Regulatory Guide 1.106

Thermal Overload Protection for Electric Motors on Motor-Operated Valves.

ML13350A288
Person / Time
Issue date:	11/30/1975
Revision:	0
From:	NRC/OSD
To:
References
RG-1.106
Download: ML13350A288 (2)

U.S. NUCLEAR. REGULATORY COMMISSIONREGULATORY GUIDEOFFICE OF STANDARDS DEVELOPMENTREGULATORY GUIDE 1.106THERMAL OVERLOAD PROTECTION FOR ELECTRIC MOTORSON MOTOR-OPERATED VALVESNovember 1975A. INTRODUCTIONCriterion I, "Quality Standards and Records," ofAppendix A, "General Design Criteria for Nuclear PowerPlants," to 10 CFR Part 50. "Licensing of Productionand Utilization Facilities," requires. in part, that corr.-thernial overload protection devices will not needlesslyprevent the motor fron, performing its safely-relatedfunction.B. DISCUSSIONponents important to safety be designed, fabricated, Motor-operated valves with thermal overload protec-erected, and tested to quality standards commensurate tion devices for the valve motors are used in safetywith the importance of the safety functions to be systems and their auxiliary supporting systems. Oper-performed. ating experience has shown that indiscriminate applica-tion of thermal overload protection devices to theseCriterion 4, "Environmental and Missile Design valve motors could-,'Iresult Ain needless hindrance toBases," of Appendix A to 10 CFR Part 50 reiuires. in successful comliletion of safety functions.part, that components important to safety be designedto accommodate the effects of and be compatible with Thernia*t overI.oaat-i'elavs are designed primarily it)the environmental conditions associated with normal protect coiitiiuo'tý.duty motors while they are running.operation. maintenance, testing, and postulated acci- rather. than during starting. Use of these overload devicesdents, including loss.of-coclant accidents. .",to protect intermittent-duty motors may therefore resultiiihrunfdesired actuation of the devices if the cumulativeCriterion 13, "Instrumentation and Control." of. "effe*Jf:.";of heating caused by successive starts at shortAppendix A to 10 CFR Part 50 requires that instrumii';"`1!,;,. inteirvals is not taken into account in determining thetation be provided to monitor variables and systenitsover ",.overload trip setting.their anticipated ranges for normal operaLionand4forpostulated accident conditions and that c6ntrolsý` b7' It is generally very difficult for any thermallyprovided to maintain these variables and systems within sensitive device to approximate adequately the varyingprescribed operating ranges. thermal characteristics of an intermittent-duty motorAMU rL ulIdlILU d I tll Its *A;~~~u"' ~.Criterion XM, "Test Control," of Appendix B,"Quality Assurance Criteria A'o. Nuclear Power Plantsand Fuel Reprocessing -Plants.;-,.,to 10 CFR Part 50requires, in part. that a test-rogram be estabished toensure that systetrm-andfcon nents perform satisfac-torily and that thiltest prod'gam include operational testsduring nuclear.poerplant.;operatton.This reg t guide describes a method acceptableto the NRC st"",, for complying with the above criteriawith regard to 'the application of thermal overloadprotection devices for electric motors on motor-operatedvalves controlled by motor starters to ensure that theThis is mainly caused by the wide variations in motorheating curves for various sizes and designs and also bythe difficulty in obtaining motor heating data to anacceptable accuracy.Since the trip functiotn in a thermal overload device isdependent on temperature. the degree of overloadprotection provided is affected by change in ambienttemperature at the nmotor or starter location. This aspectbecomes nmore complex in nuclear power plant applica-tions where the motor to he protected is inside thecontainment and the overload protection devices areoutside the containment. In such a situation. theUSNRC REGULATORY GUIDES Co,,tments should bo sent to the Secretary of the Comnmission. U.S. NuclearRegulator' Cnmmnst.on. Washington. D C 70. Atlention Dot1eting andAegulatoty Guides ate ssued to describe and make available to the public Service Section.methods Accept:ble to the NRC stall o0 specific parts of tireCommotison'I requtaliOs, to delineate techniques used by the stiaff f evalu The quide.s are issuled in the following ten broad divisionsalinq specific poblems or postulated ac cidentis, o to provide guidance It applecants Regulatory Guides ire not substitutes lot eegulations, and complarce. I Power Reoecleos 6 Product%with them is not tequted Methods and solutions different from those set out or 2 R#6eeACh a,.d Test Reactoris 7 Transportationthe guide% well be acceptable if thea provide a basis rthe fli tndings requisite to 3 Furls And Materials Facihltes 8 Occupational Healththe issuance or continuance nt a permit of licenee by the Cummission. 4 Envionmenlal Rnd Siting 9 Antitrust ReviewComments and sugjestion& teel impovement. in these guides are entcouraged 5 Materials and Plant Prote'.ton t0 Genetftlat all tImes. ared gjuides will he revised. as approprlate, Io accommodate cornmants and to te~flet.t new ,intoi,,'tion n' eltpeerencee ltowetver. cometirints on Copies of published guides na¥ he ohlatn,-d hy writlen tequest indicetingg ftithiS ri cde. f ret.eived within brintl' IwO ntt"thstrl11. fts ,sisednre. will he par ilisettns desired to the U S Nuclea, Regul09tVY Corrinnnssion. 0 Ct1culalty useful i envaluatlig the need fat ren ei.ly te¥1stoet 2055. Atteniiion Di Office ol Standard% Denolotmeinl temperature difference between the motor and theoverload device could be as high as 2000F under designbasis conditions. Thus the selection of an appropriatetrip setpoint for such a valve motor should take intoconside-ration opelation of the valve under varioustCmlicratures for'both normal and postulated accidentconditions, including loss-of-coolant accidc its.The accuracy obtainable with the thermal overloadrelay trip generally varies from -5% to 0% of trips1!tpoint. Since the primary concern in the application ofoverload devices is to protect the motor wiadings againstexcessive heating. the above negative tolerance in tripcharacteristics of the protection device is considered inthe sat', direction for motor protection. However, thisconservative design feature built into these overloaddevices for motor protection could interfere in thesuccessful functioning of a safety-related system: i.e., thethermal overload device could open to remove powerfrom a motor before the safety function has beencompleted or even initiated. In nuclear power plantapplication, the criterion for establishing an overloadtrip setpoint should be to complete the safety function(e.g.. drive the valve to its proper position to mitigatethe effects of an accident) rather than merely to protecEthe motor from destructive heating. In some plants, theth,!rmia overload devices are bypassed during normalplant operation. except that they are temporarily placediit force when the valve motors are undergoing periodictesting.C. REGULATORY POSITIONI. In order to ensure that motor-operated valveswhose motors are equipped with thermal overloadprotection devices will perform their safety-relatedfunction. those thermal overload protection devices thatare normally in furce during plant operation should bebypassed under accident conditions. The bypass initia-tion circuitry should c-inform to the criteria of IEEE279-1971, Sections 4.1, 4.2,4.3, 4.4,4.5, 4.10, and 4.13and should be periodically testes.2. As an acceptable alternative to regulatory positionC.A, the trip setpoint of the thermal overload protectiondevices should be established with all uncertaintiesresolved in favor of completing the safety-related action.With respect to those uncertainties, consideration shouldbe given to (1) vaijations in the ambient temperature atthe installed location of the overload protection devicesand the valve motors, (2) inaccuracies in motor heatingdata and the overload protection device trip character-istics and the matching of these two items, and (3)setpoint drift. In order to ensure continued functionalreliability and the accuracy of the trip point, the thermaloverload protection device should be periodically tested.D. IMPLEMENTATIONThe purpose of this section is to provide informationto applicants and licensees regarding the NRC staffsplans for using this regulatory guide.Except in those cases in which the applicant proposesan acceptable alternative method for complying withspecified portions of the Commission's regulations, themethod described herein will be used in the evaluationof submittals in connection with construction permitapplications docketed after July 15, 1976.If an applicant wishes to use this regulatory guide indeveloping submittals for applications docketed on orbefore July 15, 1976, the pertinent portions of theapplication will be evaluated on the basis of this guide.(~'u)-o4..S.oti('I3 ~..(U-z0.0.4 S'.400~040 .J~a-'.- 40.-44 4* z.4 'SU ~0*