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Approved as an American National Standard (ANSI) IEEE Std 242-2001 (Revision of IEEE Std 242-1986) IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems Sponsor Industrial and Commercial Power Systems Department of the IEEE Industry Applications Society Approved 14 June 2001 IEEE-SA Standards Board Abstract: The principles of system protection and the proper selection, application, and coordination of components that may be required to protect industrial and commercial power systems against abnormalities that could reasonably be expected to occur in the course of system operation are presented in a in a simple, yet comprehensive, format. The principles presented apply to both new electrical system design and to the changing, upgrading, or expansion of an existing electrical distribution system. Keywords: bus protection, cable protection, calibration, conductor protection, coordinating time intervals, current transformers, current-limiting fuses, fuse coordination, fuse selectivity, generator grounding, generator protection, high-voltage fuses, liquid preservation systems, low-voltage motor protection, medium-voltage motor protection, motor protection, overcurrent protection, potential transformers, power fuses, protective relays, relay application principles, relay operating principles, service protection, short-circuit protection, switchgear protection, system design, system protection, transformer protection, voltage transformers Grateful acknowledgment is made to the following organizations for having granted permission to reprint material in this document as listed below: Table 10-1 from National Electrical Manufacturers Assocation. Reprinted from NEMA MG10-1994 by permission of the National Manufacturers Assocation. © Copyright 1997 by the National Electrical Manufacturers Assocation. All rights, including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the International and Pan American Copyright Conventions. Figure 10-14, Figure 10-15, and Figure 10-18 from Bentley-Nevada. Figure 10-16 and Figure 10-17 from API 541-1995. First Printing 17 December 2001 SH94930 SS94930 The Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue, New York, NY 10016-5997, USA Copyright © 2001 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Published 17 December 2001. Printed in the United States of America ISBN 0-7381-2844-9 No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher. IEEE Standards documents are developed within the IEEE Societies and the Standards Coordinating Committees of the IEEE Standards Association (IEEE-SA) Standards Board. The IEEE develops its standards through a consensus development process, approved by the American National Standards Institute, which brings together volunteers representing varied viewpoints and interests to achieve the final product. Volunteers are not necessarily members of the Institute and serve without compensation. While the IEEE administers the process and establishes rules to promote fairness in the consensus development process, the IEEE does not independently evaluate, test, or verify the accuracy of any of the information contained in its standards. Use of an IEEE Standard is wholly voluntary. The IEEE disclaims liability for any personal injury, property or other damage, of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, or reliance upon this, or any other IEEE Standard document. The IEEE does not warrant or repr