Space Charge Characteristics in Epoxy Resin Impregnated Paper under AC and AC-DC Superimposed Electric Fields

In this paper, charge distributions in three-layered epoxy resin and epoxy resin impregnated paper samples under AC and AC-DC superimposed electric fields are measured by the improved high-speed pulsed electro-acoustic system. To exclude the interferences caused by the discontinuity of relative permittivity, a method to distinguish between net dipolar charges and free charges is proposed. Through analysis, the influences of frequency, AC component and DC component on the charge transport and trapping characteristics in multi-layered epoxy composites are obtained, which could provide important reference to the structural design and optimization of converter transformer bushings.