ThE arT SCIENCE OF PROTECTIVE RELAYING By C. Russell Mason
INDEX Abnormal conditions other than short circuits ith directionalcomparison pilot ying, A-c tripping, 335 with phase-comparison pilot relaying, Angle-impedance relay, 79 for tripping on 1088 of synchronism Broken-delta connection burden calculation 362 140 Angle of maximum torque, adjustment, for detecting grounds in ungrounded of power relays, 52, 55 for polarizing directionalground relay of shortcircuit relays. 55 Arcs, effect on distance relays, 345 resistance of capacitance potential devices, 302 135,140 Arc-furnace-transformer protection Buchholz relay, 281 270 Burden, current-transformer, 1 14 potential ASa accuracy classification,, of current transformer. 133 transformers. 121 Bus protection, automatic reclosing, 292 by of potential transformers, 193 back-up relays, 275, 291 Attenuation. carrier-current. 378 circuitbreaker by-psasing, 292 Automatic reclosing, see reclosing, combined power transformer and bus, 287 automatIc current differential with overcurrent relays Auxiliaries,, station, protection of, 229 278 current differential with overvoltage see also Motor protection relays, 288 current differential with Back-up relaying, defined, 6 284 directional effect of intermediate current sources comparison, 277 fault bus,, 275 grounding secondaries of differentially connected CT's for bus protection, 275, 291 291 partial-differential, 282 ring-bus,, 290 generator external fault, 227 testing, 292 voltage differential with linear reversed third zone. 175. 349 cou, 284 transformer external fault. 264. 268 with pilot relaying, 378, 386 Bushing potential device, see Capacitance Blind spot in pilot relaying, potential device Blinder with directional-comparison relaying 386,390 Capacitance potential device, broken burden Blocking pilot, 88, 91 140 comparison with instrument PTs, 144 Blocking terminal, with a-c wire-pilot relaying couplingcapacitor insulation coordination 142 effect of overloading, 138 NDEX
I N D E X 1 Abnormal conditions other than short circuits,, 8 A-c tripping, 335 Angle-impedance relay, 79 for tripping on 1088 of synchronism, 362 Angle of maximum torque, adjustment,, 57 of power relays, 52, 55 of shortcircuit relays, 55 Arcs, effect on distance relays, 345 resistance, 302 Arc - furnace - transformer protection, 270 ASA accuracy classification,, of current transformers,, 121 of potential transformers, 133 Attenuation, carrier-current, 378 Automatic reclosing, see Reclosing, automatic Auxiliaries,, station, protection of, 229 see also Motor protection Back-up relaying, defined, 6 effect of intermediate current sources, 347 for bus protection, 275, 291 generator external fault,227 reversed third zone, 175, 349 transformer external fault, 264, 268 with pilot relaying, 378, 386 Blind spot in pilot relaying, 94 Blinder with directional-comparison relaying, 386, 390 Blocking pilot, 88, 91 Blocking terminal, with a-c wire-pilot relaying, 375 with directionalcomparison pilot relaying, 392 with phase-comparison pilot relaying, 383 Broken-delta connection, burden calculation, 140 for detecting grounds in ungrounded systems,, 320 for polarizing directionalground relays, 151 of capacitance potential devices, 135, 140 Buchholz relay, 281 Burden, current-transformer, 114 potential transformer, 133 Bus protection, automatic reclosing, 292 by back-up relays, 275, 291 circuitbreaker by-psasing, 292 combined power transformer and bus, 287 current differential with overcurrent relays, 278 current differential with overvoltage relays, 288 current differential with percentage relays, 284 directional comparison, 277 fault bus,, 275 grounding secondaries of differentially connected CT’s, 291 partial-differential, 282 ring-bus,, 290 testing, 292 voltage differential with linear cou, 284 Bushing potential device, see Capacitance potential device Capacitance potential device, broken burden, 140 comparison with instrument PT’s, 144 couplingcapacitor insulation coordination, 142 effect of overloading, 138 INDEX
Capacitance potential device, equivalent Current-balance relay, directional type, 62 for circuit, 135 non-linear burdens, 139 standard line protection, 330 overcurrent type, 58 accuracy, 137 standard rated burdens, 136 Current biasing, for mho relay, 82 for offset Capacitor, series, effect on distance relaying, impedance relay, 77 to avoid distance-relay 367 misoperation on arcs, 346 Capacitor trippi Current compensation for ground distance relays,, 360 Carrier-current attenuation. 378 Current switching for distance relays, 368 Carrier-current-pilot relaying, see Pilot relaying, Current transformers,, accuracy calcula, 1 13 ASA accuracy classification, 121 burden, 114 Circuit breaker, by-passing, 292 standard for generator differential relaying, 198 capacities, 3 ratiocorrection-factor curves,, 116 secondary excitation curves,, 1 17 grounding the Circulating-current pilot relaying, 92, 94 secondaries of differentially connected CT's 291 overvoltage in secondary, 124 polarity Cold-load pickup 334 and connections, 126 proximity effect, 126 Cold-load restoration. 334 Current transformers, requirements for pilot elay ary leakage reactance, Compensated voltage, see Transformer 117.119.120 transient errors. 124.278.318 compensation types, 113 zero-phase-sequencecurrent shunt, 130.249 Constant-product characteristic, 38 D-c offset, effect on induction relays, 32, 39 Contact definitions. 17 overreach of distance relays, 82, 350 overreach of overcurrent relays, 308 time Contact races in pilot relaying, 91 constant. 279 Continuous pilot, 109 D-c relays, single-quantity, 22 directional, 24, 49 Control spring, 17 Differential relays, 63 see also Percentagedifferential relay Conventions. vector. 53 Directional-comparison relaying, for bus Corrosion, effect of polarity on, 19 rotection,277 principle of operation, 106 see also Line protection with pilot relays Coupling-capacitor description, 134 Directional control, of electromagnetic relays, Coupling-capacitor insulation coordination, 142 28 of single-quantity induction relays,, 32,57,310,313 Coupling-capacitor potential device, Bee capacitance potential device Directional-overcurrent relay, 57 INDEX
2 I N D E X Capacitance potential device, equivalent circuit, 135 non-linear burdens, 139 standard accuracy, 137 standard rated burdens, 136 Capacitor, series, effect on distance relaying, 367 Capacitor tripping, 335 Carrier-current attenuation, 378 Carrier-current-pilot relaying, see Pilot relaying, carrier-current Circuit breaker, by-passing, 292 standard capacities, 3 Circulating-current pilot relaying, 92, 94 Cold-load pickup, 334 Cold-load restoration, 334 Compensated voltage, see Transformer compensation Constant-product characteristic, 38 Contact definitions, 17 Contact races in pilot relaying, 91 Continuous pilot, 109 Control spring, 17 Conventions, vector, 53 Corrosion, effect of polarity on, 19 Coupling-capacitor description, 134 Coupling-capacitor insulation coordination, 142 Coupling-capacitor potential device, Bee Capacitance potential device Current-balance relay, directional type, 62 for line protection, 330 overcurrent type, 58 Current biasing, for mho relay, 82 for offset impedance relay, 77 to avoid distance-relay misoperation on arcs, 346 Current compensation for ground distance relays,, 360 Current switching for distance relays, 368 Current transformers,, accuracy calcula , 113 ASA accuracy classification, 121 burden, 114 for generator differential relaying, 198 ratiocorrection-factor curves,, 116 secondaryexcitation curves,, 117 grounding the secondaries of differentially connected CT’s, 291 overvoltage in secondary, 124 polarity and connections, 126 proximity effect, 126 Current transformers, requirements for pilot relaying, 377 secondary leakage reactance, 117, 119, 120 transient errors, 124, 278, 318 types, 113 zero-phase-sequencecurrent shunt, - 130, 249 D-c offset, effect on induction relays, 32, 39 overreach of distance relays, 82, 350 overreach of overcurrent relays, 308 time constant, 279 D-c relays, single-quantity, 22 directional, 24, 49 Differential relays, 63 see also Percentagedifferential relays Directional-comparison relaying, for bus protection, 277 principle of operation, 106 see also Line protection with pilot relays Directional control, of electromagnetic relays,, 23 of single-quantity induction relays,, 32,57,310,313 Directional-overcurrent relay, 57
Directional relays,, a-c types, 33, 52 Holding coil 18 connections,, 52 power, 52 short circuits, 56 characteristics on R-X diagram, 74 d-c types, Impedance diagram, see R-X diagram 49 use of shunts, 52 effect of mutual induction on ground relays, 393 Impedance relay, characteristic on R-X electromagnetic-attraction type, 24 ground diagram, 72 for line protection, 340 general, relay polarization, 151, 326 misoperating 70 see also Distance relays tendencies, 314 negative-Phase-aequence type, 330 operating characteristics,,37 Induction-cup and induction-loop structures negative phase sequence,, 183 response e response of polyphase relays to positive and singlephase relays to short circuits,, 187 Induction-type relay, directional, 31 general characteristics,, 26 single-quantity, 31 Distance relays,, current and voltage switching, structures, 29 torque production, 26 368 effect of power swings and lose of synchronism,, 181 effect of wye-delta Insulating transformer for pilot-wire circuits,, 98 transformer between relay and fault, 172 electronic type, 369 ground-relay connections Intermittent pilot, 109 Line protection with distance relays,, Generator protection, overvoltage, 217 adjustment of distance relays,, 341 area, effect potential-transformer fuse blowing, 228 prime of, 345 blocking tripping on 1088 of nover, 230 station auxiliary, 229 stator synchro, 304 choice between impedance, overheating, 216 stator short circuit, 195 reactance and mho. 340 connections of calculation of CT errors, 198 ground faults, ground distance relays,, 360 sensitive, 208 ground faults in unit generators, 209 overcurrent relays for, 215 Distance relays,, use of low-tension voltage, 145, turn-to-turn faults, 204 unbalanced phase 148 currents. 221 vibration. 225 ee also Line protection with distance relay Ground-distance-relay connections, 360 Distribution-circuit protection, see Lin Ground-fault neutralizer, effect on line relaying protection with overcurrent relays 321 to mitigate the effect of a fault. 2 Drop-out defined, 17 rounding protective relay for trans former protection, 263 Electric arc-furnace-transformer protection, 270 Ground preference, 91, 108 Electromagnetic-attraction relay, directional, 24 Ground resistance, 303 general characteristics,, 16 single-quantity, 22 Grounding-tranaformer protection, 268 Electronic relay, directionalcomparison pilot 396 Hsrmonic-current restraint, for distance relays 357 for transformer differential relays, 257 distance. 369 NDEX
I N D E X 3 Directional relays,, a-c types, 33, 52 connections,, 52 power, 52 short circuits, 56 characteristics on R-X diagram, 74 d-c types,, 49 use of shunts, 52 effect of mutual induction on ground relays, 393 electromagnetic-attraction type, 24 groundrelay polarization, 151, 326 misoperating tendencies, 314 negative-phase-aequence type, 330 operating characteristics,, 37 response of polyphase relays to positive and negative phase sequence,, 183 response of ainglephase relays to short circuits,, 187 Distance relays,, current and voltage switching, 368 effect of power swings and lose of synchronism,, 181 effect of wye-delta transformer between relay and fault, 172 electronic type, 369 ground-relay connections, 360 impedance seen during faults,, 167 Generator protection, overvoltage, 217 potential-transformer fuse blowing, 228 prime mover, 230 station auxiliary, 229 stator overheating, 216 stator short circuit, 195 calculation of CT errors, 198 ground faults, sensitive, 208 ground faults in unit generators, 209 overcurrent relays for, 215 turn-to-turn faults, 204 unbalanced phase currents, 221 vibration, 225 Ground-distance-relay connections, 360 Ground-fault neutralizer, effect on line relaying, 321 to mitigate the effect of a fault, 2 Grounding protective relay for trans former protection, 263 Ground preference, 91, 108 Ground resistance, 303 Grounding-tranaformer protection, 268 Hsrmonic-current restraint, for distance relays,, 357 for transformer differential relays, 257 Holding coil, 18 Impedance diagram, see R-X diagram Impedance relay, characteristic on R-X diagram, 72 for line protection, 340 general, 70 see also Distance relays Induction-cup and induction-loop structures, 30, 31 Induction-type relay, directional, 31 general characteristics,, 26 single-quantity, 31 structures, 29 torque production, 26 Insulating transformer for pilot-wire circuits,, 98 Intermittent pilot, 109 Line protection with distance relays,, adjustment of distance relays,, 341 area, effect of, 345 blocking tripping on 1088 of synchro , 304 choice between impedance, reactance, and mho,, 340 connections of ground distance relays,, 360 Distance relays,, use of low-tension voltage, 145, 148 see also Line protection with distance relays Distribution-circuit protection, see Line protection with overcurrent relays Drop-out defined, 17 Electric arc-furnace-transformer protection, 270 Electromagnetic-attraction relay, directional, 24 general characteristics,, 16 single-quantity, 22 Electronic relay, directionalcomparison pilot, 396 distance, 369
Evaluation of protective relaying, 12 loss of excitation Expulsion protective gaps, effect of, on distance relays 1088 of synchronism,, 218 miscellaneous,, 228 External-fault back-up relaying, see Back-up motoring open circuits,, 215 over excitation,, 225 over Fail ures. electrical. see Faults False residual current. 318 Line protection with distance relays, current and voltage switching, 368 expulsion Fault bus. 275 protective gaps, effect of, 367 fuse blo effect of, 361 electronic relays, 369 Faults, mitigation of effects of, 2 prevention of intermediate current sources. effect of 347 2 probability of, effect on practice, ll see also low-tension current, use of, 356 low-tension Short circuits voltage, use of, 352 magnetizing inrush, effec of, 359 overreach, 951, 360 purposeful Fire, protection against, 230 ipping on loss of synchronism, 361 reclosing, automatic, 366 series capacitor, Fire-pump-motor protection, 230 effect of, 367 see also Distance relays Footing resistance, tower, 303 Line protection with overcurrent relays, a-c and capacitor tripping, 335 uency, compensation of relays for changes adjustment of ground vs phase re lays. 316 adjustment of inverse-time-overcur effect on induction relays,, 32, arc and ground resistance, 302 directional feature. 310 Frequency-converter protection, see Generator fuses. coordination with. 335 protection ground faults in ungrounded systems, Fundamental principles of protective relaying, 4 ground-fault neutralizers, effect of, Fuse, coordinating with a, 335 instantaneous overcurrent relays,, use of.306 Fuse blowing, potential-tranaformer, effect on inverseness,, choice of, in relay char distance relays, 361 acteristics. 305 limiting ground-fault-current magn eltect on generator relays, tude. effect of. 317 loop circuits,, effect on relay adjust 303 misoperation prevention of aingle Generator protection, bearing overheating, 228 directionak-overcurrent re during ground faults. 314 external-fault back-up, m field ground, 218 negative-phase sequence ground di INDEX
4 I N D E X Evaluation of protective relaying, 12 Expulsion protective gaps, effect of, on distance relays, 367 External-fault back-up relaying, see Back-up relaying Fail ures,, electrical, see Faults False residual current, 318 Fault bus, 275 Faults, mitigation of effects of, 2 prevention of, 2 probability of, effect on practice, 11 see also Short circuits Fire, protection against, 230 Fire-pump-motor protection, 230 Footing resistance, tower-, 303 Frequency, compensation of relays for changes in, 49 effect on induction relays,, 32, 39 Frequency-converter protection, see Generator protection Fundamental principles of protective relaying, 4 Fuse, coordinating with a, 335 Fuse blowing, potential-tranaformer, effect on distance relays,, 361 effect on generator relays,, 228 Generator protection, bearing overheating, 228 external-fault back-up, m field ground, 218 loss of excitation, 223 1088 of synchronism,, 218 miscellaneous,, 228 motoring, 225 open circuits,, 215 over excitation,, 225 over speed,, 226 Line protection with distance relays, current and voltage switching, 368 expulsion protective gaps, effect of, 367 fuse blowing, effect of, 361 electronic relays, 369 intermediate current sources, effect of, 347 low-tension current, use of, 356 low-tension voltage, use of, 352 magnetizing inrush, effect of, 359 overreach, 351, 360 purposeful tripping on loss of synchronism, 361 reclosing, automatic, 366 series capacitor, effect of, 367 see also Distance relays Line protection with overcurrent relays, a-c and capacitor tripping, 335 adjustment of ground vs. phase re lays, 316 adjustment of inverse-time-overcur rent relays, 297 arc and ground resistance, 302 directional feature, 310 fuses, coordination with, 335 ground faults in ungrounded systems, detection of, 319 ground-fault neutralizers, effect of, 321 instantaneous overcurrent relays,, use of, 306 inverseness,, choice of, in relay char acteristics, 305 limiting ground-fault-current magni tude, effect of, 317 loop circuits,, effect on relay adjust , 303 misoperation prevention of aingle directional-overcurrent re during ground faults, 314 negative-phase sequence ground di