Investigation on the pulse shape of DC corona discharges in air under varying test voltage level

A continuous condition assessment of operating equipment makes a significant contribution to the service reliability. In this context the partial discharge diagnosis is of great importance. In contrast to AC applications an established diagnostic tool for DC applications does not exist, even though diverse promising approaches, such as the time domain analysis, are identified. This finding is based on investigations, which are carried out under a constant test voltage level. Consequently, additional research, considering a varying test voltage level and its influence on the pulse shape of partial discharges, is required to reach universally valid statements. Focusing on corona discharges in air, the investigations are carried out by using an optimized broadband measuring system. Whereas the corona discharges are gained from an artificial and idealized defect at high-voltage potential, the measuring system enables to capture the pulse shape devoid of reflection and refraction processes. As characterizing pulse shape parameters, the rise time, the pulse width and the fall time are determined as well as the apparent charge and the repetition rate. The gained values are compared to each other and discussed for different test voltage levels.