工作温度和绝缘温差约束下的高压直流电缆接头载流量计算

中间接头是高压电缆线路运行中故障多发的薄弱环节,电缆系统的载流量会因中间接头的结构特点而受到限制。直流下电缆载流量的约束条件与交流不同,不能直接依据交流电缆中间接头载流量的计算方法。为此,文中以直流电缆中间接头的温度场计算等理论研究为基础,提出以接头导体最高允许工作温度和绝缘层内外表面最大允许温差为两个约束条件,确定高压直流电缆中间接头载流量的方法。通过案例分析,将文中方法与IEC 60287标准计算的载流量进行了对比,并就环境温度对载流量的影响进行了分析。结果表明,中间接头的确是电缆系统载流量计算限制条件之一。两个约束条件下的载流量与环境温度的关系曲线将相交于一点,当环境温度小于该点对应温度值时,接头载流量的决定性约束条件为绝缘层内外表面最大允许温差;当环境温度大于该点对应温度值时,接头载流量的决定性约束条件为接头导体最大允许温度。研究结果可为直流电缆系统运行与载流量设计提供参考。

Calculation of Current-carrying Capacity of HVDC Cable Joint Under Constraints of Operating Temperature and Temperature Difference of Insulating Layer

The cable joint is the weak link where faults frequently occur in the operation of high voltage(HV)cable lines. The cable current-carrying capacity can be restricted for the existence of the cable joint. As a constraint on current-carrying capacity of DC cable is different from that of AC cable, it is inappropriate to apply the calculation method of current-carrying capacity of AC cable. Nevertheless, there is currently no calculation method for the DC cable joint. On the basis of theoretical research on simulation calculation of temperature field, a method for determining the current-carrying capacity of HVDC cable joint is proposed with the maximum allowable operating temperature of conductor and the maximum allowable temperature difference in the insulating layer as two constraints. Through case analysis, the proposed calculation method of current-carrying capacity is compared with the method of IEC 60287 standard, and the influence of environment temperature on the current-carrying capacity of cable joint is also studied. The results show that the cable joint is one of the constraints of current-carrying capacity calculation in the cable system. Besides, the relation curve between current-carrying capacity and environment temperature is intersected at one point under two constraints. The maximum allowable temperature difference in the insulating layer is the decisive constraint on the cable current-carrying capacity when the environment temperature is less than the corresponding temperature value at the intersected point; otherwise the maximum allowable operating temperature of the conductor is the decisive constraint on the cable current-carrying capacity. This work is supported by Guangdong Provincial Natural Science Foundation of China(No. 2014A030310371)and China Southern Power Grid Company Limited(No. K-KY2014-31).