The Effect of Humidity on the Characteristics of Partial Discharge Induced by Metal Tip in GIS

Metal tip discharge is one of the most common types of partial discharge (PD) in gas-insulated switchgear (GIS) equipment. Understanding how humidity influences PD under actual operating conditions is of great significance for assessing insulation status accurately. This paper describes a GIS prototype test platform with controllable gas humidity. It integrates detection systems, including ultra-high frequency (UHF), photomultiplier tube (PMT), and spectrometer, to investigate the PD characteristics induced by metal tips with curvature radii of 200 μm and 75 μm under varying humidity conditions. The results indicate that with increasing humidity, the PD inception voltage (PDIV) for the 200 μm tip initially decreases, then rapidly increases after 480 μL/L and stabilizes. For the 75 μm tip, PDIV decreases quickly and then stabilizes, but with increased dispersion. In terms of discharge repetition rate, the negative polarity rate first increases and then decreases with humidity, reaching a maximum at 480 μL/L; the positive polarity rate, on the other hand, monotonically increases with humidity and exhibits an earlier inception. In terms of discharge amplitude, both negative and positive polarity amplitudes gradually decrease with increasing humidity. Under high humidity conditions, UHF signals are prone to falling below the detection threshold, resulting in non-detection, whereas PMT can still record optical pulses. This phenomenon is more pronounced for small curvature tip. These conclusions provide a basis for on-site GIS PD online monitoring and insulation status diagnosis, and highlight the necessity of synchronous gas state detection.