Research on DC Breakdown Properties of HVDC Cable Materials

As DC transmission has been used widely, HVDC cables are the development direction of power grid in the future. Because of space charges accumulating in XLPE insulation, DC breakdown properties are different from AC breakdown properties. Three kinds of DC cable insulation materials were selected in this paper. Breakdown tests with step by step voltage increase mode were used to study breakdown properties. Finally, the approximate formula of life index was deduced and analyzed. The results showed that breakdown strength of DC materials were related to test temperature and step time. The higher test temperature and longer step time, the lower breakdown strength. Shape parameters of DC materials were related to step time. The longer step time, the larger shape parameter. Life index of DC materials were related to the test temperature. The higher test temperature, the lower life index. Breakdown strength of DC material B was highest at room temperature and lowest at 70°C, while life index of B was lowest at room temperature and highest at 70°C. Therefore, both breakdown results and life index should be taken into account in cable insulation life evaluation.