Losses in Induction motor


The losses in an induction motor can be classified as
  1. Constant losses. and,
  2. Variable losses

Losses in Induction motor

Constant Losses :


     Constant losses are those which doesn't affect due to variation in load conditions on the motor. These losses remain constant throughout the operation. These losses are further classified as iron and Mechanical losses.


i. Iron Losses :

     Iron or core losses occur in the stator and rotor core. These include eddy current losses and hysteresis losses. The iron losses depend on the frequency. The rotor frequency is very small which is slip times the supply frequency. Hence the rotor iron losses are very small and may be neglected.


ii. Mechanical Losses:

     Mechanical losses to those which occur without any use of electricity. As the motor shaft rotates when supply is given, friction at the bearings will tend to stop the motor. Eventually, this decreases the speed of the shaft and it is considered as the loss. Therefore friction and windage losses of the motor are considered as the mechanical losses, as this loss is very small and there are considered to be constant losses.



Variable Losses : 


     Variable losses of an induction motor include copper losses of the field winding in the stator and armature winding copper loss if it is a slip ring induction motor. This loss changes with a change in load on the motor, i.e., increases if load increases and vice-versa. Hence these losses are not constant for a long period of time, and therefore it is known as ' Variable Losses '.

     If we combined stator copper losses with stator iron losses and form total stator losses. Then rotor copper losses can be separately noted as,

Total rotor copper losses : 3 I22 
R2

Where
  • I2 = Rotor current / phase at a particular load and
  • R2 = Rotor resistance / phase.


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