覆土层含水率对直埋式电缆散热特性的影响研究

Study on the influence of water content of covering soil on the heat dissipation characteristics of direct buried cables

目的:研究直埋电缆周围环境因素对其温度场的影响规律及其显著程度。方法:根据电力电缆标准IEC-60287的适用性,应用有限元软件COMSOL建立了水平排列下的电缆计算模型,仿真计算一定环境条件下的温度场和载流量,分析覆土层(土壤、回填砂)对电缆的影响。结果:随覆土层含水率的增加,水分填充覆土层空隙取代空气,对覆土层导热系数产生显著影响。模拟计算表明,覆土层的含水率直接影响直埋电缆的缆芯温度和载流量,当含水率较低时,随覆土层含水率的增加,电缆散热增强,缆芯温度逐渐下降;当含水率增大至饱和状态后覆土层颗粒表面出现水膜影响换热,电缆温度出现升高。电缆载流量变化趋势与电缆芯温度相反。结论:直埋电缆采用回填砂作为覆土层具有比土壤更高的传热性能,有助于电缆的安全运行。

Aims: This paper investigates the influence of environmental factors on the temperature distribution of buried cables and its corresponding significance. Methods: According to the applicability of power cable standard IEC-60287, the cable calculation model under horizontal arrangement was established by using the finite element software COMSOL to simulate and calculate the temperature distribution and carrying capacity of buried cables under certain environmental conditions.The impact of overburden layer(soil, backfill sand) on the cable was analyzed. Results: With the increase of moisture proportion, the air was replaced by the liquid water that filled the gaps of the overburden, thus exerting a significant effect on the thermal conductivity of the overburden. The simulation results showed that the moisture content of the overburden had a direct influence on the core temperature of the buried cable and the carrying capacity as well. When the moisture content was relatively low, the heat dissipation of the cable increased with the increase of the moisture content of the overburden;and the cable core temperature decreased gradually. When the moisture content increased to a saturation state, the moisture film on the surface of the overburden affected heat conduction extensively, which led to the temperature increase of the cable. The deviation of the current carrying capacity was opposite to the temperature difference of the cable core. Conclusions: Employing backfilling sand as the overburden of the direct buried cable shows a better heat transfer performance than that of the ordinary soil. It is a promising application on the safe operation of the power cable.