Power system protection in engineering systems

Describe to power system protection

1. POWERSYSTEM PROTECTION AND SWITCHGEAR
FUNDAMENTALS OF PROTECTIVE RELAYING‐I
Dr. BHAVESHKUMAR BHALJA
DEPARTMENT OF ELECTRICAL ENGINEERING
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Subjectname:PowerSystemProtectionandSwitchgear
•ProtectiveDevices:Fuse/MCB/Relay:Tosensethefault
•Switchgear:CircuitBreaker(CB):functionistoisolatethefaultysection
FundamentalsofPowerSystemProtection
•Inapowersystemnetwork,faultsarecategorizedas
1.SymmetricalFaults:Involveallphases(e.g.LLL/LLLG)
2.Asymmetrical Faults: Involve on e or two phases with or without
ground(e.g.LG/LL/LLG)
•Hence, there are 10 types of faults that can occur in a power system
network.
Introduction of Relaying Scheme

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CausesofFaults
1.SymmetricalFault:
•It occurs when line is energized and earthing switch is
inadvertentlykeptON.
2.AsymmetricalFault:
•LGFault:Itoccursmainlyduetoflashover/failureofinsulator.
•LL and LLG Fault: It occurs due to swinging of two
conductors/shortingofwiresduetobirds/kitestrings/treelimb.
Introduction of Relaying Scheme

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ConsequencesofFaults
•Faultscausetwotypesofdamage.
1.Thermaldamage:
Itoccursslowlyasitisrelatedtotemperature.
(depends on thermal withstand capability of insulation which in
turndependsoninsulation)
2.Electrodynamic damage:
The repelling forces generated due to
this large current would deshape and destruct the whole
equipmentstructurally.(Instantaneoustrippingisrequired)
Introduction of Relaying Scheme

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Probabilityofoccurrenceoffaultsondifferentelements
Equipment % of occurrence of fault
Overhead Transmission Line 50%
Underground Cable 10%
Switchgears including CTs and PTs 15%
Power Transformers 15%
Miscellaneous 10%
Introduction of Relaying Scheme

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Probabilityofoccurrenceoffaultsonoverheadlines
Type of fault % of occurrence of fault
LG 80% ‐90%
LL 6% ‐10%
LLG 3% ‐6%
LLL/LLLG 1% or less
Introduction of Relaying Scheme

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Faults
1.Transient:
•Itoccursdueto
a.powerarcbetweentwophases
b.flashoveracrosslineinsulatorduetoovervoltage.
•Automaticallydieoutafterfewcycles.
2.Permanent:
•Remainforalongerdurationanddamagetheequipment.
Introduction of Relaying Scheme

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OccurrenceofaFaultcancause
•Interruptioninthepowersupplytotheconsumers
•Substantiallossofrevenueduetointerruptionofservice
•Loss of synchronism: wide spread blackout due to tripping ofmultiple
oflines/generators.
•Extensivedamagetoequipment
•SerioushazardtoPersonnel
Introduction of Relaying Scheme

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Introduction of Relaying Scheme
Functionof
Protective
System
•Standwatchandintheeventofafailuresuchasshortcircuitor
abnormaloperatingconditions,
•De‐energizetheunhealthysectionofthepowersystem.
•To indicate the type and location of failure so as to access the
effectivenessoftheprotectiveschemes.

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Majorcomponentsofapowersystemnetwork
•Singlelinediagram
•Whypowerisgeneratedatvoltagesbetween11kVand22kV?
•Hence, for each component, a specific protective device is used
(coversaspecificregion).
Introduction of Relaying Scheme

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Zones of Protection
•A power system is normally segmented into a number of protective
zones.
•A zone is protected by a system of relays, circuit breakers, and
associatedequipment.
•Thecircuitbreakersarearrangedinamannerthatmakesitpossibleto
isolate the protected zone while the remaining system continues to
supplyenergytothecustomers.
•Eachzonecoversoneormorecomponentsofthesystem.

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•Toprovidecompleteprotectionfortheentiresystem,thatis,toavoid
having an unprotected region, neighboring zones are arranged to
overlapeachother.
•When a system is experiencing an abnormal condition, the relays first
identify this condition and then send trip signals to appropriate circuit
breakersthatopentoisolatetheaffectedzone.
Zones of Protection

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Zones of Protection

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Thank You