Charge accumulation phenomenon in oil immersed pressboard exposed in positively charged transformer oil

It was dicovered that the pressboard immersed in positively charged oil were highly charged up. The experiments to evaluate the charge density and the charge distribution in the pressboard were carried out to investigate the mechanism of charge accumulation. In the experiment, positive charges generated by oil flow were supplied to the pressboard sample. Charge densities in oil and pressboard were evaluated from the potential measurement. Charge distribution in pressboard was estimated from the current-time characteristics at DC voltage application to the pressboard.