Temperature dependence of return voltage characteristics

The return voltage measurements have been proposed for the diagnostics on the high voltage equipment characterising the dielectric properties of insulation systems. The application of return voltage method at the diagnostics of the HV current transformers are 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. That indicate for a possible applicability of the technique for assessing the state of transformer insulation. The investigations of temperature influence on the return voltage characteristics were aimed at determining the state of the insulation under operating conditions. The theoretical analysis of the results allows calculation of the temperature of insulation that corresponds to the thermal breakdown of insulation.