Case studies · Failing equipment
A failing capacitor switch, found and fixed the same day
The arcing barely moved the current. DFA classified it, sized the bank, and the crew arrived knowing which switch had failed.
- Where
- Rural overhead circuit, United States
- Equipment
- 900 kvar switched line capacitor
- DFA reported
- Capacitor arcing, phase B
- Found
- A heavily damaged vacuum switch
- Outcome
- Repaired the same day
What DFA reported
Early one morning a 900 kvar switched capacitor bank switched off. Two seconds later phase B began conducting again, with arcing: its vacuum switch had partly lost vacuum. The arcing barely disturbed current and voltage, yet DFA classified it as capacitor arcing and posted it on the dashboard. It sized the bank at 900 kvar from the change in vars, and the switching time matched the utility's records.
What the crew found
Finding the bank was trivial. The crew arrived knowing the phase B vacuum switch had likely failed, found it heavily damaged, and repaired it the same day.
Why it matters
No other system reported the failure. Capacitor arcing sends transients to every device on the bus and has failed arresters and other capacitor banks on the same and neighboring circuits.
“To PG&E's knowledge, DFA is the only system that can detect capacitor arcing.”E. Schoenman and J. Mead, Pacific Gas and Electric, T&D World, August 2021
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