The influence of DC component within combined AC and DC voltage on charge dynamics in polyethylene

Abstract

The combined AC and DC voltage is often experienced by the apparatus/insulating elements in high voltage direct current (HVDC) transmission systems. There is little understanding about the effect of the composite voltage on electrical performance of the system. In the present paper, as the first step towards understanding the effect of DC component of combined AC and DC voltage on potential electrical performance, space charge dynamics in the insulation have been carried out using low density polyethylene (LDPE). Pulsed electro-acoustic (PEA) method has used in this work to detect space charge within insulation. The charge profiles under periodic applied voltage are separated and illustrated according to their applied field phases. Results under the combined voltage with different DC component ratios are compared with those results obtained separately from AC and DC voltage. Based on the results, it is clearly that the DC component within the applied fields has a significant effect on the charge formation and local field distortion within the insulation. The proposed pure AC and DC voltage tests cannot fully represent the charge dynamics under the combined voltage.