Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008 Blackstart Restoration Plans for Western Region and case studies M.G.Raoot, P. Pentayya, Sachala Mishra and Haresh Patel

Abstract— Since blackouts occur rarely, it would be difficult to of the disturbance in the NEW grid were hardly felt . train the system operators on restoration procedures. With However, the individual regions in the NEW grid are exposed significant loss to economy and great inconvenience to consumers, to both internal and external threats and a major contingency faster and efficient restoration is of utmost importance. This outside Western Region can have devastating effects in would require well documented detailed restoration plans tested through system studies, dispatcher training simulator, mock drills Western Region. Eventhough, major black outs appear to and creation of awareness the familiarity to not only system have remote chance, some incredible combination of events operators but also to operating personnel at generating stations may lead to a major disturbances encompassing the entire and sub-stations. The restoration plans also require suitable NEW grid. Such an eventuality may have far reaching revisions based on experience of actual restorations following consequences in terms of economic, political, national blackouts. The restoration plans for Western Region have been security, law & order spheres in addition to public revised incorporating the experience gained during the blackout on 30-07-2002. The paper discusses in detail the restoration inconvenience. It is therefore important to prepare restoration approaches followed in Western Region and frequently plans to restore power supply in the fastest possible manner. encountered restoration problems alongwith case studies taken At present, the existing plans envisage restoration of the from the restoration exercise following total system blackout on regions individually and inter connect the regions with each 30-07-2002. other after attaining adequate size and stability. This paper discusses the restoration plans for Western Regional Grid with Index Terms —interconnected power system, high-voltage, high-frequency, power system restoration emphasis on frequently encountered restoration problems which are illustrated through case studies. The last total black I. INTRODUCTION out in Western Region occurred on 30th July, 2002 and various incidents during restoration have been used as case studies to illustrate the restoration problems and constraints. he Indian Power System is operating as two asynchronous The Western Regional Grid comprise the states of grids viz. NEW grid comprising Northern, Eastern, T Maharashtra, Gujarat, Madhyapradesh (M.P), Chhattisgarh, Western, North Eastern grids in synchronous mode and Goa and the Union territories of Daman & Diu (DD), Dadra & Southern grid. The NEW grid is having installed capacity of Nagar Haveli (DNH). The installed capacity of Western 105856 MW and meeting of 90000 MW. The Region is 44894 MW and peak demand met is of the order of Southern grid is having installed capacity of 39695 MW and 29000 MW and energy consumption of 650MUs per day and meeting peak demand of 25000 MW. The formation of NEW peak deficit of around 9000 MW. A Grid Map of Western grid helped immensely all the regions synchronously Region is shown at Fig. 1 and also available at web link : connected through sharing of scarce generation resources , http://www.wrldc.com/maps/Powermapmarch2008.pdf. diversity of peak demands, improvement in hydro thermal mix, As there are no perfect solutions to prevent blackouts, which increase of system stiffness ( 1800 MW per Hz) and increased are usually caused by a complex sequence of cascading events, economy exchanges among the regions. The reliability of a number of different measures need to be undertaken to NEW grid also exhibited great improvement during the minimize the impact of future disturbances. The objective of disturbances like load crash due to weather effects, tripping of Recovery Procedures is to achieve restoration of total system number of lines due to fog, demand fluctuations are easily in the shortest possible time taking into account generation managed. The synergy of operating practices and uniformity securing (i.e., stabilization of saved units), start-up power to of defence mechanisms have also improved the security levels. nuclear units, essential loads, core sector industrial loads, the Loss of 3150 MW generation at Vindhyachal in generator capabilities and the transmission constraints and to Western Region on 22nd July 2008 could have led to a major achieve resynchronisation of constituent systems which have disturbance in Western Region operating alone but the effects separated from each other.The generic tasks of restoration include determination of system and equipment status, M. G. Raoot is with Powergrid Corporation of India Ltd. , WRLDC, preparation of plants and network for systematic restoration, Mumbai 400093 INDIA (phone: 91-22-28202691, 91-986955582; fax: 91- 22-28235434; e-mail: [email protected]). re-energization of the network, and system rebuilding. The P.Pentayya, is with Powergrid Corporation of India Ltd. , WRLDC, procedures for developing an effective restoration plan include Mumbai 400093 INDIA (phone: 91-022-28314609, 91-9869450206; fax: 91- formation of a qualified planning team, review of relevant 22-28235434; e-mail: ppentayya@ gmail.com). Sachala Mishra is with Powergrid Corporation of India Ltd. , WRLDC, system characteristics, formulation of assumptions regarding Mumbai 400093 INDIA (phone: 91-022-28302209, 91-9869450223; fax: 91- blackout scenarios, agreement on restoration goals, 22-28235434; e-mail: mishra_sachala@ rediffmail.com). development of strategy and tactics, validation of the plan, Haresh Patel is with Powergrid Corporation of India Ltd. , WRLDC, Mumbai 400093 INDIA (phone: 91-022-28302209, 91-9869404497; fax: 91- training, and documentation 22-28235434; e-mail: harsh_patel2k@ yahoo.co.in).

182 Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

II. RESTORATION PLAN view load characteristics, ie., variation of load with respect to voltage and frequency and stiffness of island. During cold load pick up sudden starting of motor loads or power plant A. Situational Awareness auxiliaries like BFP, PA fan etc., can cause voltage dips due to System Operators at control centres should recognize drawal of high starting currents. Essential loads can be through Supervisory Control and Data Acquisition / Energy restarted in steps smaller than 5 MW. It is preferable to Management System (SCADA/EMS) tools the number of part restore rotating type loads which contributes to inertia of the systems/islands in the grid alongwith clear demarcation of island. In any case, load pick up should not cause frequency island boundaries. If possible by deploying additional staff, excursions greater than 0.5 Hz in the island.It is of utmost each island should be entrusted to one person who would be importance to identify the loads to be restored in advance and responsible for stabilization of island, to direct and monitor the document. progress of expansion of the island, restoration of essential loads in the island, to extend startup power to generators 2) Approach-II: outside the island and to synchronize the island with other The second approach could be followed in case self start islands for better stability. It is required to estimate the facilities are available at only a few power stations or the start stiffness (MW/Hz.) of the island by observing frequency up power has to be imported from neighbouring regions at one fluctuations and the generation/load in the island. As a thumb or two points. In this approach, the start up power required to rule about 3% of the load in the island can be considered as be extended to all the generating stations on priority basis stiffness to guide load restoration in steps. At least one unit in while restoring few loads and for voltage control. the island can be assigned the role of frequency control by The start up power available from neighbouring regions at keeping the speed governor in frequency control mode. It is various interconnections have to be seriously explored since preferable to use all hydro and gas units to control frequency considerable assistance can be availed and the restored system through governor action and the droop setting of the governor is connected to stable external systems. The procedures have should be lowered to enable load pickup. to be laid down for quickly harnessing these facilities. The Transmission corridors used for startup power should be constituent receiving assistance during restoration process isolated from any damaged/faulty equipment and are of should restrict to the agreed quantum only since this may have minimum length and minimum voltage level to reduce line an adverse effect on healthy system rendering the assistance. charging Vars. Two distinct approaches are used depending on The restoration through this approach could be delayed due to the islanding schemes dispersal of facility and intra- problems in charging the lines, high-voltage, lack of regional connections. synchronising equipment at certain substations etc. and may involve system disturbances during restoration. The restored B. Restoration approaches [1] generators and loads are connected with the region supplying startup power assistance. Care has to be taken while delinking 1) Approach-I: the restored parts of the connecting links – usually bypass links In systems with a fair dispersal of Generating stations with at High Voltage Direct Current (HVDC) back to back stations. black start facilities, those generating stations where black start The bypass links should be brought to floating (MW & MVAR facilities are available, should be started up and islands formed close to zero) before opening. around these generating stations by connecting essential loads.

These islands are then interconnected at predefined locations where synchronizing facilities are available. The speed of C. Restoration in Western Region restoration enhances with increase in number of black start The restoration procedures prepared and made available at facilities and their dispersal. Gujarat, Chhattisgarh and M.P State Load Despatch Centre (SLDCs) and Regional Load have considerable number of black start facilities while Despatch Centre (RLDC) define restoration paths for Maharashtra suffers from lack of adequate number of black extending start up power to each power station clearly along start generators. In some states like Gujarat, number of with alternative paths and priorities of paths. The priorities are islanding schemes have been planned around generating generally decided based on usage of short line sections and stations with one or two units planned to island with radial lower voltage lines. loads. Such island can be used to extend startup power to neighbouring generating stations and the islands are expanded in a steady manner. It is required to carefully monitor the D. Generation securing operation of the island (re-integration with rest of the grid) due High priority is given to ensure the survival of islands that to small stiffness in islands. Each island shall be have been created either by design or by chance. One engineer independently managed and controlled. While adding loads, is assigned to each of these islands to monitor frequency care should be taken to ensure step by step addition keeping in control aspects as well as re-integration aspects. The power available from black started units is to be

183 Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

extended based on defined priorities. Highest priority will be around 49.50 Hz to avoid tripping of units on low frequency. accorded for supply of survival power to the generating At 0117 hrs on 31.7.02, Uran Units-5 & 6 tripped on under stations followed by to those units capable of hot start up, units frequency protection set at 47.5 Hz. At 0358 hrs, Uran Unit-5 capable of rapid restart and essential loads like traction. once again tripped on high-frequency. However, the restored Normally, hydro and gas units are provided with black-start part did not collapse. facilities. In case of non provision of black start facility or 2) Low stiffness [2] failure to black-start, hydro and gas units are given start-up The restored parts failed number of times during restoration power as these can come up with full load in about 10 minutes. or restoration delayed due to frequency control in islands with low stiffness. In small islands due to low stiffness frequency fluctuates widely even during load restoration. After restoring E. Synchronizing locations minimum possible load, the island should be synchronized The islands are re-connected/re-integrated at pre-defined with a larger island. The frequency fluctuations chart for the locations and the substation/generating station engineers in islanded Mumbai System look like Electro Cardiogram (ECG). Western region are well conversant with the procedures as During Grid disturbance on 23.05.02, the North Mumbai well as synchronization of islands. system had collapsed after islanding successfully due to its small size and low stiffness since the island is importing 40 MW prior to islanding. III. FREQUENTLY ENCOUNTERED RESTORATION 3) Dynamic Reserve : PROBLEMS It is essential to interconnect various islands at the earliest possible opportunity as the enlarged islands become more stable. On 30.7.02, tripping of Unit-4 (210 MW) of Ukai A. Islanding schemes & Islanding on house load thermal power station resulted in collapse of AE.Co - GIPCL- Wanakbori-Gandhinagar-Ukai(H) islands. Similarly, the The black start procedures require that thermal units island blackstarted Kawas & ESSAR Units in two different islands on house load. However, except for the Trombay units, Tata were synchronized to form one large island alongwith Power Company (TPC) and Kakarapar (nuclear) units, the Ichhapur loads before extending startup power to Tarapur islanding on house loads is not generally successful. This is a generators. Initially the under frequency relays are bypassed major constraint. and after sufficient load is restored, about 25% of this load This facility would enable faster restoration of generators as shall have feeders with UF relays energized so that adequate some generators in each power station can go to house load reserve would be available to take care of contingency of unit operation and survive supplying their own auxiliaries. Even trippings. Dynamic reserve shall also be kept on on-line nuclear units can island on house load and kakarapar units generators to take care of contingencies and to control successfully islanded on house load on 30.07.02. In the steam frequency. dumping mode nuclear units can take care of load fluctuations easily. At present none of the thermal units are successfully islanded on house load which is a major constraint. Islanding C. Ramp up and response rate limitations of Black Started schemes for power stations should be developed to enable Units [2] islanding of one unit on house load and/or radial loads, Sometimes restoration delayed due to start up of large particularly at those stations where small units are available. motors (auxiliaries) of thermal plants from black started gas For instance, one unit at Dhuvaran is islanded along with units. Normally when thermal power station auxiliaries are radial 66kV loads. Availability of on-line power would energized from black started gas units, minimum auxiliaries enhance speed of restoration. On 30.07.02 several islanding essential for start up have to be energized. Out of the various schemes successfully operated in Gujarat and helped in faster auxiliaries, the largest motor has to be started first. The other restoration. Islanding schemes of Utaran, GIPCL, ESSR, AE motors are started thereafter one by one in a sequential manner Co. (gas) and Kakarapar (nuclear) in Gujarat and TPC, REL (with larger ones preceding the smaller ones) as per the startup islands in Maharashtra sequence. During restoration on 30.07.02 [3], black started Kawas unit tripped as load restoration was too fast and in large B. Maintaining active power balance increaments not consistent with Ramp up rate of Kawas unit 1) Load Generation Balance (106 MW gas turbine) which is of the order of 7.6 MW per Maintaining load generation balance during step by step minute. Similarly, response rate violations (MW per Hz.) can restoration of minimum and essential loads is required so that also lead to unit trippings. The response rate depend upon the the islands restored will not collapse. On 30.7.02, the restored energy conversion process such as response of nuclear Koyna-Uran islands collapsed at 2245 hrs due to load reactors, gas turbines, hydro turbines, boiler dynamics etc. generation mismatch. Further, frequency should be maintained

184 Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

Some of the islands during restoration might collapse due to 30.07.02 tripping of units or load restoration in large amounts compared The following action plan is drawn up in the Blackstart to response rate of units, frequency prior to pick up of loads is proceedings to counter the problem of hunting. too low (below 49 Hz). If the islands are built around gas 1) Start one unit keeping Automatic voltage regulator (AVR) based power plants, a constraint might arise in respect of out of service. Preferably, keep the excitation around 0.85 restriction on multiple start-up and shutdowns. Documentation pu (as low as possible). At no load or reduced load on the of number of startups and shutdowns a load and duration machine rotor angle() will be small and as such under between two startups for emergency conditions is essential. excitation is permissible. Take AVR into service only after Selection of loads to be restored in various islands from the machine is loaded upto 10% to 15% and maintain black started units should be identified in advance with respect frequency around 50 Hz. to quantum of load to be restored in each step. This should be 2) At the remote end, charge one with load of consistent with ramp rate and response of the units. around 10% capacity of the machine (i.e 5 MW for Bargi Difficulties were faced while restoring loads from Jhanor machines or 7 MW for Pench machines). The transformer power station during the occurrence occurred on 30.07.02. breaker is kept closed so that if the line is charged, the load Unbalancing of loads during the restoration procedure is a immediately comes on the machine. It may be noted that very serious phenomena and should be properly dealt with. hydro machines have good response rates. 3) Observe if any hunting occurs in active power, voltage or reactive power. If no hunting is observed, take AVR into D. Hunting problem in hydro units : service. If hunting is observed add more load at the remote While supplying start up power from small hydro units over end (i.e Jabalpur for Bargi units and Kanhan/Seoni for long132kV/220kV lines, hunting of hydro units were observed Pench units) till the hunting stops and then take AVR on number of times as depicted in Table I. Hunting of Bango auto mode. As the load is picked up on the machine, the units was reported due to voltage problems and charging of excitation should be increased gradually. long section of lines during restoration of total blackout 4) With AVR in service throughout, it can be tested whether hunting occurs as it is suspected that the hunting problem is TABLE I PERFORMANCE OF BLACKSTART FACILITIES ON 30.07.02 mainly due to activation of exciter modes. Power Installed Time Time station Capacit taken taken for Remarks/ constraints (Hydro) y (Mw) For extending E. Delinking of restored parts from external systems: [4] black power to Difficulties were also encountered in delinking from the start the next (Min.) bus external systems as the tie-lines have to be operated with (Min.) almost zero active and reactive power for sometime. Gandhisaga 5x 23 2 9 After 41 minutes start 1) On 31.07.02,after availing start up power from Southern r up power to Satpura region through bypass link, Maharashtra restored units at power stations was extended. Voltage and Chandrapur, Bhusawal, Khaperkheda and Koradi. About MW hunting observed 350 MW generation, loads in Nagpur area and traction along the 132 kV start supplies were restored by 0100 hrs on 31.7.02. The bypass up path to Satpura. Pench 2x 80 44 54 Start up power extended link was brought to floating conditions. At the time of to Satpura Power opening 25 MW power was flowing towards SR. While station through 132 kV disconnecting from SR, the islands collapsed with all Pench-Seoni- Chhinwara-Satpura generating units restored tripping on high-frequency. path. High-frequency 2) On 31.7.02, Maharashtra once again availed start up power problem and voltage from Southern region at 0202 hrs. Start up power was hunting observed. Start extended to Chandrapur, Koradi, Khaperkheda, Parli and up power could not be extended to Koradi Bhusawal power stations by 0350 hrs. Traction loads were power station of also restored fully in Eastern Maharashtra by this time. By Maharashtra through 1000 hrs about 1950 MW generation and loads were 132 kV Pench-Kanhan line due to excessive restored. However, due to delay in restoration of loads, voltage hunting. power upto 600 MW was exported to SR. This had caused Bargi 2x 45 9 9 Power extended up to alert situation in SR as number of 400kV lines got critically Jabalpur. Due to high voltage problem power loaded and low voltages were also reported. At 1028 hrs, supply could not be the bypass link was once again opened to take this island extended to into the main western Grid, but the restored part of Eastern Amarkantak. Voltage Maharashtra collapsed on low frequency. At the time of

185 Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

opening, Maharashtra was restoring loads to keep the control the high-voltage problem. Another alternative could bypass link floating. Due to addition of more loads, power be to supply block load equivalent to 10% of the remote end reversed with about 80 MW power flow towards transformer capacity so that the moment the unit is Maharashtra system while frequency dropped to 47.7 Hz. synchronized to the 400kV bus block load would be incident. When the bypass link was opened, 80 MW over load This would require keeping the line and transformer breakers caused further frequency decay and collapse of the island. as well as the breakers of feeders connecting to loads in closed It is therefore essential to: condition prior to blackstarting the unit. One of the a) Bring the bypass link to floating level and keep alternatives could be selected by carrying out mock drills. frequency around 49.5 Hz. b) Proper communication among SLDC Kalwa of H. Operational practices and discipline : Maharashtra, SLDC Ambazari of Maharashtra, Bhadravati HVDC stations and WRLDC has to be Ensuring of discipline when start up power is extended from ensured. Once the link is brought to floating one utility to other utility. Due to lack of adequate monitoring condition with frequency around 49.5 Hz, code for and control, some substation operators tend to restore more opening of the bypass link can be issued and no loads loads resulting in either overloading of start up path or should be restored till the link is opened. unmanageable frequency variations.The substation operators have no documentation regarding load variations on various feeders over the day. The constituent receiving start up power F. High- voltage problems in restoration paths : should exercise proper control over their drawals. At times, 1) While extending start up power, high-voltages are usually the system providing assistance may collapse as this is too encountered. The generating units supplying start up fragile. On 30.07.02, power supply was extended to Nasik by power are operated with excitation voltage as low as charging Nasik-Navsari D/C line at 0304 hrs. At 0355 hrs, possible (much less than 1 p.u.). The non availability of Maharashtra drawal increased beyond 240MW with frequency radial load near some power stations (black started) is of the restored Gujarat system touching 47.7 Hz. To save the coming in the way of extending start up power to other restored part of Gujarat, GEB opened Nasik-Navsari lines stations due to high-voltage (e.g. Koyna). In case of high- (after warning) resulting in collapse of the Western voltage problems, we are restoring some loads along the Maharashtra islands comprising power stations of Koyna, Uran restoration path usually of low . & Nasik. It is pertinent to point that due to cold load pick up, 2) On 30.07.02, Koyna units were black started at 2020 hrs more load could have been restored than anticipated and but power supply could be extended to Pedambe only at system operators should factor in such possibilities. 2145 hrs. [4] The delay was due to high-voltages and lack of load at Pedambe. It is essential to identify loads at I. Identification/Selection of Load Pedambe so that power supply to Uran can be extended within a short duration as units at Uran can be brought back Selection of loads to be restored in various islands from quickly. black started units should be identified in advance with respect 3) On 30.07.02, restoration in Chhattisgarh was delayed as to quantum of load to be restored in each step. This should be 400 kV lines could not be restored due to high-voltage consistent with ramp rate and response rate of the units. problem. The attempts to extend start up power received Difficulties were faced while restoring loads from Jhanor from Southern and Northern regions failed repeatedly. power station during the occurrence occurred on 30.07.02. This was due to non-availability of loads following long Unbalancing of loads during the restoration procedure is a shutdown time due to black out and some industries very serious phenomena and should be properly dealt with. declared compensatory holiday. When traction loads are restored, phase balancing is an important consideration. If required some city loads on different phases can be restored along with traction loads. The G. High-voltage problems in extending start up power from feeders at the substations in the preplanned restoration path hydro stations : should be documented with MW , PF, MVAR parameters and Some of the major hydro stations like Koyna stage –IV ( their daily variation including timings of power-cuts. If voltage 4x250MW), Indira Sagar(8x125MW), Sardar Sarovar control during restoration is a priority then low power factor (6x200MW) are connected to only 400 kV and require loads can be restored. charging of long 400kV lines which trip on high-voltage. It is required to start one hydro unit at these power stations with J. Synchronisation of Islands manual excitation kept at around 60% of normal voltage and charge the local 400kV bus. Then charge one shortest 400kV One of the frequently encountered problem in restoration is line and charge the remote end 400kV bus. Load should be due to non availability of synchronization facilities, trained restored immediately at the remote bus in small increments to manpower to carry out synchronization. On some occasions,

186 Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

one of the islands collapsed due to jerk. In some cases the At the synchronising end, control of standing phase angle synchronization of islands was delayed due to lack of (SPA) to less than or equal to 200 would help in minimising synchronization facilities and trained manpower. jerk or sudden rush of power. For reduction of SPA, the On 30.07.02, Eastern Maharashtra system was restored with following measures need to be taken up. startup power from SR while Western Maharashtra system was • Reduce at those generators which are sensitive to the restored through blackstarting of Koyna Units. When both the SPA. parts of Maharashtra were having different frequencies. At • Shed loads at selected buses. 1002 hrs. 400kV Parli-Lonikhand Ckt-II was charged at • Simultaneous backing down of generation and Lonikhand in order to parallel both the parts of Maharashtra. shedding of load. While synchronizing at Parli, Jerk was observed and 400kV • Increase of generation at the sensitive buses. Indore-Asoj D/C tripped on powerswing. The recommended practice for synchronizing lines is always While charging two islands, it is preferable to charge and through check synchronization relay which normally is set for synchronise at the generating stations ends. At least, 350 above which breaker closing is not permitted. For most of synchronising end must be a generating station. In addition, the lines, SPA < 350 would suffice. However, in case of lines frequency difference should also be checked ( 0.1 Hz.). This inter connecting two major generating stations (Ex. 400kV would avoid sudden jerk. Further, charge at the end with Vindhyachal-Korba S/C line), it is prudent to limit the SPA to maximum generation level. around 200. However, for the sake of ready reference on the The restored island could be considered as stable if SPA control and sensitivity, measures to control SPA upto 200 frequency deviations and voltage deviations are manageable have been provided. The measures such as generation and there are adequate active and reactive power reserves. reduction, load shedding etc., suggested for SPA control need The compliance of 25% load or generation as dynamic reserve not be exercised for upto 350. is also important. With these conditions fulfilled, two critical On 31.7.02 at 1000 hrs, 400kV Indore-Asoj lines tripped and important islands can be synchronized with each other. while synchronising Western Maharashtra system with the rest The synchronization of two islands should not be done through of the grid. To avoid power swings while synchronising, the weak ties. The restoration plans also stipulate for connecting phase angle difference should be minimal preferably around two small islands quickly into a larger and more stable island. 20 degrees (or through synchro check relays) and frequency During restoration, a stable island system shall not be difference as small as 0.1 Hz. connected to a weak system On 30.07.02 the synchronisation of Mumbai system (TPC & BSES system) with the rest of the grid was purposefully delayed due to delays in strengthening K. Restoration of Loads of Maharashtra system. It is also not advisable to operate After the units at Vindhyachal and Korba were restored islanded systems for such long durations due to the continuous through availing start up power from NR, it is essential to frequency excursions and prolonged alert situation. Mumbai connect as much load as possible from MP and Chattisgarh system was synchronised with MSEB system at 1541 hrs on system to avoid power injection back into NR grid as well as 31.7.02. It is therefore essential to speed up the restoration of to bring up more generation at these stations. The generation the grid so that the survived islands could be saved from available at VSTPS and KSTPS was not properly utilized. On further trippings/collapse. It is also essential that TPC-BSES 30.7.02, neither MP nor Chattisgarh were able to restore loads systems island together as it happened on 30th July so that the at a faster rate even though external assistance is available. island survives properly and in case of delays in reconnection This is mainly due to none availability of load at that time and to the grid, the prolonged islanded operation may be secure high-voltage problems along the start up paths. [3] with frequency/ voltage fluctuations minimised due to large One of the main reasons for hunting of black started units on size. 30.07.02 has been the delay in providing loads along the start In MP, the restored parts from black started Gandhisagar up path. [4] units as well as those from Bargi and Tons black started units should be quickly interconnected with each other as well as to L. Cold load pick up : NR supplies.This would hasten restoration process in MP . On Cold load pick up at times leads to tripping of blackstarted 30.07.02 considerable delays were experienced in connecting units as well as lines/transformers restored. The generator restored islands in MP to NR grid. [3] under frequency trip settings at 47.5 Hz. (instantaneous) are Standing Phase Angle problems have been encountered also a concern in case of large frequency variations during during restoration while re-integrating islands or re-connecting load restoration (cold load pick up). On 23.05.2002 at 0613 the state grids with each other. Normally, the state grids are hrs. a disturbance occurred in Western Maharashtra System reconnected after sufficient level of stabilization. The SPA which led to splitting of Western Region into two parts – one problem is handled by generation re-scheduling based on the part comprising loads of Southern Maharashtra along with advice of RLDCs.

187 Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

have properly maintained breakers to avoid delays. Agra To S a wai Mehgaon TO Auraiya Madhopur POWER MAP OF WESTERN REGION NR Malanpur Another significant problem would be the condition of DC Shivpuri Kalan UTTAR PRADESH Motijheel Gwalior batteries due to inadequate charging which may effect

To Ka nkroli RAJASTHAN To R.P.Sagar TO KOTA Pichhore TO Motak communication and relay operations. Bansagar TO SINGRAULI STPS(N.R.) Akrimota Zerda (Kansari) Neem uch Rajghat Satna GUJARAT Thar ad Palanpur Deodhar Gandhisagar Bina(PG ) Rewa Sankhari Sasan 2 x 250 MW Panendro Maihar Ranchodpura KheraluVijapur Bina JHARKHAND Damoh To Rihan d Mehsana Kymore Vindhyachal STPSMorwa Anjar Jamla Himmatnagar Agar Nakhatrana Nardipur(Soja) Dehgam MADHYA PRADESH Katni N. Effect of Wind generation Waidhan Dhrarngadhra Chhatral Dhansura Suwasra Nanikhakar Mundra Ratlam Nagda Sujalpur Morbi Viramgam Kadana 4 Wanakbori Ujjain JabalpurBirsinghpur Kotma Gandhinagar Godhra Bhopal Manendragarh Naghedi Wankaner 5 Dewas Karamsad Halol Pithampur Amarkantak Vishramgarh Indore Sikka Limbdi Dhuvaran Kasor Asoj Itarsi Jabalupr (PG) During restoration,small islands with wind generation may Khambolia Jamnagar Bargi Hasdeo Bango Reliance Paliad SARDAR SAROVAR Indira Sagar Narsinghpur Bhatia Gondal Dhanduka Wagodia Jambuva Seoni Korba (E) Ranchi Ranavav Rajkot Amreli Rajgarh Burwaha GPEC 2 Korba(W) Vartej Jhanor Julwania Khandwa 1 KSTPS Budhipadar have to encounter sudden and large frequency changes due to Palithane 6 Satpura Chhindwara Pench Balaghat Jetpur Halderwa Kakr apar Nepanagar ROURKELA Savarkundla Khapaswami Sipat Utran Bhatapara Gujarat Keshod Dhokadwa Ichhapur Ukai(H) Pandurna Raigarh 3 Kanhan 1 Achhalia Una Kawas Kalmeshwar 2 Zagadia GSEG Ukai(T) Bhusawal KORADI Bhandara BHILAI starting or stopping of wind generators. It is advisable to Kodinar Essar Jalgaon Amravati 3 Kim Navsari Vav Malkapur Ambazari Diu(D&D) Sachin Paras RAIPUR 4 Ranasan Butibori Khaparkheda Dongargarh Ambheta Badnera Urla 5 Kapadwanj MagarwadaBhilad Malegaon Eldabad ORISSA Va pi Akola Ya watma l 6 Mangrol (D & D) Dhule Bhugaon disallow wind generation during restoration until partsystems Chalisagaon MAHARASHTRA Wardha Warora (Surat LPP) Karadpada Nasik Bhadravati CHHATTISGARH (DNH) Tarapur Manmad Bhiwand i Aurangabad Pusad

Dahanu(BSES) Boisar A Kharghar Jalna CHANDRAPUR

Navi Mu mbai or islands attain adequate stiffness. Maharashtra E Borivali Bableshwar Kalwa Nanded 2 x 500 MW 1 Jejuri Pa

Trombay dghe Pune(PG ) Parbhani S Bosari Ahmadnagar BARSOOR 2 Theur Ap ta Beed 3 Parvati

Uran Chinchwad Lonikhand Parli(PG ) TO RAMAGUNDAM

Nagothane 2 N Kandalgaon 3 Parli 1 Latur

Baramati Udgir A ANDHRA PRADESH IV. CONCLUSION

Lonand Osmanabad Ujani I Sholapur(PG) Sholapur TO L. SILERU New Koyna Koyna

B Q/c LEGEND

Karad Vita A Dabhol HYDRO POWER STATIONS The problems during restoration could be minimized with Miraj Kolhapur THERMAL -

R KARNATAKA GAS

A Gadinglez STATION proper planning and some of these are listed below. 400 KV TRANSMISSION LINES Tillari To Bel ga um 400 KV LINES UNDER PLAN UPTO MAR.2009 500kV HVDC Bipole • Mapusa Prepared by : To Nagjhari The restoration problems to be considered while GOA Ponda 765 kV LINE OS, WRLDC, Mumbai planning of the grids, which is not being done presently. Fig. 1. POWER MAP OF WESTERN REGION, INDIA • Voltage control along various start-up paths. This Web Link : http://www.wrldc.com/maps/Powermapmarch2008.pdf includes studies for requirement of reactors, various Flexible AC transmission (FACT) devices and identification of suitable nodes. Koyna & Parli Power Stations and a second part comprising • Deployment of synchro-check relays and other means rest of the grid. The first part collapsed. The restoration of the to avoid paralleling of different supplies. grid was achieved by 0700 hrs. and the load restoration was in • Expert systems to aid operators during restoration. progress. As the morning peak approached, unusual heavy • Expert systems to identify faulty equipment. load was incident on the system leading to severe voltage dips • and load encroachment of distance relays. Number of 400kV Expert systems for processing alarms in SCADA lines tripped which led to a major disturbance splitting the system. • Western Regional Grid into five parts. Normally, the cold Commercial means to maintain grid discipline during load pick up would be a serious problem incase loads are grid restoration. • restored within 10 to 15 minutes of the disturbance. Periodic conduction of ‘Blackstart’ workshops and mock drills in the region.

M. Protection and Substation equipment ACKNOWLEDGMENT The following are the typical problems faced The authors acknowledge with thanks the guidance and • Sometimes provision of bus coupler/line synchro check support given by the management of POWERGRID and for facilities at important substations are not available. permitting the publication of this paper. The views expressed • Problems in closing the breaker due to low gas/air in this paper are of the authors in their individual capacity and pressure. not necessarily that of Power grid Corporation of India Ltd. • Identification of suspected faulty equipment can be done using both relay indications and physical observations. REFERENCES • Control high-voltage during restoration to avoid damage [1] “Recovery procedures for western region” Aug 2006. Issued by of LAs/CVTs etc. WRLDC, file available at web link • The generator under frequency trip settings at 47.5 Hz. http://www.wrldc.com/docs/Recovery_Procedures_Aug2006.pdf [2] M. Adibi(chairman),P.clellard, L.Fink, H.Happ, R.Kafka, J. Raine , (instantaneous) and over frequency settings at 51.50 Hz D.Scheurer, F. Trefny “Power System Restoration – A Task Force are also a concern in case of large frequency variations Report” during load restoration. [3] Anjan Roy,V.K veluchamy,P.Pentayya,R.K.Mediratta,Pushpa.S,Haresh • Patel “Restoration of Western Regional Grid – A Case Study of Operation of Over-Fluxing relays, Over Voltage (O/V) 30.07.02” Presented at the National seminar on Grid operation and relay. Management organized by Central board of Irrigation & Power at th th On 30.07.02, considerable delays experienced while Chennai on 29 & 30 October 2002 [4] Anjan Roy, V.K.Veluchamy, P.Pentayya, R.K. Mediratta, Pushpa S, providing start up power to Nasik, and extending supplies Haresh Patel “Restoration of western regional grid – A case study of from Jhanor Power station due to breaker problems. All the 30.07.2002”, 2002. Presented at the workshop for load dispatch line sections involved in start up power transmission should personnel and system operators at WREB, Mumbai on 27/09/2002

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