交联聚乙烯电缆绝缘中的电树枝与绝缘结构亚微观缺陷

半结晶高聚物中的电树枝特性远比纯脆性或柔性聚合物复杂,源于材料中的结晶区和无定形区两相共存.在厚绝缘交联聚乙烯(XLPE)中还存在不均匀结晶和微孔高度集中,以及残存应力,导致电树枝特性更加复杂.本文提出利用生长速度比和扩展系数两个新参数来研究XLPE中的电树枝生长规律.根据XLPE电缆绝缘中电树枝结构特征和生长特性,研究了电树枝的影响因素和绝缘中的四种亚微观绝缘结构弱点,分析了微孔集中、大球晶边界及结晶排渣、应力、电场局部集中所导致的电树枝在绝缘内侧的迅速扩展现象,提出了超高压XLPE电缆发展所必须解决的亚微观绝缘结构缺陷在电缆绝缘内侧集中问题及其对策.

Electrical Tree and Submicroscopic Insulation Structure Weakness in XLPE Cable Insulation

The electrical tree character in semi-crystalline polymer is much more complex than in pure brittle polymers and flexible polymers, for crystalline region and amorphous region is coexisted together in this kind of material. Besides this, there are uneven crystalline, high concentrate micro-hole and survival mechanical stress existed also in ultra-high voltage cross linked polyethylen(eXLPE)cable insulation, that make electric tree initiation and propagation character more complex. In this paper, two new parameters, the ratio of the growth speed between radial and cross direction, the expand coefficient of the tree in cross direction are put forward. The influence factors to electrical tree growth and four kinds of sub-microscopic insulation structure weaknesses in XLPE cable insulation are studied. It is micro-hole, impurity and survival stress that concentrated in the boundary between big crystals and amorphous region, which makes electrical tree spread much quicker in the insulation of near the core of cable. The problem of partial insulation structure imperfection must be solved for developing of ultra high voltage XLPE cable, some suggestions is put forward in the end of this paper.