Steady-State Cascading Failure Analysis in TransCARE Models and Application

1. Steady-State Cascading Failure Analysis in TransCAREModels and Application MuraliKumbaleSouthern Company Services Inc.Bulk Transmission System ReliabilityAtlanta, GA 30308

2. Highlights of TransCAREof Cascading Failure Analysis • TRELSS has now been superseded by TransCARE • Cascading failure analysis in TransCARE is currently confined to system response in steady-state. • Cascading failure analysis requires determination of protection and control groups based on breaker locations. • WECC system breaker locations were unavailable for the CIEE project • Automatic breaker placement in TransCARE was utilized to superimpose breaker locations upon the supplied power flow model.

3. Highlights of TransCAREof Cascading Failure Analysis • Based upon breaker locations TransCAREidentifies what is termed as Protection and Control Groups (PCG) • PCGs roughly correspond with the primary zone of protection. • Simulation of breaker actions provides a more realistic foundation for performing cascading failure analysis

4. Sample Protection and Control Group (PCG)

5. First Initiating Event Start Continue solution Solve Power Flow During the solution Bus Voltages < “Voltage Collapse” Threshold? Load Bus Voltages < Threshold? No Yes Disconnect Loads No Yes Drop Load @ Affected Buses Generator Bus Voltages < Threshold? Yes Trip Generators No Largest Circuit Overload > Threshold? Trip PCG Containing Circuit Yes SimulationApproachFlowchart No No Yes Next Initiating Event Last Initiating Event? Stop

6. First Initiating Event Start Solve Power Flow SimulationApproachFlowchart

7. First Initiating Event Start Solve Power Flow During the solution Bus Voltages < “Voltage Collapse” Threshold? SimulationApproachFlowchart

8. First Initiating Event Start Continue solution Solve Power Flow During the solution Bus Voltages < “Voltage Collapse” Threshold? No Yes Drop Load @ Affected Buses SimulationApproachFlowchart

9. First Initiating Event Start Continue solution Solve Power Flow During the solution Bus Voltages < “Voltage Collapse” Threshold? Load Bus Voltages < Threshold? No Yes Drop Load @ Affected Buses SimulationApproachFlowchart

10. First Initiating Event Start Continue solution Solve Power Flow During the solution Bus Voltages < “Voltage Collapse” Threshold? Load Bus Voltages < Threshold? No Yes Disconnect Loads Yes Drop Load @ Affected Buses SimulationApproachFlowchart

11. First Initiating Event Start Continue solution Solve Power Flow During the solution Bus Voltages < “Voltage Collapse” Threshold? Load Bus Voltages < Threshold? No Yes Disconnect Loads No Yes Drop Load @ Affected Buses Generator Bus Voltages < Threshold? SimulationApproachFlowchart

12. First Initiating Event Start Continue solution Solve Power Flow During the solution Bus Voltages < “Voltage Collapse” Threshold? Load Bus Voltages < Threshold? No Yes Disconnect Loads No Yes Drop Load @ Affected Buses Generator Bus Voltages < Threshold? Yes Trip Generators SimulationApproachFlowchart

13. First Initiating Event Start Continue solution Solve Power Flow During the solution Bus Voltages < “Voltage Collapse” Threshold? Load Bus Voltages < Threshold? No Yes Disconnect Loads No Yes Drop Load @ Affected Buses Generator Bus Voltages < Threshold? Yes Trip Generators No Largest Circuit Overload > Threshold? Trip PCG Containing Circuit Yes SimulationApproachFlowchart

14. First Initiating Event Start Continue solution Solve Power Flow During the solution Bus Voltages < “Voltage Collapse” Threshold? Load Bus Voltages < Threshold? No Yes Disconnect Loads No Yes Drop Load @ Affected Buses Generator Bus Voltages < Threshold? Yes Trip Generators No Largest Circuit Overload > Threshold? Trip PCG Containing Circuit Yes SimulationApproachFlowchart No No Yes Next Initiating Event Last Initiating Event? Stop

15. Initiating Event Example Bus Tie Breaker Failure X

16. Loaded > 125% Study Event Examples Voltage < 0.85% Bus Tie Breaker Failure X

17. Study Event Examples Bus Tie Breaker Failure X

18. Loaded > 125% Study Event Examples Bus Tie Breaker Failure X

19. Study Event Examples Bus Tie Breaker Failure X

20. Types of Extreme Events • NERC Reliability Standard types • Common right-of-way & common tower • Breaker failure • Bus-tie breaker failure • Bus differential (“all voltage level at a bus”) • All units at a plant • Infrastructure security types • Complete loss of a major plant or substation • Close-in common right-of-way • Simultaneous multiple transformer outages

21. Why Analyze Extreme Events? • NERC Reliability Standard compliance • TPL-003 & TPL-004; extreme events that are not simple to simulate • Screening purposes • Identifies potential cascading or voltage collapse events for further study • Transmission project determination & prioritization • Determines projects to mitigate potential cascading failures

22. Study Event Examples NERC Types

23. Initiating Event Example Bus Tie Breaker Failure X

24. X Initiating Event Example Common ROW or Tower

25. X Initiating Event Example Common ROW or Tower

26. Initiating Event Example X Breaker Failure - Ring Bus

27. Initiating Event Example X Breaker Failure - Ring Bus

28. Study Event Examples Bus Fault - Single Bus X

29. Initiating Event Example Bus Fault - Single Bus X

30. Other Severe Event Examples

31. Other Severe Event ExamplesComplete Station Outage

32. Other Severe Event ExamplesClose-in Right-of-Way Outage

33. Other Severe Event ExamplesMultiple-Site Transformer Outages

34. Post-9/11 Event ExamplesMultiple-Site Transformer Outages

35. How The Results Are Used • Transmission project development, examples: • 230kV substation reconfiguration • Changed line terminations to prevent shared breakers between critical lines • 230kV bus differential • Changed to a ring bus • 230kV breaker failure • Installed another breaker and firewall • 230kV bus tie breaker failure • Installed a 2nd bus tie breaker • 115kV bus differential • Split the 115kV bus and installed a bus tie breaker

36. How The Results Are Used • NERC Reliability Standard compliance • Determination of reliability impacts for possible non-compliances • “Critical Asset” determination • Process required by NERC Reliability Standards • Consider all study events that exceed 300 MW load loss • Input into Southern Company Security Council for development of mitigation & physical security plans • NERC Cyber Security Standards –“Critical Cyber Asset” determination

37. Enhancing Cascading Failure Analysis Methodology

38. Enhancing Cascading Failure Analysis Methodology

39. Murali Kumbale Staff Engineer Bulk Transmission System Reliability Power Delivery/Transmission Southern Company Services, Inc. Bin 10050 241 Ralph McGill Blvd. Atlanta, Georgia 30308-3374 Tel 404.506.3715 Fax 404-506-2277 mkumbale@southernco.com