Effects of moisture on power factor of oil/paper insulation

Power factor and capacitance measurements are routinely used in the condition assessment of oil/paper insulated high voltage equipment. It is a generally accepted belief that moisture in the oil/paper insulation increases the power factor and capacitance. This paper shows from basic principles that moisture that is not uniformly distributed in the oil paper insulation of high voltage equipment with high paper to oil ratio such as CTs, and bushings, will not necessarily reflect in power factor or capacitance measurements. The results are discussed in terms of a case history involving the failure of three station class current transformers and the relevance of power factor testing.