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
rectional relays,, 330 open phases, effect of, 323, 325 reclosing, high-apeed,, 399 overreach of instantaneous overcut when to use pilot relaying, 373 rent relays,, 308 polarizing ground-relay directional Line trap, 100 unite. 326 Linear couplers, 284 reclosing, automatic, 333 Load shedding, 334, 363 restoration of service after prolonged outage, 334 Locking in, with generator differential rel single-phase vs. polyphase directional 202 with transformer differential relaying, transient ct errors. 318 Loss-of-excitation protection, 223 two vs. three relays for phase-fault Loss-of-field protection. 228 3l1 Loss of synchronism, characteristics on RX Line protection with overcurrent relays, see also diagram, 1 77 derivation of relay current and Overcurrent relay voltage, 176 effect on distance relays, 181 generator protection, 218 trip-blocking relay Line protection with pilot relays, a-c 304, 390 tripping relay, 361 wire-pilot relaying, 374 back-up protection, 378 Low-tension current for distance relays, 356 CT requirements, 377 multi terminal lines. 375 Low-tension voltage, for directional relaying, sensitivity, 374 386 for distance relaying, 148, 352 general see also Pilot relaying, a-c wire-; 145 Pilot relaying, d-c wire relaying, attenu ation. 378 Magetizing-current inrush effect on distance sleet detection. 379 relays, 359 effect on transformer differential supervision, automatic, 378 relays, 254 in parallel transformer banks, 259 combined phase-and directional com parison, mutual induction, effect Maximum torque, angle of, adjustment, 57 nd relays. 393 power relays, 52, 55 short-circuit relays, 55 when to use. 392 directional comparison, electron Memory action, described, 83 effect of voltage 396 source location. 144 low-tension voltage, use of, 386 multi terminal lines. 387 Mho relay, characteristics on R-X diagram, 81 sensitivity, 386 for line protection, 340 operating transients. effect of. 392 characteristic. 80 when to use. 386 see also Pilot relaying, carrier-cur 393 Microwave-pilot relaying, see Pilot relaying. hase comparison, back-up protec microwave tion. 386 multi terminal lines. 382 Minimum pickup of directional relays,, 38 sensitivity, 381 Mixing transformer for wire-pilot relaying, 96 see also Pilot relaying, carrier-cur NDEX
I N D E X 5 rectional relays,, 330 open phases, effect of, 323, 325 overreach of instantaneous overcur rent relays,, 308 polarizing ground-relay directional unite, 326 reclosing, automatic, 333 restoration of service after prolonged outage, 334 single-phase vs. polyphase directional relays,, 313 transient CT errors, 318 two vs. three relays for phase-fault protection, 311 Line protection with overcurrent relays, see also Overcurrent relays Line protection with pilot relays, a-c wire-pilot relaying, 374 back-up protection, 378 CT requirements, 377 multi terminal lines, 375 sensitivity, 374 see also Pilot relaying, a-c wire-; Pilot relaying, d-c wire relaying, attenu ation, 378 sleet detection, 379 supervision, automatic, 378 combined phase- and directional com parison, mutual induction, effect on ground relays, 393 when to use, 392 directional comparison, electronic, 396 low-tension voltage, use of, 386 multi terminal lines, 387 sensitivity, 386 transients,, effect of, 392 when to use, 386 see also Pilot relaying, carrier-cur , 393 phase comparison, back-up protec tion, 386 multi terminal lines, 382 sensitivity, 381 when to use, 380 see also Pilot relaying, carrier-cur rent reclosing, high-apeed,, 399 when to use pilot relaying, 373 Line trap, 100 Linear couplers, 284 Load shedding, 334, 363 Locking in, with generator differential relaying, 202 with transformer differential relaying, 251 Loss-of-excitation protection, 223 Loss-of-field protection, 223 Loss of synchronism, characteristics on RX diagram, 177 derivation of relay current and voltage, 176 effect on distance relays, 181 generator protection, 218 trip-blocking relay, 304, 390 tripping relay, 361 Low-tension current for distance relays, 356 Low-tension voltage, for directional relaying, 386 for distance relaying, 148, 352 general, 145 Magetizing-current inrush, effect on distance relays, 359 effect on transformer differential relays, 254 in parallel transformer banks, 259 Maximum torque, angle of, adjustment, 57 power relays, 52, 55 short-circuit relays, 55 Memory action, described, 83 effect of voltage source location, 144 Mho relay, characteristics on R-X diagram, 81 for line protection, 340 operating characteristic, 80 Microwave-pilot relaying, see Pilot relaying, microwave Minimum pickup of directional relays,, 38 Mixing transformer for wire-pilot relaying, 96
Modified-impendance relay, 77 nstantaneous overcurrent relays, 308 Motor protection, field ground, 237 fire-pump Over travel. defined. 48 effect of. on 230 1088 of excitation. 287 1088 of overcurrent-relay adjustment, 301 synchronism, 236 rotor overheating, 236 stator overheating, 292 stator short circuit, Overvoltage, in CI secondaries, 1 24 see also 230 unattended motors,, 230 under voltage, Generator protection Overvoltage relays, pickup or reset,, 45 time Multiterminal-line protection, with a-c wire-pilot delay. 45, 46 relaying, 376 with directional-comparieon pilot relaying, 387 with phasecomparison Percentage-differential relays, description, 65 for pilot relaying, 382 bus protection, 284 for generator protection 195 for transformer protection, 241 locking-in Mutual induction, effect of, on direc relays, for internal faults,, 202, 251 product restraint, 393 from power circuit to pilot wires,, 88 204 variable percent slope, 187, 203 Neutralizing transformers for wire-pilot circuits Petersen coil. see Ground-fault neutralizer 99 Phase-comparison relaying, principle of Normally blocked trip circuit, 109 operation, 10l see also Line protection with pilot relays Open phase, effect of, on directional relays, 323, 325 equivalent circuits for, 323 Pilot relaying, circulating current, 92, 94 protection of generators against, 215 general, 86 line protection, 373, 374 opposed voltage, 92, 95 pilot-wire protection, 98 pilc Operating principles,, basic, electromagnetic wire requirements, 97 pilot-wire supervision attraction relays, 16 97 remote tripping, 97 see also Line protection with pilot relays Operating principles, directional type, 24 single- quantity type, 22 induction relays: directiona Pilot relaying, carrier-current-, directional type, 33 singlequantity type, 31 comparison, 106 general, 86 intermittent or continuous, 109 phase comparison, 101 pilot Operation in indicator. 17 described, 100 supervision of pilot channel, 378 see also Line protection with pilot relays Operator vs. protective relays, Il Pilot relaying, d-c wire-, basic principles, 89 Opposed-voltage pilot relaying, 92, 95 description of pilot 86 Out of step, see Loss of synchronism Pilot relaying, micro-wave, description of channel, 397 general, 86, 101, 396 remote Overcurrent relays, combination of tripping, 398 see also Line protection with instantaneous and time delay, 49 pickup or P ilot relays reset, 45 time delay, 45, 46 see also Line protection with overcurrent relays Pilot relaying, principles of, ground preference, 91 purpose of a pilot, 87 sensitivity levels, 91 Overreach, of distance relays, 82, 350, 351 of 106 tripping and blocking pilots, 88, 90 INDEX
6 I N D E X Modified-impendance relay, 77 Motor protection, field ground, 237 fire-pump, 230 1088 of excitation, 237 1088 of synchronism, 236 rotor overheating, 236 stator overheating, 232 stator short circuit, 230 unattended motors,, 230 under voltage,, 237 Multiterminal-line protection, with a-c wire-pilot relaying, 376 with directional-comparieon pilot relaying, 387 with phasecomparison pilot relaying, 382 Mutual induction, effect of, on direc relays,, 393 from power circuit to pilot wires,, 88 Neutralizing transformers for wire-pilot circuits,, 99 Normally blocked trip circuit, 109 Open phase, effect of, on directional relays, 323, 325 equivalent circuits for, 323 protection of generators against, 215 Operating principles,, basic, electromagneticattraction relays,, 16 Operating principles, directional type, 24 singlequantity type, 22 induction relays: directional type, 33 singlequantity type, 31 Operation indicator, 17 Operator vs. protective relays, 11 Opposed-voltage pilot relaying, 92, 95 Out of step, see Loss of synchronism Overcurrent relays, combination of instantaneous and time delay, 49 pickup or reset, 45 time delay, 45, 46 see also Line protection with overcurrent relays Overreach, of distance relays, 82, 350, 351 of instantaneous overcurrent relays, 308 Over travel,, defined, 48 effect of, on overcurrent-relay adjustment, 301 Overvoltage, in CI secondaries, 124 see also Generator protection Overvoltage relays, pickup or reset,, 45 time delay, 45, 46 Percentage-differential relays, description, 65 for bus protection, 284 for generator protection, 195 for transformer protection, 241 locking-in for internal faults,, 202, 251 product restraint, 204 variable percent slope, 187, 203 Petersen coil, see Ground-fault neutralizer Phase-comparison relaying, principle of operation, 101 see also Line protection with pilot relays Pilot relaying, circulating current, 92, 94 general, 86 line protection, 373, 374 opposed voltage, 92, 95 pilot-wire protection, 98 pilotwire requirements, 97 pilot-wire supervision, 97 remote tripping, 97 see also Line protection with pilot relays Pilot relaying, carrier-current-, directional comparison, 106 general, 86 intermittent or continuous, 109 phase comparison, 101 pilot described, 100 supervision of pilot channel, 378 see also Line protection with pilot relays ; Pilot relaying,-d-c wire-, basic principles, 89 description of pilot 86 Pilot relaying, micro-wave-, description of channel, 397 general, 86, 101, 396 remote tripping, 398 see also Line protection with pilot relays Pilot relaying, principles of, ground preference, 91 purpose of a pilot, 87 sensitivity levels, 91, 106 tripping and blocking pilots, 88, 90
42 holding coil, seal-in coil, and target, 43 Polarizing quantity, of a-c directional relays'37 of d-c directional relays, 6l of directional Ratio correction factor. see Current units of ground relays, 151, 326 transformers: voltage trans formers Polyphase directional relays, advantages and Reactance relay, characteristic on R-x diagram disadvantages, 313 response to positive-and 79 operating characteristic, 78 partial- negative volt-amps, 183 differential bus protection, 282 see also Line protection with distance relays Potential device, see Capacitance potential device Reclosing, automatic, affected by remote tripping, 367 effect on blocking-terminal Potential transformers, accuracy, 133 ilot equipment, 376 mitigation of fault connections. 146 effect of fuse blowing on ffects, 2 of bus breakers,, 292 single-phase distance relaying, 36l on generator relaying, switching, 399 synchronism check, 333, 366 228 low-tension voltage for distance relays, with distance relaying, 366 with overcurrent 148 laying, 333 with pilot relaying, Power-balance relaying for line protection, 330 Rectifier-transformer protection, 271 Power-rectifier-transformer protection, 271 Regulating-transformer protection, ex fault back-up, 208 in-phase type, 265 phase-shiftin Power swings, see Loss of synchronism type, 267 Power transformer and autotransformer Reliability, a functional relay characteristic, 9 protection, external-fault backup, 264 gasaccumulator and pressure relays, 261 Remote tripping by carrier current, 384 by grounding protective relay, 268 overcurrent microwave, 398 by pilot wire, 97 for power relaying, 261 percentagedifferential relaying transformer protection, 268 frequency-shift 241 CT accuracy requirements, 251 CT connections. 242 CT ratios. 250 magnetizing inrush, effect of, 254 parallel banks, 258 Replica-type relays, for generator protection, percent slope, choice of, 252 two-winding 216 for motor protection, 232, 235 relay for threewinding transformer, 252 zer phasesequence-current shunt, 249 remote Reset, adjustment of, 19 defined, 17 ratio to tripping, 263 pickup, electromagnetic relays, 22 induction relays, 32 time of induction relays, 33, 49 Primary relaying defined, 4 eversed third zone for back-up with carrier Product restraint for generator differential pilot, 349 where a line includes a relays. 204 transformer. 175 Protective relaying, evaluation of, 12 function R-X diagram, los-of-synchronism char 176 of. 3 functional characteristics of 9 appearance to distance relays, 181 principle fundamental principles of, 4 of. 72. 156 short-circuit characteristics. 1 60 appearance to distance relays,, 167 wyedelta Ratings, relay, contact, 43 current and voltage, transformer between relay and fault, 172 NDEX
I N D E X 7 Polarizing quantity, of a-c directional relays’ 37 of d-c directional relays, 61 of directional units of ground relays, 151, 326 Polyphase directional relays, advantages and disadvantages, 313 response to positive- and negative volt-amps, 183 Potential device, see Capacitance potential device Potential transformers, accuracy, 133 connections, 146 effect of fuse blowing, on distance relaying, 361 on generator relaying, 228 low-tension voltage for distance relays, 148 Power-balance relaying for line protection, 330 Power-rectifier-transformer protection, 271 Power swings, see Loss of synchronism Power transformer and autotransformer protection, external-fault backup, 264 gasaccumulator and pressure relays, 261 grounding protective relay, 263 overcurrent relaying, 261 percentagedifferential relaying, 241 CT accuracy requirements, 251 CT connections, 242 CT ratios, 250 magnetizing inrush, effect of, 254 parallel banks, 258 percent slope, choice of, 252 two-winding relay for threewinding transformer, 252 zerophasesequence-current shunt, 249 remote tripping, 263 Primary relaying defined, 4 Product restraint for generator differential relays, 204 Protective relaying, evaluation of, 12 function of, 3 functional characteristics of, 9 fundamental principles of, 4 Ratings, relay, contact, 43 current and voltage, 42 holding coil, seal-in coil, and target, 43 Ratio correction factor, see Current transformers; Voltage trans formers Reactance relay, characteristic on R-X diagram, 79 operating characteristic, 78 partialdifferential bus protection, 282 see also Line protection with distance relays Reclosing, automatic, affected by remote tripping, 367 effect on blocking-terminal pilot equipment, 376 mitigation of fault effects, 2 of bus breakers,, 292 single-phase switching, 399 synchronism check, 333, 366 with distance relaying, 366 with overcurrent relaying, 333 with pilot relaying, 399 Rectifier-transformer protection, 271 Regulating-transformer protection, ex fault back-up, 208 in-phase type, 265 phase-shifting type, 267 Reliability, a functional relay characteristic, 9 Remote tripping, by carrier current, 384 by microwave, 398 by pilot wire, 97 for powertransformer protection, 263 frequency-shift system, 264 Replica-type relays, for generator protection, 216 for motor protection, 232, 235 Reset, adjustment of, 19 defined, 17 ratio to pickup, electromagnetic relays, 22 induction relays, 32 time of induction relays, 33, 49 Reversed third zone, for back-up with carrier pilot, 349 where a line includes a transformer, 175 R-X diagram, los-of-synchronism char , 176 appearance to distance relays,, 181 principle of, 72, 156 short-circuit characteristics, 160 appearance to distance relays,, 167 wyedelta transformer between relay and fault, 172
superposition of relay and system Telephone-circuit restrictions, 97 characteristics. 157 lay field, 10 eal-in coil Time characteristics, adjustment of, 45 Secondary excitation curves. 117 definitic Selectivity, a functional relay characteristic, 9 of d-c directional relays, 52 of electromagnetic-attraction relays Sensitivity, a functional relay char, 9 levels of blocking and tripping for pilot relaying, 91 of induction relays, 33, 39, 46 105.386 Time constant of d-c component, 279 Shaded-pole structure, Torque control, see Directional control Short circuits, derivation of relay current and voltage, 160 impedance seen by distance Torque production in induction relays, 2 relays,, 167 table of currents,, 1 64 table of voltages, 165 see also faults Tower-footing resistance, 303 Single-phase switching, 399 Transferred tripping, see Remote tripping Sleet-accumulation detection with carrier Transformer-drop compensation, for directional-comparison pilot relaying, 386 Speed, a functional relay or distance relaying, 352 characteristic Transformer protection, see: Electric Split-Phase relaying, combined with percentage differential. 207 Grounding-transformer protection; Power- rectifiertransformer protection for generators, 204 Powertransformer and autotransformer protection; Regulating-trans former Stability, system, benefited by protective protection; Step-voltage protection elaviL Transients, effect of, on directional pilot Step-voltage-regulator protection, 2 relaying, 392 Supervision, automatic, of carrier channel, 378 on distance relaying. 350 of pilot-wire circuits, 90, 97 on electromagnetic-attraction relays Synchronism check with automatic reclosing, on overcurrent relays, 308, 317, 3l8 Transient blocking, 392 INDEX
8 I N D E X superposition of relay and system characteristics, 157 Seal-in coil or relay, 18 Secondary excitation curves,, 117 Selectivity, a functional relay characteristic, 9 Sensitivity, a functional relay char , 9 levels of blocking and tripping for pilot relaying, 91, 105, 386 Shaded-pole structure, 29 Short circuits, derivation of relay current and voltage, 160 impedance seen by distance relays,, 167 table of currents,, 164 table of voltages,, 165 see also Faults Single-phase switching, 399 Sleet-accumulation detection with carrier current, 379 Speed, a functional relay characteristic,, Split-phase relaying, combined with percentage differential, 207 for generators, 204 Stability, system, benefited by protective relaying, 12 Step-voltage-regulator protection, 268 Supervision, automatic, of carrier channel, 378 of pilot-wire circuits, 90, 97 Synchronism check with automatic reclosing, 333, 366 Target, 17 Telephone-circuit restrictions, 97 Testing, relay, field, 10 manual, 10 Time characteristics, adjustment of, 45 definitions,, 19 of d-c directional relays, 52 of electromagnetic-attraction relays, 23 of induction relays, 33, 39, 46 Time constant of d-c component, 279 Torque control, see Directional control Torque production in induction relays, 26 Tower-footing resistance, 303 Transferred tripping, see Remote tripping Transformer-drop compensation, for directional-comparison pilot relaying, 386 for distance relaying, 352 Transformer protection, see: Electric arcfurnace-transformer protection; Grounding-transformer protection; Powerrectifiertransformer protection; Powertransformer and autotransformer protection; Regulating-trans former protection; Step-voltage protection Transients, effect of, on directional pilot relaying, 392 on distance relaying, 350 on electromagnetic-attraction relays, 23 on overcurrent relays, 308, 317, 318 Transient blocking, 392
Voltage transformers, see Capacitance potential Transient shunt, for distance relays, 351 devices: Potential transformers for overcurrent relays Watthour-meter structure 30 310 Wire-pilot relaying, see Pilot relaying, a-c wire- Transmission-line protection, with distance Pilot relaying, d-c wire Zero-phase-sequence-current shunt, current- with overcurrent relaying, 296 transformer connections. 130 used with transformer differential relays, 249 Tranemission-line protection, with pilot 373 Trap, line, 100 Tripping pilot, 88, 90 Tripping suppressor for transformer differential Tripping, undesired, vs. failure to trip, II Undercurrent and under voltage relays, pickup or reset. 45 time. 46 Universal relay torque equation, 39 Variable restraint for generator differential relays. 203 Vector conventions. 53 Vibration, of electromagnetic-attrao relays, 23 protection for generators, 210, 225 Voltage-balance relays, 61 Voltage compensation for ground distance relays, 360 Voltage-regulator protection, 26 Regulating-transformer protection; Step- voltage-regulator protection Voltage switching for distance relays, 368 NDEX
I N D E X 9 Transient shunt, for distance relays, 351 for overcurrent relays, 310 Transmission-line protection, with distance relaying, 340 with overcurrent relaying, 296 Tranemission-line protection, with pilot relaying, 373 Trap, line, 100 Tripping pilot, 88, 90 Tripping suppressor for transformer differential relays, 256 Tripping, undesired, vs. failure to trip, 11 Undercurrent and under voltage relays, pickup or reset, 45 time, 46 Universal relay torque equation, 39 Variable restraint for generator differential relays, 203 Vector conventions, 53 Vibration, of electromagnetic-attrao relays, 23 protection for generators, 210, 225 Voltage-balance relays, 61 Voltage compensation for ground distance relays, 360 Voltage-regulator protection, 268 see also Regulating-transformer protection; Stepvoltage-regulator protection Voltage switching for distance relays, 368 Voltage transformers, see Capacitance potential devices; Potential transformers Watthour-meter structure, 30 Wire-pilot relaying, see Pilot relaying, a-c wire-; Pilot relaying, d-c wire Zero-phase-sequence-current shunt, currenttransformer connections, 130 used with transformer differential relays, 249