Induction Motor

Fig. 1.
  • Even if the machine is lossless we cannot ignore the electrical portion of airgap power which
  • When we subtract friction and windage losses from the developed power then we obtain the shaft power.
  • In Induction machine we do not merge core loss and mechanical loss as rotational loss because there location inside the machine is different and hence both cannot be directly added.

Fixed loss

  • Core loss
  • Bearing friction loss
  • Brush friction loss
  • Windage loss
  • In Squirrel Cage Induction Motor (SCIM) we do not use of a brushes so brush friction loss does not appear in SCIM.

Variable Losses

  • Stator Copper (Cu) loss
  • Rotor Copper (Cu) loss
  • Brush Contact Drop (SRIM) (Slip Ring Induction Motor)
  • Stray load loss.
  • While computing the efficiency we made to consider the brush contact drop but in the condition of maximum efficiency brush contact drop does not appear.
  • To reduce the bearing friction we make use of lubricant such as grease in small induction motor and lube oil in large Induction motor.
  • Lube oil will also act as a coolant.
  • Windage loss depends on air gap and since airgap is higher in SRIM so windage loss of SRIM is higher then SCIM.


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