protective relaying - mit
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Title of BookTitle of Book::
ower ys em ro ec ve e ay ngower ys em ro ec ve e ay ng
ByBy::
..BSEE 79 / BSECE 80BSEE 79 / BSECE 80 MITMIT
11STST EDITIONEDITION
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INTRODUCTIONINTRODUCTION
Since the mid twentieth century, electricity has been an essential part of our lives. ElectricitySince the mid twentieth century, electricity has been an essential part of our lives. Electricity
powers, our appliances, office equipment and countless other devices and apparatus that wepowers, our appliances, office equipment and countless other devices and apparatus that we
use to make life safer, easier and more interesting. Use of electric power is something we takeuse to make life safer, easier and more interesting. Use of electric power is something we take
, ,, ,
mans useful resources making our life convenient and relaxing through its various usefulness.mans useful resources making our life convenient and relaxing through its various usefulness.
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22 TIME DELAY STARTING OR CLOSING RELAY.TIME DELAY STARTING OR CLOSING RELAY.
33 CHECKING OR INTERLOCKING RELAY.CHECKING OR INTERLOCKING RELAY.
2121 DISTANCE RELAY.DISTANCE RELAY.
2525 SYNCHRONIZING OR SYNCHRONISM CHECKSYNCHRONIZING OR SYNCHRONISM CHECK
RELAY.RELAY. ..
3030 ANNUCIATOR RELAY.ANNUCIATOR RELAY.
3232 DIRECTIONAL POWER RELAY.DIRECTIONAL POWER RELAY.
3737 UNDERCURRENT OR UNDERPOWER RELAY.UNDERCURRENT OR UNDERPOWER RELAY.
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.
46 REVERSE PHASE OR PHASE BALANCE CURRENT RELAY.49 MACHINE OR TRANSFORMER THERMAL RELAY.
50 INSTANTANEOUS OVERCURRENT OR RATE OF RISE RELAY.
51 AC TIME OVERCURRENT RELAY.
52 AC CIRCUIT BREAKER.
52A CIRCUIT BREAKER UXILLIARY SWITCH NORMALLY OPEN.52B CIRCUIT BREAKER AUXILLIARY SWITCH NORMALLY CLOSED.
55 POWER FACTOR RELAY.
56 FIELD APPLICATION RELAY.
59 OVERVOLTAGE RELAY.
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6464 EARTH FAULT PROTECTIVE RELAY.EARTH FAULT PROTECTIVE RELAY.
6767 AC DIRECTIONAL OVERCURRENT RELAY.AC DIRECTIONAL OVERCURRENT RELAY.
6868 BLOCKING RELAY.BLOCKING RELAY.7474 ALARM RELAY.ALARM RELAY.
..
7878 PHASE ANGLE MEASURING OR OUT OF STEPPHASE ANGLE MEASURING OR OUT OF STEPPROTECTIVE RELAY.PROTECTIVE RELAY.
7979 AC RECLOSING RELAY.AC RECLOSING RELAY.
8181 FREQUENCY RELAY.FREQUENCY RELAY.
8383 AUTOMATIC SELECTIVE CONTROL OR TRANSFERAUTOMATIC SELECTIVE CONTROL OR TRANSFERRELAY.RELAY.
..8686 LOCKING OUT RELAY.LOCKING OUT RELAY.
8787 DIFFERENTIAL PROTECTIVE RELAY.DIFFERENTIAL PROTECTIVE RELAY.
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51N51N RESIDUAL GROUND OVERCURRENT RELAY 0.5RESIDUAL GROUND OVERCURRENT RELAY 0.5 2.5 A.2.5 A.
6363 SUDDEN PRESSURE RELAY.SUDDEN PRESSURE RELAY.
63X63X AUXILLIARY RELAY FOR SUDDEN PRESSURE.AUXILLIARY RELAY FOR SUDDEN PRESSURE.7979 RECLOSING RELAY, 3 SHOT DC OPERATED TIMER.RECLOSING RELAY, 3 SHOT DC OPERATED TIMER.
..
87B87B BUS DIFFERENTIAL RELAY, HIGH SPEED, HIGHBUS DIFFERENTIAL RELAY, HIGH SPEED, HIGHINPEDANCE VOLTAGE UNITINPEDANCE VOLTAGE UNIT
WITH LOW INPEDANCE INSTANTANEOUSWITH LOW INPEDANCE INSTANTANEOUSOVERCURRENT UNIT.OVERCURRENT UNIT.
87T87T TRANSFORMER BANK DIFFERENTIAL RELAY,TRANSFORMER BANK DIFFERENTIAL RELAY,PERCENTAGE, 2 RESTRAINTS.PERCENTAGE, 2 RESTRAINTS.
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87G87G RESTRICTED EARTH FAULT RELAY.RESTRICTED EARTH FAULT RELAY.
..
AA AMMETERAMMETERKWHKWH BILLING KILOWATT HOUR METER W/ DEMAND INDICATOR.BILLING KILOWATT HOUR METER W/ DEMAND INDICATOR.
VARVAR VARMETERVARMETER
WW WATTMETERWATTMETER
ASAS AMMETER SWITCHAMMETER SWITCH
VSVS VOLTMETER SWITCHVOLTMETER SWITCH ,,
GTGT OVERCURRENT RELAY.OVERCURRENT RELAY.
1212 ZONE PACKAGE, MHO CHARACTERISTICS, COMPENSATOR DISTANCEZONE PACKAGE, MHO CHARACTERISTICS, COMPENSATOR DISTANCERELAYRELAY
-- ..
2121 ZONE PACKAGED, MHO CHARACTERISTICS WITH OFFSET OPTION,ZONE PACKAGED, MHO CHARACTERISTICS WITH OFFSET OPTION,ZZ--22 COMPENSATOR DISTANCE RELAY (ZONECOMPENSATOR DISTANCE RELAY (ZONE 2).2).
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2121 -- ZONE PACKAGED, MHO CHARACTERISTICS WITHZONE PACKAGED, MHO CHARACTERISTICS WITH-- ,,
(ZONE(ZONE 3).3).50H50H HIGH SET NONDIRECTIONAL INSTANTANEOUSHIGH SET NONDIRECTIONAL INSTANTANEOUS
OVERCURRENT RELAY.OVERCURRENT RELAY.
22 TOWTOW ZONE TIMING AUXILLIARY RELAY (ATARTINGZONE TIMING AUXILLIARY RELAY (ATARTINGOR CLOSING).OR CLOSING).
2727 UNDERVOLTAGE RELAY, 115 VOLTS.UNDERVOLTAGE RELAY, 115 VOLTS.
SCHEME.SCHEME.
5050 INSTANTANEOUS OVERCURRENT RELAYS.INSTANTANEOUS OVERCURRENT RELAYS.
5050--5151 PHASE OVERCURRENT RELAY WITH INSTATANEOUSPHASE OVERCURRENT RELAY WITH INSTATANEOUS
UNIT 1.0UNIT 1.0 12 A (612 A (6 --14 A ITT).14 A ITT).51G51G TRANSFORMER NEUTRAL GROUND OVERCURRENTTRANSFORMER NEUTRAL GROUND OVERCURRENT
RELAY 0.5RELAY 0.5 2.5 A.2.5 A.
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Part 1:
Power S stem Protection
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Electric Power SystemElectric Power SystemElectric Power SystemElectric Power System
Electricity is generated at a power plant (1), voltage is stepped-up fortransmission (2). energy travels along a transmission line to the area where thepower is needed (3). voltage is decreased or stepped-down, at another substation(4), and a distribution power line (5) carries that electricity until it reaches a home
.
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Power SystemPower System
AB
Delivery
SubstationDeliverySubstation
C
ac one
Looped Lines
Distribution
Radial Lines
Power System Protection
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LEGEND:
Initial
Bus No. 1
INCOMING
115kV LINE 1
INCOMING
115kV LINE 2
115KV Switchyard
Bank #1 Bank #2 Bank #3
83 MVA PXFwith OLTC
us o.
34.5KV Switchyard34.5kV switchgear No. 1
F1 F2 F3 F4
TYPICAL DISTRIBUTION SUBSTATION
F1 F2 F3 F4Bus tie F1 F2 F3 F47.2 MVAR
Capacitor Bank
7.2 MVAR
Capacitor Bank
7.2 MVAR
Capacitor Bank
Bus tie
Single Line Diagram
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What is Power SystemWhat is Power SystemWhat is Power SystemWhat is Power System
Protection?Protection?Protection?Protection?
also known asalso known as Protective RelayingProtective Relaying
ranc o ec r c ower ranc o ec r c ower
EngineeringEngineeringScienceScience,,ArtArt andand SkillSkill in applyingin applying
devices.devices.
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Protective relaysProtective relays are devices whichare devices whichmonitor power system conditions andmonitor power system conditions andopera e o qu c y an accura e yopera e o qu c y an accura e yisolate faults or dangerousisolate faults or dangerous
conditions. A well desi nedconditions. A well desi nedprotective system can limit damageprotective system can limit damageto equipment, as well as minimize theto equipment, as well as minimize the
interruption.interruption.
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Purpose of System ProtectionPurpose of System ProtectionPurpose of System ProtectionPurpose of System Protection
To prevent injury to personnelTo prevent injury to personnel
componentscomponentsTo limit the extent and duration ofTo limit the extent and duration of
service interruptionservice interruption
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Components of Power SystemComponents of Power SystemComponents of Power SystemComponents of Power System
ProtectionProtectionProtectionProtection
RelaysRelays
Circuit BreakersCircuit Breakers
Tripping and Auxiliary SuppliesTripping and Auxiliary Supplies
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Components of Power System ProtectionComponents of Power System Protection
Decides whether system
quantities are normal or
abnormal (Brain of the
Transducers
(PT & CT) Relay Circuit
Breaker
Power
System
* ,
no signal is sent to breaker
* If quantities are abnormal,
signal is sent to breaker to
electrical quantities to
level relays can use, i.e.,
5 amperes, 115 volts
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Sensor (Instrument
Transformers)
Feedback
Signals
Relay
Power Circuit Breaker
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Components of Power System ProtectionComponents of Power System Protection
Transmission
CBCT
Line
Trip Coil
Station
Relay Contacts
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Abnormalities in PowerAbnormalities in PowerAbnormalities in PowerAbnormalities in Power
ystemsystemsystemsystems
OvercurrentOvercurrent (overload, short circuit, open(overload, short circuit, open
Ground PotentialGround Potential (ungrounded equipment,(ungrounded equipment,
,,
Surge VoltagesSurge Voltages (lightning strokes, switching(lightning strokes, switching
sur es harmonicssur es harmonics
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Frequency of Types ofFrequency of Types ofFrequency of Types ofFrequency of Types of
FaultsFaultsFaultsFaults
Type ofFault
%Occurrence
SLG
LL
85
8DLG
3L
5
2 or less
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Equipment % of Total
Overhead lines
Cables
50
10
Transformers
CTs and PTs
12
2
Control EquipmentMiscellaneous
38
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Factors Which Influence DesignFactors Which Influence DesignFactors Which Influence DesignFactors Which Influence Design
of a Protective Systemof a Protective Systemof a Protective Systemof a Protective System
ReliabilityReliability DependabilityDependability
ecur yecur y
SensitivitySensitivity
SelectivitSelectivit
SpeedSpeed
EconomicsEconomics
ExperienceExperienceIndustry StandardsIndustry Standards
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Factors Which Influence DesignFactors Which Influence DesignFactors Which Influence DesignFactors Which Influence Design
o a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys em
ReliabilityReliabilityThe level of assurance that the rela will function asThe level of assurance that the rela will function as
intended.intended.
Reliability denotes:Reliability denotes: DependabilityDependability -- certainty of correct operationcertainty of correct operation
SecuritySecurity -- assurance against incorrect operationassurance against incorrect operation
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Factors Which Influence DesignFactors Which Influence DesignFactors Which Influence DesignFactors Which Influence Design
o a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys em
SensitivitySensitivity
that it will operate when requiredthat it will operate when required
Must discriminate normal from abnormal conditions.Must discriminate normal from abnormal conditions.
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Factors Which Influence DesignFactors Which Influence DesignFactors Which Influence DesignFactors Which Influence Design
o a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys em
SelectivitySelectivityPerformance of rotective devices to select betweenPerformance of rotective devices to select between
those conditions for which prompt operation andthose conditions for which prompt operation and
those for which no operation, or time delay operationthose for which no operation, or time delay operation
..
Isolate faulted circuit resulting in minimumIsolate faulted circuit resulting in minimum
interruptions.interruptions.
Implemented through Zone of ProtectionImplemented through Zone of Protection
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Factors Which Influence DesignFactors Which Influence DesignFactors Which Influence DesignFactors Which Influence Design
o a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys em
SpeedSpeedRemove a fault from the power system as quickly asRemove a fault from the power system as quickly as
possiblepossible
Classification:Classification:
ns an aneousns an aneous -- no n en ona e ayno n en ona e ay
High SpeedHigh Speed -- less than 3 cyclesless than 3 cycles
-- --
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Factors Which Influence DesignFactors Which Influence DesignFactors Which Influence DesignFactors Which Influence Design
o a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys em
EconomicsEconomicsMaximum protection at minimum costMaximum protection at minimum cost
the cost of installation, operation, and maintenance ofthe cost of installation, operation, and maintenance of
the protection system which must be weightedthe protection system which must be weighted
service interruption.service interruption.
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Factors Which Influence DesignFactors Which Influence DesignFactors Which Influence DesignFactors Which Influence Design
o a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys emo a ro ec ve ys em
ExperienceExperience
be encountered:be encountered:
Actual Relay PerformanceActual Relay PerformanceNature of FaultsNature of Faults
Operation and MaintenanceOperation and Maintenance
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Factors Which Influence DesignFactors Which Influence Design
of a Protective Systemof a Protective System
Industry StandardsThe Institute of Electrical and Electronic Engineers (IEEE) and other.
include specific standards for many applications.ANSI-C37.90-1989 Relays and Relay System
Apparatus
IEEE STD 242-1975 Recommended Practicefor Protection and Coordination
of Industrial and CommercialPower System
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Principles of
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Develo ment of Protective Rela sDevelo ment of Protective Rela s
Electro-mechanical relay
Solid-state relay
Digital relay
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ElectroElectro--mechanical Relay:mechanical Relay:
( 1st Generation )( 1st Generation )
The most commonly usedThe most commonly used
(watthour meter)(watthour meter)
Provides individual phaseProvides individual phaseprotectionprotection
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ElectroElectro--mechanical Relay:mechanical Relay:
( 1st Generation )( 1st Generation )
Time Adjustment:
Operator Rod
ension contro e
Contacts
Sensing Coil
DiscCore
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ElectroElectro--mechanical Relay:mechanical Relay:
( 1st Generation )( 1st Generation )
Critical Components:
Composition of the rotating disc & Coil
.
Rotating & Tripping mechanism
Lubrication & alignments. Spring & tension adjusting mechanism
Fatigue & Temperature dependence.
Design Approach: Periodic re-calibration & maintenance
- .
High burden CT, low sensitivity at higher currents.
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Static Relay:Static Relay:
( 2nd Generation )( 2nd Generation )
Characteristic curve is obtainedCharacteristic curve is obtainedthrough use ofthrough use ofRCRC timing circuitstiming circuits
Used to retrofit electroUsed to retrofit electro--mechanicalmechanical
relaysrelaysFast resetFast reset
Less maintenanceLess maintenance
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Static Relay:Static Relay:
( 2nd Generation )( 2nd Generation )
Set ValueComparator Timing Output
RC Based Timin
AC - DC
Conversion
From CTs
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Static Relay:Static Relay:
( 2nd Generation )( 2nd Generation )
r ca omponen s:
RC Timing circuit.
Tem erature de endence
Low repeatabilityV
Time
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Static Relay:Static Relay:
( 2nd Generation )( 2nd Generation )
r t ca omponents: cont nue
AC/DC Conversion.
Offset roblem
Effects of harmonics & Noise
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Static Relay:Static Relay:
( 2nd Generation )( 2nd Generation )
Periodic re-calibration & maintenance Draw-out connections.
RC & LC Based filters - Slow tripping actions
Without Filter
With RC Filter
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Digital Relay:Digital Relay:
( 3rd Generation )( 3rd Generation )
ComputerComputer--basedbased--with CPUwith CPUSelectable characteristic curvesSelectable characteristic curves
and protection functionsand protection functions
Metering and control functionsMetering and control functions
ven an or s ur anceven an or s ur ance
recordingrecording
Remote communicationRemote communication
SelfSelf--monitoringmonitoring
All inAll in
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Digital Relay:Digital Relay:
( MicroProcessor Based )( MicroProcessor Based )
Micro-processorCPU
Crystal
Data & Address BusMemory EPROM
ontro e ay ontactsu pu on ro
AC - DCConversion
Current Sampling
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Digital Relay:Digital Relay:
( MicroProcessor Based )( MicroProcessor Based )
Design Principle:
AC/ DC
Analog to Digital ConversionA to D
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Digital Relay:Digital Relay:
( MicroProcessor Based )( MicroProcessor Based )
r t ca omponents:
High Frequency Bus
Susce tible to EMI/ RFI.
AC/ DC & Digital Conversion
Effect of Offset/ Harmonics, etc.
CPU
RAMEPROM
A/D Hi-Freq Bus
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Digital Relay:Digital Relay:
( MicroProcessor Based )( MicroProcessor Based )
r t ca omponents:
High Frequency Bus
Susce tible to EMI/ RFI.
AC/ DC & Digital Conversion
Effect of Offset/ Harmonics, etc.
Noise
A to D
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Digital Relay:Digital Relay:
( MicroProcessor Based )( MicroProcessor Based )
RC & LC Based filters Slow tri in actions
Shielding & Watch-dog timers
Problem reduced not eliminated May reset randomly
CPU
RAM
EPROM
A/DWatch
DOG
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Digital Relay:Digital Relay:
( MicroController Based )( MicroController Based )
-controller Out ut Control Crystal
Steady state data
AC - DC
Current SamplingB CA E
Conversion
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Digital Relay:Digital Relay:
( MicroController Based )( MicroController Based )
es gn r nc p e:
Lesser no. of components, hence less chance of failure.
-
More functions can be built in a compact space.
Controller
RAM
Controller
A2D Converter
P C
EPROM Decoding logic
A2D Converter
Output driver
or s
Output driver
i i l li i l l
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Digital Relay:Digital Relay:
( MicroController Based )( MicroController Based )
es gn r nc p e:
Absence of exposed high frequency bus
- .
Cost effective technology appropriate for MV applications
CPU
RAM EPROM
A/D
Di it l R lDi it l R l
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Digital Relay:Digital Relay:
( Numerical Relay )( Numerical Relay )
-controllerCrystalSerial Port To Outside world
Output Control
Steady state data
Relay Contacts
Current SamplingB CA E
irect
Sampling
Di it l R lDi it l R l
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Digital Relay:Digital Relay:
( Numerical Relay )( Numerical Relay )
Design Principle:
AC attenuation
Numeric filtering & measurement
A to D
Di it l R lDi it l R l
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Digital Relay:Digital Relay:
( Numerical Relay )( Numerical Relay )
es gn r nc p e: con nue
Digital Signal Processing concepts
The normal representation i.e. with time in the X axis
The signal is sampled periodically, a different value obtained every
, .
Amplitude
Disadvantages No Phase Angle information.
No Frequency information.
Time
Digital RelaDigital Rela
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Digital Relay:Digital Relay:
( Numerical Relay )( Numerical Relay )
es gn r nc p e: cont nue
Digital Signal Processing concepts
X Axis now represents frequency, instead of time.
-
.
Amplitude
Frequency
50Hz
Digital Relay:Digital Relay:
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Digital Relay:Digital Relay:
( Numerical Relay )( Numerical Relay )
es gn r nc p e: con nue
Digital Signal Processing concepts
Any signal can be represented by infinite Nos. of Sine waves
ny r rary gna
=
+
Fundamental (50Hz). 2nd Harmonic (100 )
Digital Relay:Digital Relay:
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Digital Relay:Digital Relay:
( Numerical Relay )( Numerical Relay )
es gn r nc p e: con nue
Digital Signal Processing concepts
X Axis now represents frequency, instead of time.
Fourier Analysis
.
Amplitude
Frequency
50Hz 100Hz
Digital Relay:Digital Relay:
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Digital Relay:Digital Relay:
( Numerical Relay )( Numerical Relay )
Very quick operation. In-built immunit to DC & harmonics tuned
characteristics)
Possibility of providing additional filtering or
inhibiting actions without sacrificing speed of
response.
oss y o s ur ance recor ng us,
post-mortem analysis of fault & relay behavior.
.
Very less no. of components.
Digital Relay:Digital Relay:
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Digital Relay:Digital Relay:
( Numerical Relay )( Numerical Relay )
Additional Features:
Communication to external laptop/ computer.
programmed in a single enclosure, instead of a
combination of multi le discreet rela s.
Possibility of using non-conventional
transducers for input sensing. Eg. Hall effect
Current Transducers. A Bay-level controller instead of just a
pro ec on re ay .
C i f Diff t t f R lC i f Diff t t f R l
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Com arisons of Different t e of Rela sCom arisons of Different t e of Rela s
arac er s c ec ro-
mechanical
a c cro-
processor
based
cro-
Controller
based
umer ca
Speed of response Slow Fast Fast Fast Very Fast
Timing Accuracy Temp.
Dependant
Temp.
Dependant
Stable Stable Stable
Size Bulky Small Small Small Very Compact
Draw-out required Required Required Not required Not required Not requiredCT Burden High Low Low Low Low
Reset Time Very High Less Less Less Less
Functions Single
function
Single
function
Multi
function
Multi
function
Multi
function
Maintenance Frequent Frequent Low Low Very Low
Deterioration due to
frequent operations
Yes No No No No
SCADA Compatibility No No Possible Possible Yes
Zones of ProtectionZones of Protection
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Zones of ProtectionZones of Protection
Regions (zones) of power system that can beRegions (zones) of power system that can be
protected adequately with fault recognition andprotected adequately with fault recognition and
remova resu ng n so a on o a m n mum amoun oremova resu ng n so a on o a m n mum amoun o
equipment.equipment.
Re uirements:Re uirements:All ower s stem elements must beAll ower s stem elements must beencompassed by at least one zoneencompassed by at least one zone
Zones of protection must overlap to prevent anyZones of protection must overlap to prevent any
sys em e emen rom e ng unpro ec e no nsys em e emen rom e ng unpro ec e no n
spots).spots).
Zones of ProtectionZones of Protection
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Zones of ProtectionZones of Protection
52
87B
3 6
50/511
52
50/51
87B
OVERLAPPING ZONESG
Zones of ProtectionZones of Protection
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Zones of ProtectionZones of Protection
Overlapping zones of protection
Zones of ProtectionZones of Protection
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Zones of ProtectionZones of Protection
1 - Bus Protection
3
5
1
2 - Generator Protection
3 - Subtrans Line Protection
4 - Fee er Protection
5 - Transformer Protection
G 4
Feeder Protectioneeder Protection
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Fault
Bus Protectionus Protection
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Fault
Transformer Protectionransformer Protection
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Fault
Subtransmission Line Protectionubtransmission Line Protection
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Fault
Generator Protectionenerator Protection
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Fault
Primary and BackPrimary and Back--upupPrimary and BackPrimary and Back--upup
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Primary ProtectionPrimary Protection -- Main protection system forMain protection system for
BackBack--up Protectionup Protection -- Alternate protectionAlternate protection
BackBack--up Protectionup ProtectionBackBack--up Protectionup Protection
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Local BackLocal Back--upup -- Alternate protection at theAlternate protection at the..
Remote BackRemote Back--upup -- Alternate protection at theAlternate protection at the
fails.fails.
Local BackLocal Back--up Protectionup ProtectionLocal BackLocal Back--up Protectionup Protection
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B3B1 B2
B4 B6B5
B7 B8 B9F1
Main: B8,B9, L2 remote protection
Fault F1
Local Backup:
If B9 fails, trips B6 and B3
If B8 fails, trips B7 and sends signal to trip L1
remote protect on
Remote BackRemote Back--up Protectionup ProtectionRemote BackRemote Back--up Protectionup Protection
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B1 B2 B7 B8
F1
F2F3
B4B3
B6B5
B9 B10
Fault F1
Main: B5,B6
Fault F2
Main: B2,B4,B5
Backup: B1,B3,B6 , , ,
Fault F3
Main: B3,B4
Backup: B1,B6
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Current MagnitudeCurrent Magnitude
20 A60 A100 A
TimeTime
Inst.0.35 sec1.0 sec
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Distance MeasurementDistance Measurement
Z = V/I ohms
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Time
Current
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Zone 3Time
Zone 2
Zone 1
Distance
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87T
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Overcurrent Relays - are operated whenthe current passing to the relayexceeds a preset value. They arenot directional in nature.
Bus
I51
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a a ne ro ec ona a ne ro ec ona a ne ro ec ona a ne ro ec on
CTA
B 52
C
51
51N
Ground
Phase
Relays
e ay
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rec ona vercurren e ays - are opera e
when the current passing to it exceeds areset value but with the addition ofanother condition and that is providedthat the direction of the fault is correct
A B
I @ CB2 I @ CB3
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Directional Overcurrent Relays
I @ CB4
A B1 2 3 4
I CB3
So for a fault just after CB4 a directional over-current
relay at CB3 will see the fault in reverse while at CB4
the fault is forward looking thus i t will trip CB4 only to
isolate the fault
The scheme is now selective and a little secure
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I @ CB4
A B1 2 3 4
I CB3
,directional overcurrent relay of CB2 might see the
fault. Therefore, the scheme is now not secure.
The use of distance relay is preferred.
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s ance e ays
Measures the im edance of the line it beinproportional to the distance of the line fromthe substation hence the name implies.
Widely used protection scheme for Double-Ended Transmission Line from 69 kV up to as
g as y ransco .
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Differential RelayA rela that b its desi n or a lication is intended to
respond to the difference between incoming and
outgoing electrical quantities associated with the
.
Input Output=
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CT
PCB
50/5186T
POWERTRANSFORMER
87T TRIPS AND LOCKS-OUTHS AND LS PCB
151GPCB
CT
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Typical Bus Arrangements:
Single bus
Double bus, double breaker
Breaker-and-a-half
Ring bus
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Bus differential connection sin le-bus
87B
86B
TRIPS AND LOCKS-OUT ALL BREAKERSCONNECTED TO BUS
NOTE: All CTs connected to the bus
differential must have same ratios.BUS
Differential Protection
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Differential Protection
Primary Element
CT CT
600/5
600A
600/5
5A 5A600A
Relay 0A
5A5A
Differential Protection
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Differential Protection
PrimaryElement
Fault
CT CT
600/5
600A
600/5
600A5A 5A
Relay 10A
5A 5A
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Part :
Rela in Philoso h
Power S stemPower S stem
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Delivery
SubstationDelivery
Substation
AB
Looped Lines
(System Backbone)
Power Transformer
Distribution
34.5kV Bus
Standard ProtectionStandard Protection
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Radial Lines
Power Transformer
Capacitor Bank
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ELECTRO-MECHANICALOVERCURRENT RELAY
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OVERCURRENT RELAY
BUS
50 50N
3
TARGET
INST.
TARGET
TIME
51 51NCT
LEGEND:50 INSTANTANEOUS, PHASE OVERCURRENT RELAY
,
50N INSTANTANEOUS, GROUND OVERCURRENT RELAY
51N TIME, GROUND OVERCURRENT RELAY
43R RECLOSER SWITCH
79 AUTO RECLOSER RELAY
52 POWER CIRCUIT BREAKER
CT CURRENT TRANSFORMER
a a ne ro ec ona a ne ro ec on
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a a ne ro ec ona a ne ro ec on
A B CCT
52
single-phase
overcurrent
relays are needed to
protect a feeder
a
Ib In=Ia+Ib+Ic
PhaseRelays
roun
RelayIc
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BUS
21 21G 79CT 85
LEGEND:
21 PHASE DISTANCE RELAY67 67N
CT
43R
21G GROUND DISTANCE RELAY67 PHASE DIRECTIONAL OC RELAY
67N GROUND DIRECTIONAL OC RELAY
43R RECLOSER SWITCH
52
79 AUTO RECLOSER RELAY
85 TELEPROTECTION52 POWER CIRCUIT BREAKER
CT CURRENT TRANSFORMER
METERING
BUS PROTECTION
oope ne ro ec on
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Distance RelaDistance Rela
oope ne ro ec on
A relay that measures the impedance of the lineA relay that measures the impedance of the line
Principle of OperationPrinciple of Operation ZLINE FAULT
VFAULTIFAULT
Therefore: ZLINE = VFAULT / IFAULTZRELAY = ZLINE * CTR/PTR
FAULT FAULT LINE
X
LINE
RImpedance Relay is non-directional
oope ne ro ec on
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oope ne ro ec on
Types of Distance RelayTypes of Distance Relay
ImpedanceImpedance -- Used mainly as a fault detector in most ofUsed mainly as a fault detector in most of--
ReactanceReactance --Needs the supervision of mho to obtain itsNeeds the supervision of mho to obtain its
directionality.directionality.
oo -- os w e y use s ance c arac er s c curveos w e y use s ance c arac er s c curvedue to its inherent directionality.due to its inherent directionality.
QuadrilateralQuadrilateral --Made possible by combining reactanceMade possible by combining reactance
type principle rotated along different axes.type principle rotated along different axes.
CompositeComposite -- Combined mho and quadrilateralCombined mho and quadrilateral
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X X
ypes o stance e ay
Zone 2
Zone 1
R R
REACTANCEMHO
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X X
ypes o stance e ay
R
R
QUAD COMPOSITE
oope ne ro ec on
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p
Mho Distance Relay, 21Mho Distance Relay, 21for phasefor phase--phase or 3phase or 3--phasephase
faultsfaults,, or neor ne-- oo--groun au s ogroun au s o
cover arc resistancecover arc resistance
Phase Directional OC Relay, 67Phase Directional OC Relay, 67backback--up for phaseup for phase--
phase or 3phase or 3--phase faultsphase faultsGround Directional OC Relay, 67NGround Directional OC Relay, 67Nbackback--up for lineup for line--
toto-- round aultsround aults
Teleprotection, 85Teleprotection, 85 -- POTT (Permissive OverreachingPOTT (Permissive Overreaching
Transfer Trip)Transfer Trip)
-- ,, ,,
shotshot
oope ne ro ec on
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Im lementin Distance Rela Characteristic with
Time Graded Scheme also called Step Distance Scheme
Z1
Z2
Time = 1.0 secZ2 Time Delayed
me e aye
Time = 0.0 sec
Time = 0.35 sec
A B C D
21
Relay Location
oope ne ro ec on
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-
21
-
Must under-reach end of the line for selectivity
Typically set for 80-90% of line impedance
oope ne ro ec on
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-
21
.
Must over-reach end of the line
Must not over-reach the Zone 1 of adjacent line
-
adjacent line impedance
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y
ZL2
ZL3
.
Typically set for 100% ZL1 + 100% ZL2 (longest) +0% - 120% ZL3 (shortest)
impedance.
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90% of ZL = instant
A B
21 90% of ZL = instant
120% of ZL = 0.35 sWhat if the
On this condition CB B will trip instantaneously via Zone 1 operation whileCB A will trip after
0.35 second via Zone 2. This is not good since the fault has to be cleared
as shown?
.
So there is a need to solve this problem to coverSo there is a need to solve this problem to cover
e pro ec on o e rema n ng o e nee pro ec on o e rema n ng o e ne
Communication-Aided Protection
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A B
Z2 = 120% of ZL = 0.35 s
21= o = ns an
Z2 = 120% of ZL = 0.35 s
XMTR
A
XMTR
BZ2 Z2TRIP
TRIP
ANDAND
RCVR
ARCVR
B
Communication-Aided Protection
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= o = nstant
A B
Z2 = 120% of ZL = 0.35 s
21= o = nstant
Z2 = 120% of ZL = 0.35 s
XMTR
A
XMTR
BZ2 Z2No TRIP
No TRIP
ANDAND
RCVR
ARCVR
B
oope ne ro ec on
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6767N
Relay is set at fault at the adjacent bus
67
67N
-
Time is 0.70 second
Instantaneous unit is blocked (distance relay must
No auto-reclosure when tripping initiated by back-up
protection
oope ne ro ec on
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With Auto-Reclosing
u -
Zone 1 Tripping
Zone 2 Communication-Aided Tripping
Without Auto-Reclosing Zone 2, Zone 3 or Zone 4 (reverse zone) Tripping
Back-up Protection Tripping
Note: Auto-reclosing is single-shot and 300 msec time
delay to give time for the PCB to extinguish the fault
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Normal maximum working temp. = 95Normal maximum working temp. = 95 CC-- r se w a ve e e o er se w a ve e e o e
transformer.transformer.
vercurrenvercurrenFuses for distribution transformerFuses for distribution transformer
Overcurrent relaying for 5MVA and aboveOvercurrent relaying for 5MVA and above
Characteristics:Characteristics:
Must be below the damage curveMust be below the damage curve
Must be above magnetizing inrushMust be above magnetizing inrush
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DifferentialDifferential -- 87T87T
OverloadOverload -- 5151
BackBack--up Groundup Ground -- 151G151G
OverheatingOverheating -- Thermal RelayThermal Relay
Gas DetectionGas Detection -- Buchholz RelayBuchholz Relay Sudden PressureSudden Pressure -- Pressure Relief ValvePressure Relief Valve
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CT
52
87T
50/5186T
LEGEND:87T TRANSFORMER
CT
151G52 DIFFERENTIAL RELAY
86T AUXILIARY LOCK-OUT RELAY
50 INSTANTANEOUS OC RELAY151G BACK-UP GROUND RELAY
52 POWER CIRCUIT BREAKER
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Differential RelayDifferential Relay
A relay that by its design or applicationA relay that by its design or applicationis intended to respond to the differenceis intended to respond to the differencebetween incoming and outgoingbetween incoming and outgoing
electrical quantities associated with theelectrical quantities associated with theprotected apparatus.protected apparatus.
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Constant Percent Slope Characteristic Differential Relay
K = 25 %
K = 40 %
K = 10 %
OperateI1-I2
Restraint = (I1+I2)/2
Min. Pick-up
Percentage Differential ProtectionPercentage Differential Protection
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g o og o o
Variable Percent Slope Characteristic Differential Relay
OperateI1-I2 Slope 2TRIP ZONE
Slope 1Pick-upNO TRIP ZONE
Restraint = (I1+I2)/2
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Typical Bus Arrangements:Typical Bus Arrangements:
Single busSingle busou e us, ou e rea er ou e us, ou e rea er
BreakerBreaker--andand--aa--halfhalf
breakerbreaker
Ring busRing bus
--
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--
87B
86B
-
OUT ALL BREAKERSCONNECTED TO BUS
NOTE: All CTs connected to the bus differentialmust have same ratios.BUS
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-- ,, --
breaker)breaker)87B87B
TRIPS AND LOCKS-OUT ALL BREAKERSCONNECTED TO
BUS 1
86B
TRIPS AND LOCKS-OUT ALL BREAKERS
86B
BUS 2
BUS 1BUS 2
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-- -- --86B
TRIPS AND
86B
87B
TRIPS ANDLOCKS-OUT ALL
87B-BREAKERSCONNECTED TOBUS 1
BREAKERSCONNECTED TOBUS 2
BUS 1BUS 2
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BUS 1
BUS 2
86B1
TRIPS AND LOCKS-OUT
ALL BREAKERS
CONNECTED TO BUS 1
86B2
87B2
87B1
BUS IMAGING
RELAY
TRIPS AND LOCKS-OUT
ALL BREAKERS
CONNECTED TO BUS 2
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NOTE: No bus differential protection is needed. Thebusses are covered by line or transformer protection.
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Low ImpedanceLow Impedance -- using time overcurrentusing time overcurrent
rela srela s99 inexpensive but affected by CT saturation.inexpensive but affected by CT saturation.
99 low voltage application; 34.5kV and belowlow voltage application; 34.5kV and below
High ImpedanceHigh Impedance -- using overvoltage relaysusing overvoltage relaysthis scheme loads the CTs with a hi h im edance tothis scheme loads the CTs with a hi h im edance to
force the differential current through the CTs insteadforce the differential current through the CTs instead
of the relay operating coilof the relay operating coil.).)..
99 115kV and above voltage application or some115kV and above voltage application or some34.5kV bus voltages which require high protection34.5kV bus voltages which require high protection
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