20 kHz unipolar pulsed field surface flashover characteristics of polymer nanocomposites in subatmospheric pressure helium

The high performance electrical insulation materials and structures in power systems must be free from unwanted and unpredictable dielectric breakdown through the insulation as well as over the dielectric surfaces, and along the interfaces. Surface flashover, another form of breakdown, usually occurs over the surface of insulator between the energized electrodes, and is usually triggered by the stresses caused by the field at the insulator/electrode/ambient interfaces. Studies of surface flashover at sub-atmospheric pressures are specifically important for aerospace systems and vehicles operating in this regime. In this work we present surface flashover characteristics of two different polymer nanodielectrics filled with either TiO₂ or Al₂O₃ nanoparticles. A 20 kHz pulsed, unipolar field is applied across the electrodes positioned on top of the sample with a 0.5 cm gap distance in sub-atmospheric pressure helium. The plasma characteristics, such as voltage, current and optical emission waveforms are recorded. Breakdown voltage as a function of pressure, frequency and duty cycle of the applied field is presented. Differences between the surface breakdown of TiO₂ and Al₂O₃ filled samples are studied and results are presented. Furthermore, frame-by-frame images of the optical emission during the breakdown events are recorded and presented.