Space charge dynamics in oil-impregnated pressboard under AC electric field

Space charge has been a general concern related with the reliability and the life-time of HVDC components. In this present work, the space charge profiles in oil-impregnated pressboards are investigated by the means of the pulsed electroacoustic (PEA) technique under AC voltage with 50 Hz at the room temperature. It has been observed that the ageing status of the mineral oil and the presence of the oil gap can influence the charge accumulation significantly. In the fresh oil impregnated pressboard, considerable negative charges are accumulated near the aluminium electrode. However, only little or no space charge can be detected in the aged oil impregnated pressboard and the oil gap and pressboard composite insulation system. The results may suggest that the amount of the AC space charge is highly dependent on the charge mobility within the dielectrics. The higher charge mobility can result in a smaller amount of AC space charge.