Space Charge Behavior in Oil-Impregnated Paper Insulation Under Sinusoidal Electric Field With Wide Frequency Range

This article focuses on the space charge transport under the sinusoidal electric field with a wide frequency range of 10
⁻²
–10
⁴
Hz. Three questions are studied: whether there is obvious charge accumulation in oil-impregnated paper (OP) insulation under the ac field, the effect of charge accumulation on electric field, and the physical processes affected by the periodic electric field. Based on the pulsed electro-acoustic method, the original signal is obtained by a detection strategy that combines the pulse cluster method for low frequency and automatic equal phase shift (AEPS) principle for high frequency. It shows that charge hysteresis is a characteristic phenomenon of charge distribution under the ac field. Charge accumulation under a low frequency field is more than that under a dc field due to the higher interfacial field. Furthermore, numerical simulation is carried out to investigate the charge dynamics under ac stress. Two specific physical processes of effective charge injection and charge migration are discussed, and a charge conduction mechanism with a multi-mobility mode is proposed for charge transport under the ac field. It shows that the maximum recombination rate increases with the increase in frequency. Charge hysteresis essentially creates conditions for the charge recombination process.