Discharge characteristics at polypropylene-silicone rubber interface under AC voltage

The electric field distribution within a cable joint can be strongly distorted due to its complicated structure, which possibly leads to interface discharge between the primary insulation of cable and the insulation of cable joint. Polypropylene (PP) with excellent electrical performance is considered as a promising material used as the primary insulation of cable, while silicone rubber (SiR) has been extensively used as the insulation of cable joint. To get a better understanding of interface discharge between PP and SiR, the discharge characteristics under AC stress was investigated in this paper, and the discharge erosion on the materials was also measured and compared. Isotactic PP and HTV-SiR were employed as test samples. The discharge current was measured with a HFCT, by which PRPD features for the discharge propagation process can be extracted. A CCD camera was employed to gain a visible monitor of the discharge process. Three stages were observed which refers to (a) discharge initiation, (b) discharge channel propagation and (c) pre-breakdown. Interface discharge between PP and SiR exhibits different PRPD features at various discharge stages, which could be associated with several mechanisms such as interface charge accumulation and partial discharge. SiR is less resistive to the discharge than PP and thereby discharge channel possibly grows within SiR rather than along the interface.