Biaxially oriented polypropylene (BOPP) films

as the key insulation medium for dry DC capacitors

is prone to partial discharge during long-term operation

leading to deterioration of insulation performance. In order to study the development process of DC partial discharge of typical defects inside capacitors

we designed three types of typical partial discharge defects. The pulse current method was used to study the characteristics of partial discharge under positive polarity DC voltage. Based on the relationship between discharge amount and time

four types of statistical characteristic spectrums were further extracted. The results show that the Q-t spectrum of surface discharge defects shows obvious characteristics of partial discharge cluster. With the increase of applied voltage time

the discharge repetition rate of corona discharge increases first and then decreases. The Q-t spectrum of internal discharge defects shows hill-like characteristics. In the interval with the largest proportion of discharge amplitude

there is a correlation between two adjacent partial discharges of corona discharge defects. There is a significant correlation between the discharge amount of corona discharge and surface discharge defects and the mean value of subsequent discharge time interval. Most of the discharge amplitudes of internal discharge defects are smaller than the average discharge amplitude

showing a small amplitude dominant discharge mode. The distribution of discharge time intervals along the surface is more concentrated. It is found that the internal discharge characteristics of the metallized films are consistent with the BOPP base films. The research results provide a theoretical basis and experimental data reference for on-line monitoring and fault diagnosis of DC partial discharge of power capacitors.