Excess Current Characteristics of Typical Insulation Defects Partial Discharge Under 50Hz

Abstract

Measurements of partial discharge play an important part in the study of dielectric materials, nevertheless, the physical processes of partial discharge are not yet clear. Pulse current method is recognized as the only effective way to quantify the charge. However, there is a limitation of such approach to detect PD pulses below the noise threshold and slow charge movement. In this work, a new technology “Excess Current Method” enables the measurement of the micro discharge and slow charge movements during PD. Proposed in some published studies, the excess current is referenced as the additional current component associated with the PD process by measuring the difference of dielectric response currents through a test object without and with PD activity. A measurement setup for simultaneous measurement of PD excess currents and PD currents averaged from about 300 periods is applied and three typical insulation defect models were tested under 50Hz voltage. Results of the excess currents during and after PD activity, including waveforms and charges are showed and discussed. The results indicate that the amplitude is higher and the charges are more of the excess currents than the PD currents, which reveals that some current components are ignored by pulsed current method but detected by excess current method. Furthermore, a weak excess current is measured for the dielectric barrier and air void PD models when the voltage dropped below the Partial Discharge Extinction Voltage (PDEV). The analysis of non-PD excess current also reflects the slow charge movements during PD. The measurement of excess current provides additional insight into PD mechanisms and shows the potential of completing the conventional PD detection.