Analytic Algorithm For Additional Losses Of Stator Transposition Bar In Large AC Machine

The large AC machine is an important device to realize the conversion between mechanical energy and power.The structure of stator winding is usually in the form of a hard coil.As the stator winding is the core component of large AC machine,the related design and manufacture technology are the key problems in the design process of large AC machine.To reduce the effect of skin effect,the stator bar is usually consist of multiple strands and connected in the nose end.The strands of slot part and end part are located in a complex alternating magnetic field when an alternating current is passed through the stator bar,resulting in the additional losses appear in the stator winding.Due to the existence of additional losses,the heat problem of stator transposition bar is becoming more and more serious,which threatens the safe and stable operation of large AC machine.The additional losses of the stator bar include the circulating current loss and the eddy current loss.In this paper,taking a 140 MW hydro generator as an example,the analytic algorithms for additional losses of stator transposition bar in large AC machine are studied.Aiming at the problem of analytical calculation for the stator winding circulating current loss,an improved leakage inductance electromotive force method is proposed to improve the irrational assumption in the traditional algorithm.The distribution of the leakage magnetic field in the slot and end part is analyzed.The analytical formulas of the leakage inductance electromotive force in slot and end part are deduced,and the calculation method of the strand current and the circulating current loss are given.The leakage inductance electromotive force,the strand current and the circulating current loss in the case of 360 degree complete transposition and less than 360 degree transposition are calculated by the presented analytical formula.For the analytical calculation of the eddy current loss of the transposition strand,a conductor subdivision method by considering the actual transposition structure is proposed,and an equivalent circuit model suitable for the eddy current loss calculation with different transposition type is established.According to the distribution of leakage magnetic field in slot and end part of stator winding,the subdivision model and calculation method of eddy current loss for transposition conductor in slot and end part of stator winding are given respectively.The analytical calculation for the additional losses of the stator transposition bar is verified by establishing the experimental test platform of stator transposition bar in single slot.Combining the analytical calculation method and optimization algorithm of additional losses in Roebel bar,taking the additional losses reduction of stator transposition bar in large AC machine as the goal,selecting the incomplete transposition angle and other parameters as the optimization variables to optimize the design of stator transposition bar in large AC machine,a transposition type is present which can reduce the additional losses effectively.