Windage losses in Electric Machines

windage loss in electrical machines 

Windage is the name usually given to air resistance inside rotating electrical machines like generators or motors. Windage losses also occur in machines such as turbines and gearboxes.When the shaft rotates, it displaces air.  This incurs an expenditure of energy which is called windage loss. it represents a loss of power.
Wind Turbine Facts
Wind Turbine Facts


Windage loss in rotatory machines occur due to air resistance to the armature. Therefore, in order to even start a motor, the machine needs to overcome friction and windage torque and inertia due to its weight to start rotating. Windage is the churning effect of the rotating armature in the confined space inside the field coils. Even a smooth airflow would take some power to achieve, the very turbulent conditions inside the motor take much more power.

The windage loss depends on the design and shape of the rotating object. In synchronous machine, the salient pole rotors have more windage loss as compared to windage loss in non-salient or cylindrical rotor. If the fan is used in motors for cooling, the windage loss takes place in the fan as well.

The higher speed electrical machine has more windage loss.Therefore, the machines are specially designed to keep the windiage loss minimum.

It is very difficult to determine the windage loss of the electric rotating machine. The friction and windage loss is about 1 % of full load loss.

Windage Loss Formula

The windage loss of the  smooth cylindrical rotor can be estimated by following theoretical equation.

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