Congestion

1. 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

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

3. RESTRUCTURED ELECTRICAL INDUSTRY

4. ENTITIES RESULTING FROM DE-REGULATION GENCO SO TRANSCO DISCO 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

5. 8.0 CASE STUDY OF COGESTIO EXPERIECED O 12-12-2008: • 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-2008. • 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

6. 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

7. 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

8. 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

9. Pre-requisites • Observability of Grid (SCADA) • Scheduling mechanism • EMS tools (Contingency Analysis, Security Constrained Dispatch) • Commercial Mechanism Congestion shifts from 1 point to another

10. Congestion management in India • Congestion charges in NR @Rs.3/u for OD from 2007 • Congestion Regulations (CERC) w.e.f. 11.06.10 • 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

11. 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.

12. 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

13. 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).

14. …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

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

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

17. 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