Issued to: E&P Community, Sentinel Sponsors and registered contractors
Ref: NRA25-10
Date of issue: 02/09/2025
Location: National
Contact: Dom Banham-Hall, Network Technical Head Distribution HV/LV (Acting) 1
Overview
During Test before Earth of an isolation between Finnieston and Rutherglen in Scotland it became apparent that one of the
electrical sections was still live.
Applying the “test before earth” Life Saving Rule, the team
avoided an accident which could have led to a fatality or life
changing injury and instead led to the identification of a failure of
this circuit breaker;
Subsequent investigations have found that a Circuit Breaker,
which is an ABB supplied FSKII Circuit Breaker (top photo), had
failed in the closed position;
Failure Investigation
Investigations were carried out with collaboration of the
supplier, ABB. It has been determined that:
• Failure Cause: The operating rod became detached from its base within the high- voltage (HV) pole. This detachment disrupted the mechanical transmission chain between the actuator and the vacuum interrupter, preventing proper operation.
• Vacuum Interrupter Condition: The vacuum interrupter was inspected and found to be free of abnormalities. It remains fully functional.
• Supplier Investigation: A detailed review of the operating rod’s supplier did not reveal an underlying design flaw.
• Site Testing & Inspection: Mechanical testing was conducted on the remaining FSKII units installed in Finnieston. Measurements of closing and opening time travel curves were compared against Factory Acceptance Test (FAT) certificates, confirming consistent alignment and positive results.
• Analysis of Similar Units: A detailed examination of FSKII (FT/PR2), which had similar operational exposure to the original faulty FSKII (FT/PR1), was performed. Upon disassembly, the operating rod did not exhibit the same failure mode.
Further Investigation: A detailed analysis of an FSKII manufactured in the same batch as the faulty unit is planned to determine any potential batch related issues.