ENS 46633
ENS Event | |
|---|---|
03:01 Feb 22, 2011 | |
| Title | Auto Start and Load of Edgs on Units 1&3 Following Loss of Start-Up Transformer |
| Event Description | On February 21, 2011, at approximately 2001 Mountain Standard Time (MST) a valid actuation of the Palo Verde Nuclear Generating Station Unit 1 Train 'B' Emergency Diesel Generator (EDG) and Unit 3 Train 'A' Emergency Diesel Generator occurred as a result of undervoltage on their respective safety buses. Both EDGs started and loaded as designed to energize the respective safety buses. No Emergency Plan declaration was made and none was required.
The loss of power to the Unit 1 and Unit 3 safety buses was the result of protective relay actuations on the A-E-NANX02 Startup Transformer which deenergized the transformer and the Unit 1 13.8KV Intermediate Bus 1-E-NAN-S06 and the Unit 3 13.8KV Intermediate Bus 3-E-NAN-SOS. The affected intermediate buses provide power to the Unit 1 safety bus 1-E-PBB-S04 and the Unit 3 safety bus 3-E-PBA-S03 respectively. The Auxiliary Operators responded to inspect the Startup Transformer and affected buses and determined that there was no fire or smoke and no obvious equipment damage to transformers or associated 13.8 KV Buses. At the time of the actuations, the Unit 1 Control Room received alarms for Startup Transformer A-E-NAN-X02 'Phase, Winding Ground Differential Trip'. Subsequent inspection by the Electricians identified damage to the cabling from the 'Y' winding of A-E-NAN-X02 Start-Up Transformer to the alternate supply breaker on Unit 2 Intermediate Bus 2-E-NAN-SOS. Unit 1 and Unit 3 entered Technical Specification LCO 3.8.1, Condition 'A', for one (of two) required offsite circuits inoperable. Unit 2 currently has the 'B' EDG out of service for a planned maintenance outage and the Unit 2 safety buses and required offsite circuits were unaffected by the Startup Transformer trip. Unit 2 safety buses are being supplied by Startup Transformers A-E-NAN-X01 and A-E-NAN-X03. Both Unit 1 and Unit 3 were at approximately 100% power, at normal operating temperature and pressure prior to and following the EDG actuations. No other ESF actuations occurred and none were required. No major equipment was inoperable prior to the event that contributed to the event. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant or the health and safety of the public. The NRC Resident Inspector has been notified of the ESF actuations and this ENS notification. The licensee is working to restore normal electrical power to the affected safety buses from alternate available sources on Startup Transformers X01 and X03. The licensee stated that no significant non-safety related equipment has been deenergized. The licensee noted that while the cause of the damaged cabling noted in the above report is still under investigation, water intrusion repairs were recently conducted near the location where the current damages were found.
The licensee has restored offsite power to the affected safety buses. The Unit 3 safety bus was restored from Startup Transformer X03 at 0106 MST. The Unit 1 safety bus was restored from Startup Transformer X01 at 0153 MST. The EDGs are in the process of being shutdown and reset. The LCO for required offsite power source to the buses has been exited. R4DO (Gaddy) and NRR (Brown) notified. |
| Where | |
|---|---|
Palo Verde  Arizona (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(iv)(A), System Actuation | |
| LER: | 05000528/LER-2011-001 |
| Time - Person (Reporting Time:+-0.63 h-0.0263 days <br />-0.00375 weeks <br />-8.62974e-4 months <br />) | |
| Opened: | Bradford Robinson 02:23 Feb 22, 2011 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Feb 22, 2011 |
| 46633 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Unit 3 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 570472024-03-24T23:34:00024 March 2024 23:34:00
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