The application of novel polypropylene to the insulation of electric power cable (3)

Abstract

Having a higher melting temperature than polyethylene, polypropylene has been expected to be an insulation material for power cables. But isotactic polypropylene (i-PP) used generally is unsuitable as cable insulation because it shows poor flexibility, low breakdown strength due to growing spherulites, and so on. But stereoregular syndiotactic polypropylene (s-PP) newly developed with metallocene catalyst shows quite different properties than i-PP. In our previous paper, we investigated the basic properties of s-PP and the initial properties as a cable which was manufactured using s-PP insulation. It was revealed that s-PP had superior thermal and electrical properties to cross-linked polyethylene and the s-PP insulation table showed satisfactory initial properties. However, in order to apply to an actual cable, the properties must be maintainable over 30 years after construction. In this paper, we estimated the long-term remaining properties for s-PP insulation table. A series of experiments on long-term properties gave the following results: (1) s-PP cable shows longer life over 30 years; (2) the breakdown strength of s-PP cable after a long-term experiment equal to 30 years is slightly lower than the initial breakdown strength, but it is sufficient as a remaining property. Furthermore, water-tree resistivity of s-PP was investigated and it was revealed that s-PP significantly suppressed the water tree propagation compared with XLPE. These results suggested that s-PP cable would serve as a next-generation cable. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 1–8, 2006; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20114