Partial Discharge Inception Characteristics in Air with Solid Dielectrics under HVDC and Polarity Reversal Conditions

Abstract

In order to enhance HVDC electrical insulation performance in power equipment, an investigation on partial discharge and flashover characteristics in air-solid composite systems is required, in particular, on those under DC polarity reversal (DC-PR) conditions. By using rod-to-plane electrode systems in air with solid dielectrics of polymethyl methacrylate (PMMA) plates, DC and DC-PR voltages were applied and partial discharge inception voltage (PDIV) and flashover voltage (FOV) were measured. Experimental results revealed that the PDIVs under DC-PR show remarkable reduction characteristics compared with those with just DC voltage-on, while the FOVs show no change. The reason for the PDIV reduction at DC-PR might be the accumulated charges with DC opposite polarity on solid dielectrics, which were deposited by PD generation under the beforehand applied DC steady state-voltage (DC-SS), being referred to as DC pre-stress. It was clarified that the mechanisms causing the PDIV reduction at DC-PR can be quantitatively explained by the superposition of electric field stresses from applied DC-PR voltage and deposited charging voltages on solid insulators.