The Effect of Nonsinusoidal Voltage and Overvoltage Waves on the Development of Partial Discharges

Abstract

The results of experiments on the study of partial discharges in the insulation of cable lines at nonsinusoidal voltage are presented. With a nonsinusoidality of approximately 10%, the operation of the electrical network in normal mode was simulated, and overvoltage waves were simulated with a nonsinusoidality of about 80% and harmonics in the frequency range of 2–4 kHz. In the case of nonsinusoidality, it is statistically shown that the main factor in the development of partial discharges is the difference between the amplitude of the applied voltage and the threshold voltage of the occurrence of partial discharges, and the partial discharges’ power weakly depends on the harmonic composition of the voltage. It is shown that the greatest deviation from the linear law with an increase in the applied voltage is observed for the power of the partial discharges; therefore it is most advisable to use this dependence when analyzing the state of cable lines by the level of partial discharges. It has been shown experimentally and by simulation that with a nonsinusoidality of 80% and harmonics in the frequency range of 2–4 kHz, the number and power of partial discharges during the period of the main harmonic increase significantly. In this case, the amplitude of the harmonic is already sufficient to recharge the defect and it is the harmonic that becomes decisive in the formation of partial discharges.