Stator copper losses (I2R) –
These are the losses caused by current flowing through the windings of the stator. As seen by the formula, these losses vary with the square of the current through a conductor, and inversely with the conductor material resistance and cross-sectional area.
These losses appear in the stator and rotor. The copper losses in the stator can be exacerbated by higher frequency where the AC currents crowd in outer edges of the conductors (skin effect).
A very common misconception is that a motor with lower voltage and higher current will have higher I2R losses than an identical motor with a higher voltage. Typically the voltage of a motor is changed by changing the number of turns in the windings. The total current flowing through the slots is the same, and the losses and efficiency will be about the same.
Eddy current losses –
These are I2R losses of currents induced in the stator and rotor from AC flux. These losses are why the magnetic steel of the stator, and generally rotor are laminated, to reduce the circulating path for these losses and greatly reduce the losses. Generally these losses are in the magnetic steel laminations, but they can be in any conductive material, for example the finger plates, end bells and frame. These losses vary with the flux density and frequency of the AC flux.
-These losses appear in the stator principally because of the fundamental AC flux, and in the surface of the rotor where although principally DC flux is present, but some AC flux is induced from slot passing.