ML19308B105

Abnormal Occurrence AO-269/74-03:on 740210,during electro- Mechanical Relay Breaker Trip Test,Startup Transformer CT-1 & Redundant Power Supply CT-2 Were Locked Out by Differential Relay.Caused by Inadequate Procedures

ML19308B105
Person / Time
Site:	Oconee
Issue date:	02/22/1974
From:	DUKE POWER CO.
To:
Shared Package
ML19308B100	List: ML19308B099 ML19308B105
References
NUDOCS 7912120828
Download: ML19308B105 (3)

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DUKE POWER COMPANY OCONEE NUCLEAR STATION l

Report Number: A0-269/74-3 Report Date: February 22, 1974 Occurrence Date: February 10, 1974 Facility: Oconee Unit 1 Identification of Occurrence: Lockout of Startup Transformers Condition Prior to Occurrence: Steady-State Operation at 100 Percent Power Description of Occurrence:

On February 10, 1974, Oconee Unit 1 was operating at 100 percent full power l and Oconee Unit 2 was at cold shutdown for maintenance. Oconee operators were performing Electromechanical Relay Breaker Trip Test, PI/1&2/B/610/5B.

The testing of PCB-18 (startup transformer switchyard circuit breaker) required that Startup Transformer CT-1 not be in service and that a redundant power supply (CT-2) be connected to Unit 1. The redundant power supply was connected by closing the normally open disconnects 1, 2, 3, and 4 as noted on the enclosed electrical system drawing. It was then necessary to open CT-1 switchyard disconnects (PCB-17 and PCB-18) to isolate CT-1. When PCB-18 was opened, this removed power from the high side j

of CT-1. CT-1 was then backcharged through the 6.9 KV winding from CT-2. i The startup bus differential relay picked up, initiating the lockout of CT-2. ,

In a similar manner, CT-1 was also locked out by the differential relay. I Both Keowee hydro units then started automatically and closed into the standby bus and the main feeder bus.

Regulatory Operations, Region II, was verbally notified of the occurrence on February 11, 1974.

Designation of Apparent Cause of Occurrence:

Oconee Technical Specification 3.7 requires that two startup transformers shall be operable and available to the unit's 4160 volt Main Feeder Buses No. 1 and No. 2, except that one of the two startup transformers may be removed from service for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> for maintenance.

The occurrence resulted because Periodic Test Procedure PT/l&2/B/610/5B incorrectly called for a sequence of steps that resulted in the electrical system protective relays locking out CT-1 and CT-2.

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Analysis of Occurrence: l l

l The occurrence resulted in the loss of availability of startup transformers CT-1 and CT-2 for approximately ten minutes. No safety problem resulted since Unit 1 was operating at power and Unit 2 was at cold shutdown. Had i Unit 1 required an alternate power source during this time, other redundant l sources were available, including both Keowee hydro units through the under-ground feeder and the Lee gas turbines through the 100 KV circuit. Because of system redundancy and the short period of unavailability, it is concluded the occurrence did not adversely affect the safe operation of the unit or l the health and safety of the public. I Corrective Action:

Periodic test procedure PT/1&2/B/610/5B will be revised to prevent a similar occurrence. j 1

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