Partial Discharges in Gaseous Voids for DC Voltage

When designing ac insulation systems much knowledge and experience is available concerning partial discharges. However, for dc insulation there is a lack of knowledge of partial discharges and their effect on reliability and lifetime. For this reason we conducted a study on the distribution functions of the discharge magnitude and the time between two discharges. A model has been developed to describe the discharge behavior for dc voltage. The measurement results are in agreement with the proposed model. The extinction voltage of the discharges is close to the ignition voltage. The discharge frequency is mainly determined by the statistical time lag (period between reaching a voltage sufficient to cause breakdown and the breakdown itself). The statistical time lag depends strongly on the test voltage.