Information Notice 1988-12, Overgreasing of Electric Motor Bearings

Overgreasing of Electric Motor Bearings

ML031150512
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, 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:	04/12/1988
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-88-012, NUDOCS 8804060370
Download: ML031150512 (9)

UNITED STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 April 12, 1988 NRC INFORMATION

NOTICE NO.' 88-12: OVERGREASING

OF ELECTRIC MOTOR BEARINGS

Addressees

All holders of operating

licenses or construction

permits for nuclear power reactors.

Purpose

This information

notice is being provided to alert addressees

to problems caused by accumulation

of grease on electric motors used to drive rotating equipment

in nuclear power plants. 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:

NRC personnel

observed accumulations

of grease on the air vent screens of electric motors used for driving such rotating equipment

as fans and pumps at the Millstone

and Calvert Cliffs nuclear power plants. The grease ap-peared to have come from overgreasing

of the electric motor bearings.

Grease was forced out of the bearing seals, onto the stator windings and rotor, from where it either fell or was thrown onto the inside'of

the motor housing. Be-cause of these observations, the NRC began an investigation

'into problems that have been caused in the past, or could be caused in the future, by the over-greasing of electric motor bearings.Several electric motor overgreasing

events were identified

that have led to failures of nuclear plant components:

°- 'At a nuclear plant in 1975, overgreasing

of the motor bearings caused the failure of the containment

cooler fans when 'a bearing failed and seized.° At Susquehanna

Unit 1, on July 24, 1984, excessive'grease

buildup in the Selectric

motor of a motor generator

set caused the set to'shut down and resulted in the spurious emergency

actuations

of the standby gas treatment system and the control room emergency

outside air system (LER 387/84-036).( 8000370

IN 88-12 April 12, 1988 0 At Palisades

Unit 1, overgreasing

of the motor bearings caused the contain-ment cooler fans to fall on three different

occasions:

On July 7, 1986, overgreasing

of the motor shaft bearings caused the bearings to skid in-stead of roll. This caused the motor to overheat and automatically

shut down. On August 8, 1986, and again on August 11, 1986, overgreasing

caused the motor bearings to deteriorate

which, in turn, caused the motor and fan to vibrate, and bolts on the equipment

to loosen and fall (LER 255/86-031).

In addition to these overgreasing

events, a number of cases have been reported in which excessive

motor bearing grease caused problems that were caught before the systems actually failed. For example, at a nuclear plant in 1978, exces-sive grease in a motor bearing in the service-water

system caused the bearing to become abnormally

hot and noisy. At another nuclear plant in 1986, grease from a bearing in the component

cooling pump motor ran into the motor, causing it to smoke.Discussion:

The NRC staff has solicited

technical

information

and operating

experience

on the problems caused by the overgreasing

of electric motor bearings from motor and bearing manufacturers, as well as from other licensees.

Their responses are summarized

in this discussion.

Two basic mechanisms

involving

overgreasing

of bearings can lead to the failure of electric motors: (1) The excess grease will leak out from the bearing seal and be deposited on the stator and rotor windings.

The grease deposits create a thermal barrier between the windings and their cooling air, leading to an increase in motor temperature.

For motors designed to use outside air to cool the windings, the temperature

is increased

still more by the buildup of dirt, dust, and other foreign materials

that adhere to the grease. It is esti-mated that for every 10F rise in motor temperature, the insulation

life of the windings is reduced by half. The deterioration

of the winding insulation

then causes the motor to "short out".(2) The excess grease causes a "churning" action of the ball bearings within their housing, increasing

the temperature

of the grease and bearings.As the temperature

approaches

the upper functional

design limit of the grease, viscous or hard residues form, causing a breakdown

of the lubri-cating characteristics

of the grease. The bearing temperature

then rises higher, and eventually

causes a reduction

in bearing hardness and a sub-sequent breakdown

of the bearing. A rule of thumb, based on certain

IN 88-12 April 12, 1988 manufacturers

1 tests, is that grease life is halved for every 25 0 F increase in temperature

and is doubled for every 25 0 F decrease in temperature.

High bearing temperature

may also cause the inner race of the bearing to expand and slip on the rotor shaft. The expansion

and slippage of the bearing's

inner race leads to a misalignment

between the rotor shaft and the bearing; this misalignment

can cause contact between the rotor and stator. Once contact occurs, the windings short and burn out.One frequent cause of excess grease problems is the failure to provide an exit path for the displaced

grease when new grease is added. This can result from the failure to remove the grease drain plug, or from failure to unblock drain lines that have become plugged by hardened grease or dirt. Another frequent cause is the addition of too much grease. The correct amount must be deter-mined for each situation.

Bearing manufacturers

generally

recommend

filling the motor bearing void space from one-third

to one-half full of grease. How-ever, the optimum amount can vary from 20% to 80% full, depending

on such factors as the application

of the motor, the environment

of the motor, the retainer design, and the type of grease.The following

actions can be taken to correct or prevent motor overgreasing

and related problems: (1) Review motor lubrication

procedures

to ensure that they identify the type and quantity of grease to use, the specific fill and drain nozzles to uncap, and the length of time motors should be run with drain plugs off after greasing the bearings.(2) To prevent foreign materials

from contaminating

the grease, ensure that grease containers

are covered during periods of storage and that nozzles and grease fittings are cleaned.(3) Determine

the optimum quantity and correct type of grease required for each motor by examining

the manufacturer's

recommendations

and by monitor-Ing the behavior of grease added to motors.(4) Consider using prelubricated

sealed bearings in applications

where re-lubrication

is difficult, where contaminants

can adulterate

the grease, or where overgreasing

might damage safety systems.It should be noted that the vast majority of the reported lubrication-related

incidents

have been the result of underlubrication

rather than overlubrication.

This notice is not intended to discourage

the adequate lubrication

of motor bearings, but to prevent overgreasing

problems by encouraging

a thorough under-standing of correct lubrication

procedures.

<- -o IN 88-12 April 12, 1988 No specific action or written response is required by this information

notice.If you have any questions

about this matter, please contact the technical contact listed below or the Regional Administrator

of the appropriate

regional office.Zarles E. Rossi Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

Contacts:

James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:

List of Recently Issued NRC Information

Notices

IY-Attachment

IN 88-12 April 12, 1988 LIST OF RECENTLY ISSUED NRC INFORMATION

NOTICES Information

Date of Notice No. Subject Issuance Issued to 88-11 88-10 87-44, Supp. 1 88-09 88-08 88-07 88-06 88-05 Potential

Loss of Motor Control Center and/or Switchboard

Function Due to Faulty Tie Bolts Materials

Licensees:

Lack of Management

Controls Over Licensed Programs Thimble Tube Thinning in Westinghouse

Reactors Reduced Reliability

of Steam-Driven

Auxiliary Feedwater

Pumps Caused by Instability

of Woodward PG-PL Governors Chemical Reactions

with Radioactive

Waste Solidification

Agents Inadvertent

Transfer of Licensed Material to Uncontrolled

Locations Foreign Objects in Steam Generators

Fire in Annunciator

Control Cabinets 4/7/88 3/28/88 3/28/88 3/18/88 3/14/88 3/7/88 2/29/88 2/11/88 All holders of OLs or CPs for nuclear power reactors.All NRC licensees authorized

to use byproduct

material.All holders of OLs or CPs for nuclear power reactors that employ a Westinghouse

NSSS.All holders of OLs or CPs for nuclear power reactors.All NRC licensees generating

or pro-cessing low level radioactive

waste.All NRC broad licensees and licensees

authorized

to possess byproduct material as sealed sources in teletherapy

units or 'self-contained" irradiators.

All holders of OLs or CPs for PWRs.All holders of OLs or CPs for nuclear power reactors.OL = Operating

License CP = Construction

Permit

-IN 88-12 April 12, 1988 No specific action or written response is required by this information

notice.If you have any questions

about this matter, please contact the technical contact 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 A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCES

04/h/88 \*SELB:DEST:NRR

FRosa 03/28/88*OGCB:DOEA:NRR

DCKirkpatrick

03/24/88*C/OGCB:DOEA:NRR*PPMB:ARM

CHBerlinger

TechEd 04/04/88 03/30/88*TPAB:DSP:AEOD

• D/DEST:NRR

MRHarper LCShao 03/28/88 04/05/88*RI JAPrell 03/25/88

1.1 4 -IN 88-XX April xx, 1988 No specific action or written response is required by this information

notice.If you have any questions

about this matter, please contact the technical contact 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 A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCES

D/DWEA:NRR

CERossi 04/ /88*SELB:DEST:NRR

FRosa 03/28/88*OGCB:DOEA:NRR

DCKirkpatrick

03/24/88*RI JAPrel 1 03/25/88*C/OGCB:DOEA:NRR*PPMB:ARM

CHBerlinger

TechEd 04/04/88 03/30/88*TPAB:DSP:AEOD

D/DEST:NRR

MRHarper LCShao 03/28/88 04 {_8' I

x'* j _IN 88-XX April xx, 1988 No specific action or written response is required by this information

notice.If you have any questions

about this matter, please contact the technical contact listed below or the Regional Administrator

of the appropriate

regional office.Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Reaulation

Technical

Contacts: James A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCES

D/DOEA:NRR

CERossi 04/ /88*TPAB:DSP:AEOD

MRHarper 03/28/88 C 4 C/OGCB: DOEA: NRR CHBerlinger

044 /88*P4B:ARM TechEd 03/30/88*OGCB:DOEA:NRR

DCKirkpatrick

03/24/88*RI JAPrel 1 03/25/88*SELB:DEST:NRR

FRosa 03/28/88 IN 88-XX March xx, 1988 No specific action or written response is required by this information

notice.If you have any questions

about this matter, please contact the technical contact 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 A. Prell, RI (215) 337-5108 Donald C. Kirkpatrick, NRR (301) 492-1152 Attachment:

List of Recently Issued NRC Information

Notices*Transmitted

by dated OGCB:DOEA:NRR

DCKlirkpatric

03i /88 D?/RI A5L *4 SELB:DEST:NRR

JAPrell FRosa fIt Phefi 03/AQ788 03/2t/88 D/DOEA:NRR

CERossi 03/ /88 TPAB:DSP:AEOD

MRHarper i 03/2[r/88 A C/OGCB:DOEA:NRR

CHBerlinger

03/ /88 PPMB:ARM TechEd i 9 03/Jo/88 Wo '