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 E Office of Nuclear Reactor Regulation
To:
References
IN-88-012, NUDOCS 8804060370
Download: ML031150512 (9)

UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555April 12, 1988NRC INFORMATION NOTICE NO.' 88-12: OVERGREASING OF ELECTRIC MOTOR BEARINGS

Addressees

All holders of operating licenses or construction permits for nuclear powerreactors.

Purpose

This information notice is being provided to alert addressees to problemscaused by accumulation of grease on electric motors used to drive rotatingequipment in nuclear power plants. It is expected that recipients willreview the information for applicability to their facilities and consider-actions, as appropriate, to avoid similar problems. However, suggestionscontained 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 ofelectric motors used for driving such rotating equipment as fans and pumpsat the Millstone and Calvert Cliffs nuclear power plants. The grease ap-peared to have come from overgreasing of the electric motor bearings. Greasewas forced out of the bearing seals, onto the stator windings and rotor, fromwhere 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 thathave 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 tofailures of nuclear plant components:°- 'At a nuclear plant in 1975, overgreasing of the motor bearings caused thefailure of the containment cooler fans when 'a bearing failed and seized.° At Susquehanna Unit 1, on July 24, 1984, excessive'grease buildup in theSelectric motor of a motor generator set caused the set to'shut down andresulted in the spurious emergency actuations of the standby gas treatmentsystem and the control room emergency outside air system (LER 387/84-036).( 8000370 IN 88-12April 12, 1988 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 shutdown. On August 8, 1986, and again on August 11, 1986, overgreasing causedthe motor bearings to deteriorate which, in turn, caused the motor and fanto 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 reportedin which excessive motor bearing grease caused problems that were caught beforethe 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 bearingto become abnormally hot and noisy. At another nuclear plant in 1986, greasefrom a bearing in the component cooling pump motor ran into the motor, causingit to smoke.Discussion:The NRC staff has solicited technical information and operating experience onthe problems caused by the overgreasing of electric motor bearings from motorand bearing manufacturers, as well as from other licensees. Their responsesare summarized in this discussion.Two basic mechanisms involving overgreasing of bearings can lead to the failureof electric motors:(1) The excess grease will leak out from the bearing seal and be depositedon the stator and rotor windings. The grease deposits create a thermalbarrier between the windings and their cooling air, leading to an increasein motor temperature. For motors designed to use outside air to cool thewindings, 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 lifeof the windings is reduced by half. The deterioration of the windinginsulation then causes the motor to "short out".(2) The excess grease causes a "churning" action of the ball bearings withintheir housing, increasing the temperature of the grease and bearings.As the temperature approaches the upper functional design limit of thegrease, viscous or hard residues form, causing a breakdown of the lubri-cating characteristics of the grease. The bearing temperature then riseshigher, and eventually causes a reduction in bearing hardness and a sub-sequent breakdown of the bearing. A rule of thumb, based on certain IN 88-12April 12, 1988 manufacturers1 tests, is that grease life is halved for every 250Fincrease in temperature and is doubled for every 250F decrease intemperature.High bearing temperature may also cause the inner race of the bearing toexpand and slip on the rotor shaft. The expansion and slippage of thebearing's inner race leads to a misalignment between the rotor shaft andthe bearing; this misalignment can cause contact between the rotor andstator. Once contact occurs, the windings short and burn out.One frequent cause of excess grease problems is the failure to provide an exitpath for the displaced grease when new grease is added. This can result fromthe failure to remove the grease drain plug, or from failure to unblock drainlines that have become plugged by hardened grease or dirt. Another frequentcause is the addition of too much grease. The correct amount must be deter-mined for each situation. Bearing manufacturers generally recommend fillingthe 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 suchfactors as the application of the motor, the environment of the motor, theretainer design, and the type of grease.The following actions can be taken to correct or prevent motor overgreasingand related problems:(1) Review motor lubrication procedures to ensure that they identify thetype and quantity of grease to use, the specific fill and drain nozzlesto uncap, and the length of time motors should be run with drain plugsoff after greasing the bearings.(2) To prevent foreign materials from contaminating the grease, ensure thatgrease containers are covered during periods of storage and that nozzlesand grease fittings are cleaned.(3) Determine the optimum quantity and correct type of grease required foreach 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-relatedincidents have been the result of underlubrication rather than overlubrication.This notice is not intended to discourage the adequate lubrication of motorbearings, but to prevent overgreasing problems by encouraging a thorough under-standing of correct lubrication procedure <- -oIN 88-12April 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 technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.Zarles E. Rossi DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: James A. Prell, RI(215) 337-5108Donald C. Kirkpatrick, NRR(301) 492-1152

Attachment:

List of Recently Issued NRC Information Notices IY-AttachmentIN 88-12April 12, 1988 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to88-1188-1087-44,Supp. 188-0988-0888-0788-0688-05Potential Loss of MotorControl Center and/orSwitchboard Function Dueto Faulty Tie BoltsMaterials Licensees: Lackof Management Controls OverLicensed ProgramsThimble Tube Thinning inWestinghouse ReactorsReduced Reliability ofSteam-Driven AuxiliaryFeedwater Pumps Causedby Instability of WoodwardPG-PL GovernorsChemical Reactions withRadioactive WasteSolidification AgentsInadvertent Transfer ofLicensed Material toUncontrolled LocationsForeign Objects in SteamGeneratorsFire in Annunciator ControlCabinets4/7/883/28/883/28/883/18/883/14/883/7/882/29/882/11/88All holders of OLsor CPs for nuclearpower reactors.All NRC licenseesauthorized to usebyproduct material.All holders of OLsor CPs for nuclearpower reactors thatemploy a WestinghouseNSSS.All holders of OLsor CPs for nuclearpower reactors.All NRC licenseesgenerating or pro-cessing low levelradioactive waste.All NRC broad licenseesand licensees authorizedto possess byproductmaterial as sealedsources in teletherapyunits or 'self-contained"irradiators.All holders of OLsor CPs for PWRs.All holders of OLsor CPs for nuclearpower reactors.OL = Operating LicenseCP = Construction Permit

-IN 88-12April 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 technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:James A. Prell, RI(215) 337-5108Donald C. Kirkpatrick, NRR(301) 492-1152

Attachment:

List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCES04/h/88 \*SELB:DEST:NRRFRosa03/28/88*OGCB:DOEA:NRRDCKirkpatrick03/24/88*C/OGCB:DOEA:NRR*PPMB:ARMCHBerlinger TechEd04/04/88 03/30/88*TPAB:DSP:AEOD *D/DEST:NRRMRHarper LCShao03/28/88 04/05/88*RIJAPrell03/25/88 1.1 4 -IN 88-XXApril 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 technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:James A. Prell, RI(215) 337-5108Donald C. Kirkpatrick, NRR(301) 492-1152

Attachment:

List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCESD/DWEA:NRRCERossi04/ /88*SELB:DEST:NRRFRosa03/28/88*OGCB:DOEA:NRRDCKirkpatrick03/24/88*RIJAPrel 103/25/88*C/OGCB:DOEA:NRR*PPMB:ARMCHBerlinger TechEd04/04/88 03/30/88*TPAB:DSP:AEOD D/DEST:NRRMRHarper LCShao03/28/88 04 {_8' I x'* j _IN 88-XXApril 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 technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor ReaulationTechnical Contacts:James A. Prell, RI(215) 337-5108Donald C. Kirkpatrick, NRR(301) 492-1152

Attachment:

List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCESD/DOEA:NRRCERossi04/ /88*TPAB:DSP:AEODMRHarper03/28/88C 4C/OGCB: DOEA: NRRCHBerlinger044 /88*P4B:ARMTechEd03/30/88*OGCB:DOEA:NRRDCKirkpatrick03/24/88*RIJAPrel 103/25/88*SELB:DEST:NRRFRosa03/28/88 IN 88-XXMarch 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 technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:James A. Prell, RI(215) 337-5108Donald C. Kirkpatrick, NRR(301) 492-1152

Attachment:

List of Recently Issued NRC Information Notices*Transmitted bydatedOGCB:DOEA:NRRDCKlirkpatric03i /88 D?/RI A5L *4SELB:DEST:NRRJAPrell FRosa fIt Phefi03/AQ788 03/2t/88D/DOEA:NRRCERossi03/ /88TPAB:DSP:AEODMRHarper i03/2[r/88 AC/OGCB:DOEA:NRRCHBerlinger03/ /88PPMB:ARMTechEd i 903/Jo/88 Wo '