Characteristics of space charge distribution in epoxy-paper composite insulation system

The HVDC dry-type bushing, with its main insulating medium being epoxy-impregnated-paper composite, is a key device in the ultra-high voltage direct current power transmission system. The HVDC bushing is under the combined effect of electricity, heat, and mechanical stress when it is in operation, in which case the electric field strength in the core of bushing is high, the temperature in the central conductor is high, and the interfacial effect between the epoxy layer and insulating paper is strong. Consequently, space charge will accumulate in the epoxy-paper composite insulation. Previous studies mainly focuses on the characteristics of space charge distribution in polymer-micro-nano filler, whereas the studies on that in epoxy-insulating-paper composite are quite limited. This paper, based on the HVDC bushing made up of epoxy-insulating-paper composite, establishes and a space charge measuring system which is suitable for the pulse electro-acoustic (PEA) method at high temperature (≤110 °C). A modified PEA method which is applicable to the measurement of space charge in the multi-dielectric-layer composite with different acoustic impedance is put forward. By controlling the thicknesses of dielectric layers in the composite sample, the effect of sound wave reflection on the measuring system can be eliminated. An in-depth study is conducted on the effects of temperature and field strength on the characteristics of space charge distribution in epoxy-paper composite.