M. G. Raoot , P. Pentayya (WRLDC) and S. A. Khaparde (Indian Institute Technology Bombay)

1. Operational Experience In Managing Contingencies at Western Regional Load Despatch Center (WRLDC), India M. G. Raoot, P. Pentayya (WRLDC) and S. A. Khaparde (Indian Institute Technology Bombay) IEEE Power Engineering Society General Meeting, July 2009

2. Presentation Outline • Western Region Grid Overview • Overview of EMS implementation at WR • Contingency Analysis Methodology • Contingency Management Methodology • Western Region Grid – A Case Study

3. Indian Power Control Centers NLDC - 1 RLDC - 5 SLDC - 31 ALDC - 100+ Total installed capacity 147 GW (Source: CEA report http://www.cea.nic.in/power_sec_reports/Executive_Summary/index_Executive_Summary.html)

4. Hierarchy of Control Centers • The Unified Load Despatch and Communication (ULDC) scheme sets up the hierarchy of control centers in India 1 5 31 > 100

5. NORTHERN REGION 11,700 MW 4,900 MW NORTH-EASTERN REGION 5,850 MW 2,650 MW WESTERNREGION 1,200 MW 3,700 MW SOUTHERN REGION Inter-regional Transfer Capacity present - 22800MW 37,000 MW by 2012 EASTERN REGION

6. OVERALL POWER SCENARIO OF WESTERN REGION Madhya Pradesh Gujarat Installed Capacity 45987 MW Chhatisgarh Max Demand Met 31608 MW Max Energy Met 690 MU Maharashtra Demand Shortage 20% Energy Shortage 14 % GOA

7. WESTERN REGION-31.3.09

8. Look-up Tables • Remedial Action module is not available • Alternative is to use Look up tables • Look up tables provide following information • What are the expected contingencies? • What is the system behavior for each contingency? • Corrective actions to be taken • What actions ? • Which order ? (Ranking Criteria ?) • Which agency ? • Look up tables are prepared after extensive offline studies on the system using PSS/E

9. Co-ordination for Contingency Management: Via Look-up Tables • Multiple agencies are involved in system operation • Common real-time system model is needed for all • Studies carried out by WR for all major contingencies • Internal threats (Trippings inside WR) • External threats (Trippings outside WR) • The study cases and results are made available for all agencies for verification • Workshops conducted to disseminate look up tables • Corrective actions are agreed upon by all agencies • Permissible load angles for extremes of corridors determined through stability studies

10. Objective:To make Look-up Tables (Example below) • Ranking of Corrective Actions is based on • Sensitivity / Impact of the Corrective Action • Risk assessment based on time taken for implementation and no. of agencies involved in co-ordination loop

11. Presentation Outline • Western Region Grid Overview • Overview of EMS implementation at WR • Contingency Analysis Methodology • Contingency Management Methodology • Western Region Grid – A Case Study

13. EMS (the journey so far…..) 1 2 3

14. EMS (the journey so far…..) 4 5 6

15. Salient Features of EMS in WR • The entire Western regional grid has been modeled as per actual. • Uniform single model in RLDCs and SLDCs.

16. Model Verification and SE tuning

17. SE working status • SE working satisfactorily • Tele-metered and estimated data with in permissible limits • Real-time network analysis (RTNA) study run at least twice a day • Day-off peak @ 1200 hrs • Evening peak @ 1900 hrs • Converged RTNA made available for studies • RTNA also run in case of • Contingency • Outage clearance • Corrective measures taken for security enhancement

18. Advantages of EMS in grid operation • Outages can be planned better • The Contingency Analysis (CA) module of EMS helps in better emergency handling online. It would facilitate quicker restoration. • The State Estimator (SE) output, properly tuned, gives proper estimate of the grid measurands which can be used during non-availability of communication channels and grid operation is not affected. • The SCADA system also improves due to continuous availability, comparison and improvement in EMS output thereby improving the decision making process in real-time.

19. Presentation Outline • Western Region Grid Overview • Overview of EMS implementation at WR • Contingency Analysis Methodology • Contingency Management Methodology • Western Region Grid – A Case Study

20. Contingency Analysis (CA)

21. Contingency Analysis (CA) • The CA can be run based on the following modes 

22. Contingency Analysis Execution Modes

23. Execution Status of Contingency Case CS – Contingency Selection, CA - Contingency Analysis, RA – Remedial Action

24. Composite Severity Index (SI) indicator • Ranking of contingencies based on SI • SI = Weighted Sum of percentage limit excursions Voltage CA Branch CA • Voltage Violations • Contingencies compared based on voltage degradation profile • Corresponding ranks displayed • Branch Violations • Contingencies compared based on branch loading violations • Corresponding ranks displayed

25. Presentation Outline • Western Region Grid Overview • Overview of EMS implementation at WR • Contingency Analysis Methodology • Contingency Management Methodology • Western Region Grid – A Case Study

26. Contingency Evaluation

27. Presentation Outline • Western Region Grid Overview • Overview of EMS implementation at WR • Contingency Management Methodology • Western Region Grid – A Case Study WRLDC, Mumbai

28. Case Study:Contingency Management in WR Grid • Due to Concentration of generation in the Eastern part of the grid and major load centers in the Western part of the grid, there is bulk active power transmission from Eastern to Western part over long distances primarily through three critical flow gates viz; • 400kV Chandrapur-Parli T/C • 400kV Koradi-Bhusawal D/C • 400kV Itarsi-Khandwa-Dhule D/C WRLDC, Mumbai

29. Base Case Scenario • On 25.05.2008, Western Regional grid was running in an integrated manner and catering a demand of about 25000 MW at 1130 hours. • The import was around 1200 MW from ER, 1400 MW from NR, 750 MW was exported to SR • Due to rains in NR and ER, the frequency profile was on the higher side in the NEW grid • Therefore economy exchanges were transacted with SR (Power wheeled through WR) and consumed by WR due to low UI rates

31. Flow Gates Loaded Close to Limits It was found that around 15 lines are operating near their full capacity and angle limits with reduced margins.

32. Following contingencies were chosen for security assessment • 400kV C’pur-Parli S/C outage • 400kV C’pur-Parli D/C outage • 400kV C’pur-Parli T/C outage • 400kV Koradi-Bhusawal S/C outage • 400kV Koradi-Bhusawal D/C outage • 400kV Itarsi-Khandwa S/C outage • 400kV Itarsi-Khandwa D/C outage

35. Contingency Analysis Results • The contingencies of Chandrapur-Parli D/C, Chandrapur-Parli T/C and Koradi-Bhusawal D/C outage are extreme and the programme did not converge because the grid may not be able to sustain these contingencies under the same power system conditions. • As these contingencies are fatal, the composite severity index by voltage / branch / composite does not show any value. However, they are ranked at first in the order of severity of contingencies.

36. Contingency Analysis Results • The contingency of Itarsi-Khandwa D/C outage has been found to be harmful by CA which entails system operators to take emergency measures for restoring back the normalcy. • The composite severity index order by voltage comes to be 4150.8 whereas the composite severity index order by branch comes to 447526.5 which is ranked as the most severe contingency after the first three most severe contingencies as explained in the above paragraph.

37. Contingency Analysis Results • Similarly, other contingencies like Koradi-Bhusawal S/C outage, Chandrapur-Parli S/C outage and Itarsi-Khandwa S/C outage have been found harmful by CA which prompts operators to take emergency action. • They are also ranked subsequently based on composite severity index order by voltage and by branch violations • The corrective actions to be taken are as per the Look-up tables shown below (as we do not have Remedial Action – RA module)

38. Look-up Table for Koradi-Bhusawal SC Outage

39. Look-up Table for Chandrapur – Parli SC Outage

40. Conclusion • It is evident from the above case study that CA module of PNA extends valuable inputs to the system operators in evaluating the credible contingencies so that preventive action can be planned well in advance to ensure the security of the grid. • It is therefore important that CA is regularly run during clearing of important shut downs in the critical flow gates of Western region and for evaluating the effect of N-1 contingencies during alert grid conditions etc.

41. Thank You