Dielectric breakdown strength affected by the lamellar configuration in XLPE insulation at a semiconducting interface

It is shown experimentally that several types of glyceride additives improve the dielectric breakdown strength of polyethylene at the semiconducting electrode. The highest breakdown strength is more than twice the original one in terms of 1% Weibull breakdown strength. The average normal component, cos theta , is introduced to indicate how close the direction of the lamellar lines is to that of the line perpendicular to the interface. It increases up to 0.82 as the range of the lamellar lines increases up to 1 mu m from the interface. The effects of additives in the semiconducting material on the lamellar structure are obvious within a range <0.2 mu m from the interface in terms of cos theta . In the vicinity approximately=0.2 mu m from the interface, the lamellar structure and the 10% Weibull breakdown strength show a certain relationship. It is found that the maximum dielectric breakdown strength can be obtained at a certain cos theta value that depends on the nature of the additive used. The interface roughness delta z/sup 2/ has a value similar to the agglomeration diameter of carbon particles in the semiconducting material. There is no obvious relationship between delta z/sup 2/ and the breakdown strength.<
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