Influence of the frequency on the partial discharge inception voltage

A report about the behaviour of inhomogeneous air gaps stressed by high frequency voltages was published by Kampschulte and Lassen in 1930. The measurements had been performed within a frequency range of 50 Hz up to 100 kHz. It was the aim of that investigation to find out dimensioning criteria for the design of high power rf-transmitters. These investigations have already shown that the breakdown voltage of inhomogeneous gaps decreases significantly with the increase of the frequency. The values of the breakdown voltages even for those comparatively low frequencies may be only 50% of the 50 Hz breakdown voltages. Due to the continuous reduction of size of electrical equipment the field strength and therefore the electrical stress of installation has greatly increased. The probability of the occurence of PD is also increasing. Today high frequency voltage stress often occurs at printed circuit boards (PCB) due to the increasing use of converter circuits with high switching frequencies. This paper deals with the influence of the frequency on the PD inception voltage (U_i) and PD-intensity on PCBs for a frequency range up to 400 kHz. The investigations are performed for normal climatic conditions. Additionally point-plane air gaps are investigated to evaluate the influence of the frequency on the PD-characteristics for very inhomogeneous fields