Nanosecond PD Currents under a Needle-Plane Electrode and Different Electric Fields over Seven Kinds of Polymer Films

Partial discharge (PD) has been analyzed for a long time, but it is still difficult to understand fully because PD strongly depends on experimental conditions. To understand PD characteristics, we attempt to directly measure the fast-PD current waveforms of nanosecond order. We make the PD measurement circuit length shorter to get PD waveforms correctly. The total length of our new PD current-flow circuit is reduced to less than 150 mm. We use simple needle-plane electrodes with small discharge gaps of 0-150 µm. The needle diameter used is 1 mm with a tip radius of 300 µm. AC peak voltage of 2 and 3 kVp at 50-1000 Hz are applied to polymer films of polyimide, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, cross-linked polyethylene, low-density polyethylene, and low-density polyethylene with antioxidant. The PD current peak time exhibits approximately 5 ns for both positive and negative pulses, and the pulse width at half height of the peak value is 5-15 ns. Nuclear magnetic resonance analyses suggest that the current wave form differences may be due to the dipole movement affected by the trapped charges.