Efficient Calculation of the Strand Eddy Current Loss Distributions in the End Stepped-Stator Region of Large Synchronous Generators

This paper proposes a computationally efficient method to analyze the eddy current loss of the stator winding strands in the end stator region of large synchronous generators. The stepped shape with increased radii of the stator end packets exposes the stator coils to the intensive radial airgap flux and leads to winding temperature rise due to the resultant eddy currents. In the end region, the profile of the proximity loss induced by the slot leakage flux varies axially due to the variation of the slot configuration. In this paper, a quasi-3D formulation of the generator end region is adopted to account for the impacts of the stepped stator geometries and end fringing effect on the airgap flux. Then, the airgap flux impinging each copper strand is solved based on the conformal mapping method that allows for the slotting effect. Furthermore, a subdomain field model is proposed to predict the cross-slot leakage flux distribution with different slot/coil configurations. The strand eddy current loss density is then estimated based on the magnetic field solved in this region. The method is verified by the agreement between the results generated by the proposed efficient method and the corresponding 3D finite element analyses (FEAs), which are validated by the agreement between their predicted results and the measured temperatures.