Investigation of space charge at the interface between the insulation of cable and its accessory

According to the Maxwell-Wagner model, there is much amount of space charge at the interface between two different insulations. The more difference of ratios between dielectric constant and conductivity of both insulations, the higher amount of space charge emerges at the interface. And the higher amount of space charge stores at the interface, the more distortion of electrical field occurs. Therefore it is one of most important factors to considering the compatibility of dielectric constant and conductivity of cable and accessory insulations in polymer insulated HVDC power cable. There are many ways to evaluate the compatibility, such as calculating the ratios of dielectric constant and conductivity in both insulations at various temperatures. However, most of the ways are indirect and it is very difficult to satisfy the engineers designing cable accessory insulation. In the paper, composite samples of silicon and/ or ethylene-propylene-diene (EPDM) rubbers with LE4253 were prepared, respectively. Space charge at the interface between rubber and LE4253 were measured with pulse-acoustic method at various temperatures. It is found that character of space charge at the interface is the same in both composite samples. However, the amplitude of space charge at the interface between SIR/LE4253 is much greater than that at the interface between EPDM/LE4253 and it goes upwards quickly as the temperature arises. At the same time space charge at the interfaces in both composite samples moves distinctly towards both electrodes. In addition, the character of space charge in both kinds of rubbers varies at different vulcanizing temperatures. At last it is indicated that not only the space charge suppression of accessory insulation, but also the space charge at the interface in the composite sample should be considered as designing cable accessory.