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Overcurrent and Overload Protection Using Protective Relays Electricity and New Energy Overcurrent and Overload Protection Using Protective Relays Course Sample 589888 Order no.: 589888 First Edition Revision level: 11/2016 By the staff of Festo Didactic © Festo Didactic Ltée/Ltd, Quebec, Canada 2015 Internet: www.festo-didactic.com e-mail: [email protected] Printed in Canada All rights reserved ISBN 978-2-89747-450-8 (Printed version) ISBN 978-2-89747-452-2 (CD-ROM) Legal Deposit – Bibliothèque et Archives nationales du Québec, 2015 Legal Deposit – Library and Archives Canada, 2015 The purchaser shall receive a single right of use which is non-exclusive, non-time-limited and limited geographically to use at the purchaser's site/location as follows. The purchaser shall be entitled to use the work to train his/her staff at the purchaser’s site/location and shall also be entitled to use parts of the copyright material as the basis for the production of his/her own training documentation for the training of his/her staff at the purchaser’s site/location with acknowledgement of source and to make copies for this purpose. In the case of schools/technical colleges, training centers, and universities, the right of use shall also include use by school and college students and trainees at the purchaser’s site/location for teaching purposes. The right of use shall in all cases exclude the right to publish the copyright material or to make this available for use on intranet, Internet and LMS platforms and databases such as Moodle, which allow access by a wide variety of users, including those outside of the purchaser’s site/location. Entitlement to other rights relating to reproductions, copies, adaptations, translations, microfilming and transfer to and storage and processing in electronic systems, no matter whether in whole or in part, shall require the prior consent of Festo Didactic. Information in this document is subject to change without notice and does not represent a commitment on the part of Festo Didactic. The Festo materials described in this document are furnished under a license agreement or a nondisclosure agreement. Festo Didactic recognizes product names as trademarks or registered trademarks of their respective holders. All other trademarks are the property of their respective owners. Other trademarks and trade names may be used in this document to refer to either the entity claiming the marks and names or their products. Festo Didactic disclaims any proprietary interest in trademarks and trade names other than its own. Safety and Common Symbols The following safety and common symbols may be used in this manual and on the equipment: Symbol Description DANGER indicates a hazard with a high level of risk which, if not avoided, will result in death or serious injury. WARNING indicates a hazard with a medium level of risk which, if not avoided, could result in death or serious injury. CAUTION indicates a hazard with a low level of risk which, if not avoided, could result in minor or moderate injury. CAUTION used without the Caution, risk of danger sign , indicates a hazard with a potentially hazardous situation which, if not avoided, may result in property damage. Caution, risk of electric shock Caution, hot surface Caution, risk of danger. Consult the relevant user documentation. Caution, lifting hazard Caution, hand entanglement hazard Notice, non-ionizing radiation Direct current Alternating current Both direct and alternating current Three-phase alternating current Earth (ground) terminal © Festo Didactic 589888 III Safety and Common Symbols Symbol Description Protective conductor terminal Frame or chassis terminal Equipotentiality On (supply) Off (supply) Equipment protected throughout by double insulation or reinforced insulation In position of a bi-stable push control Out position of a bi-stable push control IV © Festo Didactic 589888 Table of Contents Preface .................................................................................................................. IX About This Manual ................................................................................................ XI To the Instructor .................................................................................................. XIII Introduction Overcurrent and Overload Protection Using Protective Relays ............................................................................................ 1 DISCUSSION OF FUNDAMENTALS ....................................................... 1 Distinguishing overcurrent protection from overload protection ................................................................................. 1 Evolution of the protective relay technology ............................ 2 Protective relay testing ............................................................ 5 Exercise 1 Overcurrent Protection ................................................................ 9 DISCUSSION ..................................................................................... 9 Introduction .............................................................................. 9 Overcurrent protection and overload protection using fuses ...................................................................................... 10 Overcurrent protection and overload protection using LV circuit breakers (MCBs and MCCBs)..................................... 15 Overcurrent protection and overload protection using protective relays and HV circuit breakers .............................. 19 Instantaneous overcurrent relay ............................................ 21 Definite-time overcurrent relay .............................................. 23 Inverse definite minimum time (IDMT) overcurrent relay ...... 24 Standard time-current characteristics of IDMT overcurrent relays .................................................................. 25 Overcurrent protection of a power transformer using a numerical overcurrent relay ................................................... 28 Main features of protection implemented with numerical overcurrent relays and HV circuit breakers ........................... 31 PROCEDURE .................................................................................. 32 Set up and connections ......................................................... 32 Operation of an instantaneous overcurrent relay .................. 33 Operation of a definite time overcurrent relay ....................... 39 Operation of an inverse definite minimum time (IDMT) overcurrent relay .................................................................... 43 Overcurrent protection of a power transformer using a numerical overcurrent relay ................................................... 49 © Festo Didactic 589888 V Table of Contents Exercise 2 Overcurrent and Overload Protection of AC Machines and Power Transformers ........................................................... 57 DISCUSSION ................................................................................... 57 Introduction ............................................................................ 57 Thermal capability and power rating of ac machines and power transformers ................................................................ 58 Machine or transformer thermal relays of the temperature-sensor type ....................................................... 60 Machine or transformer thermal relays of the thermal- replica type ............................................................................ 61 OC and OL protection of an ac machine or power transformer using a numerical protective relay combining the functions of ANSI devices no. 50 and no. 49 .................. 66 Using the IDMT overcurrent relay (ANSI device no. 51I) function to achieve overload protection ................................. 69 PROCEDURE .................................................................................. 71 Set up and connections ......................................................... 71 Settings of a machine or transformer thermal relay of the thermal-replica type ............................................................... 72 Operation of a machine or transformer thermal relay of the thermal-replica type ......................................................... 76 Time-current characteristic of a machine or transformer thermal relay of the thermal-replica type ............................... 83 Overcurrent protection ........................................................... 86 Exercise 3 Overcurrent Protection of Radial Feeders ............................... 91 DISCUSSION ................................................................................... 91 Radial feeders ........................................................................ 91 Protection of a radial feeder with overcurrent relays ............. 93 Discrimination based on coordination in current ................... 94 Discrimination based on coordination in time ........................ 98 Current settings ........................................................................ 99 Time settings ............................................................................ 99 Discrimination based on coordination in both time and current .................................................................................. 101 Generic procedure to achieve time-current coordination of IDMT overcurrent relays .................................................. 101 Information about the system ................................................. 101 Time-current characteristics
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