温度对高压直流电缆中间接头内电场分布的影响分析

Influence Analysis of Temperature on Electric-field Distribution in HVDC Cable Joint

高压直流电缆附件中的电场分布主要取决于绝缘材料的电导率而非相对介电常数,由于交联聚乙烯(XLPE)和硅橡胶(SR)2种绝缘材料电导率差异较大,且受电场强度和温度影响较严重,导致直流电缆附件的设计比交流附件复杂得多。为此,采用软件仿真手段分析了不同温度梯度作用时,直流电压、直流叠加冲击电压下电缆接头中的电场分布情况。研究结果表明:在直流电压下,随着温度的升高电缆接头内的最大电场强度(简称场强)及XLPE/SR分界面的切向场强会大幅增加,而且绝缘内最大场强出现位置也会由高压屏蔽端部转移到应力锥根部;当直流叠加冲击电压作用时,接头内的电场分布会出现3个场强极大值点,压接管端部高压屏蔽内侧的场强最大,且不随冲击电压极性和线芯温度的变化而变化;直流叠加正极性冲击电压作用下,压接管端部SR材料内侧和应力锥根部XLPE材料内侧的场强随温度的升高而降低,而在直流叠加负极性冲击电压作用下这2点的场强随温度的升高而增大。以上研究结果可供高压直流电缆附件设计参考。

Abstract： The electric field distribution in HVDC cable accessories mainly depends on the insulating materials＇ electrical conductivity rather than their relative dielectric constant. Because of the large difference in electrical conductivity be- tween cross linked polyethylene （XLPE） and silicone rubber （SR）, and the great influence of electric field strength and temperature on the conductivity of accessory insulating materials, designing DC cable accessories becomes more complex than designing AC accessories. Therefore, we simulated the electric field distribution of cable joint under various temper- ature gradients and under DC voltage, and superimposed DC impulse voltage respectively. The results show that the maximum electric field in the cable joint and the tangential electric field on XLPE/SR interface increase significantly with the increase of temperature under DC voltage, and the position of maximum electric field strength shifts from the head of high-voltage screen to the head of stress cone. When a combined DC/impulse voltage is applied, the electric field in the cable joint appears to have three maximum points, among which the inner side of high-voltage screen closed to the head of connecting pipe has the highest value, and this result is irrespective of the polarity of impulse voltage and the tempera- ture of cable core. At the inner sides of both the SR materials closed to the head of connecting pipe and the XLPE materials around the head of stress cone, the electric field decreases with the increase of temperature under combined DC/positive impulse voltage, but increases with temperature under combined DC/negative impulse voltage. The results can be used as a reference for designing HVDC cable accessories.