Power System Protection Basics..a Visit to Sheik Muhammadi Grid Peshawar.

7/31/2019 Power System Protection Basics..a Visit to Sheik Muhammadi Grid Peshawar.

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23/05/2012. power system protection 1

Power system Protection

Visited Grid stations1) 500 KV Sheik Muhammadi Grid Station.2) 220 KV Grid Station near khazana Sugar Mill .

Group members

Zahid ur RehmanShaiq Ali.Najib Ullah Afridi.Shabir Asghar.

Dept: of Electrical Power Engineering UET Peshawar.


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Why protection system is Necessary .

Impossible and uneconomical to build faultfree Power system.

Small disturbances handled by controlsystem.Severe disturbance can jeopardize P.S

Needs a separate protection for handlingthese faults.


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Protection system basic

goal.Detection & disconnection of faulty section.

Reasons:-Unnecessary interruption to consumers.

Prevention of Spreading of fault. Assures System stability .

Consumer devices are not made to carry faultcurrent for longer period of time.


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Schemes of Protection.1) Generators.2) Low tension Switch gear.3) Transformer.4) High tension Switch gear.5) Transmission lines.


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General Introduction.500kv S/C 4 bundled conductor Line fromtarbela.

Two auto transformer 500/220kv each rated450MVA .220KV line from Ghazi Brotha.

220kv/132kv khazana grid.


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Essential Elements.Power Line Carrier Traps.Mainly used for telecomm: , teleprotection & telemonitoring.Frequency Range: 272kHz-700kHz.

CCVT:Step down the EHV signals for measurmentand protection.


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Continue

Surge arresters:To protect against the lightning andswitching strokes.

Always on the live wireBased on metal oxide varistor.Eearthing of switchyard.Increased safety.


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Isolating switches:Used for de-energizing of the lines formaintenance.Earth switches.Circuit Breakers:

Used for the disconnection of the faultyelement from the PS.SF6 is used as a quenching media.


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INSULATORS:Porcelain and glass insulators are used.The dielectric strength is as follow;Porcelain:11.5kv/disc.Glass:110kv/disc.

One and half breaker scheme .To increase reliability.


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Components of Protection.

Fuses.C.Ts & P.Ts

Circuit breaker.Relays.

Auto reclosers.

Spark gap and surge arrester.Isolaters and earth switches.FACTS , SVC, TPSC,SCCL..


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Transmission lines ProtectionDistance Protection.Total length 117 km.Primary protection ( static distancerelays).L-G, L-L , L-L-L-G faults .

Back up protection (Electromechanicaldistance relays).Grid faults or system fault indications.


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Transmission lines ProtectionCarrier current protection.Carrier added protection.Pilot protection.Optical fibre / shielding line protection.

O.C relay coupled with distance relay .


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Transmission line zonesZone 1: 85% of total length.Zone 2: 50 % of total length.Zone 3: 25 % of total length.Zone 4: 15 % of total length.

No pet rule for zoning .Zoning based on importance of TX-line.


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Bus Bar protection.High impedance differential relay.

Voltage based protection.No C.T on busbars.Dangreous protection scheme.


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Transformer Protection.

Over current protection.Differential Relay.Earth fault relay.Restricted Earth fault.

Tertiary O.C protection.Over flux protection.


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Transformer Protection.

Bucholz protection.Current inrush protection.T/F fire protection.Nitrogen used mostly.

Thermal protection.Temp > 95C initiates alarm signal.Temp> 110C trips.


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Transformer Testing

Megger Testing.DGA of T/F oil.

Vacum dehydration.TTR Testing.

Capacitance & dissipation factor testing.


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Transformer Testing

Bushing tests.DC- winding resistance test.Polarity tests.Earth resistance test.


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Miscellaneous protection.

Frequency metering & Triping.

Frequency less than 48.80HZ.132kv line is tripped.

Frequency less than 48.60HZ.220kv lines may b tripped.


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Check synchronizing relay.Maximum voltage difference on L.T side of transfomer may be 20kv.Phase difference is 30.Ensure above feature before closing of

breaker.


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Over voltage .Under voltage.Power swing blocking relay.Over load protection.

Interface relay for PLC.


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End..

Power System Protection Basics..a Visit to Sheik Muhammadi Grid Peshawar.

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