超高压大截面电力电缆线路热膨胀计算分析

Analysis and Calculation of Thermal Expansion of EHV Cable Line with Large Size Conductor

为了解决电缆导体温升因负荷变化而变化,导致电缆线路热胀冷缩的问题,工程应用中通常采取蛇形敷设电缆线路。特别是隧道内的超高压、大长度、大截面电缆线路,蛇形敷设能够有效吸收热胀冷缩引起的电缆线路长度变化,防止电缆接头和终端机械应力损伤。为此,选取回路长度为1.2 km的2500 mm2/220 kV XLPE电缆线路和回路长度为17.15 km的2500 mm2/500 kV XLPE电缆线路为计算分析实例,分析和计算不同的导体温度、蛇形弧幅值和蛇形长度对弧幅轴向推力大小的影响。针对不同直径的隧道,提出了既节约隧道空间又能限制轴向推力的蛇形弧幅和蛇形长度的推荐值。当电缆线路在紧急过载情况时(导体温度θ=250°C),弧幅轴向伸缩推力约为20 kN;优化设计隧道内电缆线路蛇形敷设的蛇形长度范围为4000~8000 mm,弧幅范围为150~250 mm,蛇形弧幅的轴向伸缩推力亦可以限制在4~6 kN范围内。

Two kinds of EHV cable lines were taken as analytical examples to calculate thermal expansion quantity.One is 2500 mm^2/220 kV XLPE cable line of which the route length is about 1.2 km,and another is 2500 mm^2/500 kV XLPE cable line of which the route length is about 17.15 km.The calculation results prove that the maximum axial push force is about 20 kN when the emergency overload temperature of cable conductor reaches 250（°C）.The optimal design of snake-like laying in size and distribution of bracket,as well as different arc amplitude and pitch,was put forward based on different diameters of tunnel for not only decreasing the axial push force but also economizing space.In other words,when the arc amplitude range from 150 to 250 mm and the pitch range from 4000 to 8000 mm are selected,and the axial push force of the long length cable lines with large size conductors which are installed in the tunnel may be restricted within 4 to 6 kN range.And the arc brackets are the best design for the rounded cross section tunnel to save space.