Download 05 May 2014 Published LL Summary

EAS Lessons Learned
Summary
Lessons Learned Published in May 2014
May 2014 Lessons Learned
Three NERC lessons learned (LL) were published in May 2014
LL20140501 - High AC Voltage can lead to Remote Terminal Unit
(RTU) Failures.
LL20140502 -Circuit Breaker Modification Leads to Inadvertent
Trips.
LL20140502 - Improved Contractor Oversight.
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RELIABILITY | ACCOUNTABILITY
High AC Voltage can lead to Remote
Terminal Unit (RTU) Failures
• 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
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RELIABILITY | ACCOUNTABILITY
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
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RELIABILITY | ACCOUNTABILITY
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 startup 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
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RELIABILITY | ACCOUNTABILITY
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
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RELIABILITY | ACCOUNTABILITY
Links to Lessons Learned
• Lessons Learned
• Link to Lessons Learned
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RELIABILITY | ACCOUNTABILITY
Questions
For more information please email:
[email protected]
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RELIABILITY | ACCOUNTABILITY