ACCESSION #: 9401130254
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
All holders of operating licenses or construction permits for nuclear
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
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.
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
an electrical scheme that does not require the X-relay.
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
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
Frederick H. Burrows, NRR
1. Figure 1, X-Relay Magnetic Core
2. List of Recently Issued NRC Information Notices
IN 93-85, Rev. 1
Page 1 of 1
Figure 1 "X-relay Magnetic Core" omitted.
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
Steam Generator Tubes for pressurized water
with Kinetically Welded reactors (PWRs).
Circuit Sockets with licensed operators.
94-03 Deficiencies Identified
during Service Water System for nuclear power reactors.
94-02 Inoperability of General
Electric Magne-Blast for nuclear power reactors.
Breaker Because of Mis-
alignment of Close-Latch
Caused by Torsional for nuclear power reactors.
Excitation from Electrical
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.
93-99 Undervoltage Relay and
Thermal Overload Setpoint for nuclear power reactors.
OL = Operating License
CP = Construction Permit
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