A new diagnostic method could allow electricity substations to detect hidden insulation faults in relay-protection circuits earlier than conventional testing, according to research in the International Journal of Energy Technology and Policy.
The researchers have combined three measurements into a diagnostic model: zero-sequence current, an electrical signal indicating unintended current paths, waveform similarity, which compares measured current patterns with those expected under normal conditions, and third-harmonic content, a component of the electrical waveform that can reveal non-linear grounding faults.
In tests, they saw a 98.6 per cent detection rate for insulation faults and 94.3 per cent accuracy in locating multiple grounding points. Average diagnostic latency was less than 45 milliseconds, with a 1.5 per cent false-positive rate during normal operation. The team adds that the system can also detect insulation deterioration when resistance falls to between 50 and 100 kilohms. This offers an early warning sooner than conventional, offline methods, potentially allowing maintenance to be carried out before faults become critical.
A six-month pilot test at a 500-kilovolt substation in Nanjing with linked inspection robots demonstrated rapid communication between substation devices. Overall, the average fault-resolution time was reduced from more than four hours to just over one hour, and manual inspections were cut by 76 per cent.
Shi, H., You, H., Chen, X., Xu, S. and Chen, J. (2026) ‘Enabling holistic insulation monitoring in secondary AC protection circuits: a diagnostic algorithm’, Int. J. Energy Technology and Policy, Vol. 21, No. 5, pp.20–49.
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