ACCESSION #: 9401130254
UNITED
STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
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
Neck nuclear power plant.
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
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
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
Page 2 of 3
to the
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
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
Page 1 of 1
Figure 1 "X-relay Magnetic Core" omitted.
Attachment 2
IN 93-85, Rev. 1
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
Steam
Generator Tubes for pressurized water
with Kinetically Welded reactors (PWRs).
Sleeves
94-04 Digital
Integrated
Circuit
Sockets with licensed
operators.
Intermittent Contact
94-03 Deficiencies Identified
during Service Water System for nuclear power reactors.
Operational
Performance
Inspections
94-02 Inoperability of General
Electric Magne-Blast for nuclear power reactors.
Breaker
Because of Mis-
alignment of Close-Latch
Spring
94-01 Turbine
Blade Failures
Caused by Torsional for nuclear power reactors.
Excitation
from Electrical
System
Disturbance
93-101 Jet Pump Hold-Down Beam
Failure for boiling-water reactors.
93-100 Reporting Requirements
for Bankruptcy Commission licensees.
91-29, Potential Deficiencies
Supp. 2 Found During Electrical for nuclear power reactors.
Distribution System
Functional
Inspections
93-99 Undervoltage Relay and
Thermal
Overload Setpoint for nuclear power reactors.
Problems
OL = Operating License
CP = Construction Permit
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