Electromagnetic Forces on the End Windings and Terminal Connections of Large Electric Machines: Calculations, Considerations, and Capabilities for Stress Analysis

End windings are the integral part of electrical machines, which should be mechanically supported through appropriate measures. The determination of electromagnetic force distribution under the worst-case scenario is a prerequisite for conducting the mechanical stress analysis. This paper presents a detailed description of a proper approach for this kind of force calculation. Large turbo-generators have been targeted for this purpose, although this method can be extended to other machines. 2D transient FEA has been employed to obtain the required information for the worst-case scenario, i.e. the sudden three-phase short circuit at the machine terminals. These data, including the stator currents, field current, and rotor position, are taken as the inputs of 3D magnetostatic models, which provide the adaptive meshing capability. The force calculation has been repeated for different setups to investigate the amount of details that should be taken into account while creating the FE models. It reveals that the active (e.g. cores) and inactive (e.g. support brackets) surrounding magnetic materials as well as the rotor current and position are the most influential factors on both the distribution and magnitude of the end winding forces. Furthermore, due to conceptual and geometrical differences, both the drive and non-drive ends of the machine have been analyzed. Therefore, the forces on the circuit rings and terminal connections could also be evaluated. The geometry of the terminal connections has been modified according to these results to achieve an acceptable force distribution.