Influence of Humidity on Dielectric Characteristics of Insulator Surface in Air

摘要

Temperature and humidity affect the dielectric characteristics in air of medium-voltage electrical power equipment with composite insulation of a vacuum, solid, and air. The experimental results of dielectric characteristics for a solid and air boundary with varying ambient conditions of surrounding air, such as temperature and humidity, are presented in this paper. An experimental model was designed to create a high electric field along an insulator surface and electric lines of force parallel to the surface, which enables the dielectric characteristics along the surface to be measured. The insulator was made of epoxy resin with alumina fillers and its permittivity was 5.5. Flashover voltage for lightning impulse (FOV_(imp)), partial discharge inception voltage (PDIV), and flashover voltage for power-frequency voltage (FOV_(AC)) were measured under different temperature and humidity conditions. FOV_(imp) decreased gradually as relative humidity increased where there was no dew condensation. In contrast, when droplets were formed by dew condensation, FOV_(imp)drastically decreased. The slow decrease in FOV_(imp)without dew condensation was assumed to be because the number of water molecules on the surface of the insulator affected FOV_(imp). We confirmed that only relative humidity strongly affected FOV_(imp)by comparing the dependencies of relative humidity and absolute humidity on FOV_(imp). FOV_(AC) had the same tendencies as FOV_(imp).