Transient Recovery Voltage at Transformer Limited Fault Clearing

Transcription

1 Transient Recovery Voltage at Transformer Limited Fault Clearing H. Kagawa (Tokyo Electric power Company, Japan) A. Janssen (Liander N.V., the Netherlands) D. Dufounet (Consultant, France) H. Kajino, H. Ito (Mitsubishi Electric Corporation, Japan) 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 1

2 Contents 1. Background and Introduction 2. TRV for Transformer limited fault (TLF) Voltage drop across the TLF First-pole-to-clear factors for TLF conditions TRV for TLF conditions 3. Transformer models 4. Detailes manufacture transformer models 5. Conclusions 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 2

3 Background and Introduction Severe Transient Recovery Voltage (TRV) after the current interruption may appear when a fault occurs in the immediate vicinity of a power transformer. These faults are called Transformer Limited Fault (TLF). Kaf: Amplitude factor of TRV, Kaf=Uc/Ep Uc: TRV peak, Ep: voltage peak TRV for TLF conditions TLF may cause higher Rate-of-Rise of TRV (RRRV) than the standard values specified for terminal fault test duties T1 and T3 of IEC and IEEE standard C37.6. TRV parameters, that include the voltage drop across the transformer, the 1st/2nd/3rd pole-to-clear-factors, the amplitude factor, the rate of rise of recovery voltage have been investigated. 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada IUc Ep V 3

4 TRV for TLF HV side CB1 LV side CB2 HV side CB1 LV side CB2 Open Transformer Open Transformer HV side CB1 LV side CB2 HV side CB1 LV side CB2 Transformer Open Transformer secondary faults(tsf) Transformer Open Transformer fed faults(tff) Transformer Limited faults(tlf) The TRV frequency is generally determined by the inductance and the equivalent surge capacitance of the transformer. In such cases, the Rate-of-Rise of TRV (RRRV) may exceed the values specified in the standards for terminal fault test duties T1 and T CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 4

5 Voltage drop across the transformer Voltage drop ratio of transformer(p.u) UHV primary (1kV) UHV Secondary (5kV) 5kV Primary (5kV) 5kV Secondary (275kV) 275kV Primary (275kV) Voltage drop ratio of transformer in TLF short-circuit current is determined by the back impedance and the impedance of transformer. In the IEC Standard, the voltage drop ratio is.9 in the voltage range from 1 to 8 kv. Japan These values can be given by the ratio of the system impedance to the impedance of transformer. The voltage drops across the transformers are confirmed almost less than CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 5

6 Pole-to-clear factor[pu] Pole-to-clear factor[pu] First-pole-to-clear factors(kpp) for TLF conditions (1) Third-pole-to-clear factor: Ktp Second-pole-to-clear factor: Ksp First-pole-to-clear factor: Kpp Third-pole-to-clear factor: Ktp Second-pole-to-clear factor: Ksp First-pole-to-clear factor: Kpp Kpp< Kpp< kV/275kV/63kV-15MVA trans. 525kV/242kV/22kV-1MVA trans. 15kV/525kV/147kV-3MVA trans. 7kV/3kV/11.9kV-165MVA trans. 7kV/3kV/11.9kV-51MVA trans X/X1 [pu] Primary side 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada kV/242kV/22kV-1MVA trans. 525kV/275kV/63kV-15MVA trans. 7kV/3kV/11.9kV-51MVA trans. 15kV/525kV/147kV-3MVA trans. 7kV/3kV/11.9kV-165MVA trans X/X1 [pu] Secondary side Typical calculated values of kpp by symmetrical coordinate methods using positive and zero-sequence impedance values for various power transformer used in different projects of the rated voltages from 55kV to 11 kv. Those transformers have a delta connection for a tertiary winding. 6

7 Pole-to-clear factor[pu] Pole-to-clear factor[pu] First-pole-to-clear factors(kpp) for TLF conditions (2) Third-pole-to-clear factor: Ktp Second-pole-to-clear factor: Ksp First-pole-to-clear factor: Kpp Third-pole-to-clear factor: Ktp Second-pole-to-clear factor: Ksp First-pole-to-clear factor: Kpp Kpp< Kpp< kV/275kV/63kV-15MVA trans. 525kV/242kV/22kV-1MVA trans. 15kV/525kV/147kV-3MVA trans. 7kV/3kV/11.9kV-165MVA trans. 7kV/3kV/11.9kV-51MVA trans X/X1 [pu] Primary side The kpp for TLF conditions for a primary side range from 1. to 1.15 and those for a secondary side is lower than.95. The kpp specified in IEC for terminal fault T1 and T3 (i.e. 1.2 for UHV and 1.3 up to 8 kv) are certainly higher than those commonly observed in real cases for TLF conditions kV/242kV/22kV-1MVA trans. 525kV/275kV/63kV-15MVA trans. 7kV/3kV/11.9kV-51MVA trans. 15kV/525kV/147kV-3MVA trans. 7kV/3kV/11.9kV-165MVA trans X/X1 [pu] Secondary side 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 7

8 TRV for TLF conditions at primary side TRV peak RRRV TRV peak and RRRV calculated with different systems and transformer parameters. The TRV peak can be covered by the specifications in the IEC standard for all cases. The RRRV can be covered by the new recommendation for UHV ratings, but exceed the existing specifications in the IEC standard for 8 kv and 55 kv ratings. 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 8

9 TRV TLF conditions at secondary side TRV peak RRRV The RRRV at the secondary side exceeds the existing specifications in the IEC standard for 525 kv, 3 kv and 242 kv ratings. The maximum RRRV at the secondary side is calculated as 17. kv/μs for 245 kv transformers for secondary side TFF. 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 9

10 Transformer models Rated voltage Rated capacity Short-circuit Impedance (measured values, based on 15 MVA) Primary 525 kv / 3 Secondary Tertiary 275 kv / 3 63 kv Primary / Secondary 15 MVA Tertiary 45 MVA Primary - Secondary 13.8 % Primary - Tertiary 7.3 % Secondary - Tertiary 44.8 % 525kV-15 MVA shell-type three-phase transformer Frequency responses were obtained by FRA measurements with 525 kv-15 MVA shell - type power transformer. The same circuit that was used for the TRV measurements was used for the FRA measurements. 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 1

11 Transformer models(primary side) C1 R1 L1 C1=494 pf, R1=2.89kW,L1=82.1 mh Frequency (Hz) Simplified transformer model Frequency response Primary side The simplified transformer model can be obtained by the response of the FRA measurement. The L 1, C 1, and R 1 values applicable to the simplified transformer model can be evaluated from the slope of the gain and the gain at the resonant points. The impedance response evaluated with the simplified transformer model agreed with the FRA measurement as well. 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada Gain Z (db) Measurement R1=2.89kW L1=82.1 mh 26.4 db 7.9 khz=w1 C1=494 pf Calculation by simplified transformer model

12 Transformer models(secondary side) C1 R1 L1 C2 R2 L2 C1=28482 pf, R1=5.9 kw, L1=13.76 mh C2=2592 pf, R2=1.97 kw, L2= 4.2 mh Simplified transformer model Gain Z (db) Frequency (Hz) Frequency response Secondary side The result of FRA measurement has two resonant frequencies at 8.4 khz and 15.5 khz. It means that the simplified transformer model has a double stack of R-L-C parallel circuit. The impedance response evaluated with the simplified transformer model agreed with the FRA measurement as well Measurement L=L1+L2=17.96 mh L1=13.76 mh, L2= 4.2 mh R1=5.9kW R2=1.97kW 8.4 khz 14.1 db 5.89 db C=1334 pf 15.5 khz C=1/(1/C1+1/C2) C1=28482 pf C2=2592 pf Calculation by simplified transformer model CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 12

13 Voltage (V) Voltage (V) TRV reproduced by the simplified model 3 15 Measurement Calculation Measurement Calculation Time (ms) Time (ms) Primary side Secondary side The TRV calculated with the simplified transformer model compared with the measurement of the TRV by the capacitor current injection method. The calculated TRV waveforms showed good agreement with the measured TRVs. The simplified transformer model obtained the FRA measurements can reproduce the TRV waveform for TLF conditions very precisely CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 13

14 TRV reproduced with Manufacturer model CLM u L1 M2 M1 H H M1 M2 L2 U H : Series coil M : Common coil L : Tertiary coil L2 M2 M1 H H M1 M2 L1 DC source Charging resistor capacitor Switch I Diode M1 M2 U u H (CLM1) CLM (CLM2) L1 L2 Cross section of the coil Manufacture transformer model Each group has five separate coils consisting of a pair of primary (H) coils, two pair of secondary (M 1 and M 2 ) coils and two pair of tertiary (L 1 and L 2 ) coils. The capacitance from the tertiary coil to the ground is expressed as C LE, and that between the tertiary coil and secondary coil is expressed as C LM. CLM CLM CLM 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 14

15 TRV reproduced with Manufacturer model Voltage [V] Calculation Measurement Time [ms] Primary side TRV reproduced by the manufacturer model based on the transformer design shows good agreement with the measurements. TRV was also calculated with the capacitance (C LE ) which is reduced 1/1. Deformation of the TRV is caused by the capacitance between the tertiary winding and the ground. Voltage [V] CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 5-5 Calculation conditions : x 1/1, Dividing CLM(usingCLM1,CLM2) Calculation Measurement Time [ms] Secondary side 15

16 Conclusion The voltage drop across the transformers in the UHV and EHV network in Japan are confirmed almost less than.9. Kpp for TLF conditions for a primary side ranges from 1. to 1.15 and those for a secondary side ranges from.95 to 1.. TRV for TLF conditions were investigated using different system and transformer parameters. Calculation results shows RRRV exceeds the standard values for T1 and T3 for 8/5kV. TRV waveforms were reproduced by the simplified transformer model and the transformer model based on the design. Calculations results shows good agreement with the measurements. 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 16

17 Thank you for your kind Attention. 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada 17

18 First-pole-to-clear factors for TLF conditions Kpp : By symmetrical coordinate method Simplified circuit for primary fault Thevenin source E Xs1 Xs S Transformer with delta winding T P 3LG > Positive-sequence reactance Transformer Xs1 Xs Xp CB Simplified circuit for secondary fault CB 3LG S Transformer with delta winding > Positive-sequence reactance Xs Xp T P Thevenin source Xs1 Xs Xs1 E X > Zero-sequence reactance 1 p s s1 Transformer Xs Xs Xp X 1 s p s1 > Zero-sequence reactance Transformer Xs Xp Xs Xt Xt X K pp p Xt ( Xs s X ( X 3X 2X t s 1 ) ) s 216 CIGRE-IEC Colloquium, May 9-11, 216, Montréal, QC, Canada X K pp s Xt ( X p s) X ( X ) 3X 2X t p 1 s 18