Numerical Computation On Temperature Field And Ampacity Of Underground Cables

The high-voltage electrical power transmission in urban areas makes use of underground cables in general. The temperature of the insulated layer is not allowed to exceed the temperature limit. Especially, for the form of cable pipe , air between cable and pipe results in bad heat transfer from cable to soil. To insure the operation of cables in safety and in gear, there is an interest in accurate methods for predicting the thermal behavior of underground cables.A computational program in case of steady state and transient conditions is compiled to calculate temperature field and ampacity of underground cables which are covered up directly or buried in a pipe in advance. The governing equations are solved with the finite difference method and both cables and soil are incorporated in the program with combinatorial coordinates. Through the validation of experiment, the computational error is less than 5 percent, which is needed in the engineering.On account of the coefficient of thermal conductivity of soil has great influence on the ampacity of cables, and the factors concerned with the coefficient of thermal conductivity are numerous, therefore, the coefficient of thermal conductivity, which is considered as the computational criterion of temperature field of underground cables, is needed to be determined exactly. An experimental platform of soil's coefficient of thermal conductivity is developed. The platform is good-looking, having a good visual effect convenient and simple to be operated. The coefficient of thermal conductivity is measured accurately by it, and it makes a dependable guarantee for accurately computing the ampacity.