Development of 500-kV XLPE cables and accessories for long-distance underground transmission lines. V. Long-term performance for 500-kV XLPE cables and joints

500-kV XLPE-insulated cable with an insulation thickness of 27 nim and its joint have been developed for long distance transmission lines. First, in the basic research made irom 1989 to 1992, elicited were the perfortnance-detertnining factors of XLPE cables and joints. Their respective insulation designs were inade in terms of these factors. On the basis of these designs, full-sized cables and joints were manufactured in the course of the development research performed from 1Y92 to 1993. The next step was to evaluate the initial clectrieal pcrforinance to estimate the suitability of our designs. As the final step of our series of researchcs so far carried out, a long-term loading cycle test was carried out by means of a model line with joints as insValled and using the same lechniques as employed in the actual commercial lines for full eight months. We could thus verify the long-term reliabilily for coniinercia1 use.