About the influence of the environmental conditions on the partial discharge extinction voltage at high frequency voltage

In the last decade there has been an increasing interest on the influence of high frequency stress on insulation systems. This is caused by the increasing use of high frequency switches, e.g. in frequency converters. The experience with these systems has shown that the transients caused by the high frequency switching can have a great influence on the lifetime of the insulation. As one indicator for the quality of an insulation the partial discharge inception and extinction voltages are used. These values are commonly measured at a frequency of 50/60 Hz, but measurements at high frequency voltage are urgently needed and possible today. An other factor influencing the lifetime of insulation are the environmental conditions, e.g. humidity and temperature. For 50/60 Hz the influence of the environment on partial discharge characteristics are rather well known. There is only a small dependency of the partial discharge characteristics on temperature and humidity. Some measurements at higher frequencies have shown that these parameters can have a much greater influence on the partial discharge inception and extinction voltage. In this paper measurements at different frequencies from 50 Hz to 1 MHz for varying environmental conditions will be presented. They are done with needle-plane electrodes in order to have a well known geometry. The influence of humidity and temperature on the PD-characteristics at the different frequencies will be shown and discussed