Temperature dependence of return voltage characteristics [of power current transformers]

Recently, return voltage measurements have been proposed for the diagnosis of HV power equipment, characterising the dielectric properties of their insulation systems. The application of the return voltage method for the diagnosis of HV current transformer insulation is presented in this paper. The return voltage characteristics such as maximum of return voltage, the initial slope of return voltage and the time to peak value dependencies on charging time are discussed. These characteristics vary depending on the ageing changes of the insulation, indicating the possible applicability of the technique for assessing the state of transformer insulation. The investigations of temperature influence on the return voltage characteristics aim to determine the state of the insulation under various operating conditions. The theoretical analysis of the results allows to calculate the temperature of insulation that corresponds to the thermal breakdown