Simulation Study On Temperature Field And Current Carrying Capacity Of XLPE Power Cables Under Different Laying Methods

The load capacity is one of the most important indicators of the transmission capacity of power cables.Accurate assessment of the load capacity of power cables is of great significance to enhance the transmission capacity of power cable lines,improve the reliability and operating economy of power cables and extend their service life.However,the harsh and complex environment in which power cables are laid in actual engineering poses great difficulties for the accurate measurement or calculation of the load capacity.For the above reasons,this paper takes 110 k V and 35 k V cross-linked polyethylene(XLPE)cables as the research object,and uses COMSOL finite element software to establish simulation models of these two voltage classes under different laying methods,and calculates the temperature field distribution and the value of the load capacity of the cables to study the effect of different laying methods on the temperature rise of the cables.The effect of different laying methods on the temperature rise and load capacity of the cable was studied.The details of the study are as follows:Firstly,the differential equations of heat conduction,heat convection and heat radiation for the three heat transfer methods and the corresponding temperature field boundary conditions are introduced,the multi-physics field calculation principles for direct burial and trench laying are analyzed based on heat transfer,and the simulation models for XLPE cables and different environments under direct burial and trench laying methods are established using COMSOL finite element simulation software respectively.Secondly,on the basis of direct burial,various factors such as backfill,concrete protection plate and casing are considered to establish the coupled model of electromagnetic,thermal and fluid fields,and the effects of these factors on the change of cable temperature field and load capacity under the direct burial method are analyzed.The results show that the backfilling of sand can improve the cable load capacity,but with the increase of the backfilling thickness,the improvement of the cable load capacity becomes slower;the effect of adding concrete protection plate to improve the load capacity is not obvious,and the improvement is less than 0.5% compared with that without concrete protection plate;the filling of high thermal conductivity material in the row pipe can improve the cable load capacity,and compared with the case without filling,the difference between filling high thermal conductivity material in all three phases and Compared with the case without filling,the improvement of the load capacity of the middle phase filled with high thermal conductivity material and the other two phases filled with low thermal conductivity material is higher than 50%.Finally,the effect of trench laying on cable temperature rise and load capacity was studied.The results show that when the cables laid in the trench are of the same voltage level,the lower the number of loops laid,the higher the load capacity of the cables;for 110 k V and35 k V cables,the load capacity is increased by 9.55% and 8.86% respectively when the number of loops is reduced from three to two.The cable spacing has a greater impact on the load capacity increase,and the load capacity decreases gradually as the cable spacing decreases,especially when the spacing is smaller than the cable radius,and the load capaci ty decreases the most when the cables are arranged next to each other.For the trench isometric laying of different voltage level cables,the load capacity of high voltage level cables has increased,the load capacity of low voltage level cables is related to the location of the circuit arrangement,that is,the load capacity is increased when located above the high voltage level cables,and vice versa,there is a decline;trench is not equal spacing laying of different voltage level cables,the load capacity of each voltage level cables rise and fall is not related to the location of the circuit arrangement,all show a decreasing trend,and the low voltage level of the cable load capacity decline significantly.When the multi-loop cables are irregularly mixed,the temperature field distribution in the trench is extremely uneven,and the load capacity of each voltage level cable drops significantly.