Information Notice 1992-19, Misapplication of Potter and Brumfield Mdr Rotary Relays
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.
20555
March 2, 1992
MISAPPLICATION OF POTTER & BRUMFIELD MDR
ROTARY RELAYS
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 to alert addressees to failures caused by the misapplication of
Potter & Brumfield (P&B) MDR rotary relays. 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 September 11 1989, operators at the Shearon Harris Nuclear Power Plant
(Shearon Harris5 performed a periodic test of an emergency load sequencer.
When the operators pressed the "Test Stop" button, the sequencer did not
properly reset and generated an inadvertent start signal to the emergency
service water (ESW) pump. The control room operators noticed the inadvertent
start of the pump and secured it.
On June 15 1990, the licensee for the Waterford Steam Electric Station
(Waterford5 informed the NRC senior resident inspector that P&B MDR 66-4, MDR-4076, and MDR-5061 rotary latching relays had been determined to have a
high failure rate warranting a root cause analysis.
Licensees for other nuclear power plants have reported to the NRC that P&B
MDR relays have operated intermittently with failures that could not be
duplicated during subsequent testing.
These failures occurred in applications
of MDR relays for energizing equipment status indication lights, energizing
computer input and display lights, and switching low level loads.
Discussion
The Carolina Power and Light Company (CP&L), the licensee for Shearon Harris, investigated the inadvertent start of the ESW pump.
CP&L found that a P&B
MDR 137-8 relay, installed in the test circuit, failed to reset at the proper
time affd-cantinued to supply power to the equipment actuation relays longer
920225331
IN 92-19 March 2, 1992 than designed. This failure resulted in the inadvertent start of the ESW pump.
When the failed relay was inspected, CP&L found that the contacts were burned
and that the leaf spring contact had melted into the plastic armature.
CP8L
concluded that the relay's contacts had been overloaded.
In reviewing the problem, CP&L found that there is a substantial difference
between the current rating of contacts used with direct current and the rating
of contacts used with alternating current.
The circuit design for the failed
relay had been based on only the resistive loads and not the inductive loads
carried by the contacts.
This was also the case for other circuits using P&B
MDR latching relays and Agastat microswitches.
CP&L modified the circuits by
eliminating the microswitches and connecting two pairs of MDR relay contacts in
series to switch the inductive loads.
CP&L reviewed Licensee Event Reports
88-29 and 88-08, which documented similar failures at Shearon Harris, and
concluded that inductive loads in those circuits may have damaged the MDR relay
contacts and caused the relays to fail. Attachment 1 includes a discussion of
comments from. P&B on the use of relays for switching direct current loads.
Entergy Operations, Incorporated (Entergy), the licensee for Waterford, per- formed a root cause analysis of the failures of P&B rotary latching relays at
Waterford. The analysis found that the design of the electrical system used
some of the relays' own contacts to de-energize the relays' operate and reset
coils. However, minor variations in the amount of time for the contacts to
operate did not allow the relays' mechanisms to consistently reposition and
reset contacts for the next operation of the relays. Consequently, the relays
would fail in an intermediate position. The licensee subsequently implemented
a design change to bypass the internal contacts that were in series with the
coils.
P&B engineers informed the NRC that, if P&B had known the intended application
of the relays at Waterford, it could have designed and manufactured relays that
would have performed reliably.
P&B stated that it would assign a specific
drawing number for such relays and would expect recipients to reference the
drawing number in subsequent purchase orders to ensure that P&B furnished
identical relays as replacements.
The NRC staff and P&B engineers investigated the intermittent nonrepeatable
MDR relay failures experienced at other plants and concluded that the P&B
MDR relays may have been misapplied to switch low level loads. Attachment 1 includes a discussion of comments from P&B on the use of P&B relays for
switching low level loads.
Because the use of relays for switching direct current or low level loads may
require special features, licensees may wish to review the adequacy of their
applications of P&B MDR relays and other similar relays and improve their
communications with P&B or other manufacturers in order to accomplish special
functions reliably.
The NRC has issued the following related generic communication:
NRC
Information Notice IN 92-04, "Potter and Brumfield Model MDR Rotary Relay
Failures," January 6, 1992.
IN 92-19 March 2, 1992 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact the
technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
(h-ar es E. Rossi , Erieector
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contact:
Kamal R. Naidu, NRR
(301) 504-2980
Attachments:
1. P&B's Comments On Switching Direct Current and Low Level Loads
2. List of Recently Issued NRC Information Notices
.POTTER & BRUMFIELD A Siemens Company
FAX 1812/386-2069
Attachment 1
IN 92-19 March 2, 1992 DATE:
FACSIMILE TRANSMITTAL SHEET
December 6, 1991
Kamalakar R. Naidu
FAX TO:
FAX NUMBER:
FROM:
PAGES TO FOLLOW:
301-492-0260
William Lamb
0
Subject:
Your 12/5/91 Phone Request for Information.
The following are comments based partially on The Engineers'
published by The National Association of Relay Manufacturers
Relay Handbook
(NARM):
SWITCHING DC LOADS
D.C. loads are more difficult to turn off than A.C. loads because the DC
voltage never passes through zero.
As the contacts open, an arc is
struck and may be sustained by the applied voltage until the distance
between opening contacts becomes too great for the arc to sustain
itself. The arc energy can seriously erode away the contacts.
Frequently arc extinguishing capabilities for D.C. inductive loads can
be enhanced by connecting two contacts in series.
This provides a
larger total contact gap and a faster rate of contact separation, thereby providing improved performance.
Paralleling sets of relay contacts to
set can handle is often unsuccessful.
contact opening results in one contact
failure.
switch loads greater than a single
Lack of absolute simultaneity of
- taking all the load causing early
LOW LEVEL LOADS
A relay contact rating does not necessarily apply for all loads from
zero up to the magnitude specified. The fact that a contact can
reliably switch 10 amperes does not necessarily mean it can reliably
switch 10 milliamperes. The MDR contact structure is designed for 10
amp 115V AC 50% PF, 3 amp 28V DC resistive and 0.8 amp 125V DC resistive
load switching. It does not have the contact structure design
configuration necessary for low level switching applications that
inhibit contact resistance build up.
Attachment 2
March 2, 1992 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
92-18 Potential for Loss of Re- mote Shutdown Capability
during A Control Room Fire
02/28/92 All
for
holders
nuclear
power reactors.
92-17 NRC Inspections of Pro- grams being Developed at
Nuclear Power Plants in
Response to Generic
Letter 89-10
02/26/92
All holders of OLs or CPs
for nuclear power reactors.
92-16
Loss of Flow from the
Pump during Refueling
Cavity Draindown
02/25/92
All holders of OLs or CPs
for nuclear power reactors.
92-15
92-14
92-02, Supp. 1
92-13
92-12
92-11
Failure of Primary System
Compression Fitting
Uranium Oxide Fires at Fuel
Cycle Facilities
Relap5/Mod3 Computer Code
Error Associated with the
Conservation of Energy
Equation
Inadequate Control Over
Vehicular Traffic at
Nuclear Power Plant Sites
Effects of Cable Leakage
Currents on Instrument
Settings and Indications
Soil and Water Contamina- tion at Fuel Cycle Facil- ities
02/24/92
02/21/92
02/18/92
02/18/92
02/10/92
02/05/92
All holders of OLs or CPs
for nuclear power reactors.
All fuel cycle and uranium
fuel research and development
licensees.
All holders of OLs or CPs
for nuclear power reactors.
All holders of OLs or CPs
for nuclear power reactors.
All holders of OLs or CPs
for nuclear power reactors.
All uranium fuel fabrica- tion and conversion facil- ities.
OL = Operating License
CP = Construction Permit
IN 92-19 March 2, 1992 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact the
technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contact:
Kamaal
(301)
R. Naidu, NRR
504-2980
Attachments:
1. P&B's Comments On Switching
2. List of Recently Issued NRC
Direct Current and Low Level Loads
Information Notices
- SEE PREVIOUS CONCURRENCES
- OGCB:DOEA:NRR*VIB:DRIS:NRR
JBirmingham
KRNaidu
02/11/92
02/11/92
02/,X 92
- VIB:DRIS:NRR
GCwalina
02/11/92
- C/OGCB:DOEA:NRR
CHBerlinger
02/14/92
- C/VIB:DRIS:NRR
LNorrholm
02/12/92
- RPB:ADM
TechEd
02/03/92
- D/DRIS:NRR
BKGrimes
02/12/92 DOCUMENT NAME: IN 92-19
IN 92-XX
February xx, 1992 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact the
technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contact:
Kamal R. Naidu, NRR
(301) 504-2980
Attachments:
1. P&B's Comments On Switching
2. List of Recently Issued NRC
Direct Current and Low Level Loads
Information Notices
Document Name:
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