Coupled finite-element-analytic technique for prediction of temperature rise in power apparatus

In order to design the power apparatus such as bus bar or power cable, the current carrying capacity (or ampacity) should be determined exactly since it is limited by maximum operating temperature. The temperature rise in the power apparatus is due to Joule´s loss in the current carrying conductor and due to the induced eddy current in the tank. This paper presents a new technique that can be used to estimate the temperature rise in the extra high voltage bus bar. In this paper, the power losses are calculated from the magnetic field analysis for various materials when ac current flows into the single- and three-phase bus bar and are used as the input data to predict temperature rise for the thermal analysis. However, it is not easy to apply the heat transfer coefficient on the boundaries correctly, because the coefficient is not a constant, but depends on temperature as well as model geometry, etc. The heat transfer coefficient is calculated according to the model geometry and varying temperature and is coupled with the finite element method. The temperature distribution in the bus bar by proposed method shows good agreement with the experimental data, compared to that of the analytic method using fixed coefficient