ML18079A632

Discusses Significant Deficiency Re 4 Kv Vital Bus Differential Protection Caused by Relay Plunger Mechanism Which Is Susceptible to Seismic Vibration.Spurious Relay Operation Could Cause Loss of All 4 Kv Buses

ML18079A632
Person / Time
Site:	Salem
Issue date:	05/02/1979
From:	Martin T Public Service Enterprise Group
To:	Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML18079A631	List: ML18079A630 ML18079A632
References
NUDOCS 7907300571
Download: ML18079A632 (3)

Text

Thomas J. Martin Public Service Electric and Gas Company 80 Park Place Newark, N.J. 07101 201/430-8316 Vice President Engineering and Construction Mr. Boyce H. Grier, Director U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region l 631 Park Avenue King of Prussia, Pennsylvania 19406

Dear Mr. Grier:

May 2, 1979 4 K:V VITAL BUS DIFFERENTIAL PROTECTION 10CFR5 0. 5 5 ( e) "SIGNIFICANT. DEFICIENCY 11 NO. 2 UNIT SALEM GENERATING STATION On Ap~il 11, 1979 a verbal report was made to Region l, Office of Inspection and Enforcement representative Mr. S. Folsom, advising that a potential deficiency existed relative to General Electric l2PVD11C relays which could be susceptible to misopera-tion under conditions of a design basis earthquake.

This report was provided in accordance with the provisions of 10CFR50.55(e).

The following supplemental information is hereby submitted pur-suant to our initial report and in accordance with the require-ments of 10CFR50.55(e):

1.

Background Information Protection of the 4 KV Vital Buses against faults and transients is provided by a number of protective relays performing various functions.

The philosophy of bus protection utilizes an in-depth approach of overlapping and backup protective relay functions.

All safety-related.protective relays are required to withstand a seismic disturbance without misoperation causing a degrada-tion of plant safety.

Appropriate seismic qualification docu-mentation for the 4 KV Vital Bus Switchgear (GE 5 KV Model Switchgear) and protective relays was provided.

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Mr. B. 5/2/79 The NRC Seismic Qualification Review "T.eam reviewed thi~

documentation as part of their audit of Salem and reqµested that the report be augmented with additional data of the type recommended by IEEE Standard 501-1978, "Seismic Testing of Relays."

PSE&G requested General Electric to perform an analysis and/ or te.sting as required to generate this addi-tional. information for the relays in question and all safety-.related p_rotective relays mounted in the switchgear.

2~ Description of Deficiency In. preparing additional seismic quali.fication data. for PSE&G, General Electric used actual seismic test data. (obtained sub-sequent to the original report prepared for Salem) to develop required response spectra (RRS) for prot~ctive relays used in their 5 KV Switchgear at Salem.

The GE-developed RRS is more conservative than the Salem RRS.

However, a revie~ of the available test data. based on the GE RRS indicated that the GE 12PVDflC style relay is susceptible to misoper*tion.

All oth~r protective relay data is acceptable.

This particular rela7 is utilized for mo~itoring differential c~rrent dn the 4 KV Vital Buses.

A signal from the bus differ-ential relay initiates a multitrip which isolates the bus from offsit~ power and the diesel generators.

Misoperation of this relay during a seismic disturbance would result in isolation of the bus from its preferred power source and its emergency power source.

Each vital bus incorporates three 12PV'D.11C relays for differential protection.

The failure mode would be common to all three vital buses.

This condition is a degra-dation of the safety systems in that.the power sources for the engineered safeguards would not operate in accordance with design criteria *.

3.

Cause of Deficiency This particular relay design incorporates a plunger-type mechanism which is susceptible to seismic vibration causing spurious.operation of the relay.

4.

~ffects on Safety At least two of the three vital buses are required to maintain minimum engineered safeguards and safe plant conditions.

The spurious operation of the 12PVDllC relays could cause the total loss of all 4 KV Vital Buses, thereby compromising plant *safety.

The restoration of power to the vital buses can be accomplished subsequent to the reset of the multitrips and closure of the

Mr

• B. H

• Grier 5/2/79.

infeed breakers or the diesel generator ~reaker following the seismic event.

However, the loss of power during an earthquake could place the plant in a compromised condition until. power could be restored.

The present differential relays may cause spurious trips at Salem.

The Salem RRS

~s less than the RRS under which the misoperation of the 12PVDllC was determined.

PSE&G has elected to replace this.particular relay with a new style relay in the interests of a conservatively safe design.:

5.

Corrective Action The immediate corrective action will delete the 4 KV Vital Bus Differential Relays from the tripping circuits to. pre-vent spurious tri.;ps and subsequent loss of power during an earthquake..

Vital bus protection against bus faults is pro-vided by the overcurrent protective relays.

The overcurrent relays meet applicable seismic requirements.

In order to reinstate bus differential protection, new protecti~e relays will be installed.

-~he new relays will be GE 12PVD2l style relays which are equivalent re.lays and which meet all applicable seismic requirements.

r

6.

Schedule for Implementation A des*ign change (EC-523) has been initiated to accomplish the above-noted corrective action.

The installation of the new relays will be accomplished prior to core load of Unit 2.

Very truly yours,*