1. NERC Published Lessons Learned
March 2017

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

3. Slow Circuit Breaker Operation - Details
In , 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

4. 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

5. 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

6. 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)

7. 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

8. 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

9. Hassan Hamdar hhamdar@frcc.com