Information Notice 1988-75, Disabling of Diesel Generator Output Circuit Breakers by Anti-Pump Circuitry
I
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.
20555
September 16, 1988
NRC INFORMATION NOTICE NO. 88-75:
DISABLING OF DIESEL GENERATOR OUTPUT
CIRCUIT BREAKERS BY ANTI-PUMP CIRCUITRY
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
This information notice is being provided to alert addressees to potential
problems where the capability to either automatically or manually close
diesel generator circuit breakers from the control room may be lost. 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 do not
constitute NRC requirements; therefore, no specific action or written response
is required.
Description of Circumstances
On June 5, 1988, operators at Browns Ferry Unit 3 were unable to reclose the
diesel generator output breakers to the 4-kV shutdown boards from the control
room during a loss-of-power/loss-of-coolant-accident (LOP/LOCA) test.
During
the test, the output breakers connected the diesel generators to their respec- tive 4-kV shutdown boards after the LOP signal was generated; however, the
breakers tripped and remained open after receiving the LOCA signal.
Operators
diagnosed the output breaker lockout problem using system electrical configu- ration drawings. An operator was sent to the 4-kY shutdown board to manually
transfer output breaker control power to its alternate source. This momentarily
removed power, enabling the breaker to close when the power was restored.
On October 14, 1987, an operator at Wolf Creek Generating Station manually
tripped the output circuit breaker of the emergency diesel generator (EDG)
from the control room. At the time, the EDG was supplying a vital bus.
When
the operators tried to reenergize the vital bus from the still-operating EDG,
they found that they could not close the EDG output breaker from the control
room.
The vital bus was finally reenergized from the offsite power supply.
Through examination of the breaker control schematics the licensee later
found that the EDG circuit breaker could be closed by cycling the EDG mode
switch at the EDG local control station.
880920197
IN 88-75 September 16, 1988 Discussion:
The anti-pump circuit configuration will protect large breakers from rapid
cycling and, under certain circumstances, will prevent breaker closure. At
Browns Ferry Unit 3, a unique sequence of events, a LOP signal followed within
6 seconds by a LOCA signal, led to the discovery of a design deficiency of this
circuit configuration.
Contacts from the undervoltage relay will seal in the
breaker anti-pump relay until the undervoltage condition on the 4-kV boards
clears.
The circuit is designed such that following a LOP, the undervoltage condition
must exist for at least 5 seconds and the diesel. must reach rated speed before
the diesel generator output breaker will close on the bus.
Once the breaker
has closed, the closure spring recharge motor and the breaker anti-pump relay
will be energized. A fully discharged closure spring requires 2 seconds for
the spring to be fully recharged.
During this 2 second window the anti-pump
coil will remain energized via contacts sensing spring position, and if an
undervoltage condition exists on the 4-kY bus it will seal in and lock open
the breaker.
During the Browns Ferry event, the EDG output breaker closed 5 seconds after
the LOP signal, the undervoltage condition was eliminated, and the undervoltage
relay began its 5 second cycle to reset from the undervoltage condition. About
1.5 seconds 1ater. the. LOCA-signaL-retr-ipped-the-breaker-and-created-another--
undervoltage condition on the 4-kV bus. At this point, because the undervoltage
relay had not completed its reset cycle, the undervoltage relay remained in its
undervoltage state.
Therefore, the undervoltage relay sealed in the still- energized anti-pump relay because the undervoltage condition occurred before
the breaker charging spring was fully charged.
Thus, the breaker could not
be closed from the control room either manually or automatically until control
power was removed, which deenergized the anti-pump relay.
The Browns Ferry licensee modified the breaker control logic to prevent the anti- pump relay from sealing in during a LOCA condition by adding a time-delay relay
in the breaker trip coil circuitry.
This relay will be energized by a LOCA
signal and its contact in the anti-pump coil seal-in path will open after a
2-to 5-second delay to prevent anti-pump coil seal-in and breaker lockout.
The Wolf Creek EDG output circuit breaker has automatic closing logic to close
the circuit breaker when the following five permissives are satisfied:
(1) Both offsite circuit breakers are open'
(2 The EDG mode switch is in the automatic mode.
(3 Lockout relays are deenergized.
(4 A 3-second time delay has elapsed.
(5) The EDG has reached operating speed and voltage.
This logic sends a constant close signal to the circuit breaker that keeps the
breaker's internal anti-pump relay energized as long as the logic permissives
are satisfied. The anti-pump relay prevents the circuit breaker from cycling
if attempts are made to hold the breaker closed against a valid trip signal.
I',
IN 88-75 September 16, 1988 When the Wolf Creek operator manually tripped the EDG output breaker, the auto- matic closing logic permissives remained satisfied. Therefore, the anti-pump
relay remained energized, preventing reclosure of the circuit breaker.
Cycling
the EDG mode control switch at the local control station allowed the circuit
breaker to reclose by momentarily interrupting the automatic close signal, there- by resetting the anti-pump logic.
When the mode switch contact was reclosed by
returning the switch to the "auto' position, the circuit breaker's automatic
closing logic closed the breaker.
The Wolf Creek licensee modified the EDG breaker control switch located in the
control room to enable the operator to reclose the EDG circuit breaker from the
control room.
This switch was originally intended only as a means of paralleling
the EDG with the offsite power supply.
With the current modification, the switch
can be used to reset the anti-pump logic and allow the automatic circuit to re- close the breaker. The modification added a contact that is closed in the "normal"
position and open in the "trip" and "pull to lock" positions of the control switch.
When operators manually trip the EDG circuit breaker from this control switch, the contacts open to interrupt the close circuit and reset the circuit breaker
anti-pump relay. If the operator wishes to keep the breaker open, he must put
the switch in the "pull to lock" position.
Returning the switch to the "normal"
position completes the automatic close circuit and the breaker recloses.
It should be noted that although the above discussion has dealt only with EDG
output- circuit breakers, anti-pump circuit problems could also apply to other
breakers that use automatic closing logic, such as load-sequencing breakers
and offsite supply breakers to the emergency buses.
The information herein is being provided as an early notification of a potentially
significant matter that is still under consideration by the NRC staff. If NRC
evaluation so indicates, specific licensee actions may be requested.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the technical
contacts listed below or the Regional Administrator of the appropriate regional
office.
Di rector
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: James Lazevnick, NRR
(301) 492-0814
Carl Schulten, NRR
(301) 492-1192
Fred Burrows, NRR
(301) 492-0783 Attachment:
List of Recently Issued NRC Information Notices
Att"aant
September 16, 1988
Page I of I
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Notice No.
Subject
Issuance
88-74 Potentially Inadequate
9/14/88
Perfornance of ECCS in
PWRs During Recirculation
Operation Following a LOCA
88-73 Direction-Dependent Leak
9/8/88
Characteristics of
Containment Purge Valves
88-72 Inadequacies in the Design
9/2/88 of dc Motor-Operated Valves
88-71 Possible Environmental
9/1/88
Effect of the Reentry
of COSMOS
1900 and
Request for Collection
of Licensee Radioactivity
Measurements Attributed
to That Event
88-70
Check Valve Inservice
8/29/88
Testing Program
Deficiencies
88-69 Movable Contact Finger
8/19/88
Binding in HFA Relays
Manufactured by General
Electric (GE)
88-48, Licensee Report of Defective 8/24/88 Supplement I
Refurbished Valves
88-68 Setpoint Testing of Pres-
8/22/88 surizer Safety Valves with
Filled Loop Seals Using
Hydraulic Assist Devices
88P67-
-P-F
Zfiiairy Fiedeaer Pump
8/Z2j88
Turbine Overspeed Trip
Failure
- Operating License
- Construction Permit
Issued to
All holders of OLs
or CPs for W and
8&W-designei nuclear
power reactors.
All holders of 0Ls
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, fuel
cycle licensees, and Priority I
material 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 holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
or CPs for nuclear
power reactors.
_
UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D.C. 20555
OFFICIAL BUSINESS
PENALTY FOR PRIVATE USE, $300
FIRST CLASS MAIL
POSTAGE & FEES PAID
PERMIT No. 0-57
IN 88-75 September 16, 1988 When the Wolf Creek operator manually tripped the EDG output breaker, the auto- matic closing logic permissives remained satisfied.
Therefore, the anti-pump
relay remained energized, preventing reclosure of the circuit breaker. Cycling
the EDG mode control switch at the local control station allowed the circuit
breaker to reclose by momentarily interrupting the automatic close signal, there- by resetting the anti-pump logic. When the mode switch contact was reclosed by
returning the switch to the "auto" position, the circuit breaker's automatic
closing logic closed the breaker.
The Wolf Creek licensee modified the EDG breaker control switch located in the
control room to enable the operator to reclose the EDG circuit breaker from the
control room. This switch was originally intended only as a means of paralleling
the EDG with the offsite power supply. With the current modification, the switch
can be used to reset the anti-pump logic and allow the automatic circuit to re- close the breaker.
The modification added a contact that is closed in the "normal"
position and open in the "trip" and "pull to lock" positions of the control switch.
When operators manually trip the EDG circuit breaker from this control switch, the contacts open to interrupt the close circuit and reset the circuit breaker
anti-pump relay.
If the operator wishes to keep the breaker open, he must put
the switch in the "pull to lock" position. Returning the switch to the "normal"
position completes the automatic close circuit and the breaker recloses.
It should be noted that although the above discussion has dealt only with EDG
output circuit breakers, anti-pump circuit problems could also apply to other
breakers that use automatic closing logic, such as load-sequencing breakers
and offsite supply breakers to the emergency buses.
The information herein is being provided as an early notification of a potentially
significant matter that is still under consideration by the NRC staff. If NRC
evaluation so indicates, specific licensee actions may be requested.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the technical
contacts listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: James Lazevnick, NRR
(301) 492-0814
Carl Schulten, NRR
(301) 492-1192
Fred Burrows, NRR
(301) 492-0783 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS PAGE FOR CONCURRENCE
OFC *OEAB
- Tech
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- SL:OEAB
- C:OEAB *D:DEST
- C:OGCB
NAME CSchulten BCalure
PBaranowsky WLanning LShao
CBerlinger e l
DATE 9/7/88
7/28/88
9/7/88
9/7/88
8/24/88 9/8/88
9/(,f 88
IN 88- September
, 1988 contact was reclosed by returning the switch to the "auto" position. the
circuit breaker's automatic closing logic closed the breaker.
The Wolf Creek licensee modified the EDG breaker control switch located in the
control room to enable the operator to reclose the EDG circuit breaker from
the control room.
This switch was originally intended only as a means of
paralleling the EDG with the offsite power supply.
With the current
modification. the switch can be used to reset the anti-pump logic and allow
the automatic circuit to reclose the breaker.
The modification added a
contact that is closed in the "normal" position and open in the "trip" and
"pull to lock" positions of the control switch. When operators manually trip
the EDG circuit breaker from this control switch. the contacts open to
interrupt the close circuit and reset the circuit breaker anti-pump relay.
If the operator wishes to keep the breaker open. he must put the switch in the
"pull to lock" position.
Returning the switch to the "normal" position
completes the automatic close circuit and the breaker recloses.
It should be noted that although the above discussion has dealt only with EDG
output circuit breakers. the anti-pump circuit problem could also apply to other
breakers that use automatic closing logic, such as load-sequencing breakers and
offsite supply breakers to the emergency buses.
The information herein is being provided as an early notification of a
potentially significant matter that is still under consideration by the NRC
staff. If NRC evaluation so indicates. specific licensee actions may be
requested.
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact any of the
technical contacts listed below or the Regional Administrator of the appropriate
regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: James Lazevnick. NRR
(301) 492-0814
Carl Schulten. NRR
(301) 492-1192
Fred Burrows. NRR
(301) 492-0783
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OFFICIAL RECORD COPY
IN 88- August . 1988 contact was reclosed by returning the switch to the "auto" position. the
circuit breaker's automatic closing logic closed the breaker.
The Wolf Creek licensee modified the EDG breaker control switch located in the
control room to enable the operator to reclose the EDG circuit breaker from
the control room. This switch was originally intended only as a means of
paralleling the EDG with the offsite power supply. With the current
modification. the switch can be used to reset the anti-pumping logic and allow
the automatic circuit to reclose the breaker. The modification added a
contact that is closed in the "normal" position and open in the "trip" and
"pull to lock" positions of the control switch.
When operators manually trip
the EDG circuit breaker from this control switch, the contacts open to
interrupt the close circuit and reset the circuit breaker anti-pumping relay.
If the operator wishes to keep the breaker open. he must put the switch in the
"pull to lock" position. Returning the switch to the "normal" position
completes the automatic close circuit and the breaker recloses.
It should be noted that although the above discussion has dealt only with EDG
output circuit breakers, the same problem could also apply to other breakers
that use automatic closing logic, such as load-sequencing breakers and offsite
supply breakers to the emergency buses.
The information herein is being provided as an early notification of a
potentially significant matter that is still under consideration by the NRC
staff.
If NRC evaluation so indicates. specific licensee actions may be
requested.
No specific action or written responses is required by this information
notice.
If you have any questions about this matter, please contact either the
technical contacts listed below or the Regional Administrator of the appropriate
regional office.
Charles E. Rossi. Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
James Lazevnick. NRR
(301) 492-0814
Carl Schulten. NRR
(301) 492-1192
Fred Burrows. NRR
(301) 492-0783 OFC
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NRC INFO NOTICE 88-XX. DIESEL GENERATOR CIRCUIT BREAKERS FAIL TO AUTOMATICALLY
CLOSE
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