ISSN 2319-8885 Vol.03,Issue.10 May-2014, Pages:2005-2011 www.semargroup.org, www.ijsetr.com

Insulation Design and Simulation of Pyinmana Substation by using ATP 1 2 THEINT THEINT HNIN , THET NAUNG WIN 1Dept of Electrical Power Engineering, Mandalay Technological University, Mandalay, Myanmar, Email: [email protected]. 2Dept of Electronic Engineering, Mandalay Technological University, Mandalay, Myanmar, Email: thetnaung [email protected].

Abstract: Insulation coordination is the selection of the insulation strength and selection of the dielectric strength of the equipments in relation to the voltages which can appear on the system for which equipment is intended and taking into account the service environment and the characteristics of the available protective devices. Insulation coordination is essential power engineers to reduce the number of outage and preserve the continuity of service and electric supply. Moreover, it is concern with the design of new lines and substations with implementing measure appropriate measure to improve the lightning performance of the existing lines and substations. In practice, insulation coordination is the selection of the insulation strength for each equipment in the substation. Insulation coordination design of a substation also consists of the selection of the minimum insulation strength, or minimum clearance, since minimum strength can be equated to minimum cost in substation design. The design process begin with a selection of the reliability criteria, followed by some type of study to determine the electrical stress placed on the equipment or on the air clearance. This stress is then compared to the insulation strength characteristics, from which strength is selected. If the insulation strength or the clearance is considered to be excessive, then the stress can be reduced by use of ameliorating measures such as surge arresters, protective gaps, shield wires, and closing resistors in the circuit breakers. After the selection of the reliability criteria, the process is simply a comparison of the stress versus the strength. It expects to extend the life time of insulation and to improve the insulation coordination. For the analysis of the designed system, ATP (Alternative Transient Program) will be employed.

Keywords: Insulation Coordination Design, Insulation Strength, Substation Insulation Coordination, ATP Model, Simulation Result.

I. INTRODUCTION  that is, the BIL and BSL of all equipment. Substation contains transformer, switchgear and other  The phase-ground and phase-phase clearances or valuable equipment with non-self restoring insulation, which strike distances. Figure 1 illustrates the various strike have to be protected against failures and internal destruction. distances or clearances that should be considered in a For other apparatus, which contain self-restoring insulation, substation. like string insulators, they may be allowed to flashover in air.  The need for the location, the rating, and the number But the flashovers should be kept to a minimum so that the of surge arresters. system disturbances are the least. Hence, lightning protection  The need for the location, the configuration, and the requires establishment of protective voltage levels called spacing of protective gaps. shunt protection levels, by means of protective devices like  The need for the location, and the type (masts or lightning arresters. The protective level of the substation shield wires) of substation shielding. insulation depends on the station location, the protective level  The need for the amount and the method of of the arrester, and the line shielding used. The line insulation achieving an improvement in lightning performance in the end spans near the substation is normally reduced to of the line immediately adjacent to the station. limit the lightning over voltages reaching the substation. In a In these lists, the method of obtaining the specifications substation, the bus bar insulation level is the highest to ensure has not been stated. To the person receiving this information, continuity of supply. The circuit breakers, isolators, how the engineer decides on these specifications is not of instrument and relay transformers, etc. are given the next primary importance, only which these specifications result in lower level. Since the power transformer is costly and the desired degree of reliability. It is true that the engineer sensitive device, the insulation level for it is the lowest. must consider all sources of stress that may be placed on the II. INSULATION COORDINATION IN equipment or on the tower. That is, he must consider ELECTRICAL SUBSTATION  Lightning over voltages (LOV), as produced by For substation insulation coordination, the task is similar lightning flashes in nature It is to specify:  Switching over voltages (SOV), as produced by  The equipment insulation strength, switching breakers or disconnecting switches

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THEINT THEINT HNIN, THET NAUNG WIN  Temporary over voltages (TOY), as produced by TABLE II: Insulation Levels for Outdoor Substations faults, generator over speed , ferroresonance , etc. and Equipments  Normal power frequency voltage in the presence of contamination

Figure1. The Strike Distances and Insulation Lengths in a Substation. C. Alternative Transient Program A. Basic Lightning Impulse Insulation Level (BIL) The ATP also known as Electromagnetic Transient The BIL is the electrical strength of insulation expressed in Program (EMTP) is a computer program for simulating the terms of the crest value of the standard lightning impulse. Electromagnetic, Electromechanical and control system That is, the BIL is tied to a specific wave shape in addition transients or transient Analysis of Control Systems (TACS) being tied to standard atmospheric conditions. The BIL may on multiphase electric power systems. It was first developed be either a statistical BIL or a conventional BIL. The as a digital computer counterpart to the Analog Transient statistical BIL is applicable only to self-restoring insulations, Network Analyzer (TNA). Many other capabilities have been whereas the conventional BIL is applicable to non-self- added to the EMTP over the years and the program has restoring insulations. BILs are universally for dry conditions. become as a culture in the electric utility industry. The actual EMTP is the result of a cooperative development effort B. Basic Switching Impulse Insulation Level (BSL) among many users. Studies involving use of EMTP can be The BSL is the electrical strength of insulation expressed put into two general categories. One in design which includes in terms of the crest value of a standard switching impulse. insulation coordination, equipment ratings, protective device The BSL may be either a statistical BSL or a conventional specification, control system design, etc. The other is solving BSL. As with the BIL, the statistical BSL is applicable operating problems such as unexplained outages or system only to self-restoring insulations while the conventional failures. A partial list of typical EMTP studies follows: BSL is applicable to non-self-restoring insulations BSLs are Switching surges, Lightning Surges, Insulation Coordination, universally for wet conditions. High Voltage DC (HVDC).The EMTP provides the ability to perform insulation coordination design. The insulation TABLE I: Transformer and Bushings Bils and BSLS coordination of 230 kV Pyinmana substation will be modeled and simulated using the ATP program.

III. OVERVIEW OF THE PYINMANA SUBSTATION The Pyinmana Substation was built in 1985 and finished in 1989. The area of the Pyinmana Substation is 11 acre wide previously but now the substation have 32.01 acre. The substation is located in the east of the Pyinmana township and it is at the side of Pyinmana-Sugar station road. It is one of the largest substation in Myanmar. Naypyidaw, the capital of Myanmar is also provided electricity from this substation. Pyinmana substation is comprised with two transformers having 100 MVA and 60 MVA.100 MVA transformer connect six distribution feeders at 33 kV side and 60 MVA transformer also connect to other six distribution feeders. Presently, Pyinmana primary substation is supplying the International Journal of Scientific Engineering and Technology Research Volume.03, IssueNo.10, May-2014, Pages: 2005-2011 Insulation Design and Simulation of Pyinmana Substation by Using ATP substation are shown in Figure 2and Figure 3. There are five 230 kV transmission lines connected to Pyinmana substation. The generated power from Paung- Laung Hydro power station is supplied to Pyinmana substation with two 230 kV feeders. Naypyidaw, the capital of Myanmar is supplied from Pyinmana substation with one 230 kV feeder. Pyinmana substation is also interconnected with Tharzi substation via Shwe Myoe substation and Taungoo substation via Thae Phyu substation.The maximum and minimum power flow on 230 kV feeders are shown in Figure 4.

IV. MODELING OF PYINMANA SUBSTATION When the lightning surge strike in practical system, the practical system have actual insulation level coordinate or not coordinate compare the standard level refer to the Table. The Figure2. 100 MVA, 230/33/11 kV Transformer at implementation of ATP model involves the separation Pyinmana Substation. distance of the substation equipment and equipment’s rating. These data are measure from the layout diagram of the Pyinmana Substation. The practical insulation coordination strength of the substation equipment measure building a substation model with ATP. The actual substation insulation

Figure3. 60 MVA, 230/33/11 kV Transformer at Pyinmana Substation.

From From To To To PaungLaung 1 PaungLaung 1I Naypyitaw Shwemyo The Phyu

120 MW LA LA LA LA LA (50 MW)

CVT CVT CVT CVT CVT

DSE DSE DSE DSE DSE

CT CT CT CT CT

GCB GCB GCB GCB GCB

To 100 MVA To 60 MVA 230/33/11 kV 230/33/11 kV Transformer Transformer Figure4. Power Flow on 230 kV Transmission Lines of Pyinmana Substation. electricity to Naypyitaw Council region, Naypyitaw International Airport (Ayelar), Pyinmana township and Figure 5. Layout Diagram of the Switch Yard Security of surrounding areas. The two main transformers of Pyinmana the Pyinmana Substation. International Journal of Scientific Engineering and Technology Research Volume.03, IssueNo.10, May-2014, Pages: 2005-2011

THEINT THEINT HNIN, THET NAUNG WIN due to the fact that, some of charges and hence over voltages are discharged to the ground through the grounding resistors of the towers. The maximum lightning magnitude is about 160 kA because Pyinmana substation is locating in the middle of Myanmar. In this study, the lightning magnitudes is applied 160 kA and three wave shapes are considered as 1/70, 2/70 and 3/70 µs.

According to the measurement, the voltage at 5th tower is 2129.9 kV which is greater than the BIL of the substation. The resulting measured voltages at the 5th tower due to160 kA, 1/70 µs lightning surge under present LA installation are shown in Table III. According to the discharge through the tower grounding resistors, this voltage becomes 1540.7 kV at 1st tower which is nearest to the substation. The lightning surge voltage at 1st tower is shown in Figure 8. At 5th tower, the maximum voltage is at phase ‘b’ also at 1st tower it is at phase ‘b’. In figure 9 to 13 show the ATP simulation results at the end of the line ,at the connection point ,at the location of circuit breaker ,at the primary side of transformer and 230 kV bus. In this figures, the red line show voltage at phase

Figure 6. ATP Model for Pyinmana Substation. 1.5 [MV] levels may have coordinate or not coordinate level according 1.0 to the ATP simulation result, the results are compare the standard BILs and BSLs values. If measurement insulation 0.5 voltage level coordinates in the actual system, the actual system has acceptable insulation level. ATP model is 0.0 implemented to know the insulation coordination level in the actual system. The voltage magnitudes are measured at -0.5 specific location such as 230 kV bus, connection points, -1.0 primary and secondary of transformer. Figure 6 shows ATP model for 230 kV Pyinmana Substation. -1.5

V. STUDY ON PRESENT LA INSULATION LEVEL -2.0 0.00 0.05 0.10 0.15 0.20 [ms] 0.25 (file 28(160)s.pl4; x-var t) v:VTWR1A v:VTWR1B v:VTWR1C 2.5 Figure 8. Voltage at 1st Tower Due to 160 kA, 1/70 s [MV] Lightning Surge. 2.0 800 1.5 [kV]

1.0 500

0.5

0.0 200

-0.5 -100

-1.0 0.00 0.05 0.10 0.15 0.20 [ms] 0.25 (file 28(160)s.pl4; x-var t) v:VTWR5A v:VTWR5B v:VTWR5C th Figure7. Voltage at 5 Tower Due to 160 kA, 1/70 s -400 Lightning Surge.

For the insulation coordination study at Pyinmana -700 th 0.00 0.05 0.10 0.15 0.20 [ms] 0.25 substation, the lightning strike is applied at 5 tower from the (file 28(160)s.pl4; x-var t) v:VENDA v:VENDB v:VENDC substation. As the lightning strike is nearer to the substation, Figure 9. Voltage at the End of Line Due to 160 kA, 1/70 the more overvoltage can be applied at the substation. This is s Lightning Surge.

International Journal of Scientific Engineering and Technology Research Volume.03, IssueNo.10, May-2014, Pages: 2005-2011 Insulation Design and Simulation of Pyinmana Substation by Using ATP 800 largest which 725.5 kV as shown in figure 9 is. In figure 10,

[kV] the phase ‘a’ voltage at the connection point is largest which is 754 kV.In figure11, phase ‘a’ voltage at the bus is largest 500 which is 708.2 kV. In figure 12, phase ‘a’ voltage at the primary side of transformer is largest which is 702 kV. In

200 figure 13, phase ‘a’ voltage at the circuit breaker is largest which is 702 kV.

800 -100

[kV]

500 -400

-700 200 0.00 0.05 0.10 0.15 0.20 [ms] 0.25 (file 28(160)s.pl4; x-var t) v:VCONNA v:VCONNB v:VCONNC Figure 10. Voltage at the Connection Point Due to 160 kA, 1/70 s Lightning Surge. -100

800

[kV] -400

500

-700 0.00 0.05 0.10 0.15 0.20 [ms] 0.25 (file 28(160)s.pl4; x-var t) v:CBA v:CBB v:CBC 200 Figure 13. Voltage at the Circuit Breaker Due to 160 kA, 1/70 s Lightning Surge.

-100 TABLE III: Measure voltages in kilovolts for phase ‘a’ at 160 ka,1/70 µs lightning surge under present la -400 installation 160 kA,1/70µs lightning strike at the 5th tower

-700 Vend 725.5 kV 0.00 0.05 0.10 0.15 0.20 [ms] 0.25 (file 28(160)s.pl4; x-var t) v:VBUSA v:VBUSB v:VBUSC Vbus 708.2 kV Figure 11. Voltage at the Bus Due to 160 kA, 1/70 s Lightning Surge. Vconn 754 kV 800

[kV] Vpri 702 kV

500 VCB 754

200 800

[kV] -100

500

-400

200

-700 0.00 0.05 0.10 0.15 0.20 [ms] 0.25 (file 28(160)s.pl4; x-var t) v:VPRIA v:VPRIB v:VPRIC Figure 12. Voltage at the Primary Side of Transformer -100 Due to 160 kA, 1/70 s Lightning Surge.

-400 ‘a’, the green line show the voltage at phase ‘b’ and the blue line show voltage at phase ‘c’. In figure 9 to 13 the comparison for these three phases ‘a’, ‘b’ and ‘c’. Among the -700 three phase voltage, the amplitude of phase ‘a’ voltage is 0.09 0.10 0.11 0.12 0.13 [ms] 0.14 (file 28(160)s.pl4; x-var t) v:VENDA v:VBUSA v:VCONNA v:VPRIA largest. The phase ‘a’ voltage at the end of the red line is Figure14. Comparison for Phase ‘a’ Voltages at 160 kA. International Journal of Scientific Engineering and Technology Research Volume.03, IssueNo.10, May-2014, Pages: 2005-2011

THEINT THEINT HNIN, THET NAUNG WIN Figure 14 show the ATP simulation result, the red line for without arresters condition is described in Table VI show voltage at the end of line, the green line show voltage at compared to Table VII. the bus, the blue line show voltage at the connection point BILMax:Voltage and the pink line show voltage at the primary side of Margin  100[%] transformer. The measure voltage at 160 kA, 1/70 µs BIL (1) lightning strike at 5th tower, the connection point of the phase TABLE VI: Margin of 230 Kv Pyinmana Substations ‘a’ voltage is largest which is 754 kV. At the instant of While All Arresters Are Removed lightning surge, the magnitude of phase ‘a’ voltage is largest Measured Point 160 kA compared to other phases. Thus most of voltage magnitude Rise/Fall Time 1/70µs 2/70 µs 3/70 µs measurements are carried out at phase ‘a’. The comparison for phase ‘a’ voltages at line end, bus, connection point and Vend -15.5 24.9 36.5 primary side of transformer are shown in Figure 14. The Vbus 13.6 15.1 18.4 voltage at the connection point is noticeably large compared Vconn 9.2 16.3 20.5 to other voltages. Among the measured voltages the voltage Vpri -25.5 -20.4 -15.1 at the primary side of the transformer is smallest and that at VCB -5.9 2.4 7.2 the connection point is largest. The voltage at the connection point is exactly the same as that of circuit breaker point. TABLE VII: Margin of 230 Kv Pyinmana Substation Under Present La Installation TABLE IV: Measured Voltages in Kilovolts for Various Wave Shapes While All Arresters Are Removed Measured 160 kA Point Rise/Fall 1/70µs 2/70 µs 3/70 µs Time Vend 1212.6 788.60 666.9 Vbus 907.42 891.40 856.3 Vconn 953.11 878.56 835.10 Vpri 940.9 903.30 862.9 VCB 953.11 878.56 835.10

Without any arrester, maximum overvoltage which According to the regulations, the margin must be greater appears on the line end is 1212.6 kV, which is greater than than 20 % of BILs. For 230 kV system, substation BIL of substation. From this result, it can be concluded more equipments such as disconnecting switches, bushings, etc., arresters that needs to install for suppression of overvoltages. the BIL is 1050 kV, disconnecting switches are 900 kV and for transformers, it is 750 kV. Table VI shows the margin of TABLE V: Measure Voltages In Kilovolts For Various 230 kV Pyinmana substation while all arresters are removed. Wave Shapes Under Present La Installation The margins that are less than 20 % are highlighted in the Measured Point 160 kA Tables. Therefore, more additional LA is necessary for the safety of substation. For 160 kA, 1/70 s lightning strike, the Rise/Fall Time µs) 1/70 us 2/70 us 3/70 us margin is only about 6.4 % which is much below the standard End(kV) 725.5 650.1 562.5 margin 20 %. Therefore, more additional LA are necessary Bus(kV) 708.2 667 621.9 for the safety of transformers. Conn(kV) 754 703 631.9 VI. IMPROVEMENT ON INSULATION Pri(kV) 702 664.8 622.9 COORDINATION AT PYINMANA SUBSTATION CB(kV) 754 703 631.9 TABLE VIII: Argin of 230 Kv Pyinmana Substation With Four Additional La At 230 Kv Bus According to the simulation results, 160 kA, 1/70 µs is the Measured 160 kA largest among the three different waves shapes. From this Point result, it can be concluded that the larger the lightning Rise/Fall Time 1/70µs 2/70 µs 3/70 µs magnitude and wave shape the more over voltages are carried Vend 30.9 38.04 46.6 out at the incoming point, buses, circuit breaker, Vbus 43.3 43.9 45.1 disconnecting switches and transformers. Therefore, the more Vconn 42.3 43.4 45.4 arresters are required to cancel the over voltages in the Vpri 20 21 22.6 substation. VCB 32.7 33.9 36.3

A. Safety Margin As shown in Table VIII, the safety margin of transformers For insulation coordination study, the simulation is also can be at 20 % that is equal to recommended margin of 20 % executed for without arresters condition. The resulting data International Journal of Scientific Engineering and Technology Research Volume.03, IssueNo.10, May-2014, Pages: 2005-2011 Insulation Design and Simulation of Pyinmana Substation by Using ATP with the installation of four additional LAs at 230 kV buses. University for her encouragement, advices and continuous Therefore, it is recommended that the installation of four guidance throughout the study. additional LAs at 230 kV buses will improve the insulation coordination level of Pyinmana substation and can protect IX. REFERENCES transformers at lightning risks. [1] Andrew R. Hileman, H.Lee Willis Published in 1999, “ Insulation coordination for power system,” ABB Electric TABLE IX: Changing the Bil Calculating the Margin of Systems Technology Institute Raleigh, North Taylor 230 Kv Pyinmana Substation &Francis Group Boca Raton London New York. Measured 160 kA [2] Noor Azila Binti Khazimah, May 2006, “The analysis of Point lightning overvoltage by EMTP for lightning protection Rise/Fall Time 1/70µs 2/70 µs 3/70 µs design of 500kV substation,” Fakulti Kejuruteraan Elekerik Vend 30.9 38.1 46.4 Kolej University Teknikal Kebangsan Malaysia. th Vbus 32.6 36.5 40.8 [3] Hans Kr. Høidalen Professor, November 26 2009, “ATP draw version 5.6,” Norwegian University of Technology Vconn 28.2 33 39.8 Trondheim, Norway. Vpri 22 26.1 30.8 [4] M.Aburaida(AMIEE), “On The Insulation Coordination VCB 28.2 33.04 39.8 Studies Using (EMTP),” Electricity corporation in Sudan and SCECO-EAST in Damman, Saudi Arabia. The Table IX show does not add the LAs in the 230 kV [5] Annual Report 2013, “MyanmaElectric Power busbar. At present LAs installation, if new transformer BIL Enteprise, Ministry of Electric Power.” 900 kV is changed, the safety margin of transformers at 160 kA, 1/70µs condition can become 22 % that is greater than the recommended margin of 20 %. Also if changing the new circuit breaker BIL 1050 kV, the safety margin of circuit breaker at present LAs installation is greater than the recommended margin of 20 %. In Table VIII the transformer BIL is calculated 750 kV because that is commonly used in the substation. And low cost and save economically. The transformer is non-self restoring equipment and lowest the insulation level in the substation equipments. Besides, the cost of the transformer is very high. So, transformer insulation coordination level is not mainly change in the substation to get the safety margin of the substation.

VII. CONCLUSION For overvoltage suppression, the additional arresters are proposed at the 230 kV buses will improve the insulation level of Pyinmana substation. By addition the LA is low cost and save the economically. It is confident that, this paper can support on the well understanding for insulation coordination design of substation and the improvement scheme. ATP software can give an easy and reliable approach to the insulation coordination problem. Lightning overvoltages within substations are effectively reduced by the high performance of surge arrester. This metal oxide surge arrester is a key technology for insulation coordination. The substation is not easily breakdown. The system is more safe by reducing the breakdown sequence.

VIII. ACKNOWLEDGMENT The author would like to thank to U Thet Naung Win, lecturer Department of Electrical power Engineering Mandalay Technological University. The author is deeply grateful to U Kyaw San Lwin, lecturer Department of Electrical power Engineering Mandalay Technological University. The author also wishes you thank you to Dr.Khin Thuzar Soe, Associate Professor and Head, Department of Electrical Power Engineering, Mandalay Technological

International Journal of Scientific Engineering and Technology Research Volume.03, IssueNo.10, May-2014, Pages: 2005-2011