Information Notice 1988-75, Disabling of Diesel Generator Output Circuit Breakers by Anti-Pump Circuitry

Disabling of Diesel Generator Output Circuit Breakers by Anti-Pump Circuitry
	ML031150110
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	09/16/1988
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-88-075, NUDOCS 8809120197
	Download: ML031150110 (8)
	v • d • e

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

IN 88-75 September 16, 1988 Page I of I

LIST OF RECENTLY ISSUED

NRCINFORMATION NOTICES

Notice No. Subject Issuance Issued to

88-74 Potentially Inadequate 9/14/88 All holders of OLs

Perfornance of ECCSin or CPs for Wand

PWRs During Recirculation 8&W-designei nuclear

Operation Following a LOCA power reactors.

88-73 Direction-Dependent Leak 9/8/88 All holders of 0Ls

Characteristics of or CPs for nuclear

Containment Purge Valves power reactors.

88-72 Inadequacies in the Design 9/2/88 All holders of OLs

of dc Motor-Operated Valves or CPs for nuclear

power reactors.

88-71 Possible Environmental 9/1/88 All holders of OLs

Effect of the Reentry or CPs for nuclear

of COSMOS 1900 and power reactors, fuel

Request for Collection cycle licensees, of Licensee Radioactivity and Priority I

Measurements Attributed material licensees.

to That Event

88-70 Check Valve Inservice 8/29/88 All holders of OLs

Testing Program or CPs for nuclear

Deficiencies power reactors.

88-69 Movable Contact Finger 8/19/88 All holders of OLs

Binding in HFA Relays or CPs for nuclear

Manufactured by General power reactors.

Electric (GE)

88-48, Licensee Report of Defective 8/24/88 All holders of OLs

Supplement I Refurbished Valves or CPs for nuclear

power reactors.

88-68 Setpoint Testing of Pres- 8/22/88 All holders of OLs

surizer Safety Valves with or CPs for nuclear

Filled Loop Seals Using power reactors.

Hydraulic Assist Devices

_

88P67- -P-F Zfiiairy Fiedeaer Pump 8/Z2j88 All holders of OLs

Turbine Overspeed Trip or CPs for nuclear

Failure power reactors.

OL

Operating License

CP* Construction Permit

UNITED STATES FIRST CLASS MAIL

NUCLEAR REGULATORY COMMISSION POSTAGE & FEES PAID

USNRC

WASHINGTON, D.C. 20555 PERMIT No. 0-57 OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300

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