Influence of the ambient temperature on the impulse withstand voltage characteristics of insulation material surfaces under humidity conditions

Research work has demonstrated, that the impulse withstand voltage characteristics of insulation material surfaces are influenced by the relative humidity. As previous papers pointed out, the so called water adsorption test is suitable to determine the influence of relative humidity on the impulse withstand characteristics of insulation material surfaces. This test is performed according to a test procedure described in, which proposes an ambient temperature of /spl thetav/ = 25/spl deg/C. In order to get information about the influence of the temperature, we perform the water adsorption test at different temperature values within these investigations. All investigations presented in this paper have been carried out on an epoxy resin (FR-4) as well as on a melamine resin (MF1206) and on a polyester resin (GPO-2). Hereby, the influence of the relative humidity on the impulse withstand characteristics of these materials has been investigated at different ambient temperatures between /spl thetav/ = 20/spl deg/C and /spl thetav/ = 50/spl deg/C. The achieved test results demonstrate, that most of the investigated insulation materials show the poorest impulse withstand characteristics at an ambient temperature of /spl thetav/ = 30/spl deg/C, although the absolute humidity at /spl thetav/ = 30/spl deg/C is less than the absolute humidity at higher temperatures for the same value of the relative humidity.