Partial discharge characteristics of oil/polypropylene film with a needle-plate electrode excited by impulse voltages

Polymeric materials such as polypropylene films are widely used in electrical and electronic devices because of their good mechanical, chemical, and electrical insulation properties. The electrical behavior subjected to high electric-field and possible breakdown phenomena are of great practical interest. For high-voltage electrical equipment, insulation defects such as pointed end are unavoidable. Under high electric field, these defects may cause partial discharge, which deteriorates the insulation material and increases the probability of breakdown and failure. In this paper, the partial discharge characteristics of oil/polypropylene film under the needle-plate electrode configuration are investigated under the impulse voltage. A double exponential impulse voltage source generator is designed, and electrical partial discharge detection system based on micro-current transducer with anti-interference solution is then established. Experimental results show that at the rise stage of applied voltage and around peak value, the partial discharge pulses are mainly homopolarity with the excitation, while at the wave tail time, reverse discharge could be often observed. Surface charge on the barrier dielectric plays an important role in the formation of hetero-polarity discharge. Moreover, the influences of voltage magnitude and pulse width are also analyzed. It is very useful to investigate surface charge during surface discharge on polymeric materials, which is helpful for understanding the development of surface discharge and making proper use of polymeric materials.