1. Selective Stator Ground Protection Expo Presentation

2. Team SyncGEN Sponsor – Larry Gross Relay Application Innovation Advisors – Dr. Brian Johnson & Dr. Joe Law Webmaster / Client Contact – John Trombetta Poster / Presentations – Robert Schloss Documentation Manager – Jason Panos

3. Acknowledgments Relay Application Innovation – Larry Gross Idaho Power Schweitzer Engineering Laboratories University of Idaho - ECE Department Dr. Brian Johnson & Dr. Joe Law

4. Background RAI customer has multiple machines on common high impedance grounded bus Using traditional overvoltage protection scheme Interested in a faster and more robust protection scheme for their system

5. Standard Protection Faults detected from neutral overvoltage

6. The Problem Faults seen on all machines Impossible to directly isolate the faulted machine from system measurements 3 rd Harmonic protection cannot isolate faulted machine Multiple machines on a common high impedance bus

7. The Problem Units must be sequentially tripped until the faulted machine is isolated Non-faulted machines must be restarted if tripped in the detection process Leads to large disturbances in the system

8. Proposed Protection Selective stator ground protection using microprocessor relay directional algorithms for ungrounded distribution systems Sensitive CT’s in SEL-351 for detecting zero sequence current flow in the neutral Zero sequence current flows toward faulted machine

9. Proposed Protection Fast isolation of faulted units Selective stator ground protection in addition to standard overvoltage protection Standard sequential delays apply, but trip immediately when faulted unit is isolated

10. System Oneline

11. System Configuration

12. Protection Constraints Standard protection must be used in addition 32NF indicates unit is faulted 32NR indicates the unit is not faulted 32NF enables immediate tripping, bypassing standard delay

13. Testing Constraints Faults must be seen across the bus For bus faults, 32NR shows on all machines Fault isolation needed for faults down to lowest stator turn

14. Relay Elements SEL-351 50 Overcurrent 32 Directional SEL-300G 64G Overvoltage 59 Overvoltage Trip: IN101*64G1T (IN101 asserts for 32NF)

15. Event Report

16. Evaluation Method works for isolated machines down to lower 5% of stator windings Passed our tests for isolated machines Worked intermittently for multiple machines due to issues with the model power system

17. Issues Encountered PT’s of the model power system solidly grounded to neutral No CT in neutral line No neutral line from Avista System ground was floating Unable to elevate neutral impedance Model power system schematics were incomplete

18. Economic Analysis Setup Cost SEL-351 $4,530 Engineering design Additional hardware & wiring Repair costs Stator rewinding$500,000 Loss of Operation

19. Conclusions & Recommendations Selective stator ground protection works in lower 5% of stator windings on isolated machines Address all issues with the model power system Test further to prove the method works for multiple machine configurations Use this method as supervisory protection with traditional overvoltage protection

20. Questions?

21. Generator Specifications

22. Lab Connections

23. Distribution Box

24. Sub-coils of Stator Windings