EAS Lessons Learned Summary Lessons Learned Published in May 2014

RELIABILITY | ACCOUNTABILITY2 Three NERC lessons learned (LL) were published in May 2014 LL High AC Voltage can lead to Remote Terminal Unit (RTU) Failures. LL Circuit Breaker Modification Leads to Inadvertent Trips. LL Improved Contractor Oversight. May 2014 Lessons Learned

RELIABILITY | ACCOUNTABILITY3 RTU control output card sees high AC voltage leads to breakdown of the metal oxide varistors (MOVs) on the control card This leads to the equivalent of a control output contact(s) being shorted and/or excessive heating which has melted ribbon cables same effect Causes random operation of devices that are connected to these RTU control outputs Not exclusive to one vendor. Many RTUs are susceptible E.g. Coupling Capacitor Voltage Transformer (CCVT) delivered high voltage for approx. 3 mins before failing catastrophically Review the effect of high AC voltage on RTUs used for control High AC Voltage can lead to Remote Terminal Unit (RTU) Failures

RELIABILITY | ACCOUNTABILITY4 Circuit Breaker Modification Leads to Inadvertent Trips SF6 gas circuit breaker controls were field modified to trip on low gas and air pressure Field modification resulted in the breakers tripping when DC power was removed and then re-applied to the SF6 Gas circuit breaker When making changes to original factory equipment schemes, entities should analyze the scheme change to ensure that the removal and restoration of DC power to the scheme does not cause an undesirable operation

RELIABILITY | ACCOUNTABILITY5 Improved Contractor Oversight. Significant system disturbances caused by vendor performed work in stations without method to ensure work quality Generation facility experienced a trip due to an internal fault in a SF6 gas breaker Breaker trip interrupted power to the auxiliary transformer Fast bus transfer scheme isolates the auxiliary transformer and closes in a start-up transformer Upon closure of the start-up transformer, a 487/T1 phase start- up transformer differential relay actuated Two splices on the start-up transformer’s current transformer (CT) were missing insulating sleeves Created alternate path for the CT secondary current, causing the 487/T1 to actuate

RELIABILITY | ACCOUNTABILITY6 Improved Contractor Oversight Vendor oversight policies should include a discussion with the vendor of:  performance standards  expectations for the work  human error reduction techniques  verification of completed work Expectations between the entity and vendor with regard to the design, validation of calculations and settings, scheme testing, and commissioning must be clear to ensure a successful outcome Effective oversight of contractor work activities should be in place to help prevent these types of events

RELIABILITY | ACCOUNTABILITY7 Links to Lessons Learned Lessons Learned Link to Lessons Learned

RELIABILITY | ACCOUNTABILITY8 For more information please Questions