Nanosecond PD Currents under Needle-Plane Electrode with Different Electrode Radius over Four Kinds of Polymer Films

Partial discharge (PD) degradation in high-voltage and/or high-field equipment is a major hazard that can result in equipment breakdown. Despite extensive research, PDs remain challenging to understand owing to their strong dependence on experimental conditions. Fast-PD waveforms have garnered significant interest owing to recent advancements in high-speed oscilloscopes, which has facilitated the measurement of PD current shapes and the direct analysis of nanosecond-order waveforms. PD currents typically flow in 10–20 ns and PD measurement circuit length must be sufficiently short to get correct PD waveforms. The total length of our PD current-flow circuit is made to be less than 15 cm to get correct waveforms. The electrode consists of a simple needle-plane electrode with small discharge gaps of 0–150 μm. The needle diameter is 1 mm with tip radii of 30 μm and 300 μm. An a.c. peak voltage of 2000 V at 50–1000 Hz are applied to polyimide, polyethylene terephthalate, polyethylene naphthalate, and polycarbonate films. The PD current waveforms exhibit approximately 5 ns peak time for both positive and negative pulses and the pulse width at half height of the peak value are 5–15 ns. Those times vary depending on the film material, discharge gap length and needle tip radius. The applied a.c. voltage frequency dependence of these times are small over the applied voltage frequencies. Moreover, nuclear magnetic resonance analyses suggest that the current wave form differences may occur with the dipole movement affects the trapped charge movements.