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INDEX Abnormal conditions other than short circuits,, with directionalcomparison pilot 8 relaying, 392 A-c tripping, 335 with phase-comparison pilot relaying, Angle-impedance relay, 79 383 for tripping on 1088 of synchronism, Broken-delta connection, burden calculation, 362
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  I N D E X 1  Abnormal conditions other than short circuits,,8 A-c tripping, 335 Angle-impedance relay, 79for tripping on 1088 of synchronism,362 Angle of maximum torque, adjustment,,57of power relays, 52, 55of shortcircuit relays, 55 Arcs, effect on distance relays, 345 resistance,302 Arc - furnace - transformer protection,270 ASA accuracy classification,, of current transformers,, 121of potential transformers, 133 Attenuation, carrier-current, 378 Automatic reclosing, see Reclosing,automatic Auxiliaries,, station, protection of, 229 see also  Motor protectionBack-up relaying, defined, 6 effect of intermediate current sources,347for bus protection, 275, 291generator external fault,227reversed 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, 390Blocking pilot, 88, 91Blocking terminal, with a-c wire-pilot relaying,375 with directionalcomparison pilot relaying, 392 with phase-comparison pilot relaying,383Broken-delta connection, burden calculation,140for detecting grounds in ungroundedsystems,, 320for polarizing directionalground relays,151of capacitance potential devices,135, 140Buchholz relay, 281Burden, current-transformer, 114 potentialtransformer, 133Bus protection, automatic reclosing, 292 by back-up relays, 275, 291circuitbreaker by-psasing, 292combined power transformer and bus, 287current differential with overcurrent relays,278 current differential with overvoltagerelays, 288 current differential withpercentage relays, 284 directionalcomparison, 277 fault bus,, 275 groundingsecondaries of differentially connected CT’s,291 partial-differential, 282 ring-bus,, 290testing, 292 voltage differential with linear cou, 284 Bushing potential device, see Capacitancepotential deviceCapacitance potential device, broken burden,140 comparison with instrument PT’s, 144 couplingcapacitor insulation coordination,142 effect of overloading, 138 INDEX  2 I N D E X Capacitance potential device, equivalent circuit, 135 non-linear burdens, 139 standardaccuracy, 137 standard rated burdens, 136 Capacitor, series, effect on distance relaying,367Capacitor tripping, 335Carrier-current attenuation, 378Carrier-current-pilot relaying, see Pilot relaying,carrier-current Circuit breaker, by-passing, 292 standardcapacities, 3Circulating-current pilot relaying, 92, 94 Cold-load pickup, 334 Cold-load restoration, 334 Compensated voltage, see Transformer compensationConstant-product characteristic, 38Contact definitions, 17Contact races in pilot relaying, 91Continuous pilot, 109Control spring, 17Conventions, vector, 53Corrosion, effect of polarity on, 19Coupling-capacitor description, 134 Coupling-capacitor insulation coordination, 142Coupling-capacitor potential device, BeeCapacitance potential deviceCurrent-balance relay, directional type, 62 for line protection, 330 overcurrent type, 58Current biasing, for mho relay, 82 for offset impedance relay, 77 to avoid distance-relay misoperation on arcs, 346 Current compensation for ground distancerelays,, 360Current switching for distance relays, 368Current transformers,, accuracy calcula , 113 ASA accuracy classification, 121 burden, 114 for generator differential relaying, 198ratiocorrection-factor curves,, 116 secondary- excitation curves,, 117 grounding thesecondaries 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, 318types, 113 zero-phase-sequencecurrent shunt,- 130, 249D-c offset, effect on induction relays, 32, 39overreach of distance relays, 82, 350overreach of overcurrent relays, 308 timeconstant, 279D-c relays, single-quantity, 22 directional, 24, 49Differential relays, 63 see alsoPercentagedifferential relaysDirectional-comparison relaying, for busprotection, 277 principle of operation, 106 see also Line protection with pilot relaysDirectional control, of electromagnetic relays,,23 of single-quantity induction relays,,32,57,310,313Directional-overcurrent relay, 57  I N D E X 3 Directional relays,, a-c types, 33, 52connections,, 52 power, 52 short circuits, 56 characteristics on R-X diagram, 74 d-c types,,49 use of shunts, 52 effect of mutualinduction on ground relays, 393electromagnetic-attraction type, 24 ground- relay polarization, 151, 326 misoperatingtendencies, 314 negative-phase-aequencetype, 330 operating characteristics,, 37response of polyphase relays to positive andnegative phase sequence,, 183 response of ainglephase relays to short circuits,, 187Distance relays,, current and voltage switching,368 effect of power swings and lose of synchronism,, 181 effect of wye-deltatransformer between relay and fault, 172electronic type, 369 ground-relay connections,360 impedance seen during faults,, 167Generator protection, overvoltage, 217potential-transformer fuse blowing, 228 primemover, 230 station auxiliary, 229 stator overheating, 216 stator short circuit, 195calculation of CT errors, 198 ground faults,sensitive, 208 ground faults in unit generators, 209 overcurrent relays for, 215turn-to-turn faults, 204 unbalanced phasecurrents, 221 vibration, 225Ground-distance-relay connections, 360Ground-fault neutralizer, effect on line relaying,321 to mitigate the effect of a fault, 2Grounding protective relay for trans former protection, 263Ground preference, 91, 108Ground resistance, 303Grounding-tranaformer protection, 268Hsrmonic-current restraint, for distance relays,,357 for transformer differential relays, 257Holding coil, 18Impedance diagram, see R-X diagramImpedance relay, characteristic on R-X diagram, 72 for line protection, 340 general,70 see also Distance relaysInduction-cup and induction-loop structures,30, 31Induction-type relay, directional, 31 generalcharacteristics,, 26 single-quantity, 31structures, 29 torque production, 26 Insulating transformer for pilot-wire circuits,, 98Intermittent pilot, 109Line 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,, 360Distance relays,, use of low-tension voltage, 145,148see also Line protection with distance relaysDistribution-circuit protection, see Lineprotection with overcurrent relaysDrop-out defined, 17Electric arc-furnace-transformer protection, 270Electromagnetic-attraction relay, directional, 24 general characteristics,, 16 single-quantity, 22Electronic relay, directionalcomparison pilot,396 distance, 369
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