (i) If Frequency x < a: More control machines reserve (having requirement governor response) sh (ii)ould Synchronous be considered generation for operation is balanced sinusoi- If x>a: better operating condition (Similarly dal for waveform. other parameters, Fig 6).

Need action

Good Better

Fig.Fig. 6: 6Grid : Grid code code parameterparameter monitoring monitoring Today machines are running based on merit order dispatch and IBGs are must run. But, for RE rich Volumefuture 10 grid,v No. if 1 required, v January machines 2021 having better grid code compliance may also be required to be considered for operation irrespective of merit order dispatch to maintain minimum strength of the grid (highlighted part). With this vision, system operational aspects should also be replanned if necessary. Thus, these are the useful tools in planning of many power system aspects like; i. Frequency control reserve requirement

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Utility Roadmap for System Strength Aspects for Reliability, Stability & Flexibility of RE Rich Modern Power Grid 33

(iii) Active and Reactive power transfer influenced (i) Large scale solar and wind generally connected to by angular position and MMF. grid at larger distance from load centres (iv) Response of machine is by electrodynamics (ii) It is also remote from Synchronous generation and hence inherently act in right direction to (iii) Energy input from RE takes priority in dispatch even support/stabilize the grid. other alternate exists (v) The instantaneous response is without relying (iv) Renewable energy targets are being achieved earlier on any measurement. than planned. (vi) No requirement of minimum strength (v) Reduced synchronous generation online (vii) Predictive and linear response (vi) High power transfer over a long distance (viii) Large fault current contribution during distur- bance Impact of System strength: (ix) They act as a source of fault current having A. During normal network operation: positive contribution. (i) Poor voltage regulation, potentially exceeding (b) Inverter based generation (Traditional) the acceptable steady state limits as power flow (i) IBGs are constant current source rather than conditions vary over a time. an “Independent Voltage Source”. (ii) Large changes in voltage during and following (ii) IBGs act by measuring magnitude and phase switching events including operation of shunt angle of grid and thus they are “Grid following” connected reactive plant. generation technology. (iii) High sensitivity of voltage magnitude to changes in (iii) It is called grid following inverter active/reactive power flow can give rise to unstable behaviour of fast control systems unless they (iv) Need sufficient synchronous generation near- are appropriately tuned and coordinated. This is by for stable operation particularly when multiple IBGs are operating in close (v) Two important factors determining system sta- proximity to one another. bility (iv) Increased risk of voltage instability, including • Strength of interconnected network occurrence of localised voltage collapse. • Design and tuning of controller B. During and following contingency event: (vi) Highly controlled, sophisticated and non-linear (i) Much wider propagation of fault induced voltage response depression which can cause converter connected (vii) Limited fault current contribution generally 1 equipment to “see the fault” and foster FRT (Fault p.u. and sometimes 2 p.u. if designed due to Ride Through) mode which in turn has potential rating of semiconductor components negativity on system frequency. (viii) They act as a sink of fault current having nega- (ii) High sensitivity of voltage magnitude to changes in tive contribution active/reactive power flow making stable recovery (c) Inverter based generation (Grid forming) from FRT difficult unless active and reactive power controls are properly coordinated. Particularly area (i) Aiming to emulate synchronous machine char- where multiple IBGs operate in close proximity and acteristics as close as possible (virtual syn- attempts to recover at same time (means repeated chronous generation) FRT behaviour which is credible risk). (ii) Synthesises voltage sine wave with constant (iii) High sensitivity of voltage phase angle to changes in frequency without need of external reference. active power flow and voltage magnitude impending (iii) Do not cause any adverse interaction with oth- the performance of Phase locked loops (PLL) which er generators and grid devices. are required for stable operation of power converters (iv) Can provide black start capability where need- which are grid following. ed (iv) Voltage angle transient being mis interpreted as (v) Key concern is; how similar/dissimilar they are changes in local network frequency which creates compared to Synchronous generation risk of mal-operation of frequency based protection What are the factors weakening the grid? including ROCOF. Following are the fundamental building blocks for “Weak (v) Increased risk of over voltage if dynamic control network operating condition”. of reactive power is slow, poorly designed or not available.

Volume 10 v No. 1 v January 2021 34 CIGRE India Journal

(vi) Reduced fault currents which can reduce effectiveness (c) Can IBGs look after themselves in future? and/or impedance based or over current based Until a precise matric of system strength can be defined, protection schemes. the most reliable method to determine how to operate The most significant impact of most of these aspects power system in secure manner is to perform detailed is instability results in disconnection of generating power system simulation studies. These studies will equipments. provide insight into how system performs for varying despatch scenarios, fault conditions and thereby System Strength Parameters : evaluation of the strength of the grid. (Fig. 8) Thus system strength is a multidimensional problem. It is emphasized to identify pre-determined sets of Following are the key indicators for system strength aspects but not limited to (Fig. 7); synchronous machines needed to remain online to i. Ratio of the Non-synchronous generationmaintain to Synchronous sufficient system generation. strength, with (System high proportions Non (i) Ratiosynchronous of the Non-synchronous penetration – SNSP)generation to of non-synchronous generation/IBGs and identify “Key Synchronous generation. (System Non synchronous ii. System Inertia efficiency breakpoint”, which is the “largest overall penetration – SNSP) amount of non-synchronous generation/IBGs that can be iii. Proximity of the synchronous generation (SCR, CSCR, WSCR, ESCR) (ii) System Inertia online for the least number of synchronous generators” necessary to alleviate system strength concerns and (iii) Proximity of the synchronous generation (SCR, should be included in monitoring aspects CSCR, WSCR, ESCR) Further set of question will be: 5. System strength parameters (a) How many synchronous machines are needed to 5.1 Inertia look afteri. Ratio increased of the number Non- synchronousof IBGs? generationConcept to Synchronous : generation. (System Non (b) How muchsynchronous close synchronous penetration machines – SNSP) to load Inertia is the first and fastest line of defence after transient centres?ii. System Inertia period followed by disturbance or contingency event iii. Proximity of the synchronous generation (SCR, CSCR,MW WSCR, ESCR) MVA

Figure 7: System strength variables Further set of question will be: a. How many synchronous machines are needed to look after increased number of IBGs? b. How much close synchronous machines to load centres? MW c. Can IBGs look after themselves in future? MVA Until a precise matric of system strength can be defined, the most reliable method to determine how to operate power system in secure manner is to perform detailed power system simulation

studies. These studies will provideFigure insight7: System into strength how variables system performs for varying despatch : System strength variables scenarios,Further set fault of conditionsquestion will and be: thereby Fig. 7 evaluation of the strength of the grid. a. How many synchronous machines are needed to look after increased number of IBGs? b. How much close synchronous machines to load centres? c. Can IBGs look after themselves in future? Until a precise matric of system strength can be defined, the most reliable method to determine how to operate power system in secure manner is to perform detailed power system simulation studies. These studies will provide insight into how system performs for varying despatch scenarios, fault conditions and thereby evaluation of the strength of the grid.

FigureFig. 8 8:: Grid Grid strength strength analysis analysis criteria criteria It is emphasized to identify pre-determined sets of synchronous machines needed to remain Volumeonline 10 v to No. maintain 1 v January sufficient 2021 system strength, with high proportions of non-synchronous generation/IBGs and identify “Key efficiency breakpoint”, which is the “largest overall amount of non-synchronous generation/IBGs that can be online for the least number of synchronous generators ” necessary to alleviate system strength concerns and should be included in monitoring aspects Figure 8: Grid strength analysis criteria 5. ItSystem is emphasized strength to parameters identify pre-determined sets of synchronous machines needed to remain online to maintain sufficient system strength, with high proportions of non-synchronous 5.1.generation/IBGs Inertia and identify “Key efficiency breakpoint”, which is the “largest overall amount of Conceptnon-synchronous: generation/IBGs that can be online for the least number of synchronous generators” necessary to alleviate system strength concerns and should be included in Inertiamonitoring is the aspects first and fastest line of defence after transient period followed by disturbance or contingency event in arresting frequency drops before primary frequency response becomes 5. System strength parameters 5.1. Inertia 9 Concept: Inertia is the first and fastest line of defence after transient period followed by disturbance or contingency event in arresting frequency drops before primary frequency response becomes

9

available to supply lost energy. When sufficient rotational inertia is available, severe frequency drops can be avoided.

Figure 9: Frequency response spectrum & impact of Inertia on ROCOF As penetration levels of IBGs (that do not naturally contribute inertia to the system) continue to increase and displace synchronous generators in a power system’s generation mix, synchronous inertia will inevitably decline. World vide TSO survey shows that, ‘decreasing inertia as the most important issue of the modern power system’. In recent years, world vide number of dynamic studies are being carried out and found that; i. The amount of frequency containment reserve (called Responsive Reserve Service or RRS) needed to arrest the frequency above the AUFLS trigger after the largest generation loss depends on system inertia conditions. ii. There is a critical inertia level below which existing frequency response mechanisms are not fast enough to arrest the frequency before it reaches AUFLS after the largest generation loss. Utility Roadmap for System Strength Aspectsiii. If systemfor Reliability, inertia Stability is expected & Flexibility to fall of RE below Rich this Modern value, Power system Grid operat35ors have to follow procedures to start more synchronous generators or to consider ancillary services in order to in arresting frequency drops before primary frequencyincrease synchronous 5.1.1 Determination inertia online. of critical inertia level response becomes available to supply lost5.1.1. energy. Determination When From of the critical basic inertia swing level equation of rotating machine sufficient rotational inertia is available, severe frequency any power system has its minimum rotational ineria drops can be avoided. (Fig. 9) From the basic swing equation of rotating machine any power system has its minimum rotational ineria requirement whichrequirement is called which critical is inertia called level critical below inertia which level system below cannot withstand the As penetration levels of IBGs (that do not naturally given contingency. whichIt depends system on givencannot contingency withstand (lossthe given of power) contingency. and allowed rate of change contribute inertia to the system) continue to increase and of frequency. It depends on given contingency (loss of power) and displace synchronous generators in a power system’s allowed rate of change of frequency. generation mix, synchronous inertia will inevitably decline. World vide TSO survey shows that, ‘decreasing inertia as E kin(min) = + E kin(Cont.) ………(1)...(1) the most important issue of the modern powerWhere, system’. E kin(min) Where,is minimum E kin(min) system inertiais minimum required system (MW*sec), inertia ∆P required is the worst case multiple In recent years, world vide number of dynamiccontingency studies (MW), (MW*sec), fn is system ΔP is frequency the worst (Hz) case, RoCoF multiple is contingency predefined rate of change of are being carried out and found that; frequency(Hz/s) and(MW), E kin(Cont.) fn is system is the a frequencymount of system (Hz), RoCoF inertia lostis predefined (MW*sec) . (i) The amount of frequency containment reserve rate of change of frequency(Hz/s) and E kin(Cont.) is the For typical example;amount critical of inertia system level inertia for GETCOlost (MW*sec) grid is calculated. based on AUFLS setting (called Responsive Reserve Service orparameters RRS) needed and largest inertial loss. Worst case contingency for df/dt operation is 1800 MW at For typical example; critical inertia level for GETCO grid to arrest the frequency above the AUFLS49. 9trigger Hz base after frequency and 0.4 Hz/s as RoCoF (setting guide lines provided by WRPC). Largest is calculated based on AUFLS setting parameters and the largest generation loss depends onineria system loss inertia is CGPL Mundra’s 5 Nos 830 MW generators. Thus critical inertia arrived is 128.4 largest inertial loss. Worst case contingency for df/dt conditions. GW*sec. Now, this is another very important monitoring parameter in context to system operation is 1800 MW at 49.9 Hz base frequency and 0.4 (ii) There is a critical inertia level below strengthwhich existing. frequency response mechanisms are not fast enough Hz/s as RoCoF (setting guide lines provided by WRPC). to arrest the frequency before it reachesFor AUFLS further after analysis, Largest system ineriainertia loss of various is CGPL extreme Mundra’s scenarios 5 Nos like 830 maximum MW wind, maximum the largest generation loss. demand, minimum generators.demand etc. Thus is derived critical and inertia analysed arrived with is 128.4respect GW*sec. to minimum system ineria. (Fig.10). Now, this is another very important monitoring parameter (iii) If system inertia is expected to fall below this value, in context to system strength. system operators have to follow procedures to start For further analysis, system inertia of various extreme more synchronous generators or to consider ancillary 10 scenarios like maximum wind, maximum demand, availableservices into order supply to increase lost energy. synchronous When sufficient inertia rotational inertia is available, severe frequency online. minimum demand etc. is derived and analysed with drops can be avoided. respect to minimum system ineria. (Fig.10).

FigureFig. 9: 9 Frequency : Frequency responseresponse spectrum spectrum & impact & impact of Inertia of on Inertia ROCOF on ROCOF As penetration levels of IBGs (that do not naturally contribute inertia to the system) continue to increase and displace synchronous generators in a power system’s generation mix, synchronous inertia will inevitably decline. World vide TSO survey shows that, ‘decreasing inertia as the most important issue of the modern power system’. In recent years, world vide number of dynamic studies are being carried out and found that; i. The amount of frequency containment reserve (called Responsive Reserve Service or RRS) needed to arrest the frequency above the AUFLS trigger after the largest generation loss depends on system inertia conditions. ii. There is a critical inertia level below which existing frequency response mechanisms are not fast enough to arrest the frequencyFFigureigure 10 10 : before System: System inertia it reachesinertia analysis analy AUFLSsis after the largest generation loss. ∆In almost all the cases system inertia is comfortably above the minimum requirement except iii. If systemth inertia is expected to fall below this value, systemVolume operat 10 v orsNo. 1 have v January to follow 2021 Octoberprocedures 30 (where to start it was more just synchronous above the generatorscritical inertia) or to whichconsider was ancillary minimum services demand in order scenario to and allincrease hydro, gassynchronous and many inertia thermal online. plants were not in operation. Su5.1.1.ch practices Determination should be of adopted critical inertiaat state, level region as well as national level as reliability aspects and counter measures if any. From the basic swing equation of rotating machine any power system has its minimum rotational 5.1.2.ineria requirementReal time tracking which is ofcalled Inertia critical inertia level below which system cannot withstand the Detailsgiven contingency.of machines Itwhich depends are onconnected given contingency to grid is (lossavailable of power) on unit and commitment allowed rate and of changedespatch plan.of frequency. Based on these details, current as well as future total inertia contribution of all online synchronous generators can be calculated based on the inertia parameters of individual units in the network with aggregation.E kin(min) Thus = , system inertia+ Ecan kin(Cont.) be continuously ………(1) monitored as situational awareness tools (Fig. 11). If at any time period where the expected system inertia is less than the Where, E kin(min) is minimum system inertia required (MW*sec), ∆P is the worst case multiple criticalcontingency level can (MW), be identified fn is system and appropri frequencyate (Hz) actions, RoCoF should is predefined be planned rate to maintain of change it above of criticalfrequency level.(Hz/s) and E kin(Cont.) is the amount of system inertia lost (MW*sec) . For typical example; critical inertia level for GETCO grid is calculated based on AUFLS setting parameters and largest inertial loss. Worst case contingency for df/dt operation is 1800 MW at 49.9 Hz base frequency and 0.4 Hz/s as RoCoF (setting guide lines provided by WRPC). Largest ineria loss is CGPL Mundra’s 5 Nos 830 MW generators. Thus critical inertia arrived is 128.4 GW*sec. Now, this is another very important monitoring parameter in context to system strength. For further analysis, system inertia of various extreme scenarios like maximum wind, maximum demand, minimum demand etc. is derived and analysed with respect to minimum system ineria. (Fig.10). Figure 11: Real time monitoring of system inertia Looking to above aspects, it is preferable to include inertial aspects in grid code requirements for 10 IBGs also. Though, they inherently do not exhibit inertia but, it is possible to program the

controls to provide a form of inertial response called synthetic inertia which will add to grid strength and also reduce the reserve requirement and ancillary services. 5.2. Short Circuit Ratio (Grid stiffness) The most basic and easily applied metric to determine the relative strength of a power system is short circuit ratio (SCR). SCR is defined as the ratio between short circuit apparent power (SCMVA) from a 3LG fault at a given location in the power system to the rating of the inverter-based resource connected to that location (i.e. it is location specific unlike frequency).

SCR POI ……… (2)

where SCMVA is the short circuit capacity at PCC without current contribution from IBG, MWVER is the nominal power rating of IBG.

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36 CIGRE India Journal

ΔIn almost all the cases system inertia is comfortably where SCMVA is the short circuit capacity at PCC without above the minimum requirement except October 30 th current contribution from IBG, MWVER is the nominal (where it wasFigure just above10: System the critical inertia inertia) analy whichsis was power rating of IBG. minimum demand scenario and all hydro, gas and many Significance: ∆In almost all the cases thermal system plants inertia were is notcomfortably in operation. above the minimum requirement except October 30 th (where it was just above the critical inertia) which was minimum(i) SCRdemand is a measurescenario of thevenin impedance of AC Such practices should be adopted at state, region as system. and all hydro, gas and manywell thermalas national plants level wereas reliability not in aspectsoperation. and counter measures if any. (ii) A low SCR system (“weak system”) indicates high Such practices should be adopted at state, region as well as national level as sensitivityreliability of aspects voltage (magnitude and phase angle) and counter measures if 5.1.2any. RealFigure time tracking 10: System of Inertiainertia analysis to changes in active and reactive power injections Details of machines which are connected to grid is or consumptions. 5.1.2.∆In almostReal alltime the trackingcases system of Inertia inertia is comfortably above the minimum requirement except October 30 th (where it wasavailable just above on unit the commitment critical inertia) and despatch which wasplan. minimum Based demand(iii) High scenario SCR (“stiff”) systems have a low sensitivity and on these details, current as well as future total inertia Detailsand all of hydro, machines gas and which many arethermal connected plants were to grid not inis operation.available on unit commitmentare predominantly and despatch unaffected by changes in active contribution of all online synchronous generators can be and reactive power injection. plan. Based on these detailcalculateds, current based ason the well inertia as futureparameters total of inertiaindividual contrib ution of all online Such practices should be adopted at state, region as well as national level as reliability(iv) Low SCRaspects is of significance concern because internal synchronous generators unitscan bein thecalculated network basedwith aggregation. on the inertia Thus, parameters system of individual units in and counter measures if any. plant controls will not function in a stable manner and inertia can be continuously monitoredSignificance: as situational the network with aggregation. Thus, system inertia can be continuously monitoredmay notas representsituational the true behaviour of plant which 5.1.2. Real time trackingawareness of Inertia tools (Fig. 11). If at anyi. SCRtime isperiod a measure where ofthe thev enin impedance of AC system. awarene ss tools (Fig. 11). If at any time period where the expected system inertiaincreases is less thethan chance the of sub synchronous behaviour expected system inertia is less thanii. A lowthe critical SCR system level can (“weak system”) indicates high sensitivity of voltage (magnitude and phase criticalDetails level of machines can be which identified are connected and appropri to gridate is actions available should on unit be commitment planned to and maintainand despatch control it interactions. above be identified and appropriate actionsangle) should to changesbe planned in active and reactive power injections or consumptions. criticalplan. Blevel.ased on these details, current as well as future total inertia contribution of all online to maintain it above critical level.iii. High SCR (“stiff”) systems(v) have The aSCR low metric sensitivity is most and appropriate are predominantly when considering unaffected by changes synchronous generators can be calculated based on the inertia parameters of individuala single units inverter-based in resource operating at PCC in active and reactive power injection. the network with aggregation. Thus, system inertia can be continuously monitored as(i.e. situational does not account for the presence of other iv. Low SCR is of significance concern because internal plant controls will not function in a stable awareness tools (Fig. 11). If at any time period where the expected system inertia is lessinverter-based than the resources or power electronic-based manner and may not represent the true behaviour of plant which increases the chance of sub critical level can be identified and appropriate actions should be planned to maintainequipment it above electrically close to the PCC). synchronous behaviour and control interactions. critical level. 5.2.1 SCR in case of multiple inverter based sources v. The SCR metric is most appropriate when considering a single inverter-based resource at or near PCC operating at PCC (i.e. does not account for the presence of other inverter-based resources or power electronic-based equipmentIBGs connected electrically close close to other to the IBGs PCC). may interact with each other and oscillate which can lead to overly 5.2.1. SCR in case of multipleoptimistic inverter results based with sourcesSCR. In at this or regard,near PCC several methods are there. IBGs connected close to other IBGs may interact with each other and oscillate which can lead to (i) Composite Short Circuit Ratio (CSCR) Figure 1F1ig.: R 11eal : Realtime time monitoring monitoringoverly of of system optimisticsystem inertia inertia results with SCR. In this regard, several methods are there. Composite short circuit ratio (CSCR) estimates Looking to above aspects,Looking it is preferable to above aspects, to include it i)is inertial Compositepreferable aspects to Short include in grid Circuit code Ratiothe requirements equivalent (CSCR) system for impedance seen by multiple inertial aspects in grid code requirements for IBGs also. IBGs also. Though, they inherently do not exhibitComposite inertia but,short itcircuit is possible ratio (CSCR)inverter-based to programestimates resourcesthe the equivalent by creating system aimpedance common seen by multiple Though, they inherently do not exhibit inertia but, it is medium voltage bus and tying all inverter-based controls to provide a form of inertial response called synthetic inertia which will add to grid Figurepossible 11: R toeal program time monitoring the controlsinverter of systemto provide-based inertia aresources form of by creatingresources a common of interest medium together voltage at that bus common and tying bus. all inverter-based strength and also reduceinertial the reserve response requirement called synthetic andresources inertiaancillary whichof interservices willest add together. at that common bus. CSCR can then be calculated as; Looking to above aspects, it is preferable to include inertial aspects in grid code requirementsCSCR can for then be calculated as; to grid strength and also reduce the reserve requirement 5.2.IBGs Short also. Circuit Though Ratio, theyand (Grid inheren ancillary stiffness)tly doservices. not exhibit inertia but, it is possible to program the controls to provide a form of inertial response called synthetic inertia which will addCSCR to grid ……... (3) ...(3)

Thestrength most andbasic also and reduce easily 5.2the applied reserveShort metricCircuit requirement Ratioto determine (Grid and ancillarystiffness) the relativeservices .strength of a power system is where, MWVER is the nominal power rating of all short circuit ratio (SCR). TheSCR mostis defined basic and as theeasily ratio applied where,between metric MW shorttoVER determine is circuit the nominal apparent power power rating (SC ofMVA all) IBGs considered and CSCMVA is the composite IBGs considered and CSCMVA is the composite from5.2. aShort 3LG Circuit fault at Ratio a given the(Grid relative location stiffness) strength in the of a power powershort system circuit is to MVAshort the atcircuit rating common of bus the without inverter current-based contribution from IBG. short circuit MVA at common bus without current ratio (SCR). SCR is defined as the ratio between short resourceThe most connected basic and easilyto that applied location metric (i.e. to it determineis location the specific relative unlike strength frequency). of a power contribution system is from IBG. circuit apparent power (SC ii)) fromWeighted a 3LG Shortfault at Circuit a Ratio (WSCR) short circuit ratio (SCR). SCR is defined as the ratio betweenMVA short circuit apparent power (SCMVA) given location in the power systemThe weighted to the rating short of the circuit (ii) ratio W eighted (WSCR) Short has beenCircuit recently Ratio (W startedSCR) for more accurate metrics from a 3LG fault at a giveninverter-based location inresource the power connected system to tothat the location rating (i.e. of the inverter-based resource connected to that locationSCR (i.e. POI it is location specificapplied ……… unlike in defining(2) frequency). system strength The weighted aspects. short In circuit his method ratio (WSCR) it is assumed has been that, all IBGs are it is location specific unlike frequency). recently started for more accurate metrics applied electrically close to each other and provides SCR at a “Virtual” point of connection. WSCR is where SCMVA is the short circuit capacity at PCC withoutdefined current as; contribution fromin defining IBG, MWsystemVER isstrength aspects. In his method it is assumed that, all IBGs are electrically close to the nominal power rating of IBG.SCR POI ……… (2) ...(2) each other and provides SCR at a “Virtual” point of where SCMVA is the short circuit capacity at PCC without current contribution fromWSCR IBG,connection. MW= VER isWSCR is defined …… as; … (4) the nominal power rating of IBG. 11 where, SCMVAi is the short circuit capacity at bus i without current contribution from non- v v Volume 10 No. 1 January11 synchronous 2021 generation and PRMWi is the MW output of non-synchronous generation to be connected at bus i. N is the number of wind plants fully interacting with each other and i is the wind plant index. For typical example SCR, CSCR and WSCR parameters are calculated for some of the highest IBG penetrated area of GETCO grid (Table-II) which are at the western coast and at extreme end of the network (Fig. 12). Analysis shows that, CSCR and WSCR are at comfortable level though SCR at one bus is low.

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Significance: i. SCR is a measure of thevenin impedance of AC system. ii. A low SCR system (“weak system”) indicates high sensitivity of voltage (magnitude and phase angle) to changes in active and reactive power injections or consumptions. iii. High SCR (“stiff”) systems have a low sensitivity and are predominantly unaffected by changes in active and reactive power injection. iv. Low SCR is of significance concern because internal plant controls will not function in a stable manner and may not represent the true behaviour of plant which increases the chance of sub synchronous behaviour and control interactions. v. The SCR metric is most appropriate when considering a single inverter-based resource operating at PCC (i.e. does not account for the presence of other inverter-based resources or power electronic-based equipment electrically close to the PCC). (Table-II : SCR calculation aspects) 5.2.1. SCR in case of multiple inverter based sources at or near PCC IBGs connected close to other IBGs may interact with each other and oscillate which can lead to overly optimistic results with SCR. In this regard, several methods are there. i) Composite Short Circuit Ratio (CSCR) (Table-II : SCR calculation aspects) Composite short circuit ratio (CSCR) estimates the equivalent system impedance seen by multiple inverter-based resources by creating a common medium voltage bus and tying all inverter-based resources of interest together at that common bus. CSCR can then be calculated as;

CSCR ……... (3)

where, MWVER is the nominal power rating of all IBGs considered and CSCMVA is the composite short circuit MVA at common bus without current contribution from IBG. ii) Weighted Short Circuit Ratio (WSCR)

The weighted short circuit ratio (WSCR) has been recently started for more accurate metrics Fig. 12: Western cost high IBG penetration network applied in defining system strength aspects. In his method it is assumed that, all IBGs are electrically close to each other and provides SCR at a “Virtual” point of connection. WSCR is This is another good monitoringFig. 12: Westernaspect and cost it high is proposed IBG penetration for adoption network at state, region as well as defined as; Utility Roadmap for System Strength Aspects for Reliability, Stability & Flexibility of RE Rich Modern Power Grid 37

nationalThis level is another and should good monitoring be considered aspect for; and it is proposed for adoption at state, region as well as (ii) Mitigation measures to counter the lower SCR i. Snationalystem planning level and criteriashould be considered for; WSCR = ……… (4) aspects. ii. Mitigationi. System measures planning...(4) criteria to counter the lower SCR aspects. ii. Mitigation measures5.2.2 to Short counter Circuit the lower Interaction SCR aspects. Factor (SCRIF) where, SCMVAi is the shortwhere, circuit SCMVAi capacityis the short at circuit bus capacity i without at bus current i without contribution from non- current contribution from non-synchronous5.2.2. Short generation Circuit InteractionWhen multiple Fa ctorinverter (SCRIF) based resources are located very synchronous generation and PRMWi is the MW output 5.2.2. of non S-synhortchronous Circuit Interaction generation toFa ctor be (SCRIF) and PR is the MW output of non-synchronous close to each other, they share the grid strength and connected at bus i. N is the numberMWi of wind plantsWhen fully interactingmultiple inverter with each based other resources and i is the are located very close to each other, they share the grid generation to be connected at bus i.When N is the multiple number inverter of short based circuit resources level. Hence are located grid strength very close is much to lowereach other,than they share the grid wind plant index. wind plants fully interacting withstr engtheachstr otherength and and shortand i isshort circuitthe circuit overalllevel. level. Henceshort Hence circuit grid grid level strength strength calculated is muchmuch at buses. lower lower than than overall overall short short circuit circuit level level For typical example SCR,wind CSCR plant and index. WSCR parameterscalculated arecalculated calculated at buses. at for buses. some ofSCRIF the highestcaptures IBG the changes in bus voltage at one bus penetrated area of GETCOFor typicalgrid (Table example-II) SCR,which CSCR are at and theSCRIF WSCR western captures parameters coast the and changes atcorresponding extreme in bus end voltage to ofresulting at one from bus changes corresponding in bus voltage to resulting at from changes in the network (Fig. 12). Analysisare calculated shows for that some, CSCR of theandSCRIF highest WSCR captures IBGare atpenetrated comfortable the changes other level in bus. busthough Metricvoltage SCR considering at one bus SCRIF corresponding is ESCR (Effective to resulting from changes in bus voltage at other bus.SCR) Metric which conside can ringbe derived SCRIF is as ESCR formula (Effective mentioned SCR) which can be derived at one bus is low. area of GETCO grid (Table-II) bus which voltage are at theat other western bus. Metric considering SCRIF is ESCR (Effective SCR) which can be derived as formula mentioned hereunder.hereunder. coast and at extreme end of theas network formula (Fig. mentioned 12). Analysis hereunder. shows that, CSCR and WSCR are at comfortable level though SCR at one bus is low. (Table-II : SCR calculation aspects) Table-II : SCR calculation aspects where, Si is the short circuit capacity at bus i without where, Si is the short circuit capacity at bus i without current contribution from non-synchronous current contribution from non-synchronous generation generation and PMFi is the MW output of non-synchronous generation to be connected at bus i. and P is the MW output of non-synchronous generation where, Si is the short circuit capacityMFi at bus i without current contribution from non-synchronous PMFj is the MW output toof benon connected-synchronous at bus generation i. P is the to MW be connectedoutput of non- at bus j. WPIFii is the ratio MFj generationof change and in P busMFi isvoltage the MW at Bus output i due to of change non-synchronous in bus voltage generationat Bus j. to be connected at bus i. synchronous generation to be connected at bus j. WPIFii is PMFj is5.2.3. the MW Monitoring output of nonthe ratio-synchronous of change in generationbus voltage at to Bus be i due connected to change at bus j. WPIFii is the ratio 12 of change in bus voltage atin Busbus voltagei due to at changeBus j. in bus voltage at Bus j. Based on available generation data, SCR parameters can be derived for various extreme scenarios 5.2.3 Monitoring 5.2.3. andM utilizedonitoring for analysis, monitoring and planning. Here again typical example of GETCO grid is presented for maximumBased demand, on available minimum generation demand data,and maximum SCR parameters wind scenarios. Results shows that, Nos of IBG connectedcan be buses derived where for various SCR is extreme <5 and scenariosjust above and 5 are utilized not changing in any of the Based on available generationfor analysis, data, monitoringSCR parameters and planning. can beHere derived again typical for various extreme scenarios scenario (Fig. 13). and utilized for analysis, examplemonitoring of GETCO and planning. grid is presented Here again for maximum typical example of GETCO grid is presented for maximum demand,demand, minimumminimum demanddemand andand maximummaximum wind scenarios. Results shows scenarios. Results shows that, Nos of IBG connected that, Nos of IBG connectedbuses buses where where SCR isSCR <5 and is <5 just and above just 5 are above not changing 5 are not changing in any of the (Table-II : SCR calculation aspects) scenario (Fig. 13). in any of the scenario (Fig. 13). Fig. 12: Western cost high IBG penetration network This is another good monitoring aspect and it is proposed for adoption at state, region as well as national level and should be considered for; i. System planning criteria ii. Mitigation measures to counter the lower SCR aspects. Fig 13: SCR analysis of IBG connected Buses under various scenarios 5.2.2. Short Circuit Interaction Factor (SCRIF) 13

When multiple inverter based resources are located very close to each other, they share the grid strength and short circuit level. Hence grid strength is much lower than overall short circuit level calculated at buses. Fig 13: SCR analysisFig. 13 :of SCR IBG analysis connected of IBG connected Buses under Buses undervarious scenarios various scenarios SCRIF captures the changes in bus voltage at one bus corresponding to resulting from changes in From the unit commitment13 and despatch plan real time bus voltage at other bus. Metric considering SCRIF Fisig. ESCR 12 : Western (Effective cost high SCR)Fig. IBG 12 which penetration: Western can network costbe derived high IBG system penetration scenario network will be available. It is also possible to as formula mentioned hereunder. ThisThis is is another another good good monitoring monitoring aspect aspect and it is andproposed it is proposed track SCR for adoptionin real time at bystate, integrating region realas well time as status for adoption at state, region as well as national level and of network elements in short circuit studies to derive shouldnational be levelconsidered and should for; be considered for; short circuit levels. Then, these details can be utilized i. System planning criteria to calculate SCR, CSCR and WSCR. (i) System planning criteria ii. Mitigation measures to counter the lower SCR aspects. where, Si is the short circuit capacity at bus i without current contribution from non-synchronous 5.2.2. Short Circuit Interaction Factor (SCRIF) generation and PMFi is the MW output of non-synchronous generation to be connected at bus i. Volume 10 v No. 1 v January 2021 When multiple inverter based resources are located very close to each other, they share the grid PMFj is the MW output of non-synchronous generation to be connected at bus j. WPIFii is the ratio of change in bus voltage at Bus i due to change instr busength voltage and short at Bus circuit j. level. Hence grid strength is much lower than overall short circuit level calculated at buses. 5.2.3. Monitoring SCRIF captures the changes in bus voltage at one bus corresponding to resulting from changes in Based on available generation data, SCR parametersbus voltage can be at derived other bus. for Metricvarious conside extremering scenarios SCRIF is ESCR (Effective SCR) which can be derived and utilized for analysis, monitoring and planning.as formula Here againmentioned typical hereunder. example of GETCO grid is presented for maximum demand, minimum demand and maximum wind scenarios. Results shows that, Nos of IBG connected buses where SCR is <5 and just above 5 are not changing in any of the scenario (Fig. 13).

where, Si is the short circuit capacity at bus i without current contribution from non-synchronous generation and PMFi is the MW output of non-synchronous generation to be connected at bus i. PMFj is the MW output of non-synchronous generation to be connected at bus j. WPIFii is the ratio of change in bus voltage at Bus i due to change in bus voltage at Bus j. 5.2.3. Monitoring Based on available generation data, SCR parameters can be derived for various extreme scenarios and utilized for analysis, monitoring and planning. Here again typical example of GETCO grid is presented for maximum demand, minimum demand and maximum wind scenarios. Results shows that, Nos of IBG connected buses where SCR is <5 and just above 5 are not changing in any of the Fig 13: SCR analysis of IBG connectedscenario Buses (Fig. under 13). various scenarios 13

Fig 13: SCR analysis of IBG connected Buses under various scenarios

13

From the unit commitment and despatch plan real time system scenario will be available. It is also possible to track SCR in real time by integrating real time status of network elements in short circuit studies to derive short circuit levels. Then, these details can be utilized to calculate SCR, CSCR and WSCR. Comparison of different SCR methods are summarised hereunder. Accordingly, it should be implemented for system strength aspects.

From the unit commitment and despatch plan real time system scenario will be available. It is also possible to track SCR in real time by integrating real time status of network elements in short circuit studies to derive short circuit levels. Then, these details can(Table be -utilizedIII : SCR calculationto calculate methods SCR, and its applicability) CSCR and WSCR. From the unit commitment and despatch plan realAs time a way system forward scenario and to will add be to availabl grid strengthe. It is also aspects, technical parameters like; possible to track SCR in real time by integrating real time status of network elements in short Comparison38 of different SCR methods CIGRE are summarisedIndia Journal hereunder. Accordingly, it should be circuit studies to derive short circuit levels. Then, thesei. Synthetic details In canertia be utilized to calculate SCR, implemented for system strength aspects. ii. Voltage Control through Reactive Power Control or Power Factor Control ComparisonCSCR and of different WSCR. SCR methods are summarised hereunder. Accordingly, it should be implemented for system strengthComparison aspects. of different SCR methods are summarised hereunder. Accordingly, it should be implemented for systemTable strength III : SCR aspects. calculation methods and its applicability

0.2 From the unit commitment and despatch plan real time system scenario will be available. It is also to possible to track SCR in real time by integrating real time status of network elements in short 1 pu circuit studies to derive short circuit levels. Then, these details can be utilized to calculate SCR, of CSCR and WSCR. P Comparison of different SCR methods are summarised hereunder. Accordingly, it should be implemented for system strength aspects.

Reactive Power Compensation at POC Power Factor at POC (Table-III : SCR calculation methods and its applicability) As a way forward and to add(Table to grid-III :strength SCR calculation aspects, methods (iii) Special and its requirement applicability of voltage) control are proposed As a way forward and to add to grid strength aspects, technical parameters like; technicalAs aparameters way forward like; and to add to grid strength aspects,iii. Special technicalto review requirement parametersfor including of like;in voltage Indian grid control code standard i. Synthetic Inertia including continuous power quality monitoring (i) Synthetici. Synthetic Inertia Inertia ii. Voltage Control through Reactive Power Control or Power Factor Control (ii) Voltageii. Voltage Control Control through through Reactive Reactive Power Control Power or Control or Power Factor Control Power Factor Control

0.2 0.2to to 1 1pu Reactive current injection puof during fault for few ms P of

(Table-III : SCR calculation methods and its applicability) P

As a way forward and to add to grid strength aspects, technical parameters like; 6. Grid support technologies: i. Synthetic Inertia Reactive Power Compensation at POC are proposed Power Factor to review at POC for including in Indian grid code standard including continuous power ii. Voltage Control through Reactive Power Control or Power Factor Control Various aspects discussed in the paper reveals that, the quality monitoring ReactiveReactive Power Power CompensationCompensation at POC at POC developing Power scenario Factor has at cumulative POC impact on inertia, iii. Special requirement of voltage control reactive power support and short circuit capability

aspects (Fig. 14). Even if we build synthetic inertia in IBGs by modifying controls, it depends on measured14 iii. Special requirement of voltage control RoCoF and hence cannot be considered completely 0.2 equivalent to inertia provided by synchronous generators. to With this pace grid will face deficit of Inertia, Reactive 1 power support, Short circuit capabilities, Ride through pu capabilities etc. of Reactive current injection Here, synchronous condenser can play key role due to P during fault for few ms multifaceted characteristics (Fig.14) which supports all

above aspects like;

(i) Provide inertia due to rotating heavy mass Reactive current injection duringare faultproposed for few msto review for including in Indian grid(ii) code Meets standard reactive includingpower requirement continuous arising power out of Power Factor at POC Reactive Power Compensation at POC quality Power monit Factororing at POC retiring generators (iii) Dynamic reactive power compensation

14 iii. Special requirement of voltage control are proposed to review for including in Indian grid code standard including continuous power Volume 10 v No. 1 v January 2021 quality monitoring

14

Reactive current injection during fault for few ms

are proposed to review for including in Indian grid code standard including continuous power quality monitoring

14

6. Grid support technologies: Various aspects discussed in the paper reveals that, the developing scenario has cumulative impact on inertia, reactive power support and short circuit capability aspects (Fig.14). Even if we build synthetic inertia in IBGs by modifying controls, it depends on measured RoCoF and hence cannot be considered completely equivalent to inertia provided by synchronous generators. With this pace grid will face deficit of Inertia, Reactive power support, Short circuit capabilities, Ride Utility Roadmap for System Strength Aspects for Reliability, Stability & Flexibility of RE Rich Modern Power Grid 39 through capabilities etc.

FigureFig. 1414: :Developing Developing scenario scenario and solutionand solution (iv) Here, Ride through synchronous capabilities condenser can play key role due(ii) Installation to multifaceted of new characteristics synchronous (Fig.14)condenser which by network service providers (v) Excellentsupports shortall above circuit aspects support like;means; a) increased SCR and b) Reduced risk of converter control (iii) Retuning of inverter controller to overcome small interactionsi. Provide inertia due to rotating heavy mass signal instabilities (vi) Inherentii. Meets stabilizing reactive response power requirement arising out (iv)of retiring Installation generators of FACT devices to counter dynamic over (vii)iii. Short Dynamic project reactivecycle power compensation voltage and voltage collapse (viii)iv. Lower Ride losses through than capabilities legacy system (v) Defining fault level nodes in each region Accordingly,v. Excellent following short options circuit should support be reviewed means; for a) increased(vi) Defining SCR minimum and b) synchronous Reduced risk fault of level converter at each optimumcontrol utilization. interactions node (i) vi. Conversion Inherent ofstab Oldilizing /Obsolete response thermal generating (vii) Loss of synchronous generation support to be vii.plants Short into project Synchronous cycle condensers compensated by (ii)viii. New Lower installations losses inthan weaker legacy part system of the grid (a) Installing synchronous condensers (b) Contracting with generation for synchronous (iii) New installations at IBG end as a system strength Accordingly, following options should be reviewed for optimumcondenser utilization. mode operation or low load opera- aspect i. Conversion of Old /Obsolete thermal generating plantstion into Synchronous condensers There are other technologies also to support the grid as ii. New installations in weaker part of the grid viii) New IBGs must be able for successful operation at mentioned in the roadmap. defined minimum levels or install own equipments iii. New installations at IBG end as a system strength aspect 7. Global scenario to achieve this (i.e. “Do not harm principle”) LookingThere to arelarge other scale technologiesRE shaping in India, also manyto support actions the grid(ix) As as a mentioned last resort to in maintain the roadmap. power system security; are 7.beingGlobal taken scenario: and many more steps are required in (a) Limit Nos of online inverters at specific IBG near future. Before taking leap forward, system dynamics sites are Lookingrequired toto largebe studied scale thoroughlyRE shaping with in India,advanced many actions (b) are Dispatch being of taken particular and synchronous many more generators steps are modellingrequired and in simulation near future. practices Before (RMS taking as wellleap asforward, systemout of dynamics merit order are required to be studied EMT) in deriving the system strength aspects and need thereof.thoroughly with advanced modelling and simulation8. R practicesoadmap (RMS as well as EMT) in deriving the system strength aspects and need thereof. World vide RE rich TSOs has adopted many new It is clear that we are building a system where system solutionsWorld and vide practices RE rich in TSOs order has to maintain adopted system many newdynamics solutions are going and to practices change considerably in order toand maintain it seems prudent to address these challenges in right manner and strengthsystem in anystrength of the indispatch any of scenariosthe dispatch to avoid scenarios the to avoid the catastrophic impact on the grid even catastrophic impact on the grid even in case of high IBG look forward for new opportunities emerging from this. in case of high IBG in real time dispatch. in real time dispatch. In this regard industry domain stakeholders have to SomeSome of the of importantthe important points are;points are; come together on a common ground for moving ahead. Following are some of the aspects which could be a (i) Contracting synchronous condenser capabilities pathway for Indian power industry. offered by existing plants 15

Volume 10 v No. 1 v January 2021 40 CIGRE India Journal

A. Grid code aspects based on power system requirements in maintaining Following parameters should be reviewed for including sufficient system strength aspects. in the grid code requirement. (i) Synchronous condenser (New installation as well as (i) Synthetic Inertia conversion of old power plants) (ii) Weighted SCR, Effective SCR (ii) Grid forming inverter technologies (iii) Special requirement of Voltage Control (iii) Grid ancillary services (iv) Voltage Control through PF & Q (iv) FACT devices B. Power system monitoring and analysis E. Regulatory aspects Power system monitoring and analysis practices should Market mechanism for following ancillary services should be enhanced and system metrics should be developed be developed and considered for maintaining minimum and considered for real time system operation, outage system strength aspects in RE rich future grid. planning, merit order dispatch as well as system planning. (i) Synchronous inertial services (i) Deriving system Inertia and monitoring including Real (ii) Fast frequency response time monitoring (iii) Primary frequency response (ii) Deriving SCR, WSCR, ESCR metric of IBG prone (iv) Secondary frequency response area including Real time monitoring (v) Tertiary frequency response (iii) Grid code compliance metric (vi) Fast Ramping response (iv) Scheduling considering system strength aspects (vii) Slow Ramping response (v) Frequency reserve requirement under various dispatch scenarios 9. Conclusion Changing power system development scenario and (vi) Ramping reserve requirement under various dispatch new generation mix aspects are offering challenges at scenarios present for seamless transition to RE rich future grid (vii) Reactive power support requirement with prevailing practices of system planning, operation, C. Additional technical analysis through modelling monitoring and simulation. and simulation Hence, there is a need to have paradigm shift in these Present simulation and modelling practices should be aspects. In this regard, roadmap proposes comprehensive enhanced and following parameters should be derived multi-dimensional approach to harmonise seamless under various operating and dispatch scenarios including integration of planned Renewable generation in Indian extreme conditions and should be considered for real grid. time system operation, outage planning, merit order Significance of new grid code parameters as reliability dispatch as well as system planning. indices as well as utilization of them as emerging tools, (i) ROCOF limits system strength aspects, Inertia and SCR monitoring with typical examples of GETCO grid and roadmap are (ii) Minimum fault level of synchronous generation discussed in an attempt of deriving appropriate counter (iii) Key efficiency break point measures as well as system planning to operate future (iv) SNSP (System Non synchronous Penetration) grid in efficient and reliable manner with sufficient system ratio strength at any given time. (v) Critical Inertia level There is no any simple solution to the system strength aspects. Continuous analysis and monitoring of power (vi) Utilization of hydro plants as synchronous system is necessary for studying and analysing the condenser emerging needs and it is a continuous process. Here, (vii) Identifying weaker part of the grid and counter an effort is made to support the journey of Indian power measures system towards greener world. D. New equipments or technology Following technology (not limited to) should be promoted

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Utility Roadmap for System Strength Aspects for Reliability, Stability & Flexibility of RE Rich Modern Power Grid 41

AnnexureAnnexure -AA –– PotentialPotential DifferenceDifference SGSG && IBG IBG

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REFERENCES [7] B. Badrzadeh, S. Grogan, N. Modi AEMO Australia [1] “Fast Response Ancillary Services implementation “Minimum strength of secure operation of large scale power systems with high penetration of in Indian grid pilot project experiences and feedback report, POSOCO, July 2019. non-synchronous generations Cigre SC C4 - 117, 2018. [2] Joint working group C4/C6.35/CIRED, TB 727 [8] “South Australian system strength assessment”, “Modelling of inverter based generators for power system dynamic studies AEMO September 2017 report.

[3] Indian Grid code 2013 for Grid connectivity [9] G.A. Chown, J.G. Wright, R. Van Heerden and M. requirements Cocker PPA energy (South Africa), “System Inertia and Rate Of Change Of Frequency with increasing [4] Indian grid code 2019 for Grid connectivity non-synchronous renewable energy penetration, requirements Cigre Science and Engineering volume N011 June [5] Saulo J. N. Cisneiros; Manoel J. Botelho; Dalton O. 2018. C. Brasil and othes, Brazil, “New challenges caused [10] Implementation of Inertia monitoring in Ercot by Julia by the new energy sources In the Brazilian power Matevosyan, Nov 2018 system” Cigre SC C4 Paper 104, 2014 [11] Short circuit modelling and system strength”, NERC [6] System reliability indices daily report, National Load white paper, 2018. Despatch Centre

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[12] “Integrating inverter based resources into low short Presently, he is working as an In-Charge Superintending circuit strength system”, NERC reliability guidelines, Engineer at Engineering Department, GETCO, Corporate December 2017. office, Vadodara looking after all the engineering activities. A BVQI – TUV certified ISO auditor, he is a member of CIGRE and [13] “Greeting the grid – Pathway to integrate 175 GW various Technical Committees of Electrotechnical Department Renewable Energy into India’s Electric Grid, Vol.I of Bureau of Indian Standards (BIS). He was also a Technical – National study, Ministry of Power, Govt. of India Committee Member of CBIP for Substation Manual 2019. June 2017 He has presented Technical Papers in various National & International conferences like GRIDTECH, SWITCHCON, CBIP [14] Cigre 2020 Tutorial on “System strength Aspects – A & PowerLine events story of not enough Shepherds and too many Ships” covering following N. M. Sheth – Executive Engineer, Corporate Engineering, Obtained Graduation in Electrical Engineering from Saurashtra (a) Description of system strength and its relation University Rajkot; and Qualification of Certified Project with inertia Management Associate (Project Management Level-D, (b) How lack of system strength can create is- National Ranker) from International Project Management sues Association (IPMA). Working in GETCO since 1994. Experience in the field of Substation Operation & Maintenance as well as (c) Tools and techniques for analysing low system Commissioning. strength operating condition Presently working in Engineering department and responsible (d) Design planning and Operational requirements for Design & Engineering of Control, Protection, Automation, under low system strength condition schemes & Philosophies, Digital substation, Secondary (e) Current and prospective system strength solu- engineering as well as RE integration related domains. tions Presented several technical papers at various national and international conferences CIGRE, GRIDTECH, CBIP, Biographical Details of the POWERLINE etc. on Relay protection, Substation Automation, Authors Digital Substation and RE Integration challenges related matter. One of the contributor from GETCO to review Draft Grid code B. P. Soni – I/C Superintending Engineer Corporate standards and suggesting some of the additional Technical Engineering, Obtained Graduation in Electronics Engineering requirement in context to RE integration challenges. from Birla Vishwakarma Mahavidyalaya, Vallabh Vidyanagar (Gujarat) in 1989. He joined erstwhile Gujarat Electricity Board Member of distinguished organization committees like; (i) BIS (GEB) in 1990. Having total 30 years of experience in Power Relay committee ETD 35, (ii) 35 th RAC Committee ERDA, Generation & Transmission, he has worked in various fields e.g. (ii) Substation Automation Expert Group of CBIP and Cigre Hydro and Thermal Power Plants, Operation & Maintenance India (iv) R&D consortium of National Institute of Wind Energy of EHV Substations, Telecommunication, Protection and (NIWE) Automation, Substation Design and Equipment Engineering.

CIGRE (India) Benefits to members • Free downloading of about 9000 reference documents i.e., papers & proceedings of Session & symposium; Technical brouchure on the work of study committees and Electra technical papers etc. • A free delivery of the ELECTRA Journal, a bilingual (French/English) magazine issued every two months which publishes the results of work performed by the CIGRE Study Committees and informs on the life of the Association. • Reduced registration fees for Sessions and Symposia. • Session and Symposium Papers and Proceedings available at a preferential price (50%). • Technical Brochures and other Reports at a preferential price, or free of charge when downloaded from CIGRE on- line Bookstore. • A Membership Directory which is a link between members and an essential tool for contacts, free of charge. • Updated Information about CIGRE International and other Meetings of interest for members. • The assistance of the Central Office for any query.

Volume 10 v No. 1 v January 2021 Activities of the Society Activities of CIGRE-India - 2020-21 About CIGRE-India CIGRE-India functions as the National Committee for CIGRE and coordinates CIGRE activities in India. It Organizes National Study Committee (NSC) meetings and Events at National Level. Affairs of CIGRE-India are administered by the General Body / Governing Council Governing Body of CIGRE India President – CIGRE-India

I.S. Jha Member, CERC Vice-Presidents

U.K. Bhattacharya Renuka Gera Seema Gupta Anil Saboo Praveer Sinha Manish Agrawal Director, NTPC Director, BHEL Director, Powergrid President, IEEMA MD, Tata Power CEO, Sterlite Power Transmission Technical Council Member Secretary, CIGRE-India Director, CIGRE-India

Chair Joint Chair Sunil Misra A.K. Dinkar A.K. Bhatnagar R.P. Sasmal N.N. Misra Director General, Secretary, CBIP Director, CBIP Ex Director, Ex Director, NTPC IEEMA POWERGRID

1. Membership in CIGRE (i) Steering Committee Members: • Mr. I S Jha Hon’ble Member, CERC in 2018-2020 & 2020-2022 • Mr. R P Singh the then President CIGRE-India and Former CMD, POWERGRID in 2006-2008 (ii) Administrative Council Member: Mr. I.S.Jha Member, Steering Committee, CIGRE (Paris) & Hon’ble Member, CERC

45 Volume 10 v No. 1 v January 2021 46 CIGRE India Journal

iii. honorary Member : • Mr. C.V.J.Verma, Former -MS, CBIP iv. Growth of Membership : • In the year 2016 - 593 nos. equivalent members (Individual: 131; Young: 24; Collective-I: 69; Collective-II: 12) • In the year 2017 - 768 nos. equivalent members (Individual: 151; Young: 28; Collective-I: 91; Collective-II: 19) • In the year 2018 - 826 nos. equivalent members (Individual: 169; Young: 35; Collective-I: 98; Collective-II: 17) • In the year 2019 – 820 nos. equivalent members (Individual: 165; Young: 25; Collective-I: 96; Collective-II: 22; Student Member: 96) • In the year 2020 - 800 nos. equivalent members (Individual: 159; Young: 22; Collective-I: 95; Collective-II: 20; Student Member: 142) • Almost Maintained the 2018 figure of 826 members for 2019 also. • At present India is at fifth position in the world on the basis of membership. Four countries ahead than India are: China (1061), US (958), Brazil (939) and Japan (903). • Membership count for few more countries: German (810); Russia (790); Australia (640); U.K. (610); France (590). • The country wise rank for nine top countries where members are maximum accessing CIGRE documents are; US; India; Germany; UK; China; Australia; brazil; Canada and Japan. 2. Participation in CIGRE Study Committee meeting at various places in the world: • All the study committees in the year 2019 were attended by its members / representatives except SC B1on HV Insulated cables. • List of participants in CIGRE Study Committee at various placed from India since 2016 is attached as Annexure 1. 3. CIGRE Study Committee Meetings held in the recent past, proposed in India and status of approval by CIGRE Year Event 2013 SC D2: Information Systems & Telecommunication 2015 SC B4: DC Systems & Power Electronics 2017 SC B1: Insulated Cables SC A1: Rotating Electrical Machines SC A2 : Power Transformers & Reactors 2019 SC B2 : Overhead Lines SC D1 : Materials and Emerging Test Techniques SC B5 – Protection & Automation (Proposed Oct. 2021), Due to Shifting of Session to 2021 2021 - Approved Likely to be shifted to Oct 2023 SC A3 : Transmission & Distribution Equipment (planned on 15-20 Nov. 2021) 2023 - Proposed SC B3 : Substations & Electrical Installations SC C2 : Power System Operation & Control SC C4 : Power System Technical Performance SC C5 : Electricity Markets & Regulation 2025 - Proposed C1: Power System Development & Economics C6: Active Distribution System and Distributed Energy Resources

Volume 10 v No. 1 v January 2021 Activities of the Society 47

4. Participation in CIGRE Paris session (e session 2020 from 24th August-3rd September 2020 & Session 2021 from 20-25 August 2021) (i) Total 240 abstracts were reviewed. Synopsis accepted – 35 Nos. out of 45 recommended Full papers submit- ted to Paris. (ii) Two additional papers under Chairman Quota have also been approved one from Sterlite and another from CEA in Study Committee B2: Overhead Lines & C6: Active Distribution Systems and Distribution Energy Re- sources respectively. (iii) 2020 shall be e-session because of Covid -2019. (from 24th August – 3rd Sept. 2020). (iv) Authors have been invited to make presentations (10 Minutes time; 10 Slides), information circulated to all concerned about registration for e-session 2020. (v) Those who will register for 2021 Paris session for them e-session for 2020 shall is free. (vi) Only Cigre 2020 e-session, 100 Euro for members and 200 Euro for non-member is the Registration. E- session 2020 registration shall be done by HQ Paris. Last date for registration is 15 August 2020. (vii) Information sent to exhibitors that who are already registered for Cigre 2020 shall continue to be an exhibitor for session 2021 without any additional cost (viii) For e-session 50 Participants have already registered, so far, including Authors of papers from India. (ix) NGN – Papers for CIGRE session 2020 : • Out of four papers recommended from CIGRE India ,two papers from GETCO have been accepted. The authors have been recommended for consideration for free registration for 2021 Session (x) Participation in CEO Meet at Paris during CIGRE Session 2021 The following Sr. Executives have been invited for participation from India :

Gurdeep Singh K. Sreekant K.V.S. Baba Praveer Sinha Prateek Agarwal CMD, NTPC CMD, POWERGRID CMD, POSOCO MD, Tata Power Group CEO, Sterlite (x) Participation in Workshop in Grid Disturbance during session 2021 The presentation received from Shri K.V.S Baba, CMD, POSOCO has been sent to Paris. (xi) Reaction to Key note speech by India during Opening Panel during session 2021 Madam Seema Gupta, Director Power Grid has been invited from India on the “Long-Term Technical Chal- lenges and Opportunities of the Electrification for Decarbonisation”. (xii) India Pavilion in 2021 Session: Following are participating and make payment.

Scope (12 sqm), Paid KEI (18 sqm); Paid Modern Insul. (9 Sqm) Paid- Full IEEMA (45 sqm) Paid NTPC- 18 sqm Paid PowerGrid – 12 sqm Soon Total Space 114 sqm • Space allotted at third floor for India Pavilion. The layout has also been received. • CIGRE has informed about postponement of session to 2021. • They have requested 50% payment to ensure the booth. • All the organizations listed have made the payment except the payment from POWERGRID is under process • We have approached POSOCO to replace BHEL for 9 sqm Space as BHEL has withdrawn their participation.

Volume 10 v No. 1 v January 2021 CIGRE- India launches its Women in Engineering (WIE) forum on 18 Oct. 2019

CIGRE-India launces Women in Engineering (WIE) forum on 18.10.2019. Ms. Seema Gupta, Vice President, CIGRE-India and Director (Operation) Power Grid has consented to lead the WIE forum of CIGRE-India as its Chairperson. She addressed the participants during the occasion. Besides Mr. I.S. Jha, President CIGRE-India & Hon’ble Member, CERC, Mr. R.P. Sasmal, Technical Chair, CIGRE-India, Mr. K. Srikant, CMD, POWERGRID, Mr. R.K. Chauhan, Director (Projects), POWERGRID, Mr. V.K. Kanjlia, Secretary, CIGRE India and Mr. P.P. Wahi, Director, CIGRE-India addressed the participants.

Vision of the Forum CIGRE WiE is a forum for women engineers to interact, develop their careers, increase their self-confidence, improve their I.S. Jha K. Srikant R.P. Sasmal professional skills. 48 CIGRE India Journal President, CIGRE-India CMD, POWERGRID Chairman –Tech., CIGRE-India

5. CIGRE-India - Women in Engineering Forum Mission of the Forum CIGRE WiE inspires, Forum has been created under chairmanship of Madam Seem Gupta Director (Operation) Powergrid motivates women • 1st meeting of WIE forum held on 18/10/2019 at engineers by helping to Power Grid. provide links to global • 2nd Meeting held on 19/11/2019 at Hotel Royal thought leaders and Plaza. The report covered in Electra role models, as well as • We plan try to ensure : to demonstrate the influence and functions – Participation of at least five women engineers from of female professional India in CIGRE session 2021. V.K. Kanjlia R.K. Chauhan P.P. Wahi communities. Secretary, CIGRE India Director (Projects) POWERGRID Director, CIGRE-India – To induct at least one women engineer as member in each Aofround the 16 100 NSC. Women Engineers participated from 25 different organisations on 18.10.2019

6. NGN Forum of CIGRE India • The forum dedicated to the young professionals. • The aim is to provide a good opportunity for development through networking with global Young Members • The name of Mr. Rajesh Kumar, Sr. DGM, and distinguished member CIGRE (2020) has been nominated to lead this forum of young engineers. • We plan to induct at least one young engineer as member in each of the 16 NSC. 7. CIGRE Steering Committee Meeting at Goa in India • The meeting planned for 17-19 Nov. 2020 was cancelled due to current pandemic. • The steering committee proposed to visit India and have their meeting in April 2021, which was confirmed by Shri R.P. Sasmal technical Chair, CIGRE-India during above steering committee meeting. • As already decided, a two days Colloquium on “Grid stability with enhanced penetration of Renewables” will also be planned. 8. Distinguished Membership Award of CIGRE for 2020: The following Names as proposal have been approved by CIGRE

B.B. Chauhan Y.V. Joshi Dipal Shah Rajesh Kumar, MD, GETCO SE, GETCO Ex chair, NSC B1 DGM, POWERGRID

S.R. Narasimhan, Vivek Pandey V.K. Agrawal Director, POSOCO DGM, POSOCO Ex. ED, POSOCO

Volume 10 v No. 1 v January 2021 Activities of the Society 49

9. National Representative on Study Committee for 2020-22 from India. The proposal from India: • The approval on the proposal from India from CIGRE, has been received. We are representing in all the 16 Committees additional seat one each in two study committees i.e. C1 & C6

Seema Gupta B.B. Chauhan K.V.S. Baba Subir Sen Director, Powergrid Former MD, GETCO CMD, POSOCO ED, Powergrid Chairperson CIGRE NSC A2 Chairman CIGRE NSC C4 Chairman CIGRE NSC C2 Chairman CIGRE NSC C1

B.N. De Bhomick Anish Anand R.K. Tyagi Subhas Thakur Former ED, Powergrid ED, Powergrid ED, Powergrid AGM, NTPC Chairman CIGRE NSC C3 Chairman CIGRE NSC B2 Chairman CIGRE NSC A3 Chairman CIGRE NSC B5

D.K. Chaturvedi Dr. B.P. Muni Nihar Raj S.S. Misra Santanu Sen Former GM, NTPC GM, BHEL VP, Adani GM, NTPC DGM, CESC Ltd. Chairman CIGRE NSC A1 Chairman CIGRE NSC D1 Chairman CIGRE NSC B3 Chairman CIGRE NSC C6 Co-Chairman CIGRE NSC C1

Y. B. K. Reddy S.C. Saxena Anil Kumar Arora, Debasis De, Lalit Sharma AGM, SECI SGM, POSOCO ED, Powergrid ED, NLDC, POSOCO COO, KEI Co-Chairman Chairman CIGRE Chairman CIGRE Chairman CIGRE Chairman CIGRE CIGRE NSC C6 NSC C5 NSC B4 NSC D2 NSC B1

10. CIGRE fellow Award from India: The name of Shri D.K. Chaturvedi, Chairman, NSC A1 who fulfilled the entire requirement has been approved by CIGRE

Volume 10 v No. 1 v January 2021 50 CIGRE India Journal

11. CIGRE Events held in India in 2020-21 • International Tutorial (Online) HVAC and HVDC Cable Systems –Advances in testing and standardization areas with relevant experiences in 23rd July 2020. • International Tutorial (Online) Accessories for HV Cables with Extruded Insulation-24th September 2020 • International Tutorial (Online) High-Voltage On-Site Testing of Power Apparatus with Partial Discharge Measurement - 23rd October 2020 • International Tutorial (Online) Insulated Cables -Construction, Laying and Installation Techniques - 26th October 2020 • International Tutorial (Online) Global Trends & Innovation in Voltage Source Converter (VSC) Technology - 30th October 2020 • International Tutorial (Online) Guidelines for Altitude Correction of Pollution Performance of Insulators - 3rd November 2020 • International Tutorial (Online) Cable accessories workmanship of extruded HV Cable-24th November 2020 • International Tutorial (Online) Requirements for grid forming and grid following inverters in weak or isolated grids and AC side harmonics and appropriate harmonic limits for VSC HVDC- 26th -27th November 2020 • International Tutorial (Online) Application Guide for Partial Discharge (PD) Detection in GIS using UHF or Acoustic Methods-2nd December 2020 • International Tutorial (Online) Methods for Dielectric Characterization of Polymeric Insulation Materials for Outdoor Applications-12th December 2020 • International Tutorial (Online) Technology Selection and Specification of HVDC and Protection and local control of HVDC grids-17-18th December 2020 12. CIGRE-India - Events Planned (i) CIGRE Session at Paris – 20-25 August 2021. (ii) International Conference on Renewable integration including energy storage – 16-20 April. 2021. (iii) CIGRE SC B5 Colloquium in India - October 2023 (iv) CIGRE SC A3 Colloquium in India - Nov. 2021 (v) CIGRE-India plan to hold minimum one event by each National Committee (tutorials /workshop/conferences) in a year at National Level. 13. CIGRE AORC • CIGRE-India had a privilege to Chair CIGRE-AORC During 2016-18. • Dr. Subir Sen, Executive Director of Powergrid was, Chairman of CIGRE-AORC and Mr. P.P. Wahi, Ex-Director of CIGRE-India was the Secretary and Mr. Vishan Dutt, Chief Manager of CIGRE-India was Assistant Secretary. • CIGRE-India Conducted CIGRE-AORC Administrative Meeting at New Zealand in Sept 2017 and at Paris in August 2018. We also organized CIGRE-AORC Technical meeting at Gangtok, Sikkim, India in May 2018. 14. CIGRE India Awards To encourage & recognize the contribution of Members, CIGRE-India has recently instituted AWARDS for excellent contribution in the activities of CIGRE at National and International Level. The following were Awarded in 2019: Special Appreciation Awards were presented during opening session to the following for their excellent contribution in CIGRE activities at National & Intl. Level:

Volume 10 v No. 1 v January 2021 Activities of the Society 51

• Mr. I.S. Jha, Member, Steering Committee, CIGRE (Paris) & Hon’ble Member, CERC • Ms. Seema Gupta, Chairperson, NSC A2 and Director, POWERGRID • Mr. R.P. Sasmal Technical Chair, Former Director, POWERGRID • Mr. N.N. Misra, Joint Chair- Technical, Former Director, NTPC • Mr. Anish Anand, Chairman, NSC B2 and CGM, POWERGRID • Mr. A.K. Gupta, Director, NTPC, Vice-President, CIGRE-India • Mr. D.K. Chaturvedi, Chairman, NSC A1 and Former General Manager, NTPC

Volume 10 v No. 1 v January 2021 52 CIGRE India Journal

15. List of CIGRE Executives already visited India in recent past : • Mr. Rob Stephen, President - CIGRE • Mr. Philippe Adam, Secretary General, CIGRE • Mr. Michel Augonnet, Vice-President Finance • Mr. Nico Smit, Chairman CIGRE SC A1 • Mr. Peter Wiehe, Secretary CIGRE SC A1 • Mr. Simon Ryder, Chairman CIGRE SC A2 • Mr. Hiroki Ito, Chairman CIGRE SC A3 • Mr. Marco Marelli, Chairman CIGRE SC B1 • Mr. Pierre Argaut, Former Chairman SC B1 • Dr. Konstantin Papailiou, Former Chairman CIGRE SC B2 • Mr. Herbert Lugschitz, Chairman CIGRE SC B2 • Mr. Terry Krieg, Chairman CIGRE SC B3 • Dr. Mohamed Rashwan, Chairman CIGRE SC B4 • Ms. Chirstine Schwaegerl, Chairperson CIGRE SC C6 • Mr. Nikos Hatziargyriou, Former Chairman CIGRE SC C6 • Dr. Ralf Pietsch, Chairman CIGRE SC D1 • Mr. Carlos Samitier, Chairman CIGRE SC D2 • Ms. Khayakazi Dioka, Chairperson of CIGRE WiE International 16. Publication of half yearly CIGRE India Journal To increase the activities and membership CIGRE India has taken the initiative to publish its Journal initially with the frequency of six months. The issues of the Journal up to Dec. 2012 have already been published and the next Issue July 2013 is under print. The CIGRE India journal contains details about the activities of the association, technical articles, and data and is circulated to its members within the country. The journal serves an excellent purpose of disseminating the technological, innovative developments etc. amongst the concerned organizations of the energy sector, which are taking place at the national and international level. The journal is available both in print and online versions. 17. New Initiatives Online programme to overcome the effect of COVID 2019 CIGRE India launched series of online International Tutorials throughout the year @ each of the Studty Committee of CIGRE. Online Programme Held in: • SC B1 : on Insulated cables; • SC B4 : DC Links and Power electronics; • SC C1 : Power system development and economics • SC D1 – Materials & Emerging test Techniques. Online Programme planned : • SC B2: Overhead lines • SC C2: Power system operation and control • SC C1: Power system development and economics • SC C4: Power system technical performance • SC D2: Information systems and telecommunication Acknowledgement of support of CIGRE CIGRE India acknowledges the support and guidance extended by CIGRE, which has helped CIGRE-India in increasing the activities of CIGRE in India.

Volume 10 v No. 1 v January 2021 Activities of the Society 53

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Volume 10 v No. 1 v January 2021 54 CIGRE India Journal CIGRE India - Women in Engineering (WiE)

A. 18th October 2019: Brainstorming Session on WiE-CIGRE India

CIGRE India has launched its first “Women in engineering Forum” on 18th October 2019 at national level. The event was hosted in association with POWERGRID at its corporate office, Gurgaon. The objective of the event was to introduce CIGRE Women in Engineering forum, highlighting the contribution of women in CIGRE structure and to enable its members with knowledge transfer and networking. Participants from various organisations across INDIA such as NTPC, NHPC, POWERGRID, Sterlite, SJVN, POSOCO, KEC, L&T, NEEPCO, Siemens, TPDDL, WAPCOS, BYPL, KEI etc. has made the event remarkable. Ms. Seema Gupta, Vice President, CIGRE-India and Director (Operation) POWERGRID has led the brain storming session of WIE forum as its Chairperson. Besides Mr. I.S. Jha, President CIGRE-India & Hon’ble Member, CERC, Mr. R.P. Sasmal, Technical Chair, CIGRE-India, Mr. K. Srikant, CMD, POWERGRID, Mr. R.K. Chauhan, Director (Projects), POWERGRID, Mr. V.K. Kanjlia, Secretary, CIGRE India and Mr. P.P. Wahi, Director, CIGRE-India addressed the participants.

Volume 10 v No. 1 v January 2021 54 Activities of the Society 55

The theme of the event was “To inspire and empower women as leaders in engineering and technology.” Ms Seema Gupta introduced the participants about CIGRE WIE forum who is taking initiatives to grow women engineers and providing a platform to submit technical papers, attending workshops, technical discussions and getting mentored by experienced professionals. She presented about various study committees & working group of CIGRE- INDIA and activities to participate and get benefitted from them. She talked about women empowerment and challenges women’s usually face in a technical field and provide solutions to deal with these problems. An open house session was organised and women from various organisations shared challenges faced during their respective works and their experiences in dealing with them. The event was concluded by proposing recommendation to take full advantage of CIGRE forum and professional network of Women in Engineering was formed to connect, to interact, to share experiences in future. B. 19th November 2019: Meeting of CIGRE India Women in Engineering Forum CIGRE – INDIA organised a meeting of Women in Engineering Forum on 19th November 2019 at New-Delhi. The agenda of the meeting was to inspire women engineers to come forward, interact, develop skills and improve their participation in the engineering domain. Ms. Seema Gupta, Chairperson, CIGRE- India WiE Forum had addressed the participants and spoke about women empowerment. Ms. Khayakazi Doika, Global Chairperson for CIGRE Women in Engineering has presented a session on the initiatives CIGRE WiE is taking for encouraging women professionals to break the conventional barriers.

Ms. Tara Lee (Australia) was the moderator of the Session. Ms. Rachana Garg - IEEE India WiE Vice Chair had raised the concern about the challenges women’s face in technical field. Several Ex-CIGRE members share their experience and views that by being a member of CIGRE committee and part of its Working Group, it’s an honour and opportunity to learn about technological advancement by connecting to global knowledge partners in Power System. The meeting was concluded with remarks of creating awareness across INDIA to inspire and empower more women to become part of this professional network.

Volume 10 v No. 1 v January 2021 Series of International Tutorial (Virtual) Organize by CIGRE-India in the Recent Past

CIGRE-India is one amongst the most active national committee. It is our honor that Mr. I.S. Jha, President CIGRE-India & Hon’ble Member of Central Electricity Regulatory Commission is representing India in CIGRE Steering Committee (the decision making body of top executives) as well as in CIGRE Administrative Council. It is a matter of pride for all of us that India is represented in all the 16 CIGRE Study Committees and the members are actively involved in the activities of CIGRE study Committees. It has always been our endeavor to promote CIGRE in India through its activities like organization of regular Training programmers/ Conferences/ Workshops/ Tutorials etc., which has greatly helped involvement of maximum professionals with CIGRE – India including young professionals. In this unusal situation in the past where skill enhancement and training of professionals emerged as an important aspect and a challenge, CIGRE- India launched series of virtual Tutorials/ Workshops/ Webinars on the subject relevant to 16 CIGRE Study Committees The tutorial organized in the past are listed below:

International Tutorial (Online) HVAC and HVDC Cable Systems - Advances in Testing Procedures and Standardization Areas with Relevant Experiences (Under the aegis of CIGRE National Study Committee B1 on Insulated Cables) 23rd July 2020 Number of Total Participants : 145

International Speaker from CIGRE National Study Committee Chairman-B1

Dr. Vercellotti Uberto Mr. Lalit Sharma Italy COO, KEI

Volume 10 v No. 1 v January 2021 56 Activities of the Society 57 International Tutorial (Online) Accessories for HV Cables with Extruded Insulation (Under the aegis of CIGRE National Study Committee B1 on Insulated Cables) 24th September 2020 Number of Total Participants : 136

International SpeakerGeir from Clasen CIGRE National Study Committee Chairman-B1

Mr. Geir Clasen Mr. Lalit Sharma Norway, Convener, CIGRE SC B1, TAG COO, KEI

Takeaway • Type, routine and after lying testing /Quality • Compatibility of materials. Assurance Schemes. • Metallic screen bonding requirement & earth currents. • Maintenance of accessories. • Environmental protection/mechanical forces / • Cost considerations. climatic condition.

International Tutorial (Online) High-Voltage On-Site Testing with Partial Discharge Measurement (Under the aegis of CIGRE National Study Committee D1 on) 23rd October 2020 Number of Total Participants : 118 International Speaker from CIGRE National Study Committee Chairman-D1

Mr. Ralf Pietsch Dr. B P Muni Germany, Chairman, SCD1 General Manager, BHEL

TAKEAWAYS On-site PD measurement: HV sources and accessories for on-site applications: • Conventional PD measurement • AC, DAC (Damped AC voltage), VLF (Very-low • Non-conventional electromagnetic PD detection frequency) • Noise reduction • HV filter, coupling capacitors, connections and • Acoustic PD detection grounding

Volume 10 v No. 1 v January 2021 58 CIGRE India Journal

• Important aspects for PD evaluation • GIS /GIL (2 examples) Preconditions for on-site testing including PD • Cable systems (5 examples) measurement • Rotating machines (3 examples) Examples of test and measuring techniques for • Power Transformers (4 examples) apparatus and systems : International Tutorial (Online) Insulated Cables - Construction, Laying and Installation Techniques (Under the aegis of CIGRE National Study Committee B1 on Insulated Cables) 26th October 2020 Number of Total Participants : 40 International Speaker from CIGRE National Study Committee Chairman-B1

Mr. Sergio Chinosi Mr. Lalit Sharma Italy COO, KEI

TAKEAWAYS • Innovation, Construction & Installation Techniques • Description of the cable System • Cable laying and Installation techniques International Tutorial (Online) Global Trends & Innovation in Voltage Source Converter (VSC) Technology (Under the aegis of CIGRE National Study Committee B4 on DC Links and Power Electronics) 30th October 2020 Number of Total Participants : 80 International Speaker from CIGRE National Study Committee Chairman-B4

Mr. Les Brand Mr. Anil Kumar Arora Australia ED, POWER GRID

Volume 10 v No. 1 v January 2021 Activities of the Society 59

TAKEAWAYS contrasted and the key and defining characteristics • Introduce both VSC and LCC technologies, explain of VSC technology summarised. how they work, summarise their history and • Discuss the challenges in using VSC technology development, and provide a comparison of the two, with overhead DC lines will be presented and including which applications are suited to each and explored. why. • Include a couple of case studies of VSC applications • Focus on VSC – describing the key components, – why VSC was chosen, key elements of design the formula that govern their operation, overall and operation and how they have performed since control philosophy and available control modes commissioning. in operation. The various VSC technologies • Conclude with a summary of recent developments and topologies will be described, compared and in VSC technology and what innovations are currently being explored globally.

International Tutorial (Online) Guidelines for Altitude Correction of Pollution Performance of Insulators (Under the aegis of CIGRE National Study Committee D1 on Material and Emerging Test Techniques) Number of Total Participants : 50 03rd November 2020 International Speaker from CIGRE National Study Committee Chairman-D1

Mr. Igor Gutman Dr. B P Muni Russia General Manager, BHEL

TAKEAWAYS Collection and analysis of all available data on Physical principles related to the influence of air flashover voltages of polluted insulators: density on the discharge process: • Different altitude from sea level to 6000m • Clean conditions • Covering the period of publications 1987-2010 • Polluted conditions Practical proposals for harmonization of the Status of correction on altitude in IEC/CIGRE: correction of the required creepage distance for altitude: • AC • AC • DC • DC

Volume 10 v No. 1 v January 2021 60 CIGRE India Journal International Tutorial (Online) Cable Accessories Workmanship of Extruded HV Cable (Under the aegis of CIGRE National Study Committee B1 on Insulated Cables) 24th November 2020

Number of Total Participants : 60 International Speaker from CIGREKie ron National Study Committee Chairman-B1 Leeburnhas34yearsexperienceasanelectricalengineerwithspecialis ationinelectriccabledesign,developmentandstandardization. Since 2009 he has been Chief Engineer at CBi-electric:africancables.

During this time he has also served the National and International community in the following roles:  ConvenoroftheCigreWorkingGroupwhichproducedTechnicalBro chureTB476AccessoryWorkmanship.  MemberofCigreWorkingGrouponB1-37FluidFilledCableSystems.  ServedontheInternationalScientificandTechnicalCommitteefort he2007and2011Jicablecableconference,evaluatingandselectin gpapersforpresentation. Mr. Kieron Leeburn,  MemberoftheIndustrialAdvisoryBoardoftheElectricalanMr.dInfor mLalit Sharma ationEngineeringDepartment,attheUniversityoftheWitwatersra South Africa, CIGRE Convener, TB 476 nd. COO, KEI  MemberoftheInternationalElectrotechnicalCommission’sworkin ggrouponHighVoltagecables.InIECTC20WG16,heassistsintheg TAKEAWAYS enerationandmaintenanceofInternationalStandardsforelectricca bles. • Technical risks for components.  Serveson thelocalTechn •ic a lCo mmAssessmentitteeofSABSforEle coftricc abskillsle for jointers. s,whereheassistsinthegenerationandmaintenanceoftheSouth • Set up of jointing / installation activities.Africanstandardsforelectriccables.

International Tutorial (Online) Requirements for Grid Forming and Grid following Inverters in weak or isolated Grids and AC side Harmonics and Appropriate Harmonic Limits for VSC HVDC (Under the aegis of CIGRE National Study Committee B4 on DC Links and Power Electronics) 26-27 November 2020 Number of Total Participants : 30 International Speaker from CIGRE National Study Committee Chairman-B4

Dr. Chandana Karawita Dr. Hiranya Suriyaarachchi Dr. Nigel Shore Mr. Anil Kumar Arora

Canada, Sectetary, WG-B4 87 Canada, Converner Sweden ED, POWER GRID

Volume 10 v No. 1 v January 2021 Activities of the Society 61

TAKEAWAYS Day-1 The capabilities of the inverters currently used in renewable energy sources and HVDC systems may not be adequate for the grids with a small percentage or no synchronous generators. For more than a century, synchronous generators have been successfully operated in power systems. This tutorial will first evaluate the contributions from the synchronous generators in terms of voltage, inertia and frequency support and define the requirements for the grid-forming and grid-following inverters. The current capabilities and future expectations will be evaluated using example simulation cases. Day-2 This tutorial presents the work of Working Group B4.68, which produced TB 754. This Technical Brochure examines the harmonic aspects of voltage source converters used for HVDC transmission. The harmonic profile of such converters differs greatly from that of the more established line commutated converters. The low magnitude of harmonic generation may imply that AC filters are not needed, or may be very small. The control system factors affecting both harmonic generation and the active internal impedance are examined. Possible deleterious effects of higher frequencies, inter-harmonics and even order harmonics are discussed, and recommendations given regarding statutory limitations. Mitigation of harmonics by means of either passive filtering or active filtering by converter control action is described. The Brochure explains various techniques for modelling the harmonic behaviour of VSC HVDC, and concludes with a review of harmonic stability issues and various techniques used to identify the risk of its occurrence and to indicate means of mitigation.

International Tutorial (Online) Application Guide for Partial Discharge (PD) Detection in GIS using UHF or Acoustic Methods (Under the aegis of CIGRE National Study Committee D1 on Material and Emerging Test Techniques) 2nd December 2020 Number of Total Participants : 80 International Speaker from CIGRE National Study Committee Chairman-D1

Dr. Uwe Schichler Dr. B P Muni Germany, Convener, AGD1-03 General Manager, BHEL TAKEAWAYS Gas-insulated switchgear (GIS) have been in operation for more than 45 years and it shows a high level of reliability. However, the return of experience from GIS indicates that some of the in-service failures are related to defects in the insulation system. Many of these defects can be detected by partial discharge (PD) diagnostics. An Electra Report published in 1999 describes the two-step procedure for the sensitivity verification of the UHF and acoustic system. The CIGRE Technical Brochure No. 654 collects the available experience on sensitivity verification from the last 15 years and describes its practical applications for GIS. It summarizes the established guidelines and recommendations which will help manufacturers and users in the effective application of the UHF method for PD detection on GIS. In addition general guidelines on the acoustic method for PD detection will be presented.

Volume 10 v No. 1 v January 2021 62 CIGRE India Journal

International Tutorial (Online) Methods for Dielectric Characterization of Polymeric Insulation Materials for Outdoor Applications (Under the aegis of CIGRE National Study Committee D1 on Material and Emerging Test Techniques) 12th December 2020 Number of Total Participants : 25

International Speaker from CIGRE National Study Committee Chairman-D1

Dr. Jens Seifert Dr. B P Muni Germany, Convener WG General Manager, BHEL

TAKEAWAYS • Round Robin Testing • General Insight on Dielectric Diagnostic Methods • The Importance of Standardization of Method and (DDM) Equipment • Understanding the Physical Background and • Lessons Learned Polarization Mechanisms • Outlook to Applications for Insulation Systems in • Applications of DDM to Composite Insulating HV Equipment Materials Secretary WG D1-56 • Development of the Recommended Test Techniques

International Tutorial (Online) Technology Selection and Specification of HVDC & Protection and Local Control of HVDC Grids (Under the aegis of CIGRE National Study Committee B4 on DC Systems & Power Electronics) 17-18th December 2020 Number of Total Participants : 25

Volume 10 v No. 1 v January 2021 Activities of the Society 63

International Speaker from CIGRE NSC - Chairman - B4

Mr. Bruno Bisewski Mr. Kees Koreman Mr. Willem Leterme Mr. A K Arora Canada Netherlands, Chairman Belgium ED, Powergrid JWG B4/B5-59

TAKEAWAYS Day - 1 The key factors that the participant will take away from the tutorial is an understanding of the many considerations encountered when planning and specifying an HVDC system that will meet the requirements of the project. The material presented is based on long time experience on many projects in many countries will cover practical questions encountered while planning a new HVDC project including technology selection, cost, footprint, losses, maximum rating, and fault recovery performance that may be decisive in the selection of one technology as well as other factors which may not be decisive but could still influence the decision in favour of one technology over the other. The tutorial will also cover selected topics related to specification of both LCC and VSC technology including ratings, performance requirements and testing. Day - 2 The webinar will inform the participants about protection and local control systems in HVDC grids. First, the fault response of converters with and without fault blocking capability is compared. Then, various strategies for clearing DC-side faults are discussed. Examples of short circuit calculations examples are given for both monopole and bipole HVDC grids. Thereafter, various principles in fault detection and localisation are explained and compared. Finally, the basic operation of DC Circuit Breakers is described. Participants will get: • Information about the different HVDC converter technologies. • Short circuit phenomena in DC grids. • Basic requirements on protection and local control. • Fault clearance strategies. • Protection system components such as measurement and detection systems. • DC Circuit Breakers and fault localisation techniques. The obtained knowledge can be used in the future development, engineering, design and operation of meshed DC networks, both offshore and onshore. It will allow for the design of protection systems including the selection of fault clearance strategies that will be applied.

Volume 10 v No. 1 v January 2021 CIGRE Members from India in 2020 (As on December 2020)

Summary of Membership

Collective-1 Collective-2 Individual-1 Young (below Student (Organisation) (Regulatory & 35 years of age) Members Institution) 95 20 159 22 142 Total equivalent x 06 x03 x01 x0.5 570 60 159 11 Grand Total 800 142

Institutional Members

S. No. Organisation 10 IEEMA 1 Andhra Pradesh Electricity Regulatory 11 Indian Inst. of Technology Kanpur Commission 12 Indian Institute of Technology Bombay 2 Bihar Electricity Regulatory Commission 13 Jharkhand State Electricity Reg. Comm. 3 Central Electricity Regulatory Commission 14 Joint Electricity Reg. Com.-for Goa &Uts 4 CIGRE INDIA- COE,Centre of Excellence 15 Malaviya National Inst. of Tech.- Jaipur 5 Delhi Electricity Regulatory Commission 16 Maharashtra Electricity Regulatory Comm. 6 Electrical Research and Development 17 Punjab State Electricity Regulatory Association Commission 7 Engineering College Banswara-Rajasthan 18 Ramelex Testing & Research Institute 8 Gujarat Electricity Regulatory Commission 19 Uttarakhand Elec. Regul. Commission 9 H P Electricity Regulatory Commission 20 U.P. Electricity Regulatory Commission

Individual Members

S. Name Organisation 11 Apar Industries Ltd. Srimanta Kumar Jana No. 12 AVAADA Power Deepak Kumar 1 ABB Urmil Parikh Saxena 2 ABB Global Industries Sachin Srivastava 13 Bechtel (I) Pvt. Ltd. Sanjeev Bhatia & Services Ltd. 14 BHEL Corporate R Mohana Rao 3 ABB India Ltd. Nihar Raj & D Mandava 4 Adani Electricity Arvind Kumar Sharma 15 CBIP V K Kanjlia Mumbai Limited - 16 Consultant Narendra Nath Misra Trans 17 Consultant Virendra Kumar 5 Adani Power Niraj Agrawal Lakhiani Maharashtra Ltd. 18 Consultant N S Sodha 6 Adishaktyai- India Neeraj Khare 19 Consultant R P Sasmal 7 Aditya Birla Insulators Harleen Singh 20 Consultant Dhananjay Kumar 8 Aditya Birla Insulators Sanjeev Sachdev Chaturvedi 9 Alfa Consultants Ramesh Dattaraya 21 Consultant Sanjay Patki Suryavanshi 22 Consultant Pramod Rao 10 Anna University Usa Savadamuthu

Volume 10 v No. 1 v January 2021 64 CIGRE Members from India in 2021 65

23 Consultant Subhash Sethi 53 GETCO Bhadreshkumar B. 24 Consultant Gopal Ji Mehta 25 Consultant Krishnan S. 54 GETCO Nilesh Sheth Balasubramanian 55 GETCO Rameshchandra P. 26 Consultant Lokesh Thakur Satani 27 CTR Manufacturing T P Govindan 56 GETCO Bankim Industries Ltd. Pravinchandra Soni 28 CTR Manufacturing Vijaykumar 57 GETCO Dipak kumar Patel Industries Ltd. Wakchaure 58 GETCO Chetan G Thakkar 29 CTR Manufacturing Ravindra Vishnu 59 GETCO Bhadresh B. Chauhan Industries Ltd. Talegaonkar 60 GETCO Yogesh Vishnu Joshi 30 Central Power Dr. Burjupati 61 GETCO Asha M Agravatt Research Institute Nageshwar Rao 62 GETCO Bhavesh Bachubhai 31 Central Electricity Indu Shekhar Jha Ahir Regulatory Commission 63 GETCO Arjunbhai B. Rathod 32 Damodar Valley Abhijit Chakraborty 64 GETCO Kantilal M Chhaiya Corporation 65 Hindalco Kaushik Tarafdar 33 Deccan Vikas Jalan 66 IIT-Bombay Himanshu Bahirat 34 DNV-KEMA Ravi Kumar 67 India Infrastructure Anchal Pahwa Puzhankara Publishing Limited 35 DTL Rajesh Kumar Arora 68 Indian Institute of Joy Thomas Meledath 36 DVC Sudipta Maiti Science 37 DVC Arindam Das 69 Indian Institute of Udaya Kumar Science 38 Erode Sengunthar K. Singaram Christian Engineering College Johnson 70 Indolite Devices Pvt. Maninderjit Singh Ltd. Sethi 39 FEEM Deepak Kumar Singh 71 IRADE Vinod Kumar Agarwal 40 Free Lance Hosalli Bhashyam Mukund 72 ITER-India, Institute Bhavin Raval for Plasma Res. 41 GE Grid Solution (GE Purshottam Kalky T&D India Ltd.) 73 J&K Power Habib Chowdhary Development 42 GE T&D India Ltd. Madhu Sudan Department 43 GE T&D India Ltd. Vikrant Joshi 74 Jacobs Sanjib Mishra 44 General Electric Nitin Kumar 75 Kalpataru Power Pervinder Singh Srivastava Trans. Ltd Chowdhry 45 General Electric T&D Narendra Sharma 76 Kalpataru Power Milind Nene India Trans. Ltd 46 Govt. of Tamil Nadu K.C. Yoganandham Y. 77 KEI Industries Ltd Lalit Sharma Kumaresan 78 KEC International Sunil Bhanot 47 GETCO Pankajbhai Suthar Limited 48 GETCO Ashokkumar J. 79 M.P. Power K. Kamlesh Murty Chavda Transmission Co. Ltd 49 GETCO Jalpesh Trivedi 80 Laxmi Associates Aradhana Ray 50 GETCO Zulfikarali M Vijapura 81 Mahati Industries Pvt. Udaybabu 51 GETCO Vinay Rathod Ltd. Ratanchand Shah 52 GETCO Bhasmang N. Trivedi

Volume 10 v No. 1 v January 2021 66 CIGRE India Journal

82 Megawin Switchgear Muthuraj Ramaswamy 114 Power Grid Anish Anand (P.) Ltd. 115 Power Grid Nitesh Kumar 83 Modern Insulators Ram Kumar 116 Power Grid Dr. Sunita Chohan Limited Vaithilingam 117 Power Grid Anil Kumar Arora 84 National Inst. of I R Rao 118 Power Grid Ashok Pal Technology Karnataka 119 Power Grid Shouvik Bhattacharya 85 NEEPCO Angelica Pohshna 120 Power Grid Soni Tunisha 86 NHPC Ravindra Sharma 121 Power Grid Deepa S Kumar 87 North East Satyajit Ganguly Transmission 122 Power Grid Sangita Sarkar Company Ltd. 123 Power Grid Vineeta Agarwal 88 NTPC Ltd. Nagesh Kondra 124 Power Grid Ram Naresh Singh 89 ONGC Tripura Sanil Namboodiripad 125 Power Grid Chandra Kant 90 Oman Transformers Oommen P Joshua 126 Power Grid Rashmi Pant Joshi India Limited 127 Power Grid Sukdev Bal 91 Persotech Solutions Pravinchandra Mehta 128 Power Trans.Corp. of Lalit Kumar 92 Polycab Wires Pvt. Tony Martens Uttarakhand Ltd. Ltd. 129 Power Transmission Renu Singhal 93 POSOCO Chitrankshi RNT Consultants Ghangrekar 130 Primemeiden Limited Vijayakumaran 94 POSOCO SUBHENDU Moorkath MUKHERJEE 131 Protection Engg. & Pradeep Kumar 95 POSOCO Santosh Kumar Jain Researh Laboratories Gangadharan 96 POSOCO K V S Baba 132 Prysmian Cable SYS. Alwin Selva Paul 97 POSOCO Vivek Pandey Yesudass 98 POSOCO Aditya Prasad Das 133 Rajasthan Test & Jaspaul Kalra Research Centre 99 POSOCO Rajiv Kumar Porwal 134 Raj Petro Specialities Sushil Chaudhari 100 POSOCO S.R. Narasimhan Pvt Ltd 101 POSOCO Samir Chandra 135 Raj Petro Specialities Dr. Daya Shankar Saxena Pvt Ltd Shukla 102 POSOCO Praveen Kumar 136 Raj Petro Specialities Baburao Keshawatkar Agarwal Pvt Ltd 103 POSOCO M. Venkateshan 137 REVEN-TEC Niraj Kulkarni 104 POSOCO Sajan George 138 SIEMENS Ltd Jayasenan 105 Power Grid Subhash C Taneja Chinnathambi 106 Power Grid Gyaneshwar Payasi 139 SJVN Ltd. Rashi Tyagi 107 Power Grid Rajeev Kumar 140 Sleepwalkers Sivaji Burada Chauhan 141 Sterlite Power Parantap Krishna 108 Power Grid Subir Sen Transmission Ltd. Raha 109 Power Grid Seema Gupta 142 Sterlite Power Deepak Lakhapati 110 Power Grid Arun Kumar Mishra 143 Sterlite Power Grid Rajesh Suri 111 Power Grid B N De Bhowmick Ventures Ltd 112 Power Grid Biswajit Bandhu 144 Syselec Technologie Hrushaabh Prashaant Mukherjee Private Limited Mishra 113 Power Grid Rajesh Kumar 145 Torrent Bipin B. Shah

Volume 10 v No. 1 v January 2021 CIGRE Members from India in 2021 67

146 TAG Corporation Vivek 151 Telawne Cromptek Yogesh Telawne Thiruvenkatachari Electricals Pvt. Ltd. 147 Takalkar Powerr Subhash Chandra 152 The Tata Power Co. Rajendra Vinayak Engin&Consult. Pvt Takalkar Ltd. Saraf Ltd 153 TS Transco Arogya Raju Pudhota 148 Tata Power Skill Umesh Maharaja 154 UPPTCL Suman Guchh Development 155 WAPCOS Ltd. Hillol Biswas 149 Taurus Powertronics Narasimhan 156 Ziv Automation India R C Anand Pvt. Ltd. Ravinarayan Pvt Ltd MAKARAM 157 ZTT cable Deepal Shah 150 Technical Associates Vishnu Agarwal

Organisational Members

Sl. No. Organisation 30 NTPC Limited, H.Q 1 Adani Electricity Mumbai Limited - Tran. 31 NTPC Limited, Anta GPS 2 APAR Industries Limited 32 NTPC Limited, Auraiya 3 Atlanta Electricals Pvt.Ltd. 33 NTPC Limited, Bongaigaon TPP 4 ABB Power Products and Systems (I) Ltd. 34 NTPC Limited, Barh 5 Bhakra Beas Management Board (BBMB) 35 NTPC Limited, Dadri SSTP 6 BAJAJ ELECTRICALS LTD. 36 NTPC Limited, Faridabad 7 Bharat Heavy Electricals Ltd, Hyderabad 37 NTPC Limited, Farakka STP 8 Bharat Heavy Electricals Ltd., Noida 38 NTPC Limited, Jhanor 9 Bharat Heavy Electricals Ltd., Haridwar 39 NTPC Limited, Kudgi STPS 10 Bharat Heavy Electricals Ltd., Bhopal 40 NTPC Limited, Kahalgaon STPS 11 Bharat Heavy Electricals Ltd., Bangalore 41 NTPC Limited, Kawas GPP 12 Central Electricity Authority (CEA) 42 NTPC Limited, Korba STPS 13 Central Power Research Institute 43 NTPC Limited - Koldam 14 CESC Limited 44 NTPC Limited - Kayamkulam 15 CTR Manufacturing Industries Ltd. 45 NTPC Limited, Mouda STPP 16 CTC Global India Pvt. Ltd. 46 NTPC Limited, Rihand STPP 17 Delhi Metro Rail Corporation Ltd. 47 NTPC Limited, Ramagundam STPS 18 Easun-Mr Tap Changers (P) Limited 48 NTPC Sail Power Company Pvt. Ltd. 19 Gupta Power Infrastructure Limited 49 NTPC Limited, Singrauli STPS 20 KEI Industries Ltd. 50 NTPC Limited, Simhadri STPP 21 KSE Electricals Pvt Ltd. 51 NTPC Limited, SIPAT STPS 22 Larsen & Toubro Limited- Construction 52 NTPC Limited, Talcher STPS 23 LS Cable India Pvt. Ltd. 53 NTPC Limited, Talcher TPS 24 Larsen & Toubro Limited- Construction 54 NTPC Limited, Tanda 25 National High Power Test Lab. Pvt. Ltd. 55 NTPC Limited, Unchahar 26 NHDC Ltd. 56 NTPC Limited, Vindhyachal STPS 27 NLC India Limited 57 ONGC Tripura Power Company Ltd. 28 NHPC Limited 58 Olectra Greentech Ltd. 29 North Eastern Electric Power Corp. Ltd 59 Polycab Wires Pvt. Ltd.

Volume 10 v No. 1 v January 2021 68 CIGRE India Journal

60 Power Research & Develop. Cons. Pvt. 77 Powergrid Corporation of India, Vadodara Ltd 78 Powergrid Corporation of India, WRTS-1 61 POSOCO- ERLDC 79 Powergrid Corporation of India, Kolkata 62 POSOCO- NERLDC 80 Powergrid Corporation of India, Guwahati 63 POSOCO- H.Q. 81 Siemens Ltd, EM TS 64 POSOCO- SRLDC 82 Sterlite Power Transmission Limited 65 POSOCO- WRLDC 83 Savita Oil Technologies Ltd. 66 Powergrid Corp. of India Ltd, Lucknow 84 SJVN Limited 67 Powergrid Corp. of India Ltd, Shillong 85 Solar Energy Corporation of India Ltd. 68 Powergrid Corp. of India Ltd.,Jammu 86 Sanvijay Infrastructures Pvt. Ltd. 69 Powergrid Corp. of India Ltd., Delhi 87 Sicame India Connectors Pvt. Ltd. 70 Powergrid Corp. of India Ltd-Orissa 88 THDCIL 71 Powergrid Corp. of India Ltd-Nagpur 89 The Motwane Manufacturing Co. Pvt Ltd 72 Powergrid Corporation of India, H.Q. 90 The Tata Power Company Ltd. 73 Powergrid Corporation of India, Bangalore 91 Tata Power Delhi Distribution Limited 74 P o w e r g r i d Corporation o f I n d i a , 92 Transmission Corporation of Telangana Ltd. Kurukshetra 93 Transrail Lighting Limited 75 P o w e r g r i d Corporation o f I n d i a , 94 Universal Cables Limited Secunderabad 95 UE System Imena Pvt. Ltd. 76 Powergrid Corporation of India, Patna

Young Members S.No. Name Organistaion 12 GETCO Vasantkumar Ramanlal 1 Power Grid Ankur Kumar Patel 2 Power Grid Jeetesh Kumar 13 Power Grid Vinita Kumari 3 Power Grid Amandeep Singh 14 Power Grid Ashish Kumar Singh 4 Power Grid Prasoon Tripathi 15 Power Grid Ashutosh Digambar Rajurkar 5 POSOCO Nitin Yadav 16 Power Grid Priyam Maity 6 POSOCO Aman Gautam 17 Power Grid Aman Bansal 7 Aditya Birla Vikas Rai Insulators 18 Sterlite Power Venkata Krishnaji Palasanipalli 8 POSOCO K B V Ramkumar 19 Sterlite Power Ashok D.K. 9 POSOCO Vishal Puppala Transmission 10 GETCO Bhavesh Kumar Manubhai 20 Power Grid Vikas Bishnoi Rana 21 Power Grid Deepthy C Nair 11 GETCO Sanjay Jadav 22 Power Grid Ankit Prakash Vaishnao

Student Members

S. Organisation Name 3 Engineering College Abhishek Bhoi No. Banswara 1 College of Engineering Rijo Ranjan 4 Engineering College Manisha Bhuriya 2 College of Engineering Ramesh Rahul Banswara Guindy 5 Engineering College Ajay Bunkar Banswara

Volume 10 v No. 1 v January 2021 CIGRE Members from India in 2021 69

6 Engineering College Durgesh Bunkar 30 Indian Institute of AKHILESH Banswara Technology Kanpur PRAKASH GUPTA 7 Engineering College Ashish Chatwani 31 Indian Institute of Vineeth V Banswara Technology Kanpur 8 Engineering College Bhavesh Kumar 32 Indian Institute of Piyush Warhad Banswara Gamot Technology Kanpur Pande 9 Engineering College Meena Bhushan 33 Indian Institute of P.Naga Yasasvi Banswara Technology Kanpur 10 Engineering College Meena Mahesh 34 Indian Institute of Gaurav Khare Banswara Kumar Technology Kanpur 11 Engineering College Ashok Meena 35 Indian Institute of Priyanka Gangwar Banswara Technology Kanpur 12 Engineering College Abhishek Mishra 36 Indian Institute of Saurabh Banswara Technology Kanpur Kesherwani 13 Engineering College Ajay Ninama 37 Indian Institute of Ankit Yadav Banswara Technology Kanpur 14 Engineering College Avinash Yadav 38 Indian Institute of Avinash kumar Banswara Technology Kanpur 15 Engineering College Suraj Banjara 39 Indian Institute of Rajarshi Dutta Banswara Technology Kanpur 16 Engineering College Ratan Lal Barad 40 Indian Institute of Syed Mohammad Banswara Technology Kanpur Ashraf 17 Engineering College Suresh Chandra 41 Indian Institute of Arindam Mitra Banswara Bhedi Technology Kanpur 18 Engineering College Gautam 42 Indian Institute of Bandopant Pawar Banswara Technology Kanpur 19 Engineering College Ajay Katara 43 Indian Institute of Anamika Tiwari Banswara Technology Kanpur 20 Engineering College Ragineejoshi 44 National Institute of Amararapu Satish Banswara Technology, Calicut 21 Engineering College Rahul Singh 45 National Institute of Aswin Bhaskar P E Banswara Technology, Calicut 22 Engineering College Amit Singh 46 National Institute of Cheemala Banswara Technology, Calicut Vaishnavi 23 Engineering College Yajan Joshi 47 National Institute of Divya P Banswara Technology, Calicut 24 Engineering College Surbhi Singhale 48 National Institute of K Vamsi Krishna Banswara Technology, Calicut 25 Engineering College Abhishek Tiwari 49 National Institute of Sarov Mohan S Banswara Technology, Calicut 26 Engineering College Adarsh Verma 50 National Institute of Thalluri Chaitanya Banswara Technology, Calicut Sai 27 Indian Institute of Anamika Dubey 51 National Institute of Vipul Kumar Technology Kanpur Technology, Calicut 28 Indian Institute of J G sreenath 52 National Institute of Avinash Nelson Technology Kanpur Technology, Calicut 29 Indian Institute of Aasim 53 National Institute of Gowrishankar S Technology Kanpur Technology, Calicut

Volume 10 v No. 1 v January 2021 70 CIGRE India Journal

54 National Institute of Joyce Jacob 78 Indian Institute of soumya Ranjan Technology, Calicut Technology Bombay mohapatra 55 National Institute of Emil Ninan Skariah 79 Indian Institute of Kevin Gajjar Technology, Calicut Technology Bombay 56 National Institute of Jacob P Varghese 80 Indian Institute of Rohit Thute Technology, Calicut Technology Bombay 57 National Institute of Lakshmi Tharamal 81 Indian Institute of B. Sai Ram Technology, Calicut Technology Bombay 58 National Institute of Anjitha V 82 Indian Institute of Minal Chougule Technology, Calicut Technology Bombay 59 National Institute of Haritha G 83 Indian Institute of Soumya Kanta Technology, Calicut Technology Bombay Panda 60 National Institute of Ravishankar A N 84 Indian Institute of Joel Jose Technology, Calicut Technology Bombay 61 National Institute of Athira Raju 85 Indian Institute of Hemantkumar Technology, Calicut Technology Bombay Goklani 62 National Institute of Subin Koshy 86 Indian Institute of vinay chindu Technology, Calicut Technology Bombay 63 National Institute of Rahul S 87 Indian Institute of Gopakumar Technology, Calicut Technology Bombay 64 National Institute of Rinsha V 88 Indian Institute of PATIL NIKHIL Technology, Calicut Technology Bombay SURESH 65 National Institute of T S Bheemraj 89 Indian Institute of Pragati Gupta Technology, Calicut Technology Bombay 66 National Institute of Sanila P 90 Indian Institute of Suman Kumar Technology, Calicut Technology Bombay Neogi 67 National Institute of Najda V M 91 Indian Institute of AJITH J Technology, Calicut Technology Bombay 68 National Institute of Renuka V S 92 Indian Institute of Makarand M Kane Technology, Calicut Technology Bombay 69 Indian Institute of Lokesh Kumar 93 Indian Institute of Annoy Kumar Das Technology Bombay Dewangan Technology Bombay 70 Indian Institute of Vatsal Kedia 94 Manipal University Udayan Atreya Technology Bombay Dahmi Kalan Jaipur 71 Indian Institute of Santanu Paul 95 Indian Institute of Deep Kiran Technology Bombay Technology Delhi 72 Indian Institute of SIBA KUMAR 96 Malaviya National Sapna Ladwal Technology Bombay PATRO Institute of Tech. 73 Indian Institute of Aditya Nadkarni 97 Malaviya National Anil Kumar Technology Bombay Institute of Tech. Kesavarapu 74 Indian Institute of Kaustav Dey 98 Malaviya National MD Kaifi Anwar Technology Bombay Institute of Tech. 75 Indian Institute of Santosh V Singh 99 Malaviya National Rohit Bhakar Technology Bombay Institute of Tech. 76 Indian Institute of Kavita Kiran 100 Malaviya National Bhupesh Technology Bombay Prasad Institute of Tech. 77 Indian Institute of ANEES V P 101 Malaviya National Sandeep Chawda Technology Bombay Institute of Tech.

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102 Malaviya National Debollena 122 Malaviya National Archana Institute of Tech. Institute of Tech. 103 Malaviya National Sunil Jangid 123 Malaviya National Nilesh B Hadiya Institute of Tech. Institute of Tech. 104 Malaviya National Jitendra Kumar 124 Malaviya National Chandra Prakash Institute of Tech. Institute of Tech. Barala 105 Malaviya National Ajay Kumar 125 Malaviya National Shivani Garg Institute of Tech. Institute of Tech. 106 Malaviya National Andru Tarun 126 Malaviya National Sakshi Gupta Institute of Tech. Kumar Institute of Tech. 107 Malaviya National Prerna Kuntal 127 Malaviya National Archee Gupta Institute of Tech. Institute of Tech. 108 Malaviya National Priyanka 128 Malaviya National Bhavna Jangid Institute of Tech. Kushwaha Institute of Tech. 109 Malaviya National Parul Mathuria 129 Malaviya National Nitesh Kataria Institute of Tech. Institute of Tech. 110 Malaviya National Yash Pal 130 Malaviya National Gautam Raina Institute of Tech. Institute of Tech. 111 Malaviya National Arushi Relan 131 Malaviya National Navneet Sharma Institute of Tech. Institute of Tech. 112 Malaviya National Umesh Saini 132 Malaviya National Deepak Singh Institute of Tech. Institute of Tech. 113 Malaviya National Shalini Kumari 133 Malaviya National Yamujala Sumanth Institute of Tech. Institute of Tech. 114 Malaviya National Sunanda Sinha 134 Malaviya National Dheeraj Verma Institute of Tech. Institute of Tech. 115 Malaviya National Aniruddh Takshak 135 Malaviya National Raj Kumar Yadav Institute of Tech. Institute of Tech. 116 Malaviya National Falti Teotia 136 Malaviya National Anjali Jain Institute of Tech. Institute of Tech. 117 Malaviya National Rajive Tiwari 137 Malaviya National Rohit Vijay Institute of Tech. Institute of Tech. 118 Malaviya National Shefali Tripathi 138 Manipal University Udayan Atreya Institute of Tech. Dahmi Kalan Jaipur 119 Malaviya National Shakti Vashisth 139 MNIT, Jaipur Sumanth Yamujala Institute of Tech. 140 NIT HAMIRPUR SUCHANDAN 120 Malaviya National Shivanjali Yadav DAS Institute of Tech. 141 RGPV University Vishal Telang 121 Malaviya National Amit Kumar 142 M. S. Ramaiah Institute Wajid Ahmed Institute of Tech. of Technology

Volume 10 v No. 1 v January 2021 72 CIGRE India Journal SC D1 SC D2 T echniques T elecommunication D: N ew M aterials & I T Information Systems and M aterials and Emerging T est SC C6 SC C4 SC C5 SC C1 SC C2 SC C3 Resources Regulation C: SY S T E M and Control P erformance P ower System and Economics Electricity M arkets and and Distributed Energy P ower System T echnical P ower System O peration Active Distribution Systems Environmental P erformance P ower System Development Study Committee SC B1 SC B2 SC B3 SC B4 SC B5 Electronics Installations O verhead L ines Insulated Cables B : TEC HNOLO GIES DC Systems and P ower Substations and Electrical P rotection and Automation Four Group of CIGRE Study Committees SC A1 SC A2 SC A3 Reactors Equipment A : EQU I PM E NT P ower T ransformers and T ransmission & Distribution Rotating Electrical M achines

Volume 10 v No. 1 v January 2021 72 FIELDS OF ACTIVITY OF CIGRE STUDY COMMITTEES

Study Scope Committees No.

A1 Rotating Electrical Machines : The SC is focused on the development of new technologies and the international exchange of information and knowledge in the field of rotating electrical machines, to add value to this information and knowledge by means of synthesizing state-of-the-art practices and developing guidelines and recommendations. A2 Power Transformers and Reactors : The scope of SC A2 covers the whole life cycle of all kind of power transformers, including HVDC transformers, phase shifters, shunt reactors and all transformer components as bushing and tap- changers. A3 Transmission & Distribution Equipment : The scope of the SC A3 covers theory, design, construction and operation for all devices for switching, interrupting and limiting currents, surges arresters, capacitors, busbars, equipment insulators and instrument transformers used in transmission and distribution systems. B1 Insulated Cables : The scope of SC B1 covers the whole Life Cycle of AC and DC Insulated cables for Land and Submarine Power Transmission, which means theory, design, applications, manufacture, installation, testing, operation, maintenance, upgrading and uprating, diagnostics techniques. It has been focused on HV & EHV applications for a long time. Nowadays MV applications are more and more taken into consideration. B2 Overhead Lines : The scope of the Study Committee SC B2 covers all aspects of the design and refurbishment of overhead power lines. The Study Committee’s strategic goals include: increased acceptance of overhead lines; increased utilization of existing overhead lines; improved reliability and availability of overhead lines. B3 Substations and Electrical Installations : The scope of work for SC B3 includes the design, construction, maintenance and ongoing management of transmission and distribution substations, and the electrical installations in power stations, but excluding generators. B4 DC Systems and Power Electronics : The scope of SC B4 covers High Voltage Direct Current systems and Power Electronics for AC networks and Power Quality improvement. Overhead lines or cables, which may be used in HVDC systems are not included in the scope, but are the responsibility of SC B2 and SC B1 respectively. The members of B4 come from Manufacturers, Utilities, transmission system operators (TSOs), Consultants and Research Institutes. SC B4 is active in recruiting young engineers to participate in its activities. B5 Protection and Automation : The scope of the Committee covers the principles, design, application and management of power system protection, substation control, automation, monitoring, recording and metering – including associated internal and external communications and interfacing for remote control and monitoring.

C1 Power System Development and Economics : The SC’s work includes issues, methods and tools related to the development and economics of power systems, including the drivers to: invest in expanding power networks and sustaining existing assets, increase power transfer capability, integrate distributed and renewable resources, manage increased horizontal and vertical interconnection, and maintain acceptable reliability in a cost-efficient manner. The SC aims to support planners to anticipate and manage change. C2 Power System Operation and Control : The scope of the SC C2 covers the technical, human resource and institutional aspects and conditions needed for a secure and economic operation of existing power systems under security requirements against system disintegration, equipment damages and human injuries. C3 Power System Environmental Performance : The scope of this Study Committee is focused on the identification and assessment of electric power systems environmental impacts and the methods used for assessing and managing these impacts during the all life cycle on the power system assets. C4 Power System Technical Performance : The scope of SC C4 covers system technical performance phenomena that range from nanoseconds to many hours. SC C4 has been engaged in the following topics: Power Quality, EMC/EMI, Insulation Coordination, Lightning, and Power systems performance models and numerical analysis. C5 Electricity Markets and Regulation : The scope of the Study Committee is “to analyze the different market approaches and solutions and their impact on the electric supply industry in support of the traditional economists, planners and operators within the industry as well as the new actors such as regulators, traders, technology innovators and Independent Power producers. C6 Active Distribution Systems and Distributed Energy Resources : SC C6 facilitates and promotes the progress of engineering, and the international exchange of information and knowledge in the field of distributions systems and dispersed generation. The experts contributes to the international exchange of information and knowledge by the rizing state of the art practices and developing recommendations. D1 Materials and Emerging Test Techniques : The scope of Study Committee D1 covers new and existing materials for electrotechnology, diagnostic techniques and related knowledge rules, as well as emerging test techniques with expected impact on power systems in the medium to long term. D2 Information Systems and Telecommunication : The scope of this SC is focused on the fields of information systems and telecommunications for power systems. SC D2 contributes to the international exchange of information and knowledge, adding value by means of synthesizing state of the art practices and drafting recommendations.

73 Volume 10 v No. 1 v January 2021 Technical Data HIGHLIGHTS OF POWER SECTOR

GROWTH OF INSTALLED CAPACITY (Figures in MW)

At the end of 12th Plan (August 2017) As on 31.12.2020 THERMAL 218330.00 231590.72 HYDRO 44478.00 45798.22 NUCLEAR 6780.00 6780 RENEWABLE ENERGY SOURCES 57244.00 91153.81 TOTAL 326832.00 375322.74 Source : CEA

ALL INDIA REGION WISE INSTALLED CAPACITY As on 31.12.2020 (Figures in MW)

Region Thermal Nuclear Hydro Res Total Northern 60799.05 1620 20143.77 17581.99 100144.81 Western 86081.61 1840 7555 27933.96 123410.57 Southern 54699.99 3320 11774.83 43665.36 113460.18 Eastern 27387.05 0 4639.12 1568.11 33594.28 N. Eastern 2582.98 0 1685.5 369.17 4637.64 Islands 40.05 0 0 35.22 75.27 All India 231590.72 6780 45798.22 91153.81 375322.74 Percentage 61.70 1.81 12.20 24.29 100 Source : CEA

SECTOR WISE INSTALLED CAPACITY AND GENERATION As on 31.12.2020

Net Capacity Installed Capacity (MW) added Percentage Sector Thermal Nuclear Hydro RES Total Share During Dec. 2020

STATE 74547.36 0 26958.5 2391.52 103897.39 27.68 PRIVATE 86875.45 0 3493 87129.98 177498.43 47.29 369 MW CENTRAL 70167.91 6780 15346.72 1632.3 93926.93 25.03 TOTAL 231590.72 6780 45798.22 91153.81 375322.74 100 Source : CEA

Volume 10 v No. 1 v January 2021 74 Technical Data 75

GROWTH OF TRANSMISSION SECTOR Unit At the end of 12th As on Addition after 12th Plan Plan (August 2017) Dec. 2020 (2017-22) (up to November 2020) TRANSMISSION LINES HVDC ckm 15556 19087 765 kV ckm 31240 44855 400 kV ckm 157787 186389 220 kV ckm 163268 183179 Total Transmission Lines ckm 367851 433510 65659 SUBSTATIONS Unit At the end of 12th As on Addition after 12th Plan Plan (August 2017) Oct. 2020 (2017-22) (up to October 2020) HVDC MW 19500 27000 765 kV MVA 167500 234900 247708 400 kV MVA 240807 343872 220 kV MVA 312958 382701 TOTAL MW/ 740765 988473 247708 MVA

RURAL ELECTRIFICATION / PER CAPITA CONSUMPTION Total no. of Villages 597464 No. of Villages Electrified 597464 % of Villages Electrified 100.00 No. of Pump-sets Energized (At the end of 12th Plan) 21212860 Per Capita Consumption during 2019-20* 1208 kWh *Provisional

RE Sector in India: Potential and Achievements

Sector FY 2020-21 Cumulative Achievements FY 2020-21 Achievement (MW) GRID-INTERACTIVE POWER Target (MW) (Capacities in MWp) (April-Nov. 2020) (as on 30.11.2020) Wind 3000 689.8 38433.55 Solar Power (SPV) 11000 2282.7 36910.49 Small Hydro (up to 25 MW) 100 57.3 4740.47 Bio Power (Biomass & Gasification 250 270.61 10145.92 and Bagasse Cogeneration) Waste to Power 30 21 168.64 Total (Approx) 14380 3321.41 90399.07 OFF GRID/CAPTIVE POWER 510 77.01 1253.59

(CAPACITIES IN MWEQ) Other Renewable Energy 0.6 0.04 50.5 Systems (Biogass plants) (capacity in Nos.) Source : MNRE

Volume 10 v No. 1 v January 2021 News Govt to focus on loss-making discoms for next 3-4 yrs to achieve ‘24x7 power for all’ The government’s spotlight will be on electricity distribution utilities or discoms, which are mostly state-run and cash- strapped due to losses, to achieve the goal of 24×7 power for all, a senior official said. There is stress in the power sector due to the inability of discoms to make timely payments for supply of power by gencos (power generating firms), which affects the entire value chain. Participating in a webinar organised by the Institute of Directors, Ashish Upadhyaya, additional secretary in the Ministry of Power, said the major focus of the central government will be on the distribution sector for the next three-four years. Talking about the continuous losses of discoms, he said there is a gap between the actual rate of warnings threatening discontinuation of power supply supply of power and the cost recovered from consumers. to defaulting distribution companies. Officials in various According to power ministry data, discoms’ total outstanding electricity distribution companies said their financial dues stood at over Rs 1.42 lakh crore as of November positions deteriorated due to the impact of Covid-19 on 2020. Last year, the government announced aRs 90,000 power consumption and billing and collections. A senior crore liquidity infusion scheme for discoms which was NTPC official said more notices are likely to be issued to later expanded to Rs 1.2 lakh crore. Earlier this year, large defaulters such as Uttar Pradesh, Andhra Pradesh, some reports also suggested that the forthcoming Budget Telangana Madhya Pradesh and Assam. may unveil the second phase of the UDAY (UjwalDiscom Assurance Yojana) for revival of discoms. “The company has decided to take action against non- paying distribution companies starting Thursday with The UDAY scheme was launched in November 2015 under five utilities. More such notices to bigger states would be which the discoms’ financial performance was to be turned required to recover large amounts of receivables,” the around in three years. Upadhyaya further pointed out that official said. NTPC has invoked insolvency proceedings some states have not fixed tariff commensurate with the against BSES Delhi discoms. “In spite of repeated follow actual cost of supply for years, while expenditure on power ups at various levels in person as well as through letters generation has kept on rising. Participating in the webinar, beginning August 2020 the states have yet not liquidated Gujarat Energy Minister Saurabh Patel said the power sector the outstanding dues which are way beyond due dates. As can change if there is political will of the state governments. per various agreements and CERC Regulations, in case of He emphasised on curbing transmission and distribution defaulting making payments of bills, NTPC has the right to losses to make the power sector vibrant in the states. Citing discontinue or regulate the power supplies. Gujarat’s example, he said there has not been a single year in the last 15 years in which the four discoms in the state did Power producers’ total dues owed by distribution firms rose not report at least a minor profit. He exuded confidence that over 35% to Rs 1,41,621crore in November 2020. The total there would be 12 GW power generation capacity addition overdue amount stood at Rs 1,29,868crore Overdue of in the state in the next two years. independent power producers and Central PSUs amounted to 34% each of the total overdue. Among the central public Power gencos send payment due sector power generators, NTPC has an overdue amount notices to state discoms of Rs 19,215.97 crore on discoms, followed by NLC India at Rs 6,932.06 crore, Damodar Valley Corp at Rs 6,238.03 Consumers across India could face power supply crore, NHPC at Rs 3,223.88 crore and THDC India at Rs disruptions as central public sector undertakings (CPSUs) 2,085.06 crore. including NTPC NSE -1.30 %, NHPC and Damodar Valley Corporation have begun issuing regulation notices to state The Union power ministry had in August 2019 mandated distribution companies for non-payment of dues. maintenance of bank guarantee by distribution companies in favour of power plants. State-run financiers Power Finance On Thursday, NTPC issued notices to power utilities of Corp and REC Ltd are offering Rs 1,20,000 crore conditional Sikkim, Jammu & Kashmir, Puducherry and two discoms loans to discoms under Atmanirbhar Bharat scheme to help of Karnataka for discontinuation of aggregate 3,000- them repay the dues to power gencos. Of this close to Rs mw beginning next Friday. Government officials said all 68,000 crore has been sanctioned. CPSU power generators have decided to issue similar Source : ET Bureau, Jan 08, 2021

Volume 10 v No. 1 v January 2021 76 News 77

Government asks CERC to relieve power plants delayed due to force majeure from transmission levy The government has invoked special powers to direct electricity regulator to make changes in regulations freeing power plants delayed due to justifiable reasons from paying penalties to associated transmission projects. The penalties would now be borne equally by all beneficiary discoms of a generation project, as per the directions issued by the Union power ministry to the Central Electricity Regulatory Commission (CERC) under section 107 of the Electricity Act 2003. While power generation and transmission companies welcomed the relief, distribution companies said the move asking them to pay for delay in Electricity distribution companies opposed the move generation projects came as a shock to them. calling it unfair to be penalised for no fault. “This will lead “Penalties for delay in COD (commissioning) of generating to passing of private losses to the general public and tariff stations, or for delay in completing transmission system, shocks,” an official said. or operationalising the LTA (long-term agreement) shall The directions said events of force majeure may be invite penalties to be paid to CTU (central transmission defined by CERC and provision included enabling utility). The penalties shall be equitable; and shall the CTU to extend the commissioning of a generating not extend to compensating either the Generation station. companies for power it could not despatch because of delay in transmission or to compensate the transmission Source : ET Bureau, January 19, 2021 company for the delay in generation or the associated New power islanding for Delhi pro- transmission,” the central government directions to posed to prevent blackouts CERC to amend Sharing of Inter-State Transmission Charges and Losses Regulations, 2020 said. The government proposes to put in a robust islanding facility for power supplies in Delhi to prevent the national Power transmission projects attached to delayed capital to face electricity disruptions, especially for generation plants are considered ‘deemed commissioned’ essential services, in case of grid disturbances. and are liable to compensation but the complexity in arrangement makes it difficult to claim any amount. In the Sources said the country’s largest power producer NTPC present system, the CTU coordinates with transmission has suggested a mix of its gas-based and coal-fuelled licensees on one hand and all other users on the other. power units in the vicinity of the Capital for dedicated There are back-to-back agreements between CTU, the use for the city to create an island in the case frequency transmission licensees and distribution companies and in the main grid collapses and there is real threat of a generation companies are outside these contracts. The complete power breakdown. This, it has been suggested, power ministry is working to amend the structure to bring will balance the frequency in case of grid collapses, in transmission licensees and generators together. A ensuring that essential services in the Capital continues senior government official said the directions are aimed to receive uninterrupted supply electricity. at ease of process. “If the delay is not attributable to the Sources said that though an islanding scheme for parties, none of them should take the hit,” he said. The Delhi was developed by grid manager Power System directions said the entire burden of strengthening which Operation Corporation Limited (POSOCO) in 2017, it yet will serve many procurer or power producers in the future to be commissioned. Moreover, with over dependence of cannot be levied on one party. gas-based capacity to provide dedicated power to Delhi “Over 3-4 years, it is being realised that is possibility of in the event of a sudden drop on frequency has created a mismatch in timelines in commissioning of generation situation where despite islanding infrastructure adequate companies and associated transmission lines. The electricity supply would be hard to maintain. regulators deny compensation since the line is not being With most gas-based power plants dedicated to Delhi used. Lack of agreement with generation companies operating at around 30-35 per cent plant load factor (PLF) closed hopes of compensation. The investors to these an eventuality still puts the national capital on the risk of transmission lines have started worrying over collection a complete blackout as capacities would not be sufficient of the charges. This is a very positive development,” said to ensure adequate frequency in the power systems. an industry official.

Volume 10 v No. 1 v January 2021 78 CIGRE India Journal

“It is imperative to revisit the earlier planned islanding Power consumption grows 7.8% in scheme for Delhi to prevent a repeat of what could not first half of November have happened in Mumbai and could happen in Delhi,” India’s power consumption grew 7.8 per cent to 50.15 said the sources. It is understood that a group in the billion units (BU) in the first half of November this year, power ministry is studying various upgradations that are showing rise in economic activities, as per government required to build a robust islanding facility for Delhi and data. Power consumption in the country was recorded a decision on the same would be taken soon. at 46.52 BU during November 1-15 last year, according Sources said that NTPC is ready to keep at least two to the power ministry data. For a full month in November units of Dadri power plant and one unit of Jhajjar plant last year, power consumption was 93.94 BU. on bar at all times to take care of any grid disturbances. Thus, the extrapolation of half-month data clearly These coal-fired units would become critical in times of indicates that power consumption may witness year- frequency collapse to ensure power generated from there on-year growth for the third month in a row, according to helps to keep essential services running in the Capital. experts. After a gap of six months, power consumption “The question is whether we need to keep running coal- recorded a growth of 4.4 per cent in September this fired power plants in the vicinity of the capital as they year at 112.24 BU compared to 107.51 BU in the same are also a source of pollution the affects the region. But month last year. systems could be developed so that these units become India’s power consumption grew nearly 12 per cent to critical in times of grid disturbances,” said a former head 109.53 billion units (BU) in October this year as against of POSOCO asking not to be named. 97.84 BU in the same month last year. The growth Two severe power blackouts had affected most of in power consumption in the first half of this month Northern and Eastern India on 30 and 31 July 2012. showed that there is consistency in improvement in The blackout on 31st July was the largest power outage commercial and industrial demand due to easing of affecting more than 62 crore people in Northern, Eastern, lockdown restrictions, experts said. The government and Northeast India. Based on the recommendations of had imposed the nationwide lockdown on March 25 to enquiry committee constituted under MOP, an Islanding contain the spread of COVID-19. Power consumption scheme for Delhi was framed. started declining from March onwards due to fewer economic activities in the country. The COVID-19 The Delhi Region is a part of Northern Grid and in case situation affected power consumption for six months of any grid disturbance, this islanding scheme will isolate in a row -- from March to August this year. Power Delhi from rest of the grid. Once islanding is done, the consumption on a year-on-year basis declined 8.7 demand is matched with the own generation. The priority per cent in March, 23.2 per cent in April, 14.9 per cent is Delhi Metro, Railways, DIAL and the healthcare in May, 10.9 per cent in June, 3.7 per cent in July and facilities. As per guidelines, each state has been given 1.7 per cent in August. a share of load shedding which should contribute in case of any fall in frequency. When any grid disturbance The data showed that electricity consumption had occurs in the grid, there’d be an increase or decrease grown by 11.73 per cent in February. It has shown in frequency. an improvement post-lockdown easing for economic activities after April 20. Peak power demand met, the The Delhi Islanding scheme has incorporated load highest supply of power in the country in a day, in the shedding at Flat frequency up to stage 48.6 Hz and df/ first half of November was recorded at 160.77 GW (on dt slope stages of 0.1Hz/sec,0.2Hz/sec and 0.3Hz/sec November 3, 2020), 5.2 per cent higher than 152.77 GW for frequency less than 47.9Hz. In case the frequency on November 6, 2019. The peak power demand in the fall beyond 47.9 Hz the Islanding of Delhi is initiated by month of November last year was 155.32 GW. tripping of Circuit Breakers at various locations. The peak power demand met in October was recorded at On an average, typical daily electrical load in Delhi is 170.04 GW, 3.52 per cent higher than 164.25 GW in the around 3000 MW and internal generation is only around same month last year. Peak power demand in September 500 MW. Due to low and uncertain gas allocations to this year recorded a growth of 1.7 per cent at 176.41 GW, CCGT Bawana, Pragati, Rithala and IPGCL GT station, compared to 173.45 GW a year ago, the data showed. it has become important to keep a minimum number of Peak power demand met had recorded negative growth thermal coal-fired units on bar at all times. from April to August this year due to the pandemic. This was also envisaged in the original islanding scheme It had dropped to 24.9 per cent in April, 8.9 per cent in for Delhi. May, 9.6 per cent in June, 2.7 per cent in July and 5.6 per Source : IANS December 12, 2020 cent in August. In March, it was muted at 0.8 per cent. Source : PTI, Nov 16, 2020

Volume 10 v No. 1 v January 2021 International Council on Large Electric Systems (CIGRE)

International Headquarters: International Council on Large Electric Systems (CIGRE), 21 Rue d’Artois, 75008 Paris, France Tel: +33 1 53 89 12 90; Fax: +33 1 53 89 12 99 Email of Secretary General: [email protected] Date of inception : CIGRE was founded in 1921 with its HQ at PARIS Aims and Objectives: CIGRE (International Council on Large Electric Systems) is one of the leading worldwide Organizations on Electric Power Systems, covering their technical, economic, environmental, organisational and regulatory aspects. A permanent, non-governmental and non-profit International Association, based in France, CIGRE was founded in 1921 and aims to: • Facilitate the exchange of information between engineering personnel and specialists in all countries and develop knowledge in power systems. • Add value to the knowledge and information exchanged by synthesizing state-of-the-art world practices. • Make managers, decision-makers and regulators aware of the synthesis of CIGRE’s work, in the area of electric power. More specifically, issues related to planning and operation of power systems, as well as design, construction, maintenance and disposal of HV equipment and plants are at the core of CIGRE’s mission. Problems related to protection of power systems, telecontrol, telecommunication equipment and information systems are also part of CIGRE’s area of concern. Establishment of Indian Chapters: CIGRE India was set up as society on 24.07.91 with CBIP as secretariat. Membership: (I) Collective Members (I) - (companies of industrial and commercial nature) (II) Collective Members (II) - (Universities, Engineering Colleges,Technical Institutes and regulatory commission) (III) Individual Members - (In the engineering, teaching or research professions as well as of other professions involved in the industry (Lawyers, economists, regulators...) (IV) Young Members (Below 35 Years of Age) - (In the engineering, teaching or research professions as well as of other professions involved in the industry (Lawyers, economists, regulators...)

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