Analysis of Ambient Humidity Effects on Dielectric Liquids

This study meticulously examines the impact of ambient humidity, as an environmental factor, on the electrical discharges of transformer oils, alongside the characteristic responses of the oils under varying conditions. Three types of transformers insulating liquids were selected: mineral oil, synthetic ester liquid, and natural ester liquid, which are among the most prevalently used oils in transformer systems. A horizontal needle-plane electrode configuration was then designed to facilitate the discharges experiments within the transformer oil. This design enabled the establishment of an experimental setup conductive to conducting tests under controlled ambient humidity conditions. The experiments were performed within a range of 40% to 95% relative ambient humidity. The electrode gap was systematically varied from 1 mm to 5 mm, in 1 mm increments, and the experiments were repeated for each dielectric liquid across these five different gaps. The experiments yielded critical data on the leakage current for each dielectric liquid. To ensure the accurate interpretation of this data, an analytical method was considered. The results derived from the kurtogram analysis were scrutinized by comparing the electrical discharges responses to ambient humidity variations across the different oils. This study demonstrates that ambient humidity — even without moisture ingress — significantly alters the discharge behavior of transformer oils, as confirmed by FTIR and fast kurtogram analysis.