Residual air and moisture in impregnated paper insulation-II

The paper describes further experiments on the drying and impregnating processes of impregnated paper insulation for high-voltage cables. Conclusions are reached as to the relative advantages of drying at atmospheric pressure and under vacuum. The qualities of the product are discussed from the standpoint of conductivity, dielectric absorption, and power factor. The influence of electric stress on impregnated paper and the progressive change in power factor under stress are studied in accelerated overvoltage tests. Evidence is presented as to the nature of certain interesting types of progressive change of power factor in their relation to the amount of residual air.