Analysis Of Circulating Current Losses And Electromagnetic Force For Asymmetric-branch Winding In Turbo-generator

In large turbo-generator, increasing the number of parallel branches can effectively relive the basic copper losses and temperature of stator winding. However, the stator winding branches always are asymmetric along with the increasing of the number of parallel branches. The asymmetric-branch winding of turbo-generator is designed with magnetic motive force(MMF) method in view of the characteristics that turbo-generator has less slots and poles, and the circulating current losses and electromagnetic force of asymmetric-branch winding are calculated in this paper.Firstly, the branches MMF distributions of asymmetric-branch winding in turbo-generator are obtained with analytic method which is based on the MMF distribution of single short-distance winding. And the amplitude and phase of fundamental waves are obtained with Fourier decomposition. Thus, connection schemes of asymmetric-branch stator winding are obtained through controlling the degree of differences between amplitudes and phases of branches MMF, and the harmonics of stator winding are calculated with analytic method.Secondly, the 2-D finite element solving models of turbo-generator are established based on the different connection schemes of asymmetric stator winding. The circulating currents of turbo-generator under no-load condition are obtained with responding numerical calculation method. The harmonic characteristics of branches circulating currents in asymmetric-branch winding are obtained with Fourier decomposition, and then the circulating current losses of asymmetric-branch winding in turbo-generator are obtained. In addition, the change laws of circulating current and circulating current losses of asymmetric-branch winding are calculated under different eccentricities and excitation currents with no-load condition. The calculation results are compared with symmetric-branch winding.Finally, the 2-D finite element transient field solving model of turbo-generator is established, and the magnetic fields under no-load and rated condition are calculated with numerical calculation method. And on this basis, the electromagnetic force on the surface of rotor outer circle and unbalanced magnetic force as well as the electromagnetic force in stator winding are calculated. Meanwhile the influences of static eccentricity on electromagnetic force are researched.