Losses in Induction motor


      The losses in an induction motor can be classified as

(i)  Constant losses and

(ii) Variable losses

Losses in Induction motor


Constant Losses :

             

     These losses are further classified as iron and Mechanical losses.


i. Iron Losses :


     Iron or core losses occur in stator and rotor core.These include eddy current losses and hysteresis losses. The iron losses depends 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 tends to stop the motor. Eventually this decreases the speed of the shaft and it is considered as the loss. Therefore frictional and windage losses of the motor are considered as the mechanical losses, as this losses are very small and there are considered as the constant losses.



Variable Losses : 

      

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


     It we combined stator copper losses with a 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.



Post a Comment

0 Comments