1. NERC Lessons Learned Summary April 2015

2. NERC lessons learned published in April 2015 Two NERC lessons learned (LL) were published in April 2015 LL20150401 Detailed Installation and Commissioning Testing to Identify Wiring or Design Errors LL20150402 Severe Flooding Damages Transformer Substations

3. Detailed Installation and Commissioning Testing to Identify Wiring or Design Errors Two redundant RAS input/output (I/O) devices failed due to a firmware RAM/ROM processor error Failure alarms undetectable due to an error on the wiring diagram Positive DC did not get connected properly which disabled the signaling of the I/O device’s alarm status Wiring diagram did not match schematic Commissioning records show alarms were tested No indication of the test used Entity assumes the alarms were simulated using remote confirmation

4. Detailed Installation and Commissioning Testing to Identify Wiring or Design Errors Corrective Actions: Wiring diagram was corrected and DC rewired Alarms operationally checked and proven Webinar for field relay techs Covered print review, alarm verification, and checkout process

5. Detailed Installation and Commissioning Testing to Identify Wiring or Design Errors Lessons: Detailed checkout and commissioning process Regular review and training Comprehensive alarm simulation Peer review during design process Strong emphasis on Human Performance Standardized RAS checkout procedures are needed

6. Severe Flooding Damages Transformer Substations A storm in the Northeast resulted in record rainfall (~5 inches) 3.5 inches fell within a span of two hours Severe localized flooding of two transformer stations Stations and all terminating circuits rendered unavailable Monitoring, protection, and control equipment is located below grade in basements Damaged equipment and caused misoperation of relay systems that removed 26 230 kV and 8 115 kV connected circuits from operation Interrupted 3,800 MWs of Load for several days

7. Severe Flooding Damages Transformer Substations Corrective Actions Sandbags were applied to window wells as a temporary repair Properly sealed cable conduit Some equipment was relocated above-grade Floor drain check valves verified Both transformer stations are now equipped with gas-fired pumps, hoses and fittings, and fuel to control storm water ingress in all control and relay rooms

8. Severe Flooding Damages Transformer Substations Lessons: Identify stations with critical power system equipment located below grade and verify: Floor drain check valves; sump pits or pumps; and diesel generator capability to power sump pumps Flood protection equipment should be verified during station inspections Consider relocating all replacement or new critical power system equipment in above-grade locations New and replacement cable conduit supplying critical power system equipment should enter the building via above-grade entrances Below grade cable penetrations need routine inspection

9. Link to Lessons Learned Directions to Lessons Learned: Go to www.NERC.com > “Program Areas & Departments” tab > “Reliability Risk Management” (left side menu) > “Event Analysis” (left side menu) > “Lessons Learned” (left side menu) NERC’s goal with publishing lessons learned is to provide industry with technical and understandable information that assists them with maintaining the reliability of the bulk power system. NERC requests that industry provide input on lessons learned by taking the short survey. The survey link is provided on each Lesson Learned.

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