回填土高热阻系数下电缆集群敷设载流量的解析计算

Analytical Calculation of Carrying Capacity of Cable Cluster Laying under High Thermal resistance Coefficient of Backfill Soil

IEC60287标准给出了土壤热阻系数一致时电缆集群敷设恒定负荷载流量的解析计算方法,并给出了计及回填土与母土热阻系数差异的载流量修正计算方法.载流量数值计算结果表明该修正计算方法仅适用于回填土相对于母土为良导热介质的情况.寒冷地区为防止四季温差造成地面下沉,回填土通常会选择细沙.细沙中水分较易流失,干燥的细沙热阻系数大于母土热阻系数.以有限元法计算的电缆载流量为基准,深入分析回填土热阻系数较大时,IEC解析计算方法产生误差的原因,并修正了相应的解析计算方法,显著地提高了回填土高热阻下电缆集群敷设载流量解析方法的计算精度.

IEC 60287 standard gives the calculation method of steady state carrying capacity of cable cluster laying in homogeneous soil,and gives the amending calculation method of carrying capacity of cable cluster laying with backfill.The numerical calculation of temperature field and carrying capacity of cable cluster laying shows that the amending calculation method of this ampacity is only applicable to the case that the thermal resistance coefficient of backfill is less than that of the parent soil.Considering the ground subsidence caused by the great temperature difference in Northeast China,the cable engineering designers chose the backfill that has larger thermal resistance coefficient than the surrounding fine sand.the cable cluster calculated in this paper using the finite element method,the load flow as a benchmark,in-depth analysis when the back fill of the resistance coefficient is larger,the reason why IEC simplified calculation method causes calculation error,and gives the corresponding simplified calculation method,improves the accuracy of analytic method to calculate the ampacity of cable in cluster laying obviously.