Regulatory Guide 1.106
| ML13350A288 | |
| Person / Time | |
|---|---|
| Issue date: | 11/30/1975 |
| From: | NRC/OSD |
| To: | |
| References | |
| RG-1.106 | |
| Download: ML13350A288 (2) | |
U.S. NUCLEAR. REGULATORY COMMISSION
REGULATORY GUIDE
OFFICE OF STANDARDS DEVELOPMENT
REGULATORY GUIDE 1.106 THERMAL OVERLOAD PROTECTION FOR ELECTRIC MOTORS
ON MOTOR-OPERATED VALVES
November 1975
A. INTRODUCTION
Criterion I, "Quality Standards and Records," of Appendix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50. "Licensing of Production and Utilization Facilities," requires. in part, that corr.-
thernial overload protection devices will not needlessly prevent the motor fron, performing its safely-related function.
B. DISCUSSION
ponents 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 safety with 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 these Criterion
4,
"Environmental and Missile Design valve motors could-,'Iresult Ain needless hindrance to Bases," of Appendix A to 10 CFR Part 50 reiuires. in successful comliletion of safety functions.
part, that components important to safety be designed to 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 devices dents, including loss.of-coclant accidents.
.",to protect intermittent-duty motors may therefore result iiihrunfdesired actuation of the devices if the cumulative Criterion
13, "Instrumentation and Control." of.
"effe*Jf:.";of heating caused by successive starts at short Appendix A to 10 CFR Part 50 requires that instrumii';"`1!,;,. inteirvals is not taken into account in determining the tation be provided to monitor variables and systenitsover ",.overload trip setting.
their anticipated ranges for normal operaLionand4for postulated accident conditions and that c6ntrolsý` b7'
It is generally very difficult for any thermally provided to maintain these variables and systems within sensitive device to approximate adequately the varying prescribed operating ranges.
thermal characteristics of an intermittent-duty motor AMU
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Criterion XM,
"Test Control,"
of Appendix B,
"Quality Assurance Criteria A'o. Nuclear Power Plants and Fuel Reprocessing -Plants.;-,.,to 10 CFR Part 50
requires, in part. that a test-rogram be estabished to ensure that systetrm-andfcon nents perform satisfac- torily and that thiltest prod'gam include operational tests during nuclear.poerplant.;operatton.
This reg t
guide describes a method acceptable to the NRC st"",, for complying with the above criteria with regard to 'the application of thermal overload protection devices for electric motors on motor-operated valves controlled by motor starters to ensure that the This is mainly caused by the wide variations in motor heating curves for various sizes and designs and also by the difficulty in obtaining motor heating data to an acceptable accuracy.
Since the trip functiotn in a thermal overload device is dependent on temperature.
the degree of overload protection provided is affected by change in ambient temperature at the nmotor or starter location. This aspect becomes nmore complex in nuclear power plant applica- tions where the motor to he protected is inside the containment and the overload protection devices are outside the containment.
In such a situation. the USNRC REGULATORY GUIDES
Co,,tments should bo sent to the Secretary of the Comnmission. U.S. Nuclear Regulator'
Cnmmnst.on. Washington. D C 70.
Atlention Dot1eting and Aegulatoty Guides ate ssued to describe and make available to the public Service Section.
methods Accept:ble to the NRC stall o0 implement*ng specific parts of tire Commotison'I requtaliOs, to delineate techniques used by the stiaff f evalu The quide.s are issuled in the following ten broad divisions alinq specific poblems or postulated ac cidentis, o to provide guidance It apple cants 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 Transportation the guide% well be acceptable if thea provide a basis rthe fli tndings requisite to
3 Furls And Materials Facihltes
8 Occupational Health the issuance or continuance nt a permit of licenee by the Cummission.
4 Envionmenlal Rnd Siting
9 Antitrust Review Comments and sugjestion& teel impovement. in these guides are entcouraged
5 Materials and Plant Prote'.ton t0 Genetftl at all tImes. ared gjuides will he revised. as approprlate, Io accommodate corn mants 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 fti thiS ri cde. f ret.eived within brintl' IwO ntt"thstrl11.
fts ,sisednre. will he par ilisettns desired to the U S Nuclea, Regul09tVY Corrinnnssion. Wall*hington. 0 C
t1culalty useful i envaluatlig the need fat ren ei.ly te¥1stoet
2055. Atteniiion Di ec*lt. Office ol Standard% Denolotmeinl
temperature difference between the motor and the overload device could be as high as 2000F under design basis conditions. Thus the selection of an appropriate trip setpoint for such a valve motor should take into conside-ration opelation of the valve under various tCmlicratures for'both normal and postulated accident conditions, including loss-of-coolant accidc its.
The accuracy obtainable with the thermal overload relay trip generally varies from -5% to 0% of trip s1!tpoint. Since the primary concern in the application of overload devices is to protect the motor wiadings against excessive heating. the above negative tolerance in trip characteristics of the protection device is considered in the sat', direction for motor protection. However, this conservative design feature built into these overload devices for motor protection could interfere in the successful functioning of a safety-related system: i.e., the thermal overload device could open to remove power from a motor before the safety function has been completed or even initiated. In nuclear power plant application, the criterion for establishing an overload trip setpoint should be to complete the safety function (e.g.. drive the valve to its proper position to mitigate the effects of an accident) rather than merely to protecE
the motor from destructive heating. In some plants, the th,!rmia overload devices are bypassed during normal plant operation. except that they are temporarily placed iit force when the valve motors are undergoing periodic testing.
C. REGULATORY POSITION
I. In order to ensure that motor-operated valves whose motors are equipped with thermal overload protection devices will perform their safety-related function. those thermal overload protection devices that are normally in furce during plant operation should be bypassed under accident conditions. The bypass initia- tion circuitry should c-inform to the criteria of IEEE 279-1971, Sections 4.1, 4.2,4.3, 4.4,4.5, 4.10, and 4.13 and should be periodically testes.
2. As an acceptable alternative to regulatory position C.A, the trip setpoint of the thermal overload protection devices should be established with all uncertainties resolved in favor of completing the safety-related action.
With respect to those uncertainties, consideration should be given to (1) vaijations in the ambient temperature at the installed location of the overload protection devices and the valve motors, (2) inaccuracies in motor heating data and the overload protection device trip character- istics and the matching of these two items, and (3)
setpoint drift. In order to ensure continued functional reliability and the accuracy of the trip point, the thermal overload protection device should be periodically tested.
D. IMPLEMENTATION
The purpose of this section is to provide information to applicants and licensees regarding the NRC staffs plans for using this regulatory guide.
Except in those cases in which the applicant proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, the method described herein will be used in the evaluation of submittals in connection with construction permit applications docketed after July 15, 1976.
If an applicant wishes to use this regulatory guide in developing submittals for applications docketed on or before July 15, 1976, the pertinent portions of the application will be evaluated on the basis of this guide.
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