Impact of Shunt Reactor Bank Switching on Transformer Neutral Geomagnetic Induced Current (GIC) Monitoring

Transcription

1 Impact of Shunt Reactor Bank Switching on Transformer Neutral Geomagnetic Induced Current (GIC) Monitoring Larry Anderson Cigre GOTF Houston, TX October 2, 24

2 2 2 Background AEP started installing GIC monitors in 22 Currently 3 EHV transformer installations are monitored with more on the way Presently most installations are on 765 kv autotransformers ( out of 3 installations) AEP utilizes switched shunt reactors at specific locations on it s EHV system to assist with voltage regulation Shortly after monitor installation large DC transients were observed at locations with switched shunt reactors on site or nearby

3 3 3 Background Cont d Initially reactor bank switching was overlooked as a source of the DC transient current Only after considering what type of transient events could produce such DC transients, were the switched shunt reactor banks investigated more closely After looking at reactor breaker closing times in relation to the DC neutral transients, it was observed that they coincided At this point it was decided to study these transients more closely to understand their true nature

4 4 4 Observed Transients Sullivan Transformer # SULLIVAN TR SULLIVAN TR 2 2. SULLIVANTZ7/X 4 2. SULLIVANTZ7/X 4 GIC AMPS AMPS.6 5. RB2 MVAR.MVAR.6-4. RB2 MVAR.MVAR DI:BREED BSRB2 4 DI:BREED BSRB2 4 CB\CLOSED\OPEN.4-6. CB\CLOSED\OPEN Breaker status /28/24 :34:9.7 days 3/28/24 :44:27 6/4/24 8:2:5.9 days 6/4/24 8:32:55 765KV TR GIC 345KV CB RB2 - REACTOR 765KV TR GIC 345KV CB RB2 - REACTOR Data from AEP s SCADA system Low sampling rate Modified by data historian (swinging door compression)

5 5 5 Observed Transients Cont d Marysville Transformer #3 MARYSVILLE TR3 MARYSVILLE TR \\scadapi\marysviltn7/x 2.5 DC AMPS \\scadapi\di:marysvilbsrb 2 CB\CLOSED\OPEN \\scadapi\di:marysvilbsrb \\scadapi\marysviltn7/x DC AMPS \\scadapi\di:marysvilbsrb 2 CB\CLOSED\OPEN \\scadapi\di:marysvilbsrb /7/24 3:7: minutes 765KV TR DC AMPS NEUTRAL 765KV CB RB 8/7/24 3:26: /8/24 2:53:5 7.7 minutes 765KV TR DC AMPS NEUTRAL 765KV CB RB Red curves are the currents recorded by GIC monitors Blue curves are reactor breaker status indicates open, indicates closed 8/8/24 22::55

6 6 6 Reactor Bank Switching Transients

7 7 7 Reactor Bank Switching Transients Cont d (a) Current, A Current, A Current, A Time, sec (b) Time, sec (c) Time, sec Current calculated with equation () on previous slide Reactor switching response is similar to system fault response DC offset keeps the current just after switching the same as the current just prior to switching AC current rides on top of DC offset

8 Single Line Diagram of System Under Study 8 8

9 9 9 PSCAD Model and Simulations 5ROCKPT VRPT RPT N24329 RPT Rpt - Jeff Rpt - Sull 5JEFRSO VJEFF JEFF N SULLVA VSULL SULL N2432 TR H Sullivan TR TR2 L H TR Sullivan TR2 5SULVN 5BREED VSULL VBREED E Ideal (R=) N24765 E_24765_24323_Z N24323 L TR2 5SULVN2 VSULL2 E Ideal (R=) E_24323_24766_Z2 N24766 E_24323_34689_ + RES 7CASEY N34689 E_24323_24326_ E_24323_24326_ E_24323_24326_ E_24323_24327_ E_24323_24327_ E_24323_24327_ E_24323_254539_ E_24323_254539_ E_24323_254539_ 25 MVAR Breed Reactor [H] 5DARWIN N DEQUIN N WHEAT N The system was modeled in detail at least one bus away from the Sullivan 765 kv and Breed 345 kv buses The breaker used to switch the reactor was modeled with a pole closing span of 4.6 ms All transmission lines utilized full frequency dependent models Impact of breaker, pointon-wave closing time was investigated Impact of reactor resistance (X/R ratio) was investigated

10 Simulation Results Sullivan Transformer and 2 DC Neutral Current as a Function of Breed Reactor Closing Instant 25 Transformer DC Neutral Current, Amps Transformer # 2 Transformer # Peak DC neutral current is a function of the point-on-wave closing instant of the reactor breaker Peak DC neutral current in the simulations ranged from approximately 2 A into the transformers to approximately 2 A out of the transformers (approx. 4 A range) This variation was solely due to the point-on-wave closing instant of the reactor breaker Phase A Closing Instant, Sec

11 Simulation Results Cont d Sullivan Auto T DC Neutral Current for Breed Reactor Closing - Various Reactor Resistances 2 DC Current, A R =.25 Ω R =. Ω R =.5 Ω DC neutral current exhibits exponential decay typical of inductive circuits Time constant of decay is the ratio of reactor plus system inductance over reactor plus system resistance Time constants for the Sullivan system were typically in the range of seconds (approximately - seconds) Time, s

12 2 2 Conclusion Switching of inductive devices inherently produces electrical transients Seen in both the voltage and current Result in a decaying DC component in the current DC current: Is a function of the point on the voltage wave that each circuit breaker pole closes Will typically be different in each phase due 2 electrical separation Add in neutral connections of wye-grounded transformers Appear as a DC current transient to monitoring devices Effects of switched shunt reactor banks must be considered when implementing GIC monitoring on nearby transformers

13 Questions? 3 3