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

POWER SYSTEM DE-REGULATION (RESTRUCTING) GENCO TRANSCO DISCO Tie Lines GENCO TRANSCO DISCO Deregulation or Restructuring denotes breaking up of the Vertically Integrated Utility(VIU) structure into Competitive Market Entities.

RESTRUCTURED ELECTRICAL INDUSTRY

ENTITIES RESULTING FROM DE- REGULATION SO GENCO TRANSCODISCO SO is the Power System Operator and the Power Market Operator, which may include other entities depending on the market structure. SO, is independent of the other entities

8.0 CASE STUDY OF COGESTIO EXPERIECED O : Due to early morning fog, Talcher-Kolar HVDC had to be operated in reduced voltage mode resulting in a reduction of the total transfer capability to 3600 MW from 4000 MW between 0400 Hrs to 0900 Hrs of 12-Dec After accounting for reliability margin, long term transactions and already approved bilateral transactions, available margin on ER-SR path was 617 MW and on WR-SR path, available margin was about 490 MW during this period Based on the provisional solution received from the Power Exchanges for the period 0500 Hrs to 0600 Hrs, it was observed that the total requirement of both Exchanges was more than total import margin of Southern Grid. Accordingly available margin for each Exchange was calculated on pro-rata basis. The market was split in both the Power Exchanges and the flow was restricted to the available capacity in the final solution. As against a total provisional requisition of 1430 MW for import to Southern Grid, 1091 MW was cleared in the final solution

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 –Ancillary Services

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

Congestion mitigation Stage 1 : Ex-ante (before fact): –Bidding for transmission corridor (for bilateral trnasactions) –Market Split (for Collective transactions) Stage 2 : (Real time) – Impose Congestion charges on UI Stage 3 : (Real time) Curtailment of STOA/ Collective/ MTOA/ LTA

Pre-requisites Observability of Grid (SCADA) Scheduling mechanism EMS tools (Contingency Analysis, Security Constrained Dispatch) Commercial Mechanism

Congestion management in India Congestion charges in for OD from 2007 Congestion Regulations (CERC) w.e.f congestion charge shall be applied as a commercial measure. The congestion charge will be payable by a Regional entity or entities causing congestion in the inter-regional link or intra-regional link and receivable by a Regional entity or entities relieving congestion. In addition to the Unscheduled Interchange charges

Measures to mitigate Congestion Declare ATC by NLDC/ RLDCs / for Inter Regional/ Intra regional and each control area Congestion charge imposed on only Deviations from schedules Rate of congestion charge : Rs.5.45/u Notice of –2 time blocks for imposing –1 time block for lifting congestion charge –At frequency below 50 Hz, 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.

NLDC/ RLDC display the TTC, ATC, Actual flow on the congested corridor on common SCADA display No congestion charges if congestion is due to outage of a transmission line in the corridor, but schedules are maintained In such case, curtailment of STOA/ MTOA and then LTA

REAL TIME CONGESTION MANAGEMENT In case of transmission constraint or threat to grid security, the scheduled transactions may be curtailed in the manner as decided by the NLDC /RLDCs / SLDCs to relieve the transmission constraint/ to improve grid security. Collective Transaction through Power Exchange(s) would normally be curtailed subsequent to the Short-Term Bilateral Transaction(s).

…contd RLDCs would curtail a Transaction at the periphery of the Regional Entities. SLDC(s) shall further incorporate the inter-se curtailment of intra-State Entities to implement the curtailment. In case of curtailment of a Transaction caused by transmission constraints / threat to grid security, the Transmission Charges in respect of such Transaction shall be payable on pro-rata basis in accordance with the finally Implemented Schedules. Operating Charges shall not be revised in case of curtailment. Power Exchange (s) shall be responsible for the settlement on account of curtailment, directly with its participants. NLDC/RLDCs/SLDCs shall interact only with the respective Power Exchange(s), for the same

Payment /receipts though Congestion charge a/c Utilization of fund for studies, SPS, Shunt capacitrs

Upstream O/D &U/G relieve U/D & O/G aggravate O/D &U/G receive charges U/D & O/G pay charges Downstream U/D & O/G relieve O/D &U/G aggravate U/D & O/G receive charges O/D &U/G pay charges Congested Corridor Congestion Charge Imposition

Congestion accounting NLDC/ RLDC provide –From/To time block –corridor –and Upstream /downstream entities details to RPCs on a weekly basis when congestion charge is kicked along with reasons RPC to issue congestion account along with UI accounting