基于电磁-热-流耦合场的多回路排管敷设电缆载流量数值计算

多回路电缆以集群方式敷设时,各回路之间的电磁耦合和热耦合都将加强,对电缆导体线芯和金属外护套的交流电阻及涡流损耗的影响均不可忽略。为准确计算四回路电缆在4×4孔排管敷设方式下的载流量,借助于Comsol和MATLAB软件建立电磁-热-流耦合物理场有限元模型,将电磁场、温度场及排管内空气流速场耦合求解。首先通过求解电磁场计算电磁热损耗,然后作为载荷施加于传热模型进行温度场分布计算。该模型对电缆复杂的邻近效应、趋肤效应进行直接仿真计算,考虑了金属材料电阻率随温度的变化关系,且传热模型中耦合了空气自然对流、热辐射和固体热传导3种导热方式。利用所提模型对6种排列方式下的电磁热损耗和温度场分布进行计算;并利用二分法计算相应的载流量。结果表明,排列方式对电缆间的邻近效应有较为显著的影响,优化排列方式可降低电缆损耗、提升载流量。

Numerical Caculation of Ampacity for Multi-loop Cable System in Ducts Based on Electromagnetic-thermal-flow Coupled Field

When multi-circuit cables are laid in cluster, the electromagnetic and thermal coupling between each circuit will be strengthened which has notable effect on the AC resistance and eddy current loss of the conductor wire and the metal sheath. In order to accurately calculate the ampacity of four-circuit cables in 4×4 duct installation, the finite element model of magnetic-thermal-flow coupled physical field was built by using Comsol and MATLAB software to solve the electromagnetic field, thermal field and velocity field in a coupled way. Firstly, the electromagnetic heat loss was calculated by solving the electromagnetic field, and then the computed heat loss was taken as the the load of heat transfer model for caculating the distribution of temperature field. In this model, the proximity effect and skin effect are directly simulated and calculated, and the relationship between the resistivity of metal materials and the temperature are taken into consideration. Meanwhile, the model is coupled with 3 kinds of heat transfer mode which are air natural convection, heat conduction and heat radiation. Lastly, the electromagnetic loss and temperature field distribution of cables under 6 kinds of arrangement in 4×4 duct installation was calculated by using the proposed model, and then the ampacity was obtained after iterative computation. The results show that the arrangement has a significant effect on the proximity effect between cables and using the optimal one can reduce the electromagnetic loss and improve the ampacity of cables.