1-power system protective relaying-part one
TRANSCRIPT
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Power System Protective RelayingPower System Protective Relaying
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The purpose of network protectionequipment is tominimize the effects of faults, which cannever be entirely avoided, on an electricalpower system.
IntroductionIntroduction
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Power Systems-Fault Free
Not PossibleMany Reasons
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Power system Protection Engineering isan important component of the electricalplant system and of decisive significancefor the reliable and safe operation of apower system .
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The cause of electric power system faults
is insulation breakdownThis breakdown can be due to a variety of different factors:
Lightning. wires blowing together in the wind. animals or plants coming in contact with
the wires.
salt spray or pollution on insulators.
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Tree limbs falling on the lineInsulation deteriorationVandalism
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Nature Cause
IntroductionIntroduction
Equipment Failure
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Substation FailureSubstation Failure
The AftermathThe Aftermath
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Results of TransformerResults of Transformer FireFire
Generator FaultGenerator Fault
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Expensive Consequences forExpensive Consequences for
Protection FailureProtection Failure
IntroductionIntroduction
Human Error
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IntroductionIntroductionRelay: an electric device that isdesigned to respond to inputconditions in a prescribed mannerand , after specified conditions aremet, to cause contact operation orsimilar abrupt change in associated
electric control circuits. (IEEE)
IntroductionIntroduction
Protective Relay: A relay whosefunction is to detect defective linesor apparatus or other power systemconditions of an abnormal ordangerous nature and to initiate
appropriate control circuit action.(IEEE)
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What is RelayingDetects abnormal conditionsInitiate Corrective actionsHas fast responseDisrupts only essential and minimum
area
RequirementsDefine the undesirable conditionsRemove only the faulted equipmentand to maintain the un-faultedportion of the system.
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Power System ProtectionScience, skill and art of applying andsetting relays &fuses to maximumsensitivity to detect disturbances and toavoid the operation on all permissibletolerable conditions
Define and understand Power SystemfaultsMeasure and Monitor systemparameters V, I, f through transducers(Current, potential transformers)Detection schemes RelaysAction Equipment Circuit Breakers
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Effects of faults on power systemEffects of faults on power system
Flow of excessive currentAbnormal voltagesVoltage elevation of system neutralInduce over voltages on neighbouringequipments .
Hazards to human, equipment andanimals.
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Need for fault analysisNeed for fault analysis
Design of protection system requires theknowledge of fault current.The information obtained from thefault studies are used:to select the sizes of circuit breaker,fuse and characteristic, setting of relays.
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Types of faultTypes of fault
Symmetrical fault :Usually three phase to ground fault
Unsymmetrical (Asymmetrical) faultThe fault is unbalanced in nature
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Sources of Asymmetrical fault areSources of Asymmetrical fault are
One phase open circuit
Unbalanced in load mainly the arc loads
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One phase open circuit
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SLG fault
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Sources of Asymmetrical fault are:Sources of Asymmetrical fault are:
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Typical Protective RelaysTypical Protective Relays
Portable Protective Relay TestPortable Protective Relay TestEquipmentEquipment
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RelaysRelaysA relay is a low-powered device usedto activate a high-powered device.Relays are used to trigger circuitbreakers and other switches insubstations and transmission anddistribution systems.
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Relay CharacteristicsRelay Characteristics
ReliabilityProbability to function properly.The ability to operate fordisturbances within zone(dependability)The ability to refrain from operationfor external abnormalities( security)
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SensitivityAbility to detect abnormal quantities
SelectivityAbility to obtain the desired
operation to avoid unnecessarytripping
SpeedAbility to initiate operation in theshortest time possible
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EconomyThe ability to function at minimumcost
SimplicityAbility to function and to operatewith minimum equipment andcircuitry
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Substation control panel relays
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Relay and control panel
High Voltage FusesHigh Voltage Fuses
High voltage fuses are used toprotect the electrical system in asubstation from power transformerfaults.They are switched for maintenanceand safety.
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High voltage fuses in a switch box
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External switch for high voltage fuses
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Typical Power Circuit BreakersTypical Power Circuit Breakers
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Air circuit breaker
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Vacuum circuit breaker, inside
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Vacuum circuit breaker, outside
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SF6 gas power circuit breaker
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SF6 gas power circuit breaker
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Typical Power Circuit BreakersTypical Power Circuit Breakers
Sample Device NumbersSample Device Numbers
Master element: 1Time-delay starting or closing relay: 2Distance relay: 21Directional power relay: 32Instantaneous overcurrent relay: 50AC time overcurrent relay: 51AC directional overcurrent relay: 67Frequency relay: 81Differential protective relay: 87
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IEEE Device Numbers & Functions
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Device Description Legend49 Thermal50/51 Instantaneous & Time Overcurrent51 Time Overcurrent51N-1 Ground Time Overcurrent51N-2 Neutral Time Overcurrent51N-3 Ground Time Overcurrent63 Sudden Pressure67 Directional Overcurrent67N Directional Ground Overcurrent86 Lockout Auxiliary87T Phase Differential, 3 Phase87N Ground Differential
OP Operating CoilPol Polarizing CoilN.C. Normally Closed
Transformer BushingCS Circuit SwitcherRg Grounding Resistor
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Typical Relay and CircuitTypical Relay and CircuitBreaker ConnectionsBreaker Connections
Typical single line AC connection
Typical Relay and CircuitTypical Relay and CircuitBreaker ConnectionsBreaker Connections
Typical three-phase AC connection
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Basic Objectives of SystemBasic Objectives of SystemProtectionProtection
ReliabilitySelectivitySpeed of OperationSimplicityEconomics
Factors Affecting the ProtectionFactors Affecting the ProtectionSystemSystem
EconomicsPersonalityLocation of Disconnecting and InputDevices
Available Fault Indicators
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Philosophy of ProtectionPhilosophy of ProtectionBoth an art and a scienceWell-designed system will use: Overlapping primary zones of protection
Some form of backup protection
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Qualities Required of ProtectionSelectivity (Discrimination): Effectivenessin isolating only the faulty part of thesystem.Stability: The property of remaininginoperative with fault occurring out sidethe protected zone (called externalfaults).
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Speed of operation:The time between the incidence of a faultand the trip command being issued to thecircuit breaker by the protection.The speed of operation must be as fast aspossible.In modern power systems the relay
operates in one or fraction of a period of the power system frequency.
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Sensitivity: The level of magnitude of the fault current at which theoperation of protective deviceoccurs. Reliability: The ability of a protectivesystem to fulfill its purposethroughout its operation life.
It should not mal-operate at anytime.
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Economic of consideration:
In distribution system it is veryimportant and it overrides the technicalconsideration provided basic safetyrequirements are met.In transmission systems the technicalaspects are more important.
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Zones of protectionZones of protection
Gen Zone
Transf Zone
Bus 1Zone
Line 1 Zone
B u s
2 Z o n e
Line 3ZoneLine 2Zone
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Overlapping zonesOverlapping zones
Zones A and B overlap at circuit breaker CB Faults in overlap trip both zones No gaps in protection
Zone AZone BCB
Trip all zone A Trip all zone B
CT ACT B
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Classification of RelaysClassification of RelaysProtective RelaysRegulating RelaysReclosing, Synchronism Check, andSynchronizing RelaysMonitoring RelaysAuxiliary Relays
Others
Protective Relay PerformanceProtective Relay Performance
Since many relays near the trouble areamay begin to operate for any given fault, itis difficult to completely evaluate anindividual relays performance.Performance can be categorized asfollows: Correct: (a) As planned or (b) Not as plannedor expected. Incorrect: (a) Fail to trip or (b) False tripping No conclusion
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Principles of Relay ApplicationPrinciples of Relay ApplicationThe power system is divided into protectionzones defined by the equipment and availablecircuit breakers. Six possible protection zonesare listed below: Generators and generator-transformer units Transformers Buses Lines (Transmission, subtransmission, and distribution)
Utilization equipment Capacitor or reactor banks
Principles of Relay ApplicationPrinciples of Relay Application
Typical relay primary protection zones
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Principles of Relay ApplicationPrinciples of Relay ApplicationOverlapping protection zones
Information for ApplicationInformation for Application
One line diagram and system configurationImpedance and connection of the powerequipment, system frequency, systemvoltage, and system phase sequenceExisting protection and problems
Operating procedure and PracticesImportance of the system equipment beingprotected
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Information for ApplicationInformation for ApplicationSystem fault studyMaximum loads and system swing limitsCurrent and voltage transformer locations,connections, and ratiosFuture expansion