1. Summary Event Analysis Subcommittee – LL Update NERC OC Meeting - June 2014

2. RELIABILITY | ACCOUNTABILITY2 Verification of Alternating Current Quantities during Protection System Commissioning Line relays were placed into service with the incorrect Current Transformer (CT) ratio Defect remained undetected until a system disturbance occurred Commissioning testing must include installation tests and effective in- service tests In-service tests can uncover errors that were not discovered during installation tests Many in-service test may be used, examples are:  In-Service Voltage Tests  In-Service Current Tests  Primary Current Tests

3. RELIABILITY | ACCOUNTABILITY3 Turbine Combustor Lean Blowout on Large- Frame Combustion Turbines Voltage dropped dramatically during a fault Area load reduced, causing area generators to accelerate CTs in that area that were operating in a lean-burn mode (used for reducing emissions) tripped offline as result of “turbine combustor lean blowout” Verify combustion control systems to improve unit stability for these conditions Additional inspections of combustions systems may be warranted depending on the unit Note: General Electric (GE) issued a Technical Information Letter (TIL), dated 12/31/2010

4. RELIABILITY | ACCOUNTABILITY4 Links to Lessons Learned Lessons Learned  LL20140301 - Turbine Combustor Lean Blowout on Large-Frame Combustion Turbines LL20140301 - Turbine Combustor Lean Blowout on Large-Frame Combustion Turbines  LL20140302 - Verification of Alternating Current Quantities during Protection System Commissioning LL20140302 - Verification of Alternating Current Quantities during Protection System Commissioning

5. RELIABILITY | ACCOUNTABILITY5 For more information please email: Nerc.LessonsLearned@nerc.net