Article: Enabling holistic insulation monitoring in secondary AC protection circuits: a diagnostic algorithm Journal: International Journal of Energy Technology and Policy (IJETP) 2026 Vol.21 No.5 pp.20 - 49 Abstract: This paper addresses the problem of insulation status monitoring in secondary alternating current (AC) circuits of power system relay protection. A comprehensive diagnostic algorithm based on multi-dimensional feature fusion is proposed. This algorithm integrates distributed zero-sequence current monitoring, waveform similarity analysis, and third harmonic analysis techniques to construct a multi-dimensional feature fusion diagnostic model. By real-time acquisition of zero-sequence current in each branch, combined with the similarity changes of current waveforms under normal and abnormal operating conditions and the characteristics of third harmonic content, early identification and accurate location of typical faults such as insulation degradation, single-point grounding, and multi-point grounding are achieved. Experimental results show that the algorithm achieves a 98.6% detection rate for insulation faults, a 94.3% accuracy rate for multi-point grounding location, an average diagnostic latency of only 43.63 ms, and a false alarm rate of 1.5% under normal operating conditions. This significantly improves the timeliness and accuracy of insulation fault diagnosis, providing effective technical support for the safe and reliable operation of secondary circuits in substation relay protection. Inderscience Publishers - linking academia, business and industry through research

Title: Enabling holistic insulation monitoring in secondary AC protection circuits: a diagnostic algorithm

Authors: Hengchu Shi; Hao You; Xiaofan Chen; Shoudong Xu; Jing Chen

Addresses: Yunnan Power Grid Co., Ltd., No. 73, Tuodong Road, Kunming 650011, Yunnan, China ' Yunnan Power Grid Co., Ltd., No. 73, Tuodong Road, Kunming 650011, Yunnan, China ' Yunnan Power Grid Co., Ltd., No. 73, Tuodong Road, Kunming 650011, Yunnan, China ' Electric Power Research Institute of Yunnan Power Grid Co., Ltd., No. 105, Yundaxi Road, Kunming 650217, Yunnan, China ' Yunnan Power Grid Co., Ltd., No. 73, Tuodong Road, Kunming 650011, Yunnan, China

Abstract: This paper addresses the problem of insulation status monitoring in secondary alternating current (AC) circuits of power system relay protection. A comprehensive diagnostic algorithm based on multi-dimensional feature fusion is proposed. This algorithm integrates distributed zero-sequence current monitoring, waveform similarity analysis, and third harmonic analysis techniques to construct a multi-dimensional feature fusion diagnostic model. By real-time acquisition of zero-sequence current in each branch, combined with the similarity changes of current waveforms under normal and abnormal operating conditions and the characteristics of third harmonic content, early identification and accurate location of typical faults such as insulation degradation, single-point grounding, and multi-point grounding are achieved. Experimental results show that the algorithm achieves a 98.6% detection rate for insulation faults, a 94.3% accuracy rate for multi-point grounding location, an average diagnostic latency of only 43.63 ms, and a false alarm rate of 1.5% under normal operating conditions. This significantly improves the timeliness and accuracy of insulation fault diagnosis, providing effective technical support for the safe and reliable operation of secondary circuits in substation relay protection.

Keywords: secondary circuit; insulation status; zero-sequence current; waveform similarity analysis; harmonic analysis; comprehensive diagnosis.

DOI: 10.1504/IJETP.2026.155453

International Journal of Energy Technology and Policy, 2026 Vol.21 No.5, pp.20 - 49

Received: 18 Dec 2025
Accepted: 02 Feb 2026
Published online: 03 Aug 2026 *

Title: Enabling holistic insulation monitoring in secondary AC protection circuits: a diagnostic algorithm

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