Page 687 - Basic Electrical Engineering

Figure 8.11 (a) Stator and rotor windings of a three-phase induction motor; (b) simplified corss-
sectional view

Through this rotating magnetic field, power is transferred from stator to the
rotor via the air gap. The power transferred from stator to rotor through the

magnetic field in equal to . This is the input power to the rotor since

there in no power loss in the air gap. Torque will be developed in the rotor
which will cause the rotor to rotate at a speed N . The power developed by
r

the rotor is .

The difference between the input power and the power developed is the
loss in the rotor. In the rotor there will be copper loss and core loss.
Therefore,

= Rotor copper loss + Rotor core loss

The core loss (sum of Hysteresis loss and eddy current loss) in the rotor is
negligible as the frequency of the induced EMF in the core will have

frequency, f = Sf. f is small, and hence core loss can be considered
r
r
negligible.
Thus,