Modeling of Magnetic Fields in Deformed Air Gaps of Salient Pole Synchronous Machines

Large low-speed drives are designed with a high number of pole pairs, annular and magnetically saturated at rated operation. Large bore diameters tend to unwanted deformations of circular air gap (AG) circumference due to magnetic forces or gravitational forces. The electromagnetic computation with changing geometrical conditions therefore poses a cumbersome non-linear field problem due to its high amount of degrees of freedom. For an accurate predictive model of machine acoustics and vibrations, the study of these topological impacts on the magnetic AG field is indispensable. Particularly when considering an arbitrary AG deformation, related to additional spatial flux harmonics, the computational chain of the finite element method (FEM) involves adaptations at each stage (pre- and post-processing). The proposed modeling approach is universal and reduces the computational effort significantly using finite element (FE) solutions of symmetrical machine parts with varying AG widths. 2-D FE simulations are performed to study the impact of deformations. The results of the approach are compared with FE solutions of a complete 2-D model with an exemplary deformation for validation. The aim of this work is to study both magnetic AG fields and forces efficiently in an exemplary high-pole wind turbine generator with a deformed AG topology by interpolating and assembling appropriately partial model solutions.