Alert

Due to a lapse in appropriations, the NRC has ceased normal operations. However, excepted and exempted activities necessary to maintain critical health and safety functions—as well as essential progress on designated critical activities, including those specified in Executive Order 14300—will continue, consistent with the OMB-Approved NRC Lapse Plan.

INFORMATION NOTICE 93-85, Revision 1: Problems with X-Relays in DB- and DHP-Type Circuit Breakers Manufactured by Westinghouse

ACCESSION #: 9401130254

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON , D.C. 20555-0001

January 20, 1994

NRC INFORMATION NOTICE 93-85, REVISION 1: PROBLEMS WITH X-RELAYS IN

DB- AND DHP-TYPE CIRCUIT

BREAKERS MANUFACTURED BY

WESTINGHOUSE

Addressees

All holders of operating licenses or construction permits for nuclear

power reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice revision to correct an error that identified a Westinghouse

Electric Company (Westinghouse) DHP-type relay as a DHB-type relay in the

original notice. This error occurred in the original information notice

title, Purpose and the second paragraph of the Description of

Circumstances. As in the original, the purpose of this information notice

is to alert addressees to the possible failure of the 52X-relay (X-relay)

to reset in DB- and DHP-type Westinghouse breakers, thus preventing them

from reclosing on demand. It is expected that recipients will review the

information for applicability to their facilities and consider actions,

as appropriate, to avoid similar problems. However, suggestions contained

in this information notice are not NRC requirements; therefore, no

specific action or written response is required.

Description of Circumstances

On June 27, 1993 , power to a motor control center was lost at the Haddam

Neck nuclear power plant. Connecticut Yankee Atomic Power Company, the

licensee, determined that the possible root cause for this event was a

failure of the X-relay (anti-pump relay) to reset to the de-energized

position in a Westinghouse DB-25 circuit breaker.

Previously, between July 1 and August 24, 1984 , the licensee reported

five incidents in which one DB-25 and four DHP-250 breakers failed to

close when required. All five of those failures were attributed to

malfunctions of the X-relay. The licensee believed that dirt had caused

the problem and instituted a program for cleaning the stationary and

moving cores of the relay.

On June 11, 1991 , and on January 28, 1992 , Duke Power Company reported

that, at the Oconee Nuclear Station, X-relays failed to reset and

prevented the DB-25 breakers from closing in the Keowee hydroelectric

generator field and field flashing circuitry. (The Keowee hydrostation

supplies emergency power

IN 93-85, Revision 1

January 20, 1994

Page 2 of 3

to the Oconee station.) The licensee modified the anti-pump function with

an electrical scheme that does not require the X-relay.

Discussion

The X-relay is usually denoted by the symbol 52X in the electrical

control circuit schematic diagram for the breaker. On receipt of a signal

to close the breaker, the X-relay energizes and one set of its normally

open contacts closes to enable momentary energizing of the breaker

closing coil. After the breaker closes, the same set of X-relay contacts

opens to deenergize the closing coil even though the X-relay remains

energized by the close signal. If the close signal is still present after

the breaker trips, the X-relay serves to inhibit repeated closure

attempts until the close signal is removed. Thus, it provides anti-pump

protection to the breaker by preventing repeated breaker closure attempts

when a standing closure signal exists after a breaker trips.

The armature assembly of an X-relay (see Figure 1) fits inside a brass

sleeve and is surrounded by the electromagnetic coil (different from the

breaker closing coil) of the relay. When this coil is energized, the

plunger (moving core) is drawn up towards the top cap piece (stationary

core) of the assembly and the latch arm operates the relay contacts. In

its uppermost position, an air gap is maintained between the

bullet-shaped top of the plunger and the cavity in the cap piece, with

the shoulder of the plunger mating with the lip on the cap piece. When

the coil is de-energized, the moving core is designed to fall, by

gravity, into its lowest position. The failure of the moving core to fall

to its lowest position is the possible failure mode of interest at Haddam

Neck.

Westinghouse and the licensee believe that residual magnetism associated

with continuous energization of the relay or mechanical adherence between

the two parts are probable causes for the plunger failing to fall.

Westinghouse is testing a design enhancement that uses a brass spacer

between the moving and stationary cores to create a controlled air gap.

Westinghouse plans to issue a Nuclear Safety Advisory Letter to notify

users of this problem. The licensee is evaluating a design modification

for the X-relay function in the motor control center.

IN 93-85, Revision 1

January 20, 1994

Page 3 of 3

This information notice requires no specific action or written response.

If you have any questions about the information in this notice, please

contact one of the technical contacts listed below or the appropriate

office of Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Kamalakar Naidu, NRR

(301) 504-2980

Frederick H. Burrows, NRR

(301) 504-2901

Attachments:

1. Figure 1, X-Relay Magnetic Core

2. List of Recently Issued NRC Information Notices

Attachment 1

IN 93-85, Rev. 1

January 20, 1994

Page 1 of 1

Figure 1 "X-relay Magnetic Core" omitted.

Attachment 2

IN 93-85, Rev. 1

January 20, 1994

Page 1 of 1

LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

94-05 Potential Failure of 01/19/94 All holders of OLs or CPs

Steam Generator Tubes for pressurized water

with Kinetically Welded reactors (PWRs).

Sleeves

94-04 Digital Integrated 01/14/94 All NRC licensees except

Circuit Sockets with licensed operators.

Intermittent Contact

94-03 Deficiencies Identified 01/11/94 All holders of OLs or CPs

during Service Water System for nuclear power reactors.

Operational Performance

Inspections

94-02 Inoperability of General 01/07/94 All holders of OLs or CPs

Electric Magne-Blast for nuclear power reactors.

Breaker Because of Mis-

alignment of Close-Latch

Spring

94-01 Turbine Blade Failures 01/07/94 All holders of OLs or CPs

Caused by Torsional for nuclear power reactors.

Excitation from Electrical

System Disturbance

93-101 Jet Pump Hold-Down Beam 12/17/93 All holders of OLs or CPs

Failure for boiling-water reactors.

93-100 Reporting Requirements 12/22/93 All U.S. Nuclear Regulatory

for Bankruptcy Commission licensees.

91-29, Potential Deficiencies 12/22/93 All holders of OLs or CPs

Supp. 2 Found During Electrical for nuclear power reactors.

Distribution System

Functional Inspections

93-99 Undervoltage Relay and 12/21/93 All holders of OLs and CPs

Thermal Overload Setpoint for nuclear power reactors.

Problems

OL = Operating License

CP = Construction Permit

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