三维有限元法在局部穿管直埋电缆温度场和载流量计算中的应用

Temperature Field and Ampacity Calculation of Cable Buried in Local Conduit Using 3D Finite Element Method

保护管改变了局部穿管直埋电缆的温度场分布,且保护管部分往往是全线最热点,影响了电缆的载流量。保护管内壁和电缆外壁间包含了1个空气层,空气层内的传热是自然对流、热传导和电缆外表面和保护管内壁间热辐射的多种传热方式的耦合过程,且保护管外和电缆本体又属于固体传热,因此,局部穿管线路的散热是1个流固耦合的过程。为此,电缆本体和保护管外土壤可用热传导方程描述,保护管内空气层的传热需要求解流体的动量方程、能量方程和连续性方程,流体和固体间可以通过边界条件连续性利用迭代法求解。采用三维有限元和涡量-流函数耦合求解了上述流固耦合散热过程,从而求得局部穿管直埋电缆的温度场分布,找出其中的最热点,并利用迭代的方法计算出电缆的载流量。计算实例表明,局部穿管电缆的载流量比全程直埋电缆的载流量要低。

There is an air layer between external diameter of power cables and inner diameter of conduit,and heat transfer of air is a coupling process of air natural convection,air conduction,and radiation.Consequently,heat transfer of power cables and soil can be described by heat conduction equations.The heat transfer of air in conduit can be described by momentum conservation equation,energy equation and continuity equation,and the heat transfer between fluid and solid can be solved by iteration method.Thereby,the 3D finite element method（FEM） and vorticity-stream function are used to solve the coupling equations of fluid structure interaction,moreover,the temperature distribution of underground power cables in local segment of conduit can be calculated.Thus,the hottest point of power cables is found,and the ampacity of power cables is obtained by iteration method.The result shows that the ampacity of underground power cables in local segments of conduit is lower than power cables all directly buried in underground.