Congestion in Power Grid

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CONGESTION IN POWER

NETWORK- M B SHARMA


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Congestion

When transmission demand >capability When Voltage levels in a corridor beyond operable limits When Real time line flow exceeds the TTC Most fundamental transmission management problem A natural corollary of growth Occurs in deregulated markets Commercial signal to Tr. Requirement N-1 Planning System security at stake


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POWER SYSTEM DE-REGULATION(RESTRUCTING)

GENCO

TRANSCO

DISCO

Tie Lines

GENCO

TRANSCO

DISCO

GENCO

DISCO

GENCO

DISCO

GENCO

TRANSCO

DISCO

Deregulation or Restructuring denotes breaking up of theVertically Integrated Utility(VIU) structure into CompetitiveMarket Entities.


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RESTRUCTURED ELECTRICAL

INDUSTRY
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ENTITIES RESULTING FROM DE-REGULATION

SO

GENCO TRANSCO DISCO

SO is the Power System Operator and the Power MarketOperator, which may include other entities depending on themarket structure. SO, is independent of the other entities


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Congestion management methods

Cost free methods (Physical) Generation/ Load Control Network Reconfiguration (Parallel Paths, Loops)

FACTS/ FSC ETC Voltage improvement Non-cost free methods (Commercial )

Rescheduling of transactions

Curtailment Imposition of Congestions charge


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Congestion occurance

Real Time : Inadequate system conditions Temporary outage of Tr. Line / Generator/

Load

Ex-ante (before fact): More transactions by a far end Consumer Seasonal skew in L-G balance More demand for transmission corridor


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Congestion mitigation

Stage 1 : Ex-ante (before fact): Bidding for transmission corridor (for bilateral

transactions) Market Split (for Collective transactions)

Stage 2 : (Real time) Impose Congestion charges on UI

Stage 3 : (Real time)Curtailment of S TOA/ Collective/ MTOA/ LTA
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Pre-requisites

Observability of Grid (SCADA) Scheduling mechanism

EMS tools (Contingency Analysis, SecurityConstrained Dispatch) Commercial Mechanism


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Congestion management in India

Central Electricity Regulatory Commission (Measures torelieve congestion in real time operation) Regulations,2009

congestion charge shall be applied as a commercialmeasure.

The congestion charge will be payable by a Regionalentity or entities causing congestion in the inter-regionallink or intra-regional link

and receivable by a Regional entity or entities relievingcongestion. In addition to the Unscheduled Interchange charges


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Measures to mitigate Congestion

Transfer Capability Total Transfer Capability (TTC) means the amountof electric power that can be transferred reliably overthe inter-control area transmission system under agiven set of operating conditions considering theeffect of occurrence of the worst credible contingency .

Transmission Reliability Margin (TRM) means theamount of margin kept in the total transfer capabilitynecessary to ensure that the interconnectedtransmission network is secure under a reasonablerange of uncertainties in system conditions.


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Transfer Capability Available Transfer Capability (ATC) means

the transfer capability of the intercontrol areatransmission system available for schedulingcommercial transactions (through long termaccess, medium term open access and shortterm open access) in a specific direction,taking into account the network security.Mathematically ATC is the Total TransferCapability less Transmission ReliabilityMargin.


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Total Transfer Capability (TTC)


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Transmission Reliability Margin (TRM ) Computation of TRM for a region or

control area or group of control areaswould be based on the consideration ofthe following: Two percent (2%) of the total anticipated peak

demand met in MW of the control area/groupof control area/region ( to account forforecasting uncertainties)

Size of largest generating unit in the controlarea/ group of control area/region


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Declare ATC by NLDC/ RLDCs / for InterRegional/ Intra regional and each control area

Congestion charge imposed on only Deviationsfrom schedules

Rate of congestion charge : Rs.5.45/u Notice of

2 time blocks for imposing 1 time block for lifting congestion charge Congestion charge would be levied for

over drawal or under-injection in the importing control area under drawal or over-injection in the exporting control area.


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NLDC/ RLDC display the TTC, ATC, Actual flow on the congested corridor oncommon SCADA display

No congestion charges if congestion isdue to outage of a transmission line in thecorridor, but schedules are maintained

In such case, curtailment of STOA/ MTOAand then LTA


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REAL TIME CONGESTION MANAGEMENT

In case of transmission constraint or threat togrid security, the scheduled transactions may becurtailed in the manner as decided by the NLDC

/RLDCs / SLDCs to relieve the transmissionconstraint/ to improve grid security. Collective Transaction through Power

Exchange(s) would normally be curtailedsubsequent to the Short-Term BilateralTransaction(s).


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contd RLDCs would curtail a Transaction at the periphery of the Regional

Entities. SLDC(s) shall further incorporate the inter-se curtailment ofintra-State Entities to implement the curtailment.

In case of curtailment of a Transaction caused by transmissionconstraints

/ threat to grid security, the Transmission Charges in respect of suchtransaction shall be payable on pro-rata basis in accordance withthe finally Implemented Schedules. Operating Charges shall not berevised in case of curtailment.Power Exchange (s) shall be responsible for the settlement onaccount of curtailment, directly with its participants.

NLDC/RLDCs/SLDCs shall interact only with the respective PowerExchange(s), for the same


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Payment /receipts though Congestioncharge a/c

Utilization of fund for studies, SPS, Shuntcapacitrs


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Upstream

O/D &U/G relieveU/D & O/G aggravateO/D &U/G receive chargesU/D & O/G pay charges

DownstreamU/D & O/G relieve O/D &U/G aggravateU/D & O/G receive chargesO/D &U/G pay charges

Congestion Charge Imposition


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Congestion accounting

NLDC/ RLDC provide From/To time block corridor

and Upstream /downstream entitiesdetails to RPCs on a weekly basis whencongestion charge is kicked along withreasons

RPC to issue congestion account alongwith UI accounting


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THANKS

Congestion in Power Grid

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