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 'abearing 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 0

manufacturers1 tests, is that grease life is halved for every 25 F

0

increase in temperature and is doubled for every 25 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 Potential Loss of Motor 4/7/88 All holders of OLs

Control Center and/or or CPs for nuclear

Switchboard Function Due power reactors.

to Faulty Tie Bolts

88-10 Materials Licensees: Lack 3/28/88 All NRC licensees

of Management Controls Over authorized to use

Licensed Programs byproduct material.

87-44, Thimble Tube Thinning in 3/28/88 All holders of OLs

Supp. 1 Westinghouse Reactors or CPs for nuclear

power reactors that

employ a Westinghouse

NSSS.

88-09 Reduced Reliability of 3/18/88 All holders of OLs

Steam-Driven Auxiliary or CPs for nuclear

Feedwater Pumps Caused power reactors.

by Instability of Woodward

PG-PL Governors

88-08 Chemical Reactions with 3/14/88 All NRC licensees

Radioactive Waste generating or pro- Solidification Agents cessing low level

radioactive waste.

88-07 Inadvertent Transfer of 3/7/88 All NRC broad licensees

Licensed Material to and licensees authorized

Uncontrolled Locations to possess byproduct

material as sealed

sources in teletherapy

units or 'self-contained"

irradiators.

88-06 Foreign Objects in Steam 2/29/88 All holders of OLs

Generators or CPs for PWRs.

88-05 Fire in Annunciator Control 2/11/88 All holders of OLs

Cabinets 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

• C/OGCB:DOEA:NRR*PPMB:ARM

CHBerlinger TechEd

04/h/88 \ 04/04/88 03/30/88

• OGCB:DOEA:NRR *RI *SELB:DEST:NRR *TPAB:DSP:AEOD *D/DEST:NRR

DCKirkpatrick JAPrell FRosa MRHarper LCShao

03/24/88 03/25/88 03/28/88 03/28/88 04/05/88

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 *C/OGCB:DOEA:NRR*PPMB:ARM

CERossi CHBerlinger TechEd

04/ /88 04/04/88 03/30/88

• OGCB:DOEA:NRR *RI *SELB:DEST:NRR *TPAB:DSP:AEOD D/DEST:NRR

DCKirkpatrick JAPrel 1 FRosa MRHarper LCShao

03/24/88 03/25/88 03/28/88 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

C 4 C/OGCB: DOEA: NRR

CERossi CHBerlinger

04/ /88 044 /88

• OGCB:DOEA:NRR *RI *SELB:DEST:NRR *TPAB:DSP:AEOD *P4B:ARM

DCKirkpatrick JAPrel 1 FRosa MRHarper TechEd

03/24/88 03/25/88 03/28/88 03/28/88 03/30/88

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

D/DOEA:NRR C/OGCB:DOEA:NRR

CERossi CHBerlinger

03/ /88 03/ /88 OGCB:DOEA:NRR RI A5L

• 4 SELB:DEST:NRR TPAB:DSP:AEOD PPMB:ARM

DCKlirkpatric JAPrell FRosa fIt Phefi MRHarper i TechEd i 9

03i /88 D?/ 03/AQ788 03/2t/88 03/2[r/88 A 03/Jo/88 Wo '