Research On Analysis Method Of Circulating Current And Circulating Current Losses In Stator Bar Of AC Machine

Generally, the stator bars of AC machine are composed of several parallel strands. The influence of the leakage magnetic field will cause circulating current flowed around strands, which increases with the increase of machine capacity. The circulating current will lead to a series of problems such as uneven temperature rise, which threatens the insulation of bar and the service life of machine seriously. As a result, it is especially important to further reduce the circulating current and circulating current losses based on the traditional transposition and find accurate method to analyze them as well.Firstly, the scaled boundary finite element method(SBFEM) to analyze circulating current and circulating current losses is described. Based on Laplace equation and Poisson equation, the SBFEM equations are expressed respectively in detail. In addition, the problems related to division of solved domain and combination of passive and active region are analyzed. Several examples are compared with finite element method(FEM) to verify the accuracy of SBFEM.Secondly, the mechanism of circulating current in strands is analyzed, and the mathematical model of two dimensional stator bar with no transposition is set up by SBFEM. Then the circulating current and circulating current losses are calculated. In comparison with FEM, the results indicate that SBFEM can be verified in analyzing magnetic field problems of electric machine.Finally, the traditional transposition methods of stator bars and their working principle of reducing circulating current are introduced. Based on the traditional transposition methods, a new improve transposition method is proposed and described. Using the three dimensional FEM, the circulating current and circulating current losses of strands by traditional transposition method and improved transposition method are calculated and analyzed. Through the experiment of circulating current, the results between measurement and simulation show that the accuracy in modeling transposition bars and calculating circulating current losses by three dimensional FEM is verified.