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Short-Circuit Current Calculations And SHORT-CIRCUIT CURRENT CALCULATIONS L .. AND PROTECTIVE RELAY COORDINATION FOR INDUSTRIAL AND COMMERCIAL POWER SYSTEMS, A Thesis Presented to The Faculty of the College of Engineering and Technology Ohio University In Partial Fulfillment of the Requirements for the Degree Master of Science Houshang C. Mohammadi s August, 1986 OHIO UNIVERSITY LIBRARY ACKNOWLEDGEMENTS I would like to offer my appreciation and thanks to Dr. Albert J.F. Keri my advisor, and Dr. H.W. Hill for their guidance and encouragement in the preparation of this thesis. I owe a great deal to my employer, E.I. Dupont company who gave me this opportunity to continue my education while I was working. I would also like to express my thanks to Mr. R.L. Doughty senior project engineer at E.I. Dupont company who checked my work through this study. Finally, I would like to express my thanks to the faculty and all members of staff at Ohio University who have contributed a great deal towards this work. TABLE OF CONTENTS ABSTRACT ................................ xii CHAPTER 1 . Introduction ............................ 1 1.1 Statement of the problem ................ 1 1.2 Literature search ....................... 4 1.3 State of the art ......................... 5 CHAPTER 2 . Sources of short circuit ................. 7 2.1 Generator ............................... 8 2.2 Synchronous motors ....................... 8 2.3 Induction motors ......................... 10 2.4 Electric utility systems ................. 11 2.5 Rotating machine reactance ............... 12 2.6 Symmetrical and asymmetrical currents .... 15 CHAPTER 3 . Short-circuit-current calculation ........ 17 3.1 Important assumptions .................... 18 3.2 Single line diagram ...................... 18 3.3 Impedance diagram ........................ 19 3.4 Type and location of faults required ..... 22 3.5 Symmetrical short-circuit current ........ 22 calculation 3.6 Momentary short circuit calculation ...... 25 3.7 Interrupting short circuit calculation ... 27 CHAPTER 4 . General equipment used for protection .... 31 4.1 Overcurrent relays ................. ....... 32 4.2 Fuses .................................... 33 4.3 Circuit breakers ......................... 38 4.4 Generator protection .................... 40 4.5 Transformer protection .................. 44 CHAPTER 5 . Coordination of protective devices ....... 47 5.1 Primary considerations for coordination .. 48 5.2 Data required for a coordination ......... 51 5.3 Methods of coordination .................. 52 5.4 Testing of protective devices ............ 66 CHAPTER 6 . Conclusion .............................. 72 BIBLIOGRAPHY .................... APPENDIX 1 . Impedance data .......................... 77 Al.l ANSI standard reactance values .......... 77 A1.2 Transmission line impedances ............ 78 A1.3 15KV cable impedances ................... 79 A1.4 5KV cable impedances .................... 80 A1.5 Correction factors for non magnetic ducts 81 APPENDIX 2 . Belle plant short circuit study ......... 82 A2.1 Description of the work ................. 82 A2.2 12KV air circuit breaker ratings ........ 84 A2.3 System assumptions ...................... 84 A2.4 Belle plant single line diagram ......... 85 A2.5 Belle plant impedance diagrams .......... 87 A2.6 Belle plant short circuit calculation ... 93 APPENDIX 3 . System generator protection ............. 98 A3.1 Belle plant generator protection ........ 98 A3.2 Belle plant bus protections ............. 115 APPENDIX 4 . Belle plant- transformer protection ..... 120 A4.1 ~~~e HU-1 transformer differential relay 120 APPENDIX 5 . Belle plant coordination curves ........ 126 and detailed diagrams "A" switch house. BANK No.1 and 12KV BUS 126 ECR No.6. 12KV BUS "A'f.................. 128 ECR No.6, 12KV BUS "B" .................. 130 Cogeneration generator .................. 132 BANK No.7 feeder No.18.................. 134 2.4KV 600HP motor river pump house ...... 136 2.4KV 450HP motor boiler feeder pump No.5 138 A5.8 2.4KV 75HP motor ash pump ............... 140 A5.9 2.4KV 200HP motor recirculating pump .... 142 A5.10 2.4KV 200HP motor F.D. fan boilers ...... 144 No.6 & 9 A5.11 2.4KV feeders sheet No.1 & BANK No.60 ... 146 A5.12 2.4KV feeders sheet No.2 & BANK No.59 ... 148 A5.13 2.4KV feeders ECR No.5 .................. 150 A5.14 2.4KV 150HP motor boiler No.10 mills .... 152 A5.15 2.4KV 550HP motor 1.D fan boilers ....... 154 No . 14 & 15 A5.16 2.4KV 400HP motor 1.D fan boilers ....... 156 No.6 & 9 A5.17 480V feeders ECR No.8 sheet 1 ........... 158 A5.18 480V feeders ECR.No.8 sheet 2 ........... 160 A5.19 480V feeders ECR No.8 sheet 3 ........... 162 A5.20 2.4KV 550HP motors 1.D fan boiler No.10. 164 APPENDIX 6 . Westinghouse overcurrent relay curves ... 166 A6.1 Type CO-7 Over Current Relay ............ 166 A6.2 Type CO-9 Over Current Relay ............ 167 A6.3 Type CO-11 Over Current Relay ........... 168 A6.4 Type COM-5 Over current Relay ........... 169 A6.5 Type CV-2 Under Voltage Relay ............ 170 A6.6 Type CV-7 Under Voltage Relay ........... 171 A6.7 Westinghouse type Amptector 11-A ........ 172 A6.8 Westinghouse type DSL-206 Limiters ...... 173 A6.9 Two pole type AA12P Overload Relay ...... 174 APPENDIX 7 . Buss fuses curves ....................... 180 A7.1 Type LPS-RK Low Peak Dual Element fuse .. 180 A7.2 Type KRP-C HI-CAP Fuses ................ 181 APPENDIX 8 . ASA Device numbers and functions ........ 182 LIST OF FIGURES 2.1 Total short circuit current equals sum of sources 9 2.2 Symmetrical short circuit currents from .......... 13 four surces 5.1 Typical time curves of CO-9 Relay ................ 63 5.2 Portion of Belle plant relaying detailed diagram . 64 5.3 Portion of Belle plant co-ordination curves ...... 65 A2-1 Block diagram of system setup .................... 83 A2-2 Belle plant single line diagram .................. 86 A2-3 Multiplying factors for three phase & line ....... 91 to ground faults A2-4 Belle plant simplified impedance diagram ......... 92 A2-5 Equivalent circuit for fault "A" (momentary) ..... 93 A2-6 Simplified equivalent circu'it for fault "A"...... 94 Wye-Delta transformation for fault "A". .......... 94 Equivalent circuit for fault "A" (interrupting) . 95 Wye-Delta transformation for fault "A"(interrup.) 96 Typical time curves for the 10% sensitivity ...... 100 type CA generator relay Limits for application of the CWC time curves .... 102 Typical time curves of the type CWC relay ........ 103 Generator over voltage curve ..................... 108 Generator reactive capability curve .............. 109 Machine capability curve ......................... 110 A3-7 SDF-1 tripping relay under declining frequency ... 113 A3-8 Operating time variations with changes in ........ 114 time-dial setting A3-9 KAB relay voltage unit setting ................... 118 A3-10 KAB relay current unit setting ................... 119 LIST OF TABLES Machine reactance and multiplying factors ....... Fuse classification ............................. Current limiting characteristics of c-s one ..... time fuse Transformer ANSI data ........................... Rating ratios for safe co-ordinations ........... Power air circuit breaker minimum band .......... ANSI Standard reactance values .................. Transmission line impedances .................... 15KV cable impedances ........................... 5KV cable impedances ............................ Correction factors for non magnetic ducts ........ 81 Result of Belle plant short circuit study ....... 97 Limits for application of CWC relay ............. 101 ABSTRACT The calculation of ac short-circuit currents, essential to the selection of adequately rated protective devices and equipment in industrial and commercial power systems, is becoming increasingly important to the system designer. Today, power systems carry larger blocks of power, are more important to the operation of the plant and building, and have greater safety and reliability requirements. Meeting these requirements necessitates the fulfillment of certain criteria, including the use of adequately rated equipment. This report outlines state of-the-art industrial power system engineering practices which should be especially valuable to industrial plant engineers and electricians, industrial power application engineers and others who are involved with the planning of electrical facilities for industrial plants or commercial buildings. The method of short-circuit-current calculation has been selected, so that adequate ratings of all the air circuit breakers were obtained. Fault protective devices were selected to maintain proper relay coordination throughout the system. These devices has been selected and set so that only the device nearest a fault opened to clear the fault without affecting larger devices nearer the source of power or causing a wider outage than the minimum. -xii- CHAPTER ONE INTRODUCTION All power systems, whether they be utility, industrial, commercial, or residential, have the common purpose of providing electric energy to the utilization equipment as safely and as reliably as is economically feasible. The relative importance of economic, reliability, and safety considerations may vary somewhat with the type of system, but all three elements must be taken into consideration in any good system design, and certain minimum safety and reliability requirements must be satisfied. 1.1 STATEMENT OF THE PROBLEM Electric power system in today's industrial plants and large commercial establishments handle enormous quantities of energy. A review of the trend
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