Calculation of Electric Field in Safety Film Capacitors

The failure mechanism of a safety film capacitor is a little different from that of an all-film capacitor. Experiments were carried out on a number of safety film pulse capacitors. A careful examination is made of the capacitor film after discharge. It is found that the failure of the capacitor comes from the capacitance loss, which is caused by the partial discharge (PD) at the edge of the segment electrode. The electric field is calculated in the paper and the results show that the electric field distortion is the main reason for PD at the edge of electrodes. The paper uses the electric field distortion range (EFDR) to review the influences of thickness of electrode, thickness of film and reversal coefficient of discharge voltage on PD at the edge of electrodes. As a result, the EFDR will be more intense and the PD at the edge of electrode will be more obvious if the electrode is thinner, the film is thicker or the amplitude of reversal coefficient of discharge voltage is higher. And when there is free surface charge on the film near the electrode, the PD will be more serious.