Analysis of Internal Partial Discharge Based on PD Current Waveform

The analysis of partial discharge (PD) phenomenon to cause long-term degradation of electrical insulation systems is essential to development of electrical insulation technology. The PD pattern on the relation between PD magnitude and the phase of applied voltage is well known one of the electrical insulation diagnosis methods for high voltage equipment. In the general, an acquired PD pattern from equipments is compared with accumulated data base which provides the correlation between the PD pattern and insulation status like degradation or defects. However, clarification for generation of such PD pattern based on physics is not yet of satisfactory. The PD patterns within an internal void generally consist of several PDs of continuance in half cycle within void. It became clear by the past research that the formation of the following PD differs from the first PD within one half cycles in the continuous PD's. It was considered that the following PD seems to turn to the Townsend-like PD from the Streamer-like PD under the influence of first PD. In this study, we studied the first and the following PD more in detail in terms of the PD current waveforms applying a square or triangle wave high voltage. The results suggested that the PD properties depend on applied voltage and its frequency but independent from applied offset voltage. It was also proved that the first PD provides the influence to the following PD.