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April 15 and May 15, 2003 ERCOT System Disturbances

April 15 and May 15, 2003 ERCOT System Disturbances. ERCOT TAC Meeting June 4, 2003. April 15, 2003 Bryan-College Station Voltage Collapse. What Happened?.

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April 15 and May 15, 2003 ERCOT System Disturbances

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  1. April 15 and May 15, 2003 ERCOT System Disturbances ERCOT TAC Meeting June 4, 2003

  2. April 15, 2003Bryan-College Station Voltage Collapse

  3. What Happened? • At 11:39 CenterPoint Energy took an ERCOT approved planned outage of the Roans Prairie to Kuykendall 345KV line to accommodate highway department work • When breakers at Roans Prairie and Kuykendall opened, clearing the line, breakers controlling the following 345 KV lines also opened: • Gibbons Creek– Roans Prairie • Gibbons Creek – O’Brien • Gibbons Creek – Twin Oak (one line) Leaving Gibbons Creek plant connected through only one breaker to Twin Oak and both buses serving the two Gibbons Creek 345/138KV autotransformers deenergized

  4. What Happened? (cont.) • With both autotransformers deenergized, there was not enough support of the load serving 138KV system in the Bryan-College Station area • Voltage collapsed in the area resulting in a blackout of approximately 212 MW of load and 63,000 people • Load in the area was completely restored in about 4 hours around 1600.

  5. Why it Happened • The deenergization of Roans Prairie to Kuykendall 345KV line caused increased flows on Roans Prairie to Gibbons Creek 345 KV line • Faulty control equipment at Gibbons Creek sensed this increased flow as a fault and also incorrectly initiated a breaker failure operation that deenergized both Gibbons Creek busses and the two autotransformers serving the Bryan - College Station area

  6. One-Line of B-CS Area

  7. What’s Been Done About It? • Faulty control equipment at Gibbons Creek has been fixed by TMPA • ERCOT is working with Garland to prevent telemetry failures that happened during the event from reoccurring • The System Protection Working Group of the Reliability and Operations Subcommittee of TAC is investigating to see if additional follow-up is needed

  8. May 15, 2003Under-Frequency Firm Load Shedding

  9. What Happened? • At about 2:54 a.m. an insulator flashed on the Comanche Peak – Parker 345 KV line, probably due to lightning • Primary protective relaying at Comanche Peak did not respond • Back-up protective relaying at Comanche Peak also failed to respond • Breaker failure relaying at each substation connected to Comanche Peak tripped all 345 KV lines connected to Comanche Peak

  10. What Happened? (cont.) • With loss of lines out of the plant, both Comanche Peak units were tripped (total 2275 MW) • A number of other units in ERCOT (total 1146 MW) tripped a few seconds afterward and another large unit (775 MW) tripped about 43 seconds later • ERCOT frequency got down to 59.26 Hz • 471 MW of High-set Underfrequency load providing Responsive Reserve tripped at 59.7 Hz • The first stage of underfrequency firm load shedding representing 5% of ERCOT load (~1549 MW) tripped at 59.3 Hz • Frequency returned to normal in about 12 minutes • All firm load restored by 6:30 am

  11. ERCOT Frequency

  12. Going Forward • Bad News – It happened - It happened at 3:00 am • Good News – It happened at 3:00 am - A successful real test of firm underfrequency load shedding • Further Action • ERCOT and System Protection Working Group will get details of relay failure and follow up • ERCOT will determine why generation other than Comanche Peak tripped and what might be done to avoid in future

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