Effects of bulk pre-stress on interfacial breakdown voltage in XLPE/SIR laminate

The interface between accessory insulation and cable insulation suffers not only bulk electric stress along cable radial direction, but also interfacial electric stress along cable axial direction. The above orthogonal electric stress makes the interfacial space charge property complex. In this paper, cross-linked polyethylene (XLPE) and silicone rubber (SIR) were selected to form a laminate with double layers, so as to imitate the actual cable and accessory structure. Then, the interfacial space charge profile and breakdown voltage were measured under different bulk pre-stresses and under different coating conditions. The test results show that interfacial breakdown voltage increases with interface pressure whatever the interface coating condition is. When the polarity of bulk pre-stress is consistent with that of interfacial electric stress, interfacial breakdown voltage decreases, and vice versa. Moreover, the XLPE/SIR interface coated with fluoride silicon grease will accumulate lots of space charge, which results in a more obvious variation of interfacial breakdown voltage than that in the sample coated with the ordinary silicon grease.