Regulatory Guide 1.106
| ML003740323 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/1977 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| References | |
| RG-1.106 Rev 1 | |
| Download: ML003740323 (2) | |
Revision 1 March 1977 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
A. INTRODUCTION
motor starter for electric motors on motor-operated valves. This method would ensure that the thermal Criterion 1, "Quality Standards and Records," of overload protection devices will not needlessly pre Appendix A, "General Design Criteria for Nuclear vent the motor from performing its safety-related Power Plants," to 10 CFR Part 50, "Licensing of function. The Advisory Committee on Reactor.,
Production and Utilization 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 quality standards commensurate with the importance of the safety functions to be performe
d.
B. DISCUSSION
Criterion 4, "Environmental and Missile Design Motor-operated valves with thermal overload Bases," of Appendix A to 10 CFR Part 50 requires, in protection devices for the valve motors are used in part, that components important to safety be safety systems and in their auxiliary supporting designed to accommodate the effects of and be com systems. Operating experience has shown that in patible with the environmental conditions associated discriminate application of thermal overload protec with normal, operation, maintenance, testing, and tion devices to these valve motors could result in postulated accidents, including loss-of-coolant acci needless hindrance to successful completion of safety dents. functions.
Criterion 13, "Instrumentation and Control," of Appendix A to 10 CFR Part 50 requires that in Thermal overload relays are designed primarily to strumentation be provided to monitor variables and protect continuous-duty motors while they are run systems over their anticipated ranges for normal ning rather than during starting. Use of these operation and for postulated accident conditions and overload devices to protect intermittent-duty motors that controls be provided to maintain these variables may therefore result in undesired actuation of the and systems within prescribed operating ranges. devices if the cumulative effect of heating caused by successive starts at short intervals is not taken into Criterion XI, "Test Control," of Appendix B, account in determining the overload trip setting.
"Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants," to 10 CFR
Part 50 requires, in part, that a test program be es It is generally very difficult for any thermally sen tablished to ensure that systems and components per sitive device to approximate adequately the varying form satisfactorily and that the test program include thermal characteristics of an intermittent-duty motor operational tests during nuclear power plant opera over its full range of starting and loading conditions.
tion. This is mainly caused by the Wide variations in motor heating curves for various sizes and designs and also This regulatory guide describes a method accept by the difficulty in obtaining motor heating data to able to the NRC staff for complying with the above an acceptable accuracy.
"01 criteria with regard to the application of thermal overload protection devices that are integral with the
0 Lines indicate substantive changes from previous issue.
sent to the Secretary should beWashington. of the Commission. Nuclear US. ing Regu USNRC REGULATORY GUIDES Comments latory, Commission. D.C. 20555. Attention: Docket &nW Servce tranch.
Regulatory Guides are issued to describe and make available to the public methods acceptable to the NRC staff of implementing specific parts of the Commission's The guides se issued in the following ten broad divisions:
regulations, to delineate techniques used by the staff in evaluating specific problems or postulated accidents, or to provide &uidance to applicant
s. Regulatory Guides
1. Power Reactors 6. Products are not substitutes for regulations, and compliance with them is not required. 7. Transportation accept- 2. Research and Test Reactors Methods and solutions different from those set out In the guides will be
4. Environmental andcSiting 9. Antitrust Review able if they provide abasis for the findings requisite to the issuance or continuance of . permit or license by the Commission. 5. Materials and Plant Protection 10. General Comments and suwestions for improvements In these guides ae encouraged at all Requests for single copies of Issued guides (which may be reproduced) or for place times, and guides will be revised. as appropriate, to accommodate commeMts and ment on an automatic distribution list for single copies of future guides in specific to reflect new information or experience. -This guide was revised as a mull of divisions should be made in writing to the US. Nuclear Regulatory Commission.
Washington, D.C. 2055./Attention: Director. Division of Document Control.
substantive comments received from the public and additional staff review.
Since the trip function in a thermal overload device
C. REGULATORY POSITION
is dependent on temperature, the degree of overload protection provided is affected by change in ambient In order to ensure that safety-related motor temperature at the motor or starter location. This operated valves whose motors are equipped with aspect becomes more complex in nuclear power plant thermal overload protection devices integral with the motor starter will perform their function, one of the K
applications where, in some cases, the motor to be two alternatives described in regulatory position I or protected is inside the containment and the overload the one described in regulatory position 2 should be protection devices are outside the containment. In implemented:
such a situation, the temperature difference between the motor and the overload device could be as high as I. Provided that the completion of the safety func
2000 F under design basis conditions. Thus, the selec tion is not jeopardized or that other safety systems tion of an appropriate trip setpoint for such a valve are not degraded, (a) the thermal overload protec motor should take into consideration operation of tion devices should be continuously bypassed and the valve under various temperatures for both normal temporarily placed in force only when the valve and postulated accident conditions, including loss-of motors are undergoing periodic or maintenance coolant accidents. testing or (b) those thermal overload protection devices that are normally in force during plant opera tion should be bypassed under accident conditions.
The accuracy obtainable with the thermal overload relay trip generally varies from -5% to 0% 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, overload devices is to protect the motor windings 4.5, 4.10, and 4.13 of IEEE Std 279-1971, "Criteria against excessive heating, the above negative for Protection Systems for Nuclear Power tolerance in trip characteristics of the protection Generating Stations," and should be periodically device is considered in the safe direction for motor tested.
protection. However, this conservative design feature 2. The trip setpoint of the thermal overload built into these overload devices for motor protection protection devices should be established with all un could interfere in the successful functioning of a certainties resolved in favor of completing the safety safety-related system; i.e., the thermal overload related action. With respect to those uncertainties, device could open to remove power from a motor consideration should be given to (a) variations in the before the safety function has been completed or even ambient temperature at the installed location of the initiated. In nuclear power plant application, the overload protection devices and the valve motors, (b)
criterion for establishing an overload trip setpoint inaccuracies in motor heating data and the overload should be to complete the safety function (e.g., drive protection device trip characteristics and the the valve to its proper position to mitigate the effects matching of these two items, and (c) setpoint drift. In of an accident) rather than merely to protect the order to ensure continued functional reliability and motor from destructive heating. In some plants, the the accuracy of the trip point, the thermal overload thermal overload devices are bypassed during normal protection device should be periodically tested.
plant operation, except that they are temporarily placed in force when the valve motors are undergoing
D. IMPLEMENTATION
periodic testing, The purpose of this section is to provide informa tion to applicants regarding the NRC staff's plans for using this regulatory guide.
Where the thermal overload protection devices are bypassed, it is important to ensure that the bypassing This guide reflects current NRC staff practice.
does not result in jeopardizing the completion of the Therefore, except in those cases in which the appli safety function or in degrading other safety systems cant proposes an acceptable alternative 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 devices provided in the motor combination starter submittals for construction permit applications until breaker may not adequately protect the circuit at all this guide is revised as a result of suggestions from the times against sustained locked-rotor currents. public or additional staff review.
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