Space Charge Measurement Under DC and DC Periodic Waveform

In High Voltage systems, Partial Discharges (PDs) monitoring are one of the main diagnostic instrument to evaluate the reliability of the apparatus. Under Alternating Current (AC) stress, PDs detection and recognition techniques are well consolidated. On the contrary, the monitoring of PDs under Direct Current (DC) stress is difficult due to complexities related to the nature of the phenomenon, which cause the beginning of PDs events in proximity of the dielectric breakdown. This problem has been partially overcome by using a continuous Periodic waveform (DCP) with positive average value, as described in a recent published work. Under DC stress, another degradation factor is the Space Charge accumulation phenomenon. Considering that the latter phenomenon is widely influenced on the applied voltage, the aim of the proposed work was to confirm that the effect of this new DCP waveform is the same of that generated by a constant DC stress, from the space charge accumulation phenomenon point of view. The experimental tests have been performed by using the Pulsed Electro-Acoustic (PEA) method and the comparison between the charge profiles obtained by stressing the specimen with both the DC and DCP waveforms has been carried out.