1. Copyright © MCEC and SEL 2014 Mitigation of Undesired Operation of Recloser Controls Due to Distribution Line Inrush Lee Ayers Mid-Carolina Electric Cooperative Larry Wright Schweitzer Engineering Laboratories, Inc.

2. 53,000 active meters South Carolina counties ♦ Lexington ♦ Richland ♦ Newberry ♦ Saluda ♦ Aiken Mid-Carolina Electric Cooperative

3. MCEC Discussion Reasoning for changing recloser style Experience with tripping due to inrush Factors affecting inrush Solutions to tripping during inrush Future plans to address feeder circuit coordination

4. Example MCEC Distribution Circuit

5. Hydraulic Recloser Clearing Curves Two Fast A and Two Slow B Curves

6. Fast Curve Clears Temporary Faults Saves fuses Reduces outages

7. Historical Data 90% of faults clear on fast curve 5% of faults clear on slow curve 5% of faults proceed to lockout

8. Aging Recloser Fleet Reclosers were at least 20 years old One manufacturer was out of business Insufficient stock was available

9. Solid Dielectric Recloser With Microprocessor-Based Control

10. Reasons for Selecting New Reclosers Maintenance costs Coordination Safety Environmental concerns Testing Additional advantages

11. Hydraulic Maintenance Costs Maintenance required every 3 years Costs associated with maintenance – about $350 per recloser ♦ Parts and oil ♦ MCEC hours to change out recloser

12. Solid Dielectric Maintenance Costs No Regular Maintenance Required

13. Hydraulic Recloser Coordination Less reliable than expected Not repeatable Insufficient margin Prolonged outages due to poor selectivity

14. Solid Dielectric Recloser Coordination Microprocessor-based control Accurate and repeatable More curves available

15. Hydraulic Recloser Safety Hot stick is used for manual close and nonreclose Operator stands directly under recloser

16. Solid Dielectric Recloser Safety Operated remotely or on time delay No hot stick required (except yellow handle) Improved safety with hot-line tagging ♦ No closing ♦ More sensitive tripping

17. Hydraulic Environmental Concerns Mineral Oil Release Requires Cleanup Contaminated soil removal Decontamination Restoration

18. Solid Dielectric Environmental Concerns None

19. Hydraulic Testing Requires low-voltage, high-current test set Can only be done in shop

20. Solid Dielectric Testing Relay test set Recloser test set Soldering gun?

21. Additional Advantages of µP Control Forensic data Communications Self-monitoring and alarm Simpler-to-change settings

22. Initial Experience With µP Control More than 150 reclosers (35 A and 50 A) changed out Many event reports received Noticed unintended operations on fast curve when power restored

23. First Recloser Trip – Raw Event

24. Second Recloser Trip – Raw Event

25. µP Control Operate Curve

26. First Recloser Trip – Filtered Event

27. Second Recloser Trip – Filtered Event

28. Is This Normal? “There is an argument that a recloser rarely closes in and holds on second fast operations due to inrush current.” – McGraw Edison Power Systems Division, “Overcurrent Protection for Distribution Systems – Seminar Notes,” May 1984

29. Is This Acceptable? No. Why Unnecessarily Blink Customer Power?

30. Transformer Inrush

31. Inrush Current

32. Second Harmonic

33. One Method to Secure Relays Change Settings Change curve shape Raise pickup Raise time dial

34. Testing Other Fast Curves

35. Test Results CurveTrip 4No R N 17No 1Yes A (TD = 2)Yes

36. Disadvantages of Changing Settings Slows protection Is difficult to quantify distribution line inrush ♦ EMTP ♦ Real-time digital simulation

37. A Better, Easier Solution: Second-Harmonic Blocking

38. First Recloser Trip – Raw Event

39. First Recloser Trip Harmonics

40. Second Recloser Trip – Raw Event

41. Second Recloser Trip Harmonics

42. Second-Harmonic Blocking Logic

43. First Event With Second-Harmonic Blocking

44. Second Event With Second-Harmonic Blocking

45. Substation Recloser Inrush Event

46. Incorrect Second-Harmonic Blocking Step change in fundamental frequency ♦ Fourier transform ♦ Short-lived blocking (0.25 cycles) CT saturation ♦ Has low fault current and low X / R ratio ♦ Is backed up by slow curve

47. CT Excitation Curve

48. Path Forward Install three-phase 70 A reclosers with single-pole tripping Implement second-harmonic blocking on reclosers and feeder relays Perform coordination studies again

49. Transformer Fuse Coordination

50. Questions?