Case studies · Failing equipment
79 warnings over 200 days, then a cable fitting found and fixed
Pulses of hundreds to thousands of amperes cleared themselves every time. DFA tracked all 79, and an acoustic camera found the failing fitting.
- Where
- Underground residential cable, United States
- DFA reported
- 79 self-clearing pulses; likely cable termination
- Search area
- 1.2 km of underground cable
- Found
- A failing fitting in a junction box
- Before the find
- Three nuisance trips, 1,900 customers each
What DFA reported
In late December 2021, DFA began recording half-cycle pulses of hundreds to thousands of amperes and classified them as a likely failing cable termination. No protection operated, and DFA was the only independent notice, although the circuit had line sensors. Impedance-based fault location does not work on pulses this short.
What the crew found
The utility and researchers used line sensors and fault indicators to narrow the search to a 1.2 km section of underground cable in a residential neighborhood. After 200 days and 79 pulses, they found a failing cable fitting in a junction box by visual inspection and an acoustic camera. The utility repaired it the same day, and the pulses stopped.
Why it matters
Meanwhile the utility had switched on fast, sensitive trip settings for fire season. Three times a pulse cleared itself and a recloser tripped anyway, interrupting 1,900 customers for hours; one trip came at 23:36. Finding the fitting ended both the pulses and the nuisance trips.
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