Windage Losses in Electric Machines

Windage losses refers to the losses sustained by a machine due to the resistance offered by air to the rotation of the shaft.  Windage Losses occurs in electric rotating machines such as motors and generators.  Windage losses also occur in machines such as turbines and gearboxes.Windage Loss

When the shaft rotates, it displaces air.  This incurs an expenditure of energy which is called windage loss.

The windage loss depends on the design and shape of the rotating object.  For example, in the synchronous machine, salient pole rotors will have more windage loss than non-salient or cylindrical rotors.

In motors where fans are used for cooling, windage loss occurs in the fans as well.

The windage loss increases with the peripheral speed.  Thus a shaft with a larger diameter will have more loss as compared to a shaft with a smaller diameter.  Machines which operate at high speeds will also have higher windage losses.  Hence, these rotors are specially designed with improved aerodynamics.