05000346/LER-1981-008-03, /03L-0:on 810127,345 Kv Switchyard Bus K Tripped & Locked out,de-energizing Startup Transformer 02.Caused by Action from Directional Ground Current Relay & Charred Phase Lightning Arrestor C on Startup Transformer

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/03L-0:on 810127,345 Kv Switchyard Bus K Tripped & Locked out,de-energizing Startup Transformer 02.Caused by Action from Directional Ground Current Relay & Charred Phase Lightning Arrestor C on Startup Transformer
ML19341C614
Person / Time
Site: Davis Besse 
Issue date: 02/26/1981
From: Matheny D
TOLEDO EDISON CO.
To:
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19341C607 List:
References
LER-81-008-03L, LER-81-8-3L, NUDOCS 8103030834
Download: ML19341C614 (3)
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LER-1981-008, /03L-0:on 810127,345 Kv Switchyard Bus K Tripped & Locked out,de-energizing Startup Transformer 02.Caused by Action from Directional Ground Current Relay & Charred Phase Lightning Arrestor C on Startup Transformer
Event date:
Report date:
3461981008R03 - NRC Website
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DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-81-08 DATE OF EVENT: January 27, 1981 and February 1, 1981 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:

Loss of Startup Transformer #02 in Mode 5 and Loss of Startup Transformer #01 in Mode 3 Conditiona Prior to Occurrence: The unit was in Mc3e 5 with Power (MRT) = 0 and Load (Gross MWC) = 0.

Description of Occurrence: On January 27, 1981 at 2222 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.45471e-4 months <br />, 345 KV switchyard bus K tripped and Jocked out, de-energizing Startup Transforer 02 and causing the station 13.8 KV bus being powered by Startup Transformer 02 to fast transfer to Startup Transformer C10 Being in Mode 5 the station did not enter the action statement of Technical Speci-fication 3.8.1.2 which requires the operability of only one circuit between the of fsite transmission network and the onsite Class lE distribution system. These requirements were being met.

On February 1, 1981 at 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br />, a very similar instance occurred in which "J" bus tripped and locked out, de-energizing Startup Transformer 01 and causing the station

1. O KV bus A to fast transfer to Startup Transformer 02.

Being in Mode 3, the station entered the action statement of Technical Specification 3.8.1.1 which requires the opera-bility of two independent circuits between the offsite transmission network and the onsite Class lE distribution system. The action statement requires that within one hour the correct breaker alignments and indicated power availability be verified. This must be re-verified every eight hours thereafter until both circuits are restored to operable status. These requirements were met.

Designation of Apparent Cause of Occurrence:

Investigation by maintenance personnel revealed that the K bus trip had occurred due to action from a directional ground currnnt relay and that the "C" phase lightning arrester on Startup Transformer 02 appeared charred.

Subsequent testing verified that the lightning arrester was in fact damaged and shorted.

This could have been caused by an internal failure or from being struck by a bolt of lightning or electrical surge.

In the cause of the Startup Transformer 01 trip, testing determined that the "B" phase lightning arrester had faulted. There was no visible evidence of the fault.

It should be noted here that the weather was similar at the time of both occurrences.

In both instances the weather was snowy and wet.

Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel.

In both cases there was an automatic transfer of loads to the operabic startup transformer.

LER #81-008

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r TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-81-08 PACE 2

Corrective Action

Under Maintenance Work Order (IMO) 81-1400 the failed lightning arrester on Startup Transformer 02 was removed. The 02 Transformer was returned to service at 2331 hours0.027 days <br />0.648 hours <br />0.00385 weeks <br />8.869455e-4 months <br /> on January 28, 1981 without the lightning arrester.

Under MWO 81-1426, the failed lightning arrester on Transformer 01 was removed, and the transformer was returned to service at 1920 hours0.0222 days <br />0.533 hours <br />0.00317 weeks <br />7.3056e-4 months <br /> on February 1, 1981.

These actions were taken pending receipt of replacement parts.

Installation of new lightning arresters was done under Facility Change Request 81-050.

On February 7, 1981 the 02 Transformer was removed from service to install new lightning arresters. The work was completed and 02 again returned to service at 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> on February 7, 1981. On February 8, 1981, the 01 Transformer was removed from service to install new lightning arresters.

The work was completed and 01 again i

returned to service at 1540 hours0.0178 days <br />0.428 hours <br />0.00255 weeks <br />5.8597e-4 months <br /> on February 8, 1981.

Failure Data: There have been no previous similar occurrences.

LER #81-008 t

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