Case studies · Failing equipment
Fourteen hours of escalating faults, ended at one arrester
DFA watched a failure build overnight. When a 3,000 A burst placed it at the substation, a lineman went straight there.
- Where
- Distribution substation, United States
- DFA reported
- A developing failure; 10 short-lived faults by 07:00
- Located by
- A 3,000 A burst at 12:55
- Found
- A failing arrester on the substation getaway cable
- Lead time
- More than 14 hours
What DFA reported
Late one evening DFA began reporting a developing failure: brief bursts of about 100 A, then hours of low-level arcing under 5 A on one phase. By 07:00 the next morning it had reported 10 short-lived faults, coming closer together and growing, a sign that final failure was near. A fault of almost 3,000 A at 12:55 placed the problem in or very near the substation.
What the crew found
The utility sent a lineman. Finding nothing obvious, he disconnected the lightning arrester on the getaway cable for the affected phase, and all fault activity on the circuit stopped.
Why it matters
The relay logged one minimum-trip record and nothing more. The utility engineer said he would not have sent a crew on that record alone. A failed arrester could have caused an outage for every customer on the circuit and other hazards, such as a fire ignition.
Keep reading
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A glowing substation switch, found within two hours
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