Calculation Of Thermal Distribution And Ampacity For High-voltage Power Cables By Using Multi-physics Coupled Model

Power cables are widely used in many electric power transmission and distribution systems. To operate cable networks securely and stably, it is quite important to accurately estimate its ampacity. The methods of calculating the cable ampacity include analytical method, numerical method, and experimental method. Determining the ampacity of power cables by experiment is high cost. The analytical approach based on IEC-60287 has been widely used by most engineers to calculate the ampacity of power cable for its ease of use, yet at the cost of accuracy. But in recent years, numerical method based on the finite element method gains more and more attention on the calculation of the cable ampacity, which has overcome the shortcomings of the two previous methods.In this paper, a multi-physics coupled model is proposed and numerically calculated by finite element method(FEM). Case studies of different layout of power cables are given. This paper mainly for the following research:(1) The calculation of thermal distribution and ampacity for a single-phase cable, of which the surface temperature is set at 42.6℃, is conducted by using electromagnetic-thermal coupled model. Calculation using IEC-60287 and experiment are also made for comparative purpose. The thermal distribution and ampacity obtained from our model agrees very well with that from IEC-60287 and experiment.(2) The calculation of thermal distribution and ampacity for underground directly buried cables is conducted by using electromagnetic-thermal coupled model, for cables in ducts and groove using electromagnetic-thermal-fluid coupled model. Calculation using IEC-60287 are also made for comparative purpose. Results show that the ampacity obtained from our model agrees very well with that from IEC-60287 for one-circuit cables, yet apparently deviates for multi-circuit cables. Obviously, such deviation is primarily caused by the capability of our model to precisely calculate the losses. Meanwhile, it validates the advantage of our model in calculation of ampacity for multi-circuit cables.(3) The calculation of thermal distribution and ampacity for the cable under specified laying conditions, which are not pointed out clearly in IEC-60287 standard, is conducted by using multi-physics coupled model. Results show that the multi-physics coupled model computed by using finite element method(FEM) is an effective means to calculate the ampacity of the cable under special structure and complex laying conditions.