Conductivity and interface charge accumulation between XLPE and SIR for HVDC cable accessory

Interface charge accumulation between cross linked polyethylene (XLPE) and silicone rubber (SIR) is the key factor causing discharge failure for high voltage direct current (HVDC) cable accessory. However, the properties and mechanisms of interface charge behaviors in double-layer dielectric are not detailed. In the present work, dielectric performance and conductivity properties related to interface charge have been measured, and interface charge distributions between XLPE and SIR have been calculated based on Maxwell–Wagner polarization model. The experimental results indicate that charge conduction of SIR is larger than that of XLPE at room temperature, and the conductivity of SIR has a weak dependence on the temperature. By contrast, the conductivity of XLPE increases by three orders when the temperature increases from 25 °C to 90 °C, result in that the conductivity of XLPE exceed that of SIR at a certain temperature. The mismatch of conductivity properties for the two materials will cause charge accumulation at the interface. The interface charge density firstly decreases and then increases with the increasing temperature, and the polarity of charges are different for different temperature regions. Under 10 kV/mm, the transition temperature is about 40 °C. When the temperature exceeds the transition temperature, electric field in the two materials will reverse, and the polarity of interface charge will be changed accordingly.