Importance of Iron-Loss Modeling in Simulation of Wound-Field Synchronous Machines

Effect of hysteresis, eddy-current and excess-loss modeling on the 2-D field solution of 12.5-MW and 150-kVA wound-field synchronous machines is studied. The study is performed by comparing the differences in the solutions obtained with three different finite element formulations: one with iron losses fully included, one using only single-valued material properties, and one completely neglecting the iron losses from the solution. The electrical operating points, i.e., the terminal currents and powers are found to be only little influenced by the iron-loss model. However, the rotor eddy-current losses are found to be overestimated, if the skin effect of the eddy currents is uncoupled from the solution. Using single-valued material properties instead of hysteretic ones has a smaller effect on the rotor side, but increases the hysteresis losses in the stator. The effects on the total core losses thus depend on their distribution between the stator and the rotor. It is concluded that using single-valued material properties is reasonable in order to improve the computational performance despite the slight overestimation in the computed core losses. However, for accurate modeling of the rotor losses, the skin effect of the eddy currents should be included in the solution.