Minimum Oil Circuit Breaker (MOCB) No Vendor Spares & Service

Electrical engineering root cause analysis (RCA) related to 110 KV Minimum Oil Circuit Breakers (MOCB); No Vendor Spares & Service threaten their sudden failure and indefinite outage.

Article Type:Root Cause Analysis (RCA)
Equipment Type:Circuit Breakers
Author:S. Raghava Chari

Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of two or three decades ago. These articles will help you to improve your troubleshooting skills and knowledge.


The author found the Feeder-A and Feeder B Minimum Oil Circuit Breaker (MOCB) top dome level glasses (LG)  missing.

The crew reported the vendor had neither supplied the 4‑years ago ordered LGs and MOCB overhaul services.

Several follow-ups to the vendor lead to no response and went in vain.

The author solves the problem

He sketched the LG guessing from the remaining LG portions. He talked a laboratory glass parts maker into supplying these agreeing to his 100 Nos. min order though only the plant had two MOCBs only! Fortunately, the glassmaker charged ½ of what the breaker vendor quoted for the two LGs.

He found the Electricity Board using tens of the same make MOCBs. Checking with them, he found they have well-trained MOCB overhaul crews. Finding their MOCBs to having no LGs the author offered them 90 LGs and requested their overhaul help. Their crew finely Overhauled one MOCB at a time.

Benefits Received

  1. MOCB-B had handled several on-offs and MOCB-A several on-offs and numerous lightening arrester heavy fault current trips. The electricity board crew completed the long due safety need.
  2. Giving away the negligible cost LGs influenced the EB engineer to do the direly needed but not available elsewhere overhaul
  3. Assurance of a ready source for the fragile LGs and overhaul services

Author: S. Raghava Chari

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