Breakdown strength affected by the interface roughness at the semiconducting layer in XLPE power cables

The authors describe the relationship between the breakdown strength and the roughness of the semiconducting interface in model XLPE (cross-linked polyethylene) power cables with insulation of 3.5 mm thickness. Nine kinds of specimen cables were manufactured out of seven kinds of semiconducting layer materials. Six kinds of additives were used to modify the semiconducting materials. The maximum breakdown strength of the specimens was about 1.6 MV/cm (1% Weibull strength) and 1.2 times higher than that of a specimen without additives. The semiconducting interface roughness of less than 1 mu m was quantized by taking transmission electron microscopic photographs of the interface. It was found that the roughness of the outer semiconducting interface is larger than that of the inner ones and has a strong correlation with the breakdown strength.<>