Information Notice 1989-87, Disabling of Emergency Diesel Generators by Their Neutral Ground-Fault Protection Circuitry

Disabling of Emergency Diesel Generators by Their Neutral Ground-Fault Protection Circuitry

ML031190049
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:	12/19/1989
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-89-087, NUDOCS 8912130473
Download: ML031190049 (4)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 December 19, 1989 NRC INFORMATION NOTICE NO. 89-87: DISABLING OF EMERGENCY DIESEL GENERATORS

-BY THEIR NEUTRAL GROUND-FAULT PROTECTION

CIRCUITRY

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

This information notice is intended to alert addressees to possible uncon- sidered failure modes in which emergency diesel generators could be rendered

inoperable as a result of their neutral ground-fault protection circuitry.

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. I

Description of Circumstances

On May 25, 1989, a plant engineering design review at Perry Unit 1 revealed

a design anomaly whereby ground faults on emergency diesel generator loads

coincident with loss of offsite power during a seismic event or fire could

lead to the inoperabllity of more than one emergency diesel generator. As

a result, the Perry staff-declared several of the emergency-diesel generators

inoperable until temporary modifications could be made to disable the neutral

ground-fault relay contacts that were designed to trip the emergency diesel

generators.

Discussion:

At Perry Unit 1, each emergency diesel generator was designed with a neutral

ground circuit consisting of a high Impedance path from the neutral to ground, which limits ground-fault current to no more than 2 amperes (see typical net- work in Figure 1). The purpose of providing this grounding path (inlieu of

an ungrounded system) isto limit the buildup of high voltage stress during

certain ground-fault conditions that could ultimately result inthe breakdown

of the insulation of such'components as motors and cables. Italso provides

a convenient means of detecting a ground inthe system so that a search can

be made to eliminate the ground before a second ground occurs and causes a.

phase-to-phase fault.

8912130473

<_IN 89-87

_

December 19, 198- Ground faults are detected by sensing the voltage that is developed

emergency diesel generator grounding circuit whenever a ground fault in the

in the electrical distribution system supplied by the emergency dieselexists

ator. In the Perry design, a voltage sensing relay would initiate a gener- the corresponding emergency diesel generator whenever this voltage exceeded trip of

the relay's pickup value. This relay's contacts are bypassed by the

response to a loss-of-coolant accident. For non-LOCA events, however,automatic

fault in any component, including non-Class 1E components, would have a ground

desirable result of shutting down the emergency diesel generator. Thisthe un- the concern that a seismic event or fire could have resulted in simultaneous raises

ground faults in non-safety components supplied by all of the redundant

emergency diesel generators. Action by the protection circuitry at

Perry

could then have shut down all of the emergency diesel generators, preventing

them from performing their intended safety functions.

The Perry staff has temporarily disabled the neutral ground-fault relays

prevent them from shutting down the emergency diesel generators. Permanent to

modifications are planned to replace the ground-fault emergency diesel

ator trip function with ground-fault alarms in the control room. These gener- fications will be supported by alarm response procedures requiring modi- that

operators determine the location and safety significance of ground faultsthe

take appropriate action. and

This information notice requires no specific action or written response.

you have any questions about the information in this notice, please If

technical contact-listed below or-the appropriate-NRR.-projeN contact the

rot-nkttaaec

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

F. Burrows, NRR

(301) 492-0833 Attachments:

1. Figure 1

2. List of Recently Issued NRC Information Notices

• & \_) VAttachment I

HeU IN 89-87 December 19, 1989 Page 1 of I

TYPICAL HIGH RESISTANCE NEUTRAL GROUNDING SYSTEM

C

B

Postulated ground

fault

4160-1201240

LEGEND

64 - Voltage sensing relay, provides alarm actuation

FIGURE 1 or trip.

64X - Provides overvoltage

protection for the 64 relay.

Attachment 2 IN 89-87 December 19. 1989 Page I of 1, LIST OFRECENTLY ISSUED

NRCINFORMATION NOTICES

Intormatlon Date of

Notice No. Subject Issuance Issued to

89-45, Metalclad, Low-Voltage 12/I15/89 All holders of OLs

Supp. 2 Power Circuit Breakers or CPs for nuclear

Refurbished with power reactors.

Substandard Parts

89-86 Type HKCircuit Breakers 12/15/89 All holders of OLs

Missing Close Latch Anti- or CPs for nuclear

Shock Springs. power reactors.

89-85 EPA's Interim Final Rule 12/15/89 All medical, academic.

on Medical Waste Tracking industrial, waste

and Management broker. and waste

disposal site licensees.

89-84 Failure of Ingersoll Rand 12/12/89 "All holders of OLs

Air Start Motors as a Result or CPs for nuclear

of Pinion Gear Asseably power reactors.

Fitting Problems

89-83 Sustained Degraded Volt ge 12/11/89 All holders of OLs

on the Offsite Electrical or CPs for nuclear

Grid and Loss of Other power reactors.

Generating Stations as

a Result of a Plant Trip

89-82 Recent Safety-Related 12/7/89 All NRClicensees

Incidents at Large authorized to

Irradiators possess aneuse

sealed sources at

large irradiators.

89-59. Suppliers of Potentially 12/6/89 All holders of OLs

Supp. 1 Nisrepresented Fasteners or CPs for nuclear

power reactors.

_ 89-81 -___ Inadequate, Con)Pol af_ -126/89 _All holders of OLs

Teporary hodifications or s-fF nilclar

to Ssfety-Related Systems power reactors.

OL

• Operating License

CP

• Construction Permit

UNITED STATES FIRST CLASS MAIL

POSTAGE b FEES PAID

NUCLEAR REGULATORY COMMISSION USNAC

WASHINGTON, D.C. 20555 PERMIT hNe.C7 OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE. $300

DC 2055 C: