About the PD-testing of insulation systems with high-frequency voltages

In the last decade, there has been an increasing interest in partial discharges (PD) at high frequency stress on insulation systems. At present, high-frequency working voltages exceeding 100 kHz are often used in low-voltage equipment and the frequencies are still increasing. Due to the switching in the power supplies, the voltage shapes are usually nonsinusoidal. The aspects of these nonsinusoidal voltages regarding the electrical stress are discussed by harmonic analysis. The difficulties of performing PD measurements at impulse voltages are shown and the alternative of measurements using sinusoidal voltages is discussed. Regarding the nonsinusoidal voltages and the increasing operating frequencies, test frequencies in the MHz range are of future interest. The requirements on the test equipment for these high-frequency tests are discussed. Finally, this paper describes how PD tests can be performed with respect to high-frequency stress and some examples are shown.