Some aspects or a digital method for the measurement of loss factor of high voltage insulation

Periodic monitoring of the insulation condition of power system apparatus is necessary in order to estimate its deterioration and maintain the reliability of electric power supply. In this paper a digital technique for the on-line evaluation of loss factor is presented. The Discrete Fourier Transform is applied to the acquired voltage and current signals and the loss factor computed by consideration of the phase shift between the fundamental quantities of voltage and current. The effects of sampling rate, the number of measurements and system frequency fluctuation on the estimated value of loss factor are discussed.