NERC Published Lessons Learned March 2017

NERC Lessons Learned Two Lessons Learned (LL) were published in March 2017 LL20170301 Slow Circuit Breaker Operation LL20170302 Loss of State Estimator due to Propagated Database points

Slow Circuit Breaker Operation - Details In 2015 - 2016, 19 circuit breaker fail-to-trip operations were been reported through the EA Process 12 of which were slow-to-trip circuit breakers Slow-to-trip circuit breakers are often linked to mechanism lubrication issues Often the failure cannot be repeated right away – the first slow operation breaks the failing lubricant’s adhesion on the mechanism, and subsequent operations appear normal… until the adhesion has time to re-establish This led to the idea that frequent operation can prevent slow operation, but that is a temporary measure Proper cleaning and re-lubrication is necessary

Items to Consider in Breaker Lubrication The environment the circuit breaker resides in The age of the existing lubricant – some separate & harden over time The type of components used in the mechanism assembly Whether a penetrant solvent has been used on the mechanism, which can remove lubrication Bearing from a Breaker Mechanism with Thickened, Hardened Grease

Slow Circuit Breaker Operation - Lessons Circuit breakers have become a maintenance challenge due to their extended time in the field without re-lubrication Some circuit breaker mechanism failures have been traced to faulty lubricants and/or questionable lubrication practices TOs, GOs and DPs need to have a maintenance policy around the types of approved lubricants to be used and a policy on when to remove and replace circuit breaker mechanism lubrication Use vendor-recommended lubrication maintenance practices Use periodic breaker timing tests or breaker analyzer checks to discover sticky breaker issues prior to breaker failure

Loss of State Estimator - Details An Entity’s state estimator (SE) didn’t converge due to encountering invalid data referred to as NaN (Not A Number, resulting typically from a divide by zero) Real Time Contingency Analysis (RTCA) application stopped running Invalid data was sent via an ICCP link to other entities including its RC, causing other entities SEs to fail The NaN values were eventually manually overwritten with valid data to allow the SEs to converge, including those of the other Entities The SE and RTCA vendor released a patch to prevent NaN propagation Reliability Coordinator (RC)

Loss of State Estimator - Lessons If an Entity is performing updates that could result in sending SE invalid data or if the Entity does not have a vendor issued corrective solution implemented for the NaN issue, other parties can be protected if the originating Entity: Halts the incoming ICCP and/or RTU data exchange (to “hold” last known good data) immediately before reinitializing the SE; Checks the SE result after re-initialization while still using last known good data and; If no “NaN” or other invalid data problems are encountered, restore the ICCP data exchange

Lessons Learned Survey Link 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. A link is provided in the PDF version of each Lesson Learned

Hassan Hamdar hhamdar@frcc.com