Pilot at Nanjing substation combines three signals to help catch faults earlier

At a 500-kilovolt substation in Nanjing, a diagnostic system spent six months listening to three electrical signals at once. Linked inspection robots helped test whether the approach could spot hidden insulation faults in relay-protection circuits before they became critical.

The model combines zero-sequence current, a signal that can reveal unintended current paths; waveform similarity, which compares measured current patterns with normal ones; and third-harmonic content, a waveform component that can expose nonlinear grounding faults. The point is not a single warning light, but a more complete picture assembled from signals that reveal different kinds of abnormal behavior.

In tests, the system detected 98.6% of insulation faults and located multiple grounding points with 94.3% accuracy. Average diagnostic latency was less than 45 milliseconds, while the false-positive rate during normal operation was 1.5%. The team also reported that the method could detect insulation deterioration when resistance fell between 50 and 100 kilohms, earlier than conventional offline methods.

In practice, the gain is time. During the Nanjing pilot, average fault-resolution time fell from more than four hours to just over one hour, and manual inspections fell by 76%. The pilot also demonstrated rapid communication between substation devices.

The reported results come from researchers' tests and a six-month field pilot, not from a broad rollout. That makes the system a credible step toward faster substation maintenance, while leaving its performance across other sites and operating conditions to be established.