Impact of rotor winding and stator stepped end core on magnetic force distribution on stator end-winding of turbogenerators

Impact of the rotor end-winding on the force distribution of the stator end-winding using equivalent current sheets or a concentrated coil in each rotor slot has been so far considered in the literatures. However, the impact of the stator stepped end core on the force has not been studied yet. In this paper calculation methods for magnetic force exerted on the stator end-winding are first reviewed comprehensively; then the impact of some parameters on the magnetic force distribution on the stator end-winding of a 2-pole, 200 MVA turbo-generator under sudden three-phase short-circuit are studied. Three-dimensional finite element method (FEM) based on the reduced magnetic scalar potential formulation is used. The stator and rotor end-windings actual geometry is taken into account, except their cross section areas which are approximated by combination of straight line segments. To simplify the meshing process, stator stepped end core geometry is replaced by equivalent ramp geometry. Short-circuit currents of the generator windings are computed using two-dimensional transient FEM. It is shown that these parameters affect the stator end-winding magnetic force, particularly in the involutes part of the stator end-coils.