Research On Thermal Calculation Of Permanent-Magnet Machines

With the development of single-machine capacity, heat generation and cooling are becoming more and more important. It is one of the most important issues in the process of electric machine design and has impact on operating life and operational reliability of the electric machine. Temperature field of permanent-magnet machines is studied in this thesis. Heat generation and temperature distribution during the steady-state operation are researched. The practical operation of the permanent-magnet is a complex physical process, and the heat transfer process in electric machine is also very complex. In order to describe this physical process it is necessary to exactly calculate the value of the thermal parameter of every component of the machine.Losses of permanent-magnet machine are represented firstly in the thesis, and equivalent insulation material is used. Winding insulations and insulation layers are usually ignored in previous temperature field calculation. Although winding insulation is thin, the whole area of stator winding insulation may exceed that of one piece of winding. The coefficient of heat conductivity of insulation materials is very small and has influence on temperature field variation. So it will have a certain effect on the calculation precision. The insulation layers are very thin and the stator winding insulation distributes thickly in the slot, which make the meshing more complex. In order to simplify the calculation process on the basis of acceptable calculation precision, the stator winding insulations are treated with equivalent method in this paper.Second, coefficients of heat conductivity in electric machines are corrected by machines with the same material and temperature test results. According to fluid mechanics and heat transfer theory, fluid field of 90kW permanent-magnet machine is analyzed and calculated. Then air speed distribution diagram is attained. Coefficients of heat transmission are determined by experience formulas. 3D temperature field is calculated and coefficients of heat transmission are corrected by temperature test results. 2D temperature field is calculated and compared to test results, and then the error of 2D results and 3D results is analyzed.Finally, according to the corrected coefficients of heat conductivity and transmission, fluid field and temperature field of 950kW prototype model are calculated by the software of ANSYS with the finite element method. Temperature distribution of the prototype model is attained. And the temperature distributions of the stator, windings and insulations are also analyzed, which offer an instruction to electric machine design.