Breakdown processes of solid composite insulation system with defects under high frequency

Behaviors of composite insulation system are strongly affected by the performance of interface between dielectrics, which mostly correlates to the direction of applied electrical field and the frequency of applied voltage. In this paper, experiments were carried out to study the breakdown characteristics of solid composite insulation system, consisted of a polyethylene (PE) film (with a copper needle electrode) and a glass slice. A sine wave power supply with a frequency range from 50 Hz to 100 kHz was established to fit our purposes. Voltage was smoothly raised from 0 kV to 5 kV. The processes of breakdown can be divided into four stages: (1) Electrical tree inception and propagation in polyethylene; (2) Sliding discharge along the interface between polyethylene and glass; (3) Streamer across the glass; (4) Return streamer initiation from the ground electrode and breakdown. A model was established to analyze the mechanism of sliding discharge between solid dielectrics. The influence of frequency on thermo effect is considered as the main causes of the experiment results, which can well explain the reason of insulation premature inactivation in high-frequency electrical equipment.