The effect of morphology on electric characteristics of polymer-insulated DC cable

We have carried out a basic study for the development of polymer-insulated DC cable focusing on the relation between the morphology and the space charge accumulation in the insulation. This paper describes the results of investigating the effect of the morphology on electric characteristics of polymer-insulated DC cable using the cable samples with different spherulite size. In the experiments, the hetero charge accumulated only in the insulation near the outer semiconductive layer when the DC voltage was applied on the sample. The amount of the accumulated charge increases with the rise of an applied voltage and the temperature, and it's amount in the sample with large spherulites is larger because the thickness of the amorphous region, in which a charge can move easily, increases with spherulite size. The sample with large spherulites indicates a low breakdown voltage to the application of the DC, the impulse and the impulse superimposed DC. It is considered that the electric stress is strongly emphasized by the space charge accumulation and the thickness of the amorphous region is larger.