Material Characterization and Stator Core Loss Computation of Synchronous Generators With Stacking Force Accounted

In electrical machines, electrical steels are stacked together with forces to maintain mechanical rigidity. This stacking force alters the magnetic properties of laminated steel and consequently changes its loss behavior. Failing to consider the stacking force can lead to increased errors in core loss computation. This article investigates the impact of stacking force on the stator core loss of synchronous generators. Magnetic properties (magnetization and loss) of the electrical steel M400-50A are measured in a special-designed ring core test, and during the test, the ring core is subjected to normal pressing force controlled in closed loop. This test reveals that stacking stress reduces permeability and results in more specific loss for a given flux density. Furthermore, it demonstrates that the weakening of magnetic properties is nonlinearly correlated with the applied stress. Two core loss models are used to compute the stator core loss of a 100 kVA synchronous generator. Lab tests conducted on this generator demonstrate a noticeable improvement in computational accuracy when the stacking force is considered. Among the two core loss models, the two-component frequency-domain Bertotti method requires less implementation effort and yields better accuracy.