Effect of rotor pole-shoe construction on losses of inverter-fed synchronous motors

The effect of rotor pole-shoe construction on the electromagnetic losses of a 12.5-MW frequency-converter-fed wound-field synchronous motor is studied by numerical simulations. The simulations are done with the finite-element method including a dynamic model for the eddy-current, hysteresis, and excess losses in the core laminations. In the machine under examination, a reduction of 6.8% in the rated-load total electromagnetic losses was achieved merely by modifying the rotor pole-shoe shape and the damper-winding slots. Furthermore, a 15.4% reduction was achieved by removing the damper winding and changing the rotor lamination material to a 0.5-mm Fe-Si sheet instead of the original 2-mm steel sheet. Calorimetric measurements with a 150-kVA generator confirm the significant effect of the rotor lamination material under frequency-converter supply.