Abnormal conditions other than short circuits
A-c tripping
Angle-impedance relay
for tripping on 1088 of synchronism
Angle of maximum torque, adjustment
of power relays
of shortcircuit relays
Arcs, effect on distance relays, 345 resistance
Arc - furnace - transformer protection
ASA accuracy classification,, of current transformers
of potential transformers
Attenuation, carrier-current
Automatic reclosing, see Reclosing,automatic
Auxiliaries,, station, protection of
see also Motor protection Back-up relaying, defined,
effect of intermediate current sources,
for bus protection
generator external fault
reversed third zone
transformer external fault
with pilot relaying
Blind spot in pilot relaying
Blinder with directional-comparison relaying
Blocking pilot
Blocking terminal, with a-c wire-pilot relaying,
with directionalcomparison pilot relaying,
with phase-comparison pilot relaying,
Broken-delta connection, burden calculation,
for detecting grounds in ungrounded systems
for polarizing directionalground relays
of capacitance potential devices
Buchholz relay
Burden, current-transformer,
potentialtransformer,
Bus protection
automatic reclosing
back-up relays
circuitbreaker by-psasing
combined power transformer and bus,
current differential with overcurrent relays,
current differential with overvoltagerelays,
current differential withpercentage relays,
directional comparison,
fault bus
grounding
secondaries of differentially connected CTs,
partial-differential,
ring-bus,
testing,
voltage differential with linear cou
Bushing potential device,
see Capacitance potential device
Capacitance potential device
broken burden
comparison with instrument PTs,
couplingcapacitor insulation coordination,
effect of overloading
Capacitance potential device, equivalentcircuit,
non-linear burdens,
standard accuracy,
standard rated burdens,
Capacitor, series, effect on distance relaying,
Capacitor tripping,
Carrier-current attenuation,
Carrier-current-pilot relaying, see Pilot relaying,
carrier-current
Circuit breaker, by-passing,
standard capacities,
Circulating-current pilot relaying,
Cold-load pickup,
Cold-load restoration,
Compensated voltage,
see Transformer
compensation
Constant-product characteristic,
Contact definitions,
Contact races in pilot relaying,
Continuous pilot,
Control spring,
Conventions, vector,
Corrosion, effect of polarity on
Coupling-capacitor description,
Coupling-capacitor insulation coordination,
Coupling-capacitor potential device, Bee Capacitance potential device
Current-balance relay, directional type,
for line protection,
overcurrent type,
Current biasing, for mho relay,
for offset impedance relay,
to avoid distance-relay misoperation on arcs,
Current compensation for ground distance relays
Current switching for distance relays
Current transformers,
accuracy calcula
ASA accuracy classification, burden,
for generator differential relaying,
ratiocorrection-factor curves
secondaryexcitation curves
grounding the
secondaries of differentially connected CTs,
overvoltage in secondary,
polarity and connections,
proximity effect,
Current transformers, requirements for pilot relaying, 377 secondary leakage reactance,
transient errors,
types,zero-phase-sequencecurrent shunt
D-c offset, effect on induction relays,
overreach of distance relays,
overreach of overcurrent relays,
time constant,
D-c relays, single-quantity,
directional,
Differential relays,
see alsoPercentagedifferential relays
Directional-comparison relaying,
for bus protection,
principle of operation,
see also Line protection with pilot relays
Directional control, of electromagnetic relays
of single-quantity induction relay
Directional-overcurrent relay
Directional relays,, a-c types
connections,,
power,
short circuits,
characteristics on R-X diagram,
d-c types,,
use of shunts,
effect of mutual
induction on ground relays,
electromagnetic-attraction type,
groundrelay polarization,
misoperating
tendencies,
negative-phase-aequence
type, 330 operating characteristics,
response of polyphase relays to positive and negative phase sequence,,
response ofainglephase relays to short circuits
Distance relays,, current and voltage switching,
effect of power swings and lose of
synchronism,, effect of wye-deltatransformer between relay and fault,
electronic type, ground-relay connections,
impedance seen during faults,,
Generator protection, overvoltage,
potential-transformer fuse blowing,
prime mover,
station auxiliary,
stator overheating,
stator short circuit,
calculation of CT errors,
ground faults,
sensitive,
ground faults in unit generators,
overcurrent relays for,
turn-to-turn faults,
unbalanced phase currents,
vibration,
Ground-distance-relay connections,
Ground-fault neutralizer, effect on line relaying,
to mitigate the effect of a fault,
Grounding protective relay for trans forme rprotection,
Ground preference,
Ground resistance,
Grounding-tranaformer protection,
Hsrmonic-current restraint, for distance relays,,
for transformer differential relays,
Holding coil,
Impedance diagram, see R-X diagram Impedance relay, characteristic on R-X
diagram, for line protection, general, see also Distance relays Induction-cup and induction-loop structures,
Induction-type relay, directional, generalcharacteristics,,
single-quantity, structures, torque production, Insulating transformer for pilot-wire circuits,,
Intermittent pilot,
Line protection with distance relays adjustment of distance relays area, effectof, blocking tripping on of
synchro , choice between impedance, reactance, and mho,, connections of ground distance relays,,Distance relays,, use of low-tension voltage
see also Line protection with distance relaysDistribution-circuit protection, see Lineprotection with overcurrent relays
Drop-out defined, Electric arc-furnace-transformer protection,
Electromagnetic-attraction relay, directional,
general characteristics,, single-quantity,
Electronic relay, directionalcomparison pilot,
Evaluation of protective relaying,
Expulsion protective gaps, effect of, on distance relays,
External-fault back-up relaying, see Back-up relaying
Fail ures,, electrical, see Faults
False residual current,
Fault bus,
Faults, mitigation of effects of, prevention of,
probability of, effect on practice, 11 see also Short circuits
Fire, protection against,
Fire-pump-motor protection,
Footing resistance, tower-,
Frequency, compensation of relays for changes
in, effect on induction relays
Frequency-converter protection, see Generator
protection
Fundamental principles of protective relaying,
Fuse, coordinating with a,
Fuse blowing, potential-tranaformer, effect on distance relays
effect on generator relays
Generator protection, bearing overheating,
external-fault back-up, m field ground,
loss of excitation,
of synchronism,, miscellaneous,
motoring,
open circuits,, 215 over excitation,, over speed,,
Line protection with distance relays, current
and voltage switching, expulsion protective gaps, effect of, fuse blowing,
effect of, electronic relays,
intermediate current sources, effect of,
low-tension current, use of, low-tension
voltage, use of, magnetizing inrush, effect
of, overreach, purposeful
tripping on loss of synchronism,
reclosing, automatic, series capacitor,
effect of, 367 see also Distance relays
Line protection with overcurrent relays,
a-c and capacitor tripping,
adjustment of ground vs. phase re lays,
adjustment of inverse-time-overcur
rent relays,
arc and ground resistance,
directional feature,
fuses, coordination with,
ground faults in ungrounded systems,
detection of,
ground-fault neutralizers, effect of,
instantaneous overcurrent relays,, use of,
inverseness,, choice of, in relay char acteristics,
limiting ground-fault-current magni tude, effect of,
loop circuits,, effect on relay adjust
misoperation prevention of aingle
directional-overcurrent re during ground faults,
negative-phase sequence ground di rectional relays,,
open phases, effect of,
overreach of instantaneous overcur
rent relays,,
polarizing ground-relay directional
unite,
reclosing, automatic,
restoration of service after prolonged outage,
single-phase vs. polyphase directional relays,,
transient CT errors,
two vs. three relays for phase-fault protection,
Line protection with overcurrent relays, see also
Overcurrent relays
Line protection with pilot relays, a-c
wire-pilot relaying,
back-up protection,
CT requirements,
multi terminal lines,
sensitivity,
see also Pilot relaying, a-c wire-;
Pilot relaying, d-c wire relaying, attenu ation,
sleet detection,
supervision, automatic,
combined phase- and directional com
parison, mutual induction, effect on ground relays,
when to use,
directional comparison, electronic,
low-tension voltage, use of,
multi terminal lines,
sensitivity,
transients,, effect of,
when to use,
see also Pilot relaying, carrier-cur ,
phase comparison, back-up protection,
multi terminal lines,
sensitivity,
when to use,
see also Pilot relaying, carrier-cur
rectional relays,,
open phases, effect of,
overreach of instantaneous overcur
rent relays,,
polarizing ground-relay directional
unite,
reclosing, automatic,
restoration of service after prolonged
outage,
single-phase vs. polyphase directional
relays,,
transient CT errors,
two vs. three relays for phase-fault
protection,
Line protection with overcurrent relays, see also
Overcurrent relays
Line protection with pilot relays, a-c
wire-pilot relaying,
back-up protection,
CT requirements,
multi terminal lines,
sensitivity,
see also Pilot relaying, a-c wire-;
Pilot relaying, d-c wire relaying, attenuation,
sleet detection,
supervision, automatic,
combined phase- and directional com
parison, mutual induction, effect
on ground relays,
when to use,
directional comparison, electronic,
low-tension voltage, use of,
multi terminal lines,
sensitivity,
transients,, effect of,
when to use,
see also Pilot relaying, carrier-cur ,
phase comparison, back-up protection,
multi terminal lines,
sensitivity,
when to use,
see also Pilot relaying, carrier-current
reclosing, high-apeed,,
when to use pilot relaying,
Line trap,
Linear couplers,
Load shedding,
Locking in, with generator differential relaying,
with transformer differential relaying,
Loss-of-excitation protection,
Loss-of-field protection,
Loss of synchronism, characteristics on RX
diagram, derivation of relay current and
voltage, effect on distance relays,
generator protection, trip-blocking relay,tripping relay,
Low-tension current for distance relays,
Low-tension voltage, for directional relaying,
for distance relaying, general,
Magetizing-current inrush, effect on distance
relays, effect on transformer differential
relays, in parallel transformer banks,
Maximum torque, angle of, adjustment,
power relays, short-circuit relays, 55
Memory action, described, effect of voltage
source location,
Mho relay, characteristics on R-X diagram,
for line protection, operating
characteristic,
Microwave-pilot relaying, see Pilot relaying,
microwave
Minimum pickup of directional relays
Mixing transformer for wire-pilot relaying,
Modified-impendance rela
Motor protection, field ground, fire-pump,
of excitation, of
synchronism, rotor overheating,
stator overheating, stator short circuit,
unattended motors, under voltage,,
Multiterminal-line protection, with a-c wire-pilot
relaying, with directional-comparieon
pilot relaying, with phasecomparison
pilot relaying,
Mutual induction, effect of, on direc relays,,
393 from power circuit to pilot wires,, 88
Neutralizing transformers for wire-pilot circuits,,
Normally blocked trip circuit,
Open phase, effect of, on directional relays,
equivalent circuits for,
protection of generators against,
Operating principles,, basic, electromagneticattraction relays,,
Operating principles, directional type, singlequantity type, induction relays: directional
type, singlequantity type,
Operation indicator,
Operator vs. protective relays,
Opposed-voltage pilot relaying,
Out of step, see Loss of synchronism
Overcurrent relays, combination of
instantaneous and time delay, pickup or
reset, time delay see also Line
protection with overcurrent relays
Overreach, of distance relays, of
instantaneous overcurrent relays,
Over travel,, defined, effect of, on
overcurrent-relay adjustment,
Overvoltage, in CI secondaries, see also
Generator protection
Overvoltage relays, pickup or reset,, time
delay,
Percentage-differential relays, description, for
bus protection, for generator protection,
for transformer protection, locking-in
for internal faults product restraint,
variable percent slope,
Petersen coil, see Ground-fault neutralizer
Phase-comparison relaying, principle of
operation, see also Line protection with
pilot relays
Pilot relaying, circulating current,
general, line protection, opposed
voltage, pilot-wire protection, pilotwire requirements,
pilot-wire supervision,
remote tripping, see also Line
protection with pilot relays
Pilot relaying, carrier-current-, directional
comparison, general, intermittent or
continuous, phase comparison, pilot
described, supervision of pilot channel,
see also Line protection with pilot relays ;
Pilot relaying,-d-c wire-, basic principles,
description of pilot
Pilot relaying, micro-wave-, description of
channel, general, remote
tripping, see also Line protection with
pilot relays
Pilot relaying, principles of, ground preference,
purpose of a pilot, sensitivity levels,
tripping and blocking pilots,
Polarizing quantity, of a-c directional relays
of d-c directional relays, of directional
units of ground relays,
Polyphase directional relays, advantages and
disadvantages, response to positive- and
negative volt-amps
Potential device, see Capacitance potential
device
Potential transformers, accuracy,
connections, effect of fuse blowing, on
distance relaying, on generator relaying,
low-tension voltage for distance relays,
Power-balance relaying for line protection,
Power-rectifier-transformer protection,
Power swings, see Loss of synchronism
Power transformer and autotransformer
protection, external-fault backup,
gasaccumulator and pressure relays,
grounding protective relay, overcurrent
relaying, percentagedifferential relaying,
CT accuracy requirements, CT
connections, CT ratios, magnetizing
inrush, effect of, parallel banks,
percent slope, choice of, two-winding
relay for threewinding transformer, zerophasesequence-current shunt, remote
tripping,
Primary relaying defined,
Product restraint for generator differential
relays,
Protective relaying, evaluation of, function
of, functional characteristics of,
fundamental principles of,
Ratings, relay, contact, current and voltage,
holding coil, seal-in coil, and target,
Ratio correction factor, see Current
transformers; Voltage trans formers
Reactance relay, characteristic on R-X diagram,
operating characteristic, partialdifferential bus protection, see also Line
protection with distance relays
Reclosing, automatic, affected by remote
tripping, effect on blocking-terminal
pilot equipment, mitigation of fault
effects, of bus breakers,, single-phase
switching, synchronism check
with distance relaying, with overcurrent
relaying, with pilot relaying,
Rectifier-transformer protection,
Regulating-transformer protection, ex fault
back-up, in-phase type, phase-shifting type,
Reliability, a functional relay characteristic,
Remote tripping, by carrier current, by
microwave, by pilot wire, for powertransformer protection, frequency-shift system,
Replica-type relays, for generator protection,
for motor protection,
Reset, adjustment of, defined, ratio to
pickup, electromagnetic relays, induction
relays, time of induction relays,
Reversed third zone, for back-up with carrier
pilot, where a line includes a
transformer,
R-X diagram, los-of-synchronism char ,
appearance to distance relays principle
of, short-circuit characteristics,
appearance to distance relays wyedelta
transformer between relay and fault
superposition of relay and system
characteristics,
Seal-in coil or relay,
Secondary excitation curves,,
Selectivity, a functional relay characteristic,
Sensitivity, a functional relay char , levels of
blocking and tripping for pilot relaying
Shaded-pole structure,
Short circuits, derivation of relay current and
voltage, impedance seen by distance
relays,, table of currents,, 164 table of
voltages,, see also Faults
Single-phase switching,
Sleet-accumulation detection with carrier
current,
Speed, a functional relay
characteristic,,
Split-phase relaying, combined with percentage
differential,
for generators,
Stability, system, benefited by protective relaying,
Step-voltage-regulator protection,
Supervision, automatic, of carrier channel,
of pilot-wire circuits,
Synchronism check with automatic reclosing,
Target,
Telephone-circuit restrictions,
Testing, relay, field, manual,
Time characteristics, adjustment of, definitions,,
of d-c directional relays,
of electromagnetic-attraction relays,
of induction relays,
Time constant of d-c component,
Torque control, see Directional control
Torque production in induction relays,
Tower-footing resistance,
Transferred tripping, see Remote tripping
Transformer-drop compensation, fordirectional-comparison pilot relaying,
for distance relaying,
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,
on distance relaying,
on electromagnetic-attraction relays,
on overcurrent relays,
Transient blocking,
Transient shunt, for distance relays,
for overcurrent relays,
Transmission-line protection, with distance relaying,
with overcurrent relaying,
Tranemission-line protection, with pilot relaying,
Trap, line,
Tripping pilot,
Tripping suppressor for transformer differential relays,
Tripping, undesired, vs. failure to trip,
Undercurrent and under voltage relays, pickup or reset,
Universal relay torque equation,
Variable restraint for generator differential relays,
Vector conventions,
Vibration, of electromagnetic-attrao relays,
protection for generators,
Voltage-balance relays,
Voltage compensation for ground distance relays,
Voltage-regulator protection, see also
Regulating-transformer protection; Stepvoltage-regulator protection
Voltage switching for distance relays,
Voltage transformers, see Capacitance potential
devices; Potential transformers
Watthour-meter structure,
Wire-pilot relaying, see Pilot relaying, a-c wire-;
Pilot relaying, d-c wire
Zero-phase-sequence-current shunt, currenttransformer connections, used with
transformer differential relays
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