ML19221A924
| ML19221A924 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/1977 |
| From: | NRC OFFICE OF STANDARDS DEVELOPMENT |
| To: | |
| References | |
| REGGD-01.106, REGGD-1.106, NUDOCS 7907100392 | |
| Download: ML19221A924 (2) | |
Text
Revision 1
, f ucg *S, U.S. NUCLEAR b GULt.iORY COMMISSION March 1977
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W6N PAGU LATORY GLDE gv OFFICE OF STANDARDS DEVELOPMENT REGULATORY GUIDE 1.106 THERf.1AL OVFRLO AD PRO TECTION FOR ELECTRIC MOYORC ON MOTOh-OPERATF.D VALVES A. INTRODUCTION motor starter for eteetne motors on motor-opera:cd !
s ah es. T his mAod.s ould ensure that the thermal Criterion 1. " Quality Standards and Records." of ourload protection detices will not needlessly pre-Appenda A. " General Design Criteria for Nuclear tent the motor from performing its safety-related Power PlantsJ' to 10 CFR Part 50 " Licensing of function. T he Advisory Committee on Reactor Production and Utih/ation Facilities / requires, in Safeguards has been consulted concerning this guide part. that components important to safety be and has concurred in the regulatory position.
designed, fabricated, erected, and tested to quaht) standards commensurate with the importance of Gc safety functions to be performed.
B. DISCUSSION Criterion 4, " Environmental and Niinile Design BasesJ of Appendis A to 10 CFR Part 50 requires,in N10 tor-operated vals es with thermal os erload part, that components important to safety be pnitection desiees for the satse mctors are used in desiened to accommodate :he effects of and be com.
sa fety sy stem s and in their auuhary supportmg patiole with the ensironmental conditions associated systems Operating experience has show n that in-with normal operation, maintenance, testiog, and discrin inate application of thermal oserload protec-tmn desices to these vaive motors could result in postulated accidents, includ'ng loss-of-coolant acci.
dents.
needless hindrance to successfui completion of safety functions.
Criterion 13. " Instrumentation and Control,' of Appendix A to 10 Cl-R Pan 50 requires that in-strumentation be provided to monitor sariables and Thernial overload relays are designed primanly to ss stems oser their anticipated ranges for normal protect continuous-duty motor 3 w hile they are run-operation and for postulated accidcnt conditions and ning rather than during starting. U se of these that controls he prosided to maintain these variables oserload desices to protect intermittent-duty motors and systems within prescribed operating ranges.
may therefore result in undesired actuation of the desices if the cumulatise effect of heating caused by Criterion XI, " Test Control / of Appendix B, successise starts at short intervals is not taken into
" Quality Assurance Criteria ior Nuclear Power account in determining the oserload tr etting.
Plants and Fuel Reprocessing Plantsf to 10 CFR Part 50 requires, in part, that a test program be es-It is generally sery difficult for any thermally sen-tablished to ensure that systems and components per-sitise desice to approximate adequately the sar)mg form satisfactonly and that the test program include thermal characteristics of an intermittent-duts motor operational tests Juring nuclear power plant opera-oser its full range of starting and loading con'ditions.
tion.
This is mainly caused by the wide variations in motor heatine curses for various sizes and desiens and also This regulatory guide desenbes a method accept-by the' difficulty in obtaining motor hea' ting data to able to the NRC staf f for complying with the abose an acceptable accuracy.
criteria with regard to the application of thermal oserload protection desiees that are integral with the
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Since the trip function in o thermi merload desice C. REGULATORY POSITION is dependent or. temper iture, the degree of merload protection prosided is affected by change in ambient in order to ensure that safety-related motor-temperature at the momr or starter location. T his operated vahes whose motors are equipped with aspect becomes more comples in nuclea. power plant thermal eserload protection devices integral with the applications w here, in :,ome cases, the motor to be motor starter will perform their function, one of the protected is inside the containment and the oserload two alternathes described in regulatory position I or protection Geuces are outside the containment. In the one described m regulatory position 2 should be such a situatior., the tempera'ure dif ference be: ween implemented:
the motor and the merload desice could be as high a'
- l. Prosided that the completion of the safety func-Wi-under design basis conditions. l hus, the selee-tion is not jeopardized or that other safety systems tion of an appropriate trip setpoint for such a sake are not degraded, (a) the thermal oserload protec-motor should take into consideration operation of tion devices should be continuously bypassed and the sahe under urious temperatures for both normal temporarily placed in force onh when the sale and postulated accident conditions,includmg loss-of-
~ undergomg periodid or maintenance motors are coolant accidents.
testing or (b) those thermal oserload protection desices that are normally in force during plant opera-The accuracy obt. unable with the thermal m erload tion should be bypawed under accident conditions.
relay trip generally s aries from -50 to 0S of trip set-The bypass initiation system circuitry should point. Since the primary concern in the application of conform to the criteria of Sections 4.1, 4.2, 4. 3, 4.4, merload desiees is to protect the motor windings 4.5, 4.10, and 4.13 of liilili Std 279-1971, " Criteria a g,n a s t excessis e heating, the abme negatis e for Protection Sy stems fo r Nuclear Pow er tolerance m trip charactenstics of the protection Generating Stations," and should be periodically desice is considered in the safe direction for motor tested.
protection. Ilowes er, this consers atise design feature built into these m erload desices for motor protection e tdp setpoint of the thermal merload pmtution desices should be established with all un-could interfere in the successful functioning of a sa fets -related ss stem; i.e.,
the thermal oserload anamtb whed in fas or of completing the safety-
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related action. W,ith respect to those uncertamties, device could open to remose power from a motor before the safety function has been comp!cted or esen consideration should be gnen to (a) variations in the ambient temperature at the installed location of the initiated. In nuclear power plant application, the m edoa pmtatbn devices and the vah e motors,(b) criterion for establishine an oscrload trip setroint should be to complete the safety function (e g., drise inaamacies in nmtor heating data and the merload pmtunon des ice trip characteristics and the the sabe to its proper position to miticate the effects of an accident) rather than merely io protect the matdung of these two items, and (c) setpoint drift. In er to ensure continued functional reliability and o
motor from destructise heatine. In some plants, the thermal merload desiees are by' pawed durine norma the accuracy of the trip point, the thermal overload plant operation, except that they are teniporarily p tution desiee should be periodically tested.
placed in force w hen the vahe motors are undergoing D. IMPLEMENTATION periodic testing.
.The purpose of this section is to prmide informa-tion to appheants regarding the NRC staffs plans for usine this reculators guide.
%.here the thermal oserload protection deu.ces are by passed, it is important to ensure that the bypassing This guide renects current NRC staff practice.
does not result in jeopardizing the completion of the Therefore, except in those cases in w hich the appli-safety function or in degrading other safety systems cant proposes an acceptable alternatise method for because of any sustained abnormal motor circuit cur-complying with specified portions of the Commis-rents that may be present. As an example, for small sion's regulations, the method described herein is be-motors (1/2 horsepower or less), the magnetic trip ing and will continue to be used in the evaluation of desices prosided in the motor combination starter-submittah for construction permit applications until breaker may not adequately protect the circuit at all this guide is resised as a result of suggestions from the times against sustain J locked-rotor currents.
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