Study on Partial Discharge Characteristics of Dielectric Films for Metallized Film Capacitors

This paper investigates the partial discharge (PD) characteristics of biaxially oriented polypropylene (BOPP) films and metallized films based on the actual structure of metallized film capacitors. The PD inception voltage of metallized films is 30.2% lower than that of BOPP films due to the uneven voltage distribution along the films. Under the low electric field, the internal discharge occurs in the gaps between films. Under the high electric field, the surface discharge is more intensive. And the equivalent frequency of PD in metallized films can reach 15 MHz, surpassing that of BOPP films. Additionally, as the voltage increases, the phase distribution of PD in metallized films is more extensive with a lower phase correlation of the PD repetition rate. However, the average PD amplitude decreases. The complex nature of the PD is facilitated by the migration and accumulation of surface charge generated by previous PDs at the margin of metallized films, leading to distortion of the electric field. This is an essential element of metal electrodes loss near the margin leading to the reduction in capacitance. This paper aims to provide a theoretical basis for refining the capacitance loss mechanism of metallized film capacitors.