|Reporting criterion:||10 CFR 50.73(a)(2)(iv)(A), System Actuation|
|2472003003R00 - NRC Website|
FACILITY NAME (1)
- 1 DOCKET
- 2 PLANT AND SYSTEM IDENTIFICATION
- 3 EVENT IDENTIFICATION
- 4 EVENT DATE
- 5 REFERENCE
- 6 PAST SIMILAR EVENTS
- 7 EVENT DESCRIPTION
- 8 DOCKET
- 9 SEQUENT
- 10 IAL
- 11 MHPARPP
- 12 REOSI
- 13 ON
- 14 EVENT ANALYSIS
- 15 EVENT SAFETY SIGNIFICANCE
- 16 DOCKET
- 17 SEQUENT
- 18 IAL
- 19 NI URPP
- 20 ON
- 21 CORRECTIVE ACTION
- 22 PREVIOUS OCCURRENCES
l) I SEOUENT REVISI IAL � ON � NI IKARFP � 'hoe us aor LER NUMBER (6
PLANT AND SYSTEM IDENTIFICATION
Westinghouse 4-Loop Pressurized Water Reactor
April 28, 2003
Condition Reporting System Number: 200302511
PAST SIMILAR EVENTS
Licensee Event Report Number: 2001-007-00 Licensee Event Report Number: 1997-018-00
On April 28, 2003 at1648 hours
The auto stop oil turbine trip was caused by a trip of the over frequency relays actuated by a disturbance associated with the 345kV North Ring Bus at the Buchanan Substation and the Consolidated Edison 138kV system. This disturbance was caused by a Phase A ground fault on 345kV transmission line Y94. Following the grid disturbance breakers 11 and 7 opened at the Buchanan Substation followed by a Phase A ground fault on 138kV breaker F7. When Consolidated Edison attempted to re-energize line Y94 by closing breaker 11 a CEYB (General Electric type) relay malfunction occurred causing output breaker 9 to open resulting in a turbine trip.
The resultant trip placed the plant in natural circulation with 480-volt buses 2A and 3A de-energized as per design. All three Emergency Diesel Generators (EDGs) started and buses 2A and 3A were manually energized by 22 EDG, this was an expected response. 480-volt buses 5A and 6A remained energized from off-site sources during this event. No steam generator or pressurizer safety valves lifted and actuation of the Safety Injection System was not required. No radioactive release to the environment occurred as a result of this transient.
This event is reportable in accordance with 10CFR50.73(a)(2)(iv)(A) which requires a Licensee Event Report (LER) for any event that resulted in manual or automatic actuation of the Reactor Protection System (RPS) including: reactor scram or reactor trip.
EVENT SAFETY SIGNIFICANCE
This event was initiated as a result of a grid disturbance on the North 345kV ring bus at the Buchanan switchyard. This is an expected plant response due to the actuation of the over-frequency protection circuit:
These relays were added as part of a plant modification after a similar event in July 1997 resulted in a 100% load reject. Since this event is bounded by section 14.1.12 (Loss of all power to the Station Auxiliaries) of the Updated Final Safety Analysis Report (UFSAR) the safety significance was determined to be minimal.
FACILITY NAME (1)
The root cause of this event was the malfunction of the CEYB relay.
This relay detected the fault in the wrong direction. The CEYB relay detected a fault on line W93 when the fault was actually on line Y94.
This malfunction caused breaker 9 to open resulting in Unit 2 tripping off line. Consolidated Edison removed the CEYB relay from the system to determine cause of malfunction. There are redundant relays in place .
monitoring the distribution system. Entergy has assigned Corrective Actions to follow up with Consolidated Edison and obtain their root cause report for the faults on the Y94 feeder and breaker F7 and the failure of the CEYB relay. The root cause report from Consolidated Edison is expected by the end of the third quarter 2003. This report will also contain Consolidated Edison's actions to prevent re- occurrence. Entergy Management has increased their involvement in the substation activities since the event. Senior levels of Entergy management have been meeting with their Consolidated Edison counterparts to ensure that appropriate actions are being taken to increase the reliability of the electrical system. Entergy has named a switchyard coordinator who is responsible for the interface between the plant and Consolidated Edison.
Similar events occurred December 26, 2001 and July 26, 1997 and are documented in LER 2001-007-00 and LER 1997-018-00. The root cause of the December 2001 event was the failure of a blocking relay on Consolidated Edison's 345kV line Y94. The root cause of the July 1997 event was malfunction of a directional relay device associated with transformer TA5. As a result of the July 1997 event, over-frequency relays were added to the overall unit protection scheme. The over- frequency relays actuated as per design for the December 26, 2001 event.