Experimental determination and numerical evaluation of core losses in a 150-kVA wound-field synchronous machine

The losses in the laminated core of a 150-kVA wound-field synchronous machine are investigated with calorimetric measurements and a numerical iron-loss model for steel laminations. Both grid supply and pulse-width modulated inverter supply with 1 kHz and 6 kHz switching frequencies are studied. The effect of rotor lamination material on total core losses is studied by measuring and simulating the machine with three prototype rotors, the first one being stacked of insulated 0.5-mm Fe-Si sheets and the last two of uninsulated 1-mm and 2-mm steel sheets, respectively. At no load, the losses in the frame of the machine are shown to be extremely significant with voltages above the rated one. The results on load operation show that the additional inverter-induced core losses are significantly larger with the thicker sheets. The rotor eddy-current loss is the most affected component because of loading and the distorted supply voltage. However, unlike expected and predicted by the model, the differences in the losses between the 1-mm and 2-mm rotors are negligible in no-load operation and relatively small also at load operation.