ENS 40565
ENS Event | |
|---|---|
18:45 Mar 3, 2004 | |
| Title | Swing Diesel Generator Auto Started from a Bus Undervoltage Valid Signal |
| Event Description | At the time of this occurrence Unit 1 is in a scheduled Refueling Outage and Unit 2 is at 100% Maximum Operating Power. Also note, the 1 B Diesel Generator is a Swing Diesel Generator which is capable of supplying Unit 1 1F 4160 Volt bus and also when required 2F 4160 Volt bus.
At 13:45 EST on 03/03/04, the 1B Diesel Generator auto started due to a momentary Bus Undervoltage sensed on the 1F 4160 volt bus. At the time of the occurrence the 1F 4160 Volt bus was energized with the Normal Supply Breaker racked out and the Alternate Supply Breaker closed in and supplying the 1F 4160 Volt bus. The Normal Supply Breaker was racked out for a scheduled breaker replacement. At the time of the occurrence 2 electricians were removing the Racked Out Normal Supply breaker from the cubicle. The breaker shutter mechanism (a component of the breaker) fell off of the breaker inside the cubicle causing the 1F 4160 Volt bus to sense a momentary bus undervoltage, the Alternate Supply breaker momentarily cycled open and re-closed causing the 1B Diesel Generator to auto start. Since the 1 B Diesel Generator auto started from a valid signal (Bus Undervoltage) an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> report is being made. At the time of this report the 1B Diesel Generator has been Shutdown and restored to a standby Lineup. The 1B Diesel Generator remains Operable. The licensee notified the NRC Resident Inspector.
Subsequent investigation revealed the most probable cause of this event was the trip of the alternate supply breaker to the emergency bus, resulting in its momentary de-energization and an automatic start of the diesel generator on an actual bus undervoltage signal. The alternate supply breaker apparently tripped as a result of the shutter in the formal supply breaker cubicle falling against the fingers of the breaker when as the breaker was being removed from the breaker cubicle. The affected breaker was already n the racked out position. When the breaker was moved to allow its removal from the cubicle, the shutter was apparently forced upward by the movement of the breaker musing the shutter to move upward and the shutter actuating lever to pivot downward until the moc switch mechanism actuated the logic causing the alternate supply breaker to -rip and the diesel generator to start. The shutter actuating lever became separated from the shutter allowing the moc switch to return to its expected open position thereby allowing the alternate supply breaker to recluse and provide power to the bus before the swing diesel generator had sufficient permissives to tie to the bus. Even with the condition found in this breaker cubicle the breaker can be safely racked out. It is when the breaker is removed from the cubicle that there is an increased potential for the shutter and its connected lever arm to cause a logic actuation similar to that experienced in this event. The condition does not create an operability concern for the bus and at most could cause a logic actuation in the conservative direction and does not present any known operability issues for the associated 4160 volt buses. Additional inspections have been performed on 6 balance of plant 4160 volt breakers that are identical in design with acceptable clearances observed in the locations where problems were noted in the subject breaker cubicle. The normal supply breaker for the 1F 4160V bus has been inspected with no problems noted. The associated shutter and lever mechanisms for this breaker have been inspected, components replaced and the breaker returned to service. The alternate supply breaker on the safety related 4160 volt switchgear that was involved in this event was also checked and found to have acceptable clearances and no problems noted with the shutter mechanism. At this point this condition is limited to the breaker cubicle that is the subject of this notification based on extent of condition review performed up this point. There are currently no operability concerns for the affected 4160 volt switchgear or associated diesel generator. Notified R2DO (R. HAAG). |
| Where | |
|---|---|
Hatch  Georgia (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(iv)(A), System Actuation | |
| Time - Person (Reporting Time:+-1.73 h-0.0721 days <br />-0.0103 weeks <br />-0.00237 months <br />) | |
| Opened: | Greg Johnson 17:01 Mar 3, 2004 |
| NRC Officer: | Arlon Costa |
| Last Updated: | Mar 5, 2004 |
| 40565 - NRC Website
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WEEKMONTHYEARENS 573432024-09-27T07:46:00027 September 2024 07:46:00
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