Numerical Computation On Temperature Field Of Underground High Voltage Cables

With the implementation of the retrofit of city and countryside electrical grid, more and more underground cables are installed in power system. The temperature of the insulated layer is not allowed to exceed the temperature limit. There are lots of variable factors that affect the heat dissipation of cables, so it will not meet the actual needs to determine the ampacity of the cables only according to the regulations. To insure the safe and steady operation of cables, it is meaningful to simulate the thermal behavior of underground cables in accurate method.A computational program used to compute the steady state temperature field and ampacity of direct buried cables is complied, in which finite volume method is applied to discrete the heat transfer equation and combinatorial coordinates method is adopted to solve the problem brought by the boundary difference of soil and cables area. Uneven mesh and alternate direction iteration method quicken the solving speed. Due to all kinds of factors affecting the ampacity can be taken into consideration in the program, the model can much closely approach to the fact. The comparison with results of IEC—60287 proved the validity and reliability.A fast program based on the combination of the merit of equivalent heat circuit method and numerical calculation is complied. Regarding the cable as point heat source, the numerical computation is only in process in soil area and the temperature drop of the layers of cables is obtained by equivalent heat circuit, in which the connection of the two areas is by quadratic interpolation in the soil circuit.On the basis of direct buried cables program, through the calculation of air equivalent thermal conductivity, program used to compute the steady state temperature field and ampacity of cables laid in dispersed- installed pipes is complied. The translation of eccentric circle into concentric circle is proceeded in the eccentric form of cables in pipe. Through the deprivation of quadratic interpolation in uninformed media, the resolution of the cables in compact arrangement pipes is obtained.Through the analysis of the simulation of ampacity of underground cables in different burial conditions, the good suggestions of the layout of underground cables are presented.