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May 15 th Unit Trips

May 15 th Unit Trips. 8 plants tripped offline during or shortly after the transmission fault and misoperation events.

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May 15 th Unit Trips

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  1. May 15th Unit Trips • 8 plants tripped offline during or shortly after the transmission fault and misoperation events. • ERCOT Operations and Compliance have contacted the QSEs or PGCs to identify cause of the trips, whether they were avoidable, and corrective actions. Results are summarized on the following slides.

  2. May 15th Unit Trips and Follow up • Units A & B breakers tripped correctly following mis-operation of protective relaying to a ground fault. • Unit C tripped in response to over speed protection. The QSE has determined that this function should not have activated. They have investigated and found other plants in their portfolio that have the same configuration. These have been corrected.

  3. May 15th continued • Unit D was manually tripped 43 seconds after the event. It was determined that the “Frequency Abnormal Condition” screen remained displayed to the Operator even after the event returned to normal causing the Operator to act on incorrect information. Corrective action was taken including revising the display and additional Operator training.

  4. May 15th continued • Unit E tripped due to a coordination problem related to the mis-operation of both relaying carriers at Comanche Peak. Unit E tripped 3 seconds after the start of the event. Corrective action includes replacing transmission breaker directional ground relays at the plant substation and issuing new settings that will coordinate with existing generation protective ground relaying.

  5. May 15th continued • Unit F was tripped approximately 8 minutes into the event due to a high drum level. Operator was unable to intervene quickly enough as the unit responded to the frequency drop. • Unit G tripped in response to a low frequency relay operation at 59.4 hertz. The plant hired a consultant to review settings shortly after the incident. The relay for Unit G and other units at the same facility are being re-set to meet ERCOT Operating Guide recommendations. • Unit H tripped due to high temperature in the turbine exhaust stream. The cause was determined to be related to the combustion controls for the unit. The combustion controls have been re-tuned.

  6. May 15th continued • The cause of each unit’s trip appears to be well understood • Corrective actions have been identified and steps taken where possible to prevent recurrence • Reviews have been extended to include other plants that did not trip, but have similar controls • DOES ROS FEEL THAT ADDITIONAL INPUT IS NEEDED FROM ANY OF THESE PLANTS AT THE NOVEMBER MEETING?

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