Evaluation of partial discharge under inverter surge application using current waveform

The partial discharge (PD) generated by the surge voltage is an issue in inverter-fed motor for the reliability of the electrical insulation. The measurement of PD waveform with a wide frequency range is one way to investigate the PD phenomenon. The PD waveform with a wide frequency range may imply information such as mechanisms beginning from initiation of avalanche and its propagation. Authors have reported that PD current waveform in case of a twisted-pair sample could be extracted from observed current waveform using a transfer function. However, a lot of PD´s occur at a lot of points, then the possibility of superposition of the PD current waveforms increases especially under the surge voltage. In order to evaluate PD current waveform at the limited area, an electrode configuration was modified. The PDIV under AC voltage application was compared to that based on Paschen´s curve. Although the PDIV at a gap length of around D = 0.03 mm could be estimated using Pachen´s curve, it became clear that the difference between estimated PDIV and measured PDIV increased with increasing gap length of D. The PD current waveform was also observed under a pulse voltage application. It became also clear that parameters such as the peak value and/or a half bandwidth were directly evaluated from observation of current waveform. It was because the PD component in PD current waveform was bigger than the charging component under a surge voltage application.