The various power losses in an induction motor can be classified as,
Core losses occur in stator core and rotor core. These are also called
iron losses. These losses include eddy current losses and hysteresis
losses. The eddy current losses are minimised by using laminated
construction while hysteresis losses are minimised by selecting high
grade silicon steel as the material for stator and rotor.
The iron losses depends on the frequency. The stator frequency is
always supply frequency hence stator iron losses are dominate. As
against this in rotor circuit, the frequency is very small which is slip
times the supply frequency. Hence rotor iron losses are very small and
hence generally neglected, in the running condition.
The mechanical losses include frictional losses at the bearings and
windings losses. The friction changes with speed but practically the
drop in speed is very small hence these losses are assumed to be the
part of constant losses.
This include the copper losses in stator and rotor winding due to
current flowing in the winding. As current changes as load changes as
load changes, these losses are said to be variable losses.
Generally stator iron losses are combined with stator copper losses at a
particular load to specify total stator losses at particular load