TRANSFORMERS

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1 Magnetic Flux test,2 Magnetizing current,3 TAN Delta of H V M V and LV. 5 Dissolved Gas Analysis,6 Winding Resistance,Q Probable cause of failure. 1 Magnetizing current in Y phase was found to be 1 06 A which is very high as compared to. 3 6 mA in R ph and 3 5 mA in B ph Also very low voltage 0 506 V was observed in Y ph. in magnetic balance test when 231 V was applied on R phase which indicates problem in Y. phase winding DGA of oil indicated high concentration of Hydrogen H2 2064ppm. Ethylene C2H4 271 ppm Methane CH4 148 ppm Acetylene C2H2 398 8 Total. Dissolved Combustible Gases TDCG was 3064 which is higher than normal value These. high concentration of acetylene gas could be due to high energy arcing inside the tank. 2 Significant variation was observed while comparing the pre and post fault signatures traces. of SFRA tests carried out on transformer The test result indicates problem in core coil. assembly Operation of Differential Buchholz OSR PRV relays indicates internal fault of. the transformer The internal winding insulation failure might have led to inter turn winding. insulation failure which is also supported by the test results and preliminary internal. inspection, 3 High energy arcing inside the transformer tank might have led to sudden pressure rise and. tripping of oil surge relay PRV Rate of rise of gas pressure might be very high before. operation of PRV which might have resulted in cracks at weak areas of the transformer tank. 4 The fault is most likely in Y ph of winding The detailed investigation after opening of tank. will provide the extent of damage type of failure s and other valuable information. 2 Failure of 315 MVA 400 220 33 kV Auto transformer at 400 kV Bawana substation of. A Name of Substation 400 kV Bawana substation,B Utility Owner of substation DTL. C Faulty Equipment Auto transformer,D Rating 315 MVA 400 220 33 kV.
E Make EMCO,F Sr No HT 1798,G Year of manufacturing 2009. H Year of commissioning 2010,I Date and time of 08 03 2016 at 1201 hrs. occurrence discovery of,J Information received in 08 03 2016. K Fault discovered during Operation,L Present condition of Replaced. M Details of previous,maintenance,Tests carried out on 12 07 2010.
Sr No Test for Permissible limits Sample 1,1 Water Content ppm 10 Max 8. 2 Breakdown Voltage rms kV 60 Min 80,Tests carried out on 19 07 2010. Sr Test for Permissible limits Sample 2 Sample 3 Sample 4. 1 Water Content ppm 10 Max 10 9 9,2 Breakdown Voltage 60 Min 72 72 73. Sr TEST FOR PERMISSIBLE LIMITS SAMPLE 1, 1 Appearance Clear free from sediment Clear free from. and suspended matter sediment and,suspended matter.
2 Density 29 5 C gm cm3 0 89 Max 0 82,3 Kinematic Viscosity 27 C cSt 27 Max 16. 4 Pour point C 6 Max Less than 6,5 Interfacial Tension N m 0 035 Min 0 039. 6 Flash Point C 140 Min 153,7 Neutralisation Value mg g 0 03 Max Nil. 8 Breakdown Voltage rms kV 60 Min 78, 9 Dielectric Dissipation Factor Tan 0 010 Max 0 0014. delta 90 C,10 Specific Resistance X 1012 Ohm 6 Min 60.
11 Water Content ppm 10 Max 9,Tests carried out on 21 07 2010. i PI measurement using 5 kV Megger,REF 60 sec 600 sec PI REMARKS. HV IV to EARTH 199 0 G 281 0 G 1 412,LV to EARTH 223 0 G 260 0 G 1 165. HV IV to LV 163 0 G 179 0 G 1 098,ii MAGNETIC BALANCE IN HV. IX N IY N IZ N IX N IY N IZ N I mag,232 4 V 219 2 V 16 8 V 2 1.
225 6 V 132 0 V 92 0 1 40,229 4 V 20 24 V 217 8 2 0. iii MAGNETIC BALANCE IN IV,2X N 2Y N 2Z N 2X N 2Y N 2Z N I mag. 229 1 223 7 V 13 10 V 3 96,224 4 V 126 7 V 97 8 V 3 35. 228 7 V 18 6 223 0 V 3 47,iv MAGNETIC BALANCE IN LV. 3X 3Y 3Y 3Z 3Z 3X 3X 3Y 3Y 3Z 3Z 3X I mag,400 9V 197 5 V 202 2 V 42 1.
400 7 V 347 0 V 202 9 V 49 4,399 6 V 335 6 V 206 9 V 55 6. v RATIO TEST BETWEEN HV to LV,Tap Theoretical Ratio 1X 1Y 1Z. No 3X 3Y 3Z,9b 12 12 12 36 12 12 12 02,vi RATIO TEST BETWEEN IV to LV. Tap Theoretical Ratio 2X 2Y 2Z,No 3X 3Y 3Z,9b 6 66 6 86 6 59 6 61. vii RATIO TEST BETWEEN HV to IV,Tap Theoretical Ratio 1XN 1YN 1ZN.
No 2XN 2YN 2ZN,1 2 000 2 206 2 021 2 014,2 1 977 1 980 1 949 1 975. 3 1 955 1 943 1 962 1 963,4 1 932 1 934 1 919 1 947. 5 1 909 1 914 1 911 1 916,6 1 886 1 908 1 881 1 894. 7 1 864 1 870 1 854 1 869,8 1 841 1 842 1 844 1 843. 9 1 818 1 801 1 824 1 825,10 1 795 1 791 1 785 1 807.
11 1 773 1 760 1 775 1 774,12 1 750 1 752 1 742 1 751. 13 1 727 1 724 1 718 1 730,14 1 705 1 704 1 686 1 699. 15 1 685 1 679 1 684 1 692,16 1 654 1 658 1 650 1 659. 17 1 636 1 634 1 616 1 637,viii VECTOR GROUP MESUREMENT YN a 0d 11. 1Y 3Y 1Z 3Z 1Y 3Z Z 3Y,APPLIED VOLTAGE MESURED ACROSS MEASURED VOLTS.
1X 1Y 401 1Z Z 388,1Y 1Z 426 1X N 228 5,1X 3Z 25 2. 1Z 1X 424 3Z N 202,ix SHORT CIRCUIT CURRENT LV SHORT 3X 3Y 3Z. Tap APPLIED VOLTAGE IN MEASURED AMPS IN MEASURED AMPS IN. No PRIMARY Volts PRIMARY Amp SECONDARY Amp,XY YZ ZX 1X 1Y 1Z 2X 2Y 2Z. 9b 398 3 398 1 397 5 0 59 0 59 0 59 7 15 7 15 7 15. x WINDING RESISTANCE IN HV SIDE IN m,MEASURED RESISTANCE. TAP NO 1X N 1Y N 1Z N,1 331 6 331 3 330 9,2 325 9 324 4 324 5.
3 319 8 319 4 318 4,4 314 7 313 7 312 9,5 308 6 308 0 307 4. 6 301 8 300 8 301 2,7 296 8 295 7 295 5,8 290 8 290 0 290 3. 9B 284 3 283 5 283 5,10 290 7 290 2 290 3,11 297 0 296 4 295 8. 12 302 4 301 5 301 1,13 308 1 307 3 307 0,14 314 1 313 3 313 6. 15 320 6 319 6 319 0,16 325 9 325 9 324 7,17 332 2 330 8 332 2.
xi WINDING RESISTANCE IN IV SIDE IN m,Tap No 2X N 2Y N 2Z N. Normal 354 8 350 7 354 8,xii WINDING RESISTANCE IN LV SIDE IN m. Tap No 3X3Y 3Y3Z 3Z3X,Normal 15 4 16 4 15 3,Tests carried out on 22 12 2015. Dissolved Gas Results in ppm Key Gas Concentration Limits As per IEEE Std. Present st,1 Prior C57 104 2008,Test Date 22 12 15 09 06 1 in ppm. Hydrogen H 10 14 100,Carbon Di oxide CO 5774 5580 2500.
Carbon Mono oxide 274 216 350,Ethylene C2 H4 7 5 50. Ethane C2 H6 6 6 65,Methane CH4 12 11 120,Acetylene C2 H2 0 5 0 5 1. TDCG 309 252 720,Roger s Ratio Indicates for Present Simple only. CH4 H2 1 23,C2 H2 C2 H4 0 09,C2 H4 C2 H6 1 28,C2 H6 CH4 0 48. CO2 CO 21 10, IEEE Std C57 104 2008 by comparing present and previous TDCG values suggests.
Change in TDCG Value 57 ppm Rate 0 3 ppm day,sampling Interval 6 Months. Tests carried out on 19 02 2016, Sr Insulatio Make Yr of Mod Voltag Capacitance Dissipation Factor. No n Tested SI No Menu e e pF,f Yr Applie,of d kV Measu CORRECTE. comm red D,1 HV LV UST 10 6471 60 0 20 0 18,2 HV GSTg 10 7851 56 0 22 0 20. 3 TV E GSTg 10 15630 52 0 20 0 18,4 400 kV CGL S70954 2009 UST 10 521 74 0 26.
5 400 kV CGL S70972 2009 UST 10 529 93 0 28,6 400 kV CGL S70969 2009 UST 10 548 14 0 29. 7 220 kV CGLS24530021 2009 UST 10 373 40 0 30,8 220 kV CGLS24530021 2009 UST 10 380 76 0 23. 9 220 kV CGLS24530021 2009 UST 10 374 71 0 22,10 33 kV CGL 2009 UST 10 198 06 0 26. R 52100553 R,11 33 kV CGL 2009 UST 10 203 47 0 27,Y 52100600 R. 12 33 kV CGL 2009 UST 10 204 12 0 27,B 52100604 R,13 220 kV BHEL 2448925 2005 UST 10 783 21 0 33.
14 220 kV BHEL 2448924 2005 UST 10 817 67 0 24,15 220 kV BHEL 2448923 2005 UST 10 817 28 0 27. 16 Excitation Current Test,18 10 kV R Y B,15 42 13 41 14 99. N Details of previous failure Nil,O Sequence of events. Description of failure, i On 08 03 16 at 1201 hrs EMCO make 315 MVA auto transformer ICT 4 tripped with. heavy jerk and sound with following facia relay indications and caught fire. a Differential protection 87 T1,b Differential 3 ph trip.
c Differential R ph trip,d Differential Y ph trip,e Differential B ph trip. f WTI PRV trip,g Overcurrent and earth fault Protection. h 64 T2 REF protection,i REF trip,j Buchholz trip,k OLTC Buchholz Y ph trip. ii After hearing the sound staff present at substation rushed to the switchyard and found 220. kV bushing of Y B phase of ICT 4 under fire Nitrogen Injection Fire Protection System. and High Velocity Water Spray System operated but fire could not be controlled Fire tenders. from nearby Bawana Power Plant of PPCL rushed to the site and quenched the fire. P Details of Tests done after The bushings were dislocated from its original. failure position and damage to the transformer due to fire. was so severe that it was not possible to carry out. any test on failed transformer,Q Observations, i Prior to fault load on transformer was 121 MW The transformer was operating on normal. tap 9B at the time of failure OLTC had not been operated since commissioning. ii During physical inspection of the failed transformer at site it was observed that MV. Bushings of Y B phase had completely damaged due to fire burnt insulation paper and. connecting rods of bushings were visible ceramic housing was found scattered around. transformer and flanges had damaged, iii MV bushing of R phase and tertiary bushings were also found damaged Since the direction.
of wind was away from HV bushings not much damage to HV bushings was observed. however some petticoats of bushings had chipped, iv Transformer tank was found bulged at MV side and it had cracked at a number of places. v 220 kV Surge Arresters had completely damaged due to heat surge counters had melted. and ZnO blocks pieces of arrester housing were scattered on the ground. vi 220 kV Bus Post Insulators aluminium pipes and disc insulators of jack bus on MV side. were also burnt due to fire, vii One of the tertiary bushings was removed in front of the CEA team and tank was inspected. through that opening No visible damage to tertiary terminals was observed. viii Tertiary of transformer is unloaded All three terminals of tertiary winding have been. brought outside the tank and terminals were not insulated. ix The event logger data indicates that the fault current level was 44 827 kA 400 kV side. main breaker and tie breaker had opened within 53 ms and 57 ms respectively of operation of. differential relay, x The event logger data also indicates operation of Differential relay and PRV Buchholz. which might have led to operation of Nitrogen Injection Fire Protection System. xi It was informed by DTL representative that High Velocity Water Spray HVWS System. had operated however it could not quench the fire of bushings It appears that water mist from. water spray system could not provide sufficient cooling effect around transformer tank. bushings due to wind and thus HVWS system was not able to extinguish fire. xii It was informed by DTL that surge counter of 220 kV R phase surge arrester was not. functional and it was bypassed through a cable, xiii Common earthing pit was provided for all three SAs R Y B phases on 220 kV side. Earthing electrode was not visible in any of the earth pits for transformer neutral and SAs on. 400 kV 220 kV side, xiv It was observed that the high resistive gravels spread over the earthmat in the switchyard.
area was covered with grasses in many areas of the switchyard defeating the very purpose of. spreading of gravels,R Probable cause of failure, Operation of Differential relay along with operation of Buchholz OSR OLTC Buchholz. PRV relays indicates fault inside the transformer Operation of REF indicates that fault. involves ground The flow of heavy fault current in windings might have led to rise in winding. temperature and operation of WTI Trip, High energy arcing due to fault inside the transformer tank might have led to sudden pressure. rise in tank and tripping of Buchholz PRV PRV being a slow operating device might not. have been able to bring down the gas pressure inside the tank to safe value and high rate of. rise of gas pressure might have resulted in cracks at weak areas of the transformer tank. It was informed by DTL staff that at first fire was noticed on Y phase MV bushing only and. later on it spread to other accessories and equipment It is possible that damage to insulation. of Y phase MV winding might have taken place This is also supported by event logger data. showing 44 kA fault current in Y phase, Buchholz relay OSR of OLTC of Y B phase had operated indicating oil surge in respective. OLTCs which might be due to fault in regulating tap windings. 3 Failure of 100 MVA 220 66 33 11 kV Power Transformer at 220kV Pappankalan I. Substation of Delhi Transco Ltd DTL, A Name of Substation 220kV Pappankalan I Substation. B Utility Owner of substation DTL,C Faulty Equipment Power transformer.
D Rating 100 MVA 220 66 33 11 kV,E Make EMCO,F Sr No HT 1644 12460. G Year of manufacturing 2006,H Year of commissioning 2006 30 04 06. I Date and time of 04 09 16 at 0635 hrs,occurrence discovery of fault. J Information received in CEA 07 09 16,K Fault discovered during Operation. L Present condition of EMCO recommended to send the failed transformer. equipment to their works for further assessment The transformer. is to be repaired by OEM,M Details of previous,maintenance.
N Details of previous failure No previous failures. O Sequence of events On 04 09 16 at 0635 hrs the transformer tripped on. Description of failure differential relay Buchholz relay PRD and SPRV. On inspection it was found that flange plates of all. three phases of HV and MV windings were cracked,and oil was leaking. 2 Failure of 315 MVA 400 220 33 kV Auto transformer at 400 kV Bawana substation of DTL A Name of Substation 400 kV Bawana substation B Utility Owner of substation DTL C Faulty Equipment Auto transformer D Rating 315 MVA 400 220 33 kV E Make EMCO F Sr No HT 1798 G Year of manufacturing 2009

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