Effect of insulating oil degradation on power transformer capacitance

Power transformer is indispensable and expensive equipment in the power system that transfers energy from one voltage level to another through magnetic field. Core and winding of these transformers are immersed in mineral oil that works both as an insulator and coolant. But as transformer continues service, its oil is subjected to degradation. This paper aims to verify whether the deterioration of insulating oil has any influence on the change in capacitance of power transformer. To accomplish this, a theory is proposed that helps to explain why, and how, the oil quality affects the power transformer capacitance. Experiments are also performed on several new and old transformers that have good and degraded oil respectively. The experimental results conform to our theory that as the quality of the insulating oil decreases, the capacitance of a power transformer increases.