Effect of dynamic glass transition on space charge behavior in epoxy resin

The mechanical and dielectric properties change significantly when the temperature is close to the glass transition temperature (T_g) for epoxy resin, which is a dry-type insulation materials used in the high voltage direct current (HVDC) power transmission system. In order to study the effect of dynamic glass transition on space charge behavior in epoxy resin, samples with T_g as approximately 82 °C were prepared and space charge distribution was measured with an improved pulsed electro-acoustic (PEA) set-up at temperatures far below (40 °C) and close to T_g (75 °C) respectively. When the temperature is far below T_g, both homocharge (close to cathode) and heterocharge (close to both electrodes) accumulation can be found with poling time at different poling fields (10 kV/mm, 30 kV/mm). It implies that charge injection and ionization of the organic species have taken place in epoxy resin. However, when the temperature is close to T_g, only heterocharge (close to both electrodes) distribution can be observed in the epoxy resin samples for different poling fields. The injected negative homocharge might be neutralized by the large amount of positive heterocharge arising from the ionization of the organic species in epoxy resin. And this is thought to be related to temperature enhanced dissociation of the organic species and charge mobility in epoxy resin when the temperature is increased to T_g.