穿过不利散热区域地下电力电缆周期负荷因数的研究

Research on Cyclic Load Factor of Underground Power Cable Across Thermally Unfavorable Regions

在实际电缆敷设时,由于受到环境条件的限制,电缆有时会穿过不利于散热的区域,此时电缆线路的周围环境为非均匀介质环境,在不利散热区电缆段的环境温度或者周围土壤热阻高于其线路的其他地方,导致处于此区电缆段导体成为热点,其会呈现电流峰值,从而会影响整条线路的载流量。文中通过分析电缆周围介质不同的热特性,且考虑电缆线路存在轴向热流,建立了不利散热区的电缆离散的空间三维热路模型;基于标准IEC 60287和IEC 60853电缆载流量的计算,提出不利散热区电缆周期负荷因数的计算方法,从而获得电缆日(24 h)周期内允许电流峰值。经过MATLAB软件进行计算仿真后,得到沿电缆轴向的导体温升分布值。结果显示:处于不利散热区的电缆段在周期负荷运行时,会使电缆线路载流量的峰值降低,本例敷设条件下,三回路YJV8.7/10kV 3×300电缆载流量降低达30%左右。通过文中的修正计算,将会为地下电缆安全可靠的运行及电力部门工作人员解决相关问题提供了一种有效的参考。

In the laying of cable,it sometimes across the thermally unfavorable regions due to the limitation of ambient condition. At this time,the surrounding environment of the cable line is of non-homogeneous environment. The ambient temperature of the cable section at the thermally unfavorable region or the thermal resistivity of surrounding soil is higher than those in other places of the line,causing the conductor of cable section to be hot bottleneck,which shows peak current and affects current carrying capacity of the whole line.In this paper,the three-dimensional thermal path model of cable of cable discretization of thermally unfavourable region is set up by analyzing different thermal characteristic of surrounding medium and considering axial heat flow of cable. Based on the current carrying calculation of cable in IEC 60287 and IEC 60853,the calculation method of periodical load factor of cable in the thermally unfavorable region is proposed so to obtain the permissible current in the period of 24 hours. The temperature rise distribution of the conductor along the axial direction of cable is obtained after calculation and simulation by MATLAB software.The result shows that the cable operating in the periodical load section in the thermally unfavourable region will reduce the peak of current carrying ability of the line and,in case of unfavourable laying condition,the current carrying capability of three circuits YJV8.7/10kV 3×300 cable reduces around 30%. The calculation in this paper can provide a kind of effective reference for safe and reliable operation of underground cable and for solving related problems by the utility staffs.