柔性直流电缆附件应力锥设计研究

Design of Stress Cone for Flexible DC Cable Accessories

应力锥结构设计是柔性直流电缆附件开发的重点和难点,目前还没有柔性直流电缆附件应力锥电场的系统研究及相关设计理论。本文通过试验研究了柔性直流电缆绝缘交联聚乙烯(XLPE)和附件应力锥绝缘三元乙丙橡胶(EPDM)材料的电阻率与温度和电场强度的关系。结果表明:电阻率与温度和场强分别呈e指数及幂指数关系,且随这两个参数的增大而减小。基于热路方程,计算了柔性直流电缆绝缘和应力锥绝缘组成的双层介质的温度分布,进一步利用欧姆定律及绝缘材料的电阻率表达式,得到了双层绝缘介质中的电场分布。根据应力锥曲线上任意点的总电场方向垂直于切线方向的特点,利用应力锥绝缘电场表达式及数值求解方法,提出了应力锥曲线设计方法。最后,以±320 kV柔性直流电缆终端为例,根据现有相关参数,得到了具体的应力锥曲线形状。

The structure design of stress cone is the difficult point and key point of development for flexible DC cable accessory, and there is no comprehensive research of electric field and design theory for the stress cone. In this paper, the relationship between the resistivity of crosslinked polyethylene(XLPE)of flexible DC cable insulation and ethylene propylene diene monomer(EPDM) of accessory stress cone insulation and temperature and electric field were investigated by experiments. The results show that the resistivity shows e exponential relation with temperature and shows power exponential relation with electric field, and the resistivity decreases with the increase of temperature and electric field. Based on heat path equation, the temperature distribution of double layers media composed of flexible DC cable insulation and stress cone insulation was calculated, and the electric field distribution of double layer insulating media was obtained by Ohm’s law and resistivity expression. According to the characteristic that the direction of total electric field is perpendicular to the tangential direction at any point of the stress cone curve, the design method of stress cone curve was proposed based on the electric field expression of stress cone insulation and numerical solution method. Finally, taking a ±320 kV flexible DC cable terminal as example, the concrete stress cone curve shape was obtained according to the existing relevant parameters.