Losses in Induction Motor

Losses in Induction Motor

The losses in induction motor are broadly categorized into two classes, namely constant losses and variable losses.

Constant losses in Induction Motor

These losses do not depend on the load hence they are known as constant losses. These can be further categorized as under:

  • Core losses: These include eddy current and hysteresis losses in stator as well as in rotor magnetic core. Eddy current losses in rotor core are negligible since rotor current frequency is very small in the order of 0.5 to 2 Hz.
    These losses of induction motor are constant since these depend upon voltage and frequency which is practically constant.
    The hysteresis losses can be reduced by selecting a high permeability material for the core. The eddy current losses can be reduced by using the laminated cores instead of solid ones.
  • Friction and windage losses: These losses are also constant losses as these losses depend upon the speed of the induction motor. The speed of the induction motor is approximately constant.

The no-load test is performed on induction motor to determine the constant losses in the induction motor.

Variable Losses of Induction Motor

These are:

  • I2R losses in the stator winding.
  • I2R losses in the rotor winding.

These losses occur due to the resistance of rotor winding as well as the resistance of stator winding. These losses are also called copper losses.
These are proportional to the square of stator and rotor currents respectively. As these currents depend on the load, copper losses vary with the change in load.
Hence these are known as variable losses. The blocked rotor test is performed on induction motor to determine the variable losses.

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