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I N D E X1Abnormal conditions other than short circuits,8A-c tripping,335Angle-impedance relay,79for tripping on 1088 of synchronism,362Angle of maximum torque,adjustment,57of power relays,52,55of shortcircuit relays,55Arcs,effect on distance relays,345 resistance,302Arc-furnace-transformer protection,270ASA accuracy classification,of currenttransformers,121of potential transformers,133Attenuation,carrier-current,378Automatic reclosing,see Reclosing,automaticAuxiliaries,station,protection of,229see also Motor protectionBack-up relaying,defined,6effect of intermediate current sources,347for bus protection,275,291generator external fault,227reversed third zone,175,349 transformer external fault,264,268with pilot relaying,378,386Blind spot in pilot relaying,94Blinder with directional-comparison relaying,386,390Blocking pilot,88,91Blocking terminal,with a-c wire-pilot relaying,375with directionalcomparison pilotrelaying,392with 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 byback-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 CTs,291 partial-differential,282 ring-bus,290testing,292 voltage differential with linearcou,284Bushing potential device,see Capacitancepotential deviceCapacitance potential device,broken?burden,140 comparison with instrument PTs,144couplingcapacitor insulation coordination,142 effect of overloading,138I N D E X2I N D E XCapacitance potential device,equivalentcircuit,135 non-linear burdens,139 standardaccuracy,137 standard rated burdens,136Capacitor,series,effect on distance relaying,367Capacitor tripping,335Carrier-current attenuation,378Carrier-current-pilot relaying,see Pilot relaying,carrier-currentCircuit breaker,by-passing,292 standardcapacities,3Circulating-current pilot relaying,92,94Cold-load pickup,334Cold-load restoration,334Compensated 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,134Coupling-capacitor insulation coordination,142Coupling-capacitor potential device,BeeCapacitance potential deviceCurrent-balance relay,directional type,62 forline protection,330 overcurrent type,58Current biasing,for mho relay,82 for offsetimpedance relay,77 to avoid distance-relaymisoperation on arcs,346Current compensation for ground distancerelays,360Current switching for distance relays,368Current transformers,accuracy calcula?,113ASA accuracy classification,121 burden,114for generator differential relaying,198ratiocorrection-factor curves,116 secondary-excitation curves,117 grounding thesecondaries of differentially connected CTs,291 overvoltage in secondary,124 polarityand connections,126 proximity effect,126Current transformers,requirements for pilotrelaying,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,106see also Line protection with pilot relaysDirectional control,of electromagnetic?relays,23 of single-quantity induction relays,32,57,310,313Directional-overcurrent relay,57I N D E X3Directional relays,a-c types,33,52connections,52 power,52 short circuits,56characteristics 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 ofainglephase relays to short circuits,187Distance relays,current and voltage switching,368 effect of power swings and lose ofsynchronism,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 statoroverheating,216 stator short circuit,195calculation of CT errors,198 ground faults,sensitive,208 ground faults in unitgenerators,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 formerprotection,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-Xdiagram,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,26Insulating transformer for pilot-wire circuits,98Intermittent pilot,109Line protection with distance relays,adjustment of distance relays,341 area,effectof,345 blocking tripping on 1088 ofsynchro?,304 choice between impedance,reactance,and mho,340 connections ofground 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,24general characteristics,16 single-quantity,22Electronic relay,directionalcomparison pilot,396distance,3694I N D E XEvaluation of protective relaying,12Expulsion protective gaps,effect of,on distancerelays,367External-fault back-up relaying,see Back-uprelayingFail ures,electrical,see FaultsFalse residual current,318Fault bus,275Faults,mitigation of effects of,2 prevention of,2 probability of,effect on practice,11 see alsoShort circuitsFire,protection against,230Fire-pump-motor protection,230Footing resistance,tower-,303Frequency,compensation of relays for changesin,49effect on induction relays,32,39Frequency-converter protection,see GeneratorprotectionFundamental principles of protective relaying,4Fuse,coordinating with a,335Fuse blowing,potential-tranaformer,effect ondistance relays,361effect on generator relays,228Generator protection,bearing overheating,228external-fault back-up,m field ground,218loss of excitation,2231088 of synchronism,218 miscellaneous,228motoring,225open circuits,215 over excitation,225 overspeed,226Line protection with distance relays,currentand voltage switching,368 expulsionprotective gaps,effect of,367 fuse blowing,effect of,361 electronic relays,369intermediate current sources,effect of,347low-tension current,use of,356 low-tensionvoltage,use of,352 magnetizing inrush,effectof,359 overreach,351,360 purposefultripping on loss of synchronism,361reclosing,automatic,366 series capacitor,effect of,367 see also Distance relaysLine protection with overcurrent relays,a-c and capacitor tripping,335adjustment of ground vs.phase relays,316adjustment of inverse-time-overcurrent relays,297arc and ground resistance,302directional feature,310fuses,coordination with,335ground faults in ungrounded systems,detection of,319ground-fault neutralizers,effect of,321instantaneous overcurrent relays,useof,306inverseness,choice of,in relay characteristics,305limiting ground-fault-current magnitude,effect of,317loop circuits,effect on relay adjust?,303misoperation prevention of aingle?directional-overcurrent re?during ground faults,314negative-phase sequence ground diI N D E X5rectional relays,330open phases,effect of,323,325overreach of instantaneous overcurrent relays,308polarizing ground-relay directionalunite,326reclosing,automatic,333restoration of service after prolongedoutage,334single-phase vs.polyphase directional?relays,313transient CT errors,318two vs.three relays for phase-faultprotection,311Line protection with overcurrent relays,see alsoOvercurrent relaysLine protection with pilot relays,a-cwire-pilot relaying,374back-up protection,378CT requirements,377multi terminal lines,375sensitivity,374see also Pilot relaying,a-c wire-;Pilot relaying,d-c wire?relaying,attenuation,378sleet detection,379supervision,automatic,378combined phase-and directional comparison,mutual induction,effecton ground relays,393when to use,392directional comparison,electronic,396low-tension voltage,use of,386multi terminal lines,387sensitivity,386transients,effect of,392when to use,386see also Pilot relaying,carrier-cur?,393phase comparison,back-up protection,386multi terminal lines,382sensitivity,381when to use,380see also Pilot relaying,carrier-currentreclosing,high-apeed,399when to use pilot relaying,373Line trap,100Linear couplers,284Load shedding,334,363Locking in,with generator differential relaying,202 with transformer differential relaying,251Loss-of-excitation protection,223Loss-of-field protection,223Loss of synchronism,characteristics on RXdiagram,177 derivation of relay current andvoltage,176 effect on distance relays,181generator protection,218 trip-blocking relay,304,390 tripping relay,361Low-tension current for distance relays,356Low-tension voltage,for directional relaying,386 for distance relaying,148,352 general,145Magetizing-current inrush,effect on distancerelays,359 effect on transformer differentialrelays,254 in parallel transformer banks,259Maximum torque,angle of,adjustment,57power relays,52,55 short-circuit relays,55Memory action,described,83 effect of voltagesource location,144Mho relay,characteristics on R-X diagram,81for line protection,340 operatingcharacteristic,80Microwave-pilot relaying,see Pilot relaying,microwaveMinimum pickup of directional relays,38Mixing transformer for wire-pilot relaying,966I N D E XModified-impendance relay,77Motor protection,field ground,237 fire-pump,230 1088 of excitation,237 1088 ofsynchronism,236 rotor overheating,236stator overheating,232 stator short circuit,230 unattended motors,230 under voltage,237Multiterminal-line protection,with a-c wire-pilotrelaying,376 with directional-comparieonpilot relaying,387 with phasecomparisonpilot relaying,382Mutual induction,effect of,on direc?relays,393 from power circuit to pilot wires,88Neutralizing transformers for wire-pilot circuits,99Normally blocked trip circuit,109Open phase,effect of,on directional?relays,323,325 equivalent circuits for,323protection of generators against,215Operating principles,basic,electromagnetic-attraction relays,16Operating principles,directional type,24 single-quantity type,22 induction relays:directionaltype,33 singlequantity type,31Operation indicator,17Operator vs.protective relays,11Opposed-voltage pilot relaying,92,95Out of step,see Loss of synchronismOvercurrent relays,combination ofinstantaneous and time delay,49 pickup orreset,45 time delay,45,46 see also Lineprotection with overcurrent relaysOverreach,of distance relays,82,350,351 ofinstantaneous overcurrent relays,308Over?travel,defined,48 effect of,onovercurrent-relay adjustment,301Overvoltage,in CI secondaries,124 see alsoGenerator protectionOvervoltage relays,pickup or reset,45 timedelay,45,46Percentage-differential relays,description,65 forbus protection,284 for generator protection,195 for transformer protection,241 locking-infor internal faults,202,251 product restraint,204 variable percent slope,187,203Petersen coil,see Ground-fault neutralizerPhase-comparison relaying,principle ofoperation,101 see also Line protection withpilot relaysPilot relaying,circulating current,92,94general,86 line protection,373,374 opposedvoltage,92,95 pilot-wire protection,98 pilot-wire requirements,97 pilot-wire supervision,97 remote tripping,97 see also Lineprotection with pilot relaysPilot relaying,carrier-current-,directionalcomparison,106 general,86 intermittent orcontinuous,109 phase comparison,101 pilotdescribed,100 supervision of pilot channel,378 see also Line protection with pilot relays;Pilot relaying,-d-c wire-,basic principles,89description of pilot 86Pilot relaying,micro-wave-,description ofchannel,397 general,86,101,396 remotetripping,398 see also Line protection withpilot relaysPilot relaying,principles of,ground preference,91 purpose of a pilot,87 sensitivity levels,91,106 tripping and blocking pilots,88,90I N D E X7Polarizing quantity,of a-c directional relays 37of d-c directional relays,61 of directionalunits of ground relays,151,326Polyphase directional relays,advantages anddisadvantages,313 response to positive-andnegative?volt-amps,183Potential device,see Capacitance potentialdevicePotential transformers,accuracy,133connections,146 effect of fuse blowing,ondistance relaying,361 on generator relaying,228 low-tension voltage for distance relays,148Power-balance relaying for line protection,330Power-rectifier-transformer protection,271Power swings,see Loss of synchronismPower transformer and autotransformerprotection,external-fault backup,264gasaccumulator and pressure relays,261grounding protective relay,263 overcurrentrelaying,261 percentagedifferential relaying,241 CT accuracy requirements,251 CTconnections,242 CT ratios,250 magnetizinginrush,effect of,254 parallel banks,258percent slope,choice of,252 two-windingrelay for threewinding transformer,252 zero-phasesequence-current shunt,249 remotetripping,263Primary relaying defined,4Product restraint for generator differentialrelays,204Protective relaying,evaluation of,12 functionof,3 functional characteristics of,9fundamental principles of,4Ratings,relay,contact,43 current and voltage,42 holding coil,seal-in coil,and target,43Ratio correction factor,see Currenttransformers;Voltage trans formersReactance relay,characteristic on R-X diagram,79 operating characteristic,78 partial-differential bus protection,282 see also Lineprotection with distance relaysReclosing,automatic,affected by remotetripping,367 effect on blocking-terminalpilot?equipment,376 mitigation of faulteffects,2 of bus breakers,292 single-phaseswitching,399 synchronism check,333,366with distance relaying,366 with overcurrentrelaying,333 with pilot relaying,399Rectifier-transformer protection,271Regulating-transformer protection,ex faultback-up,208 in-phase type
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