Windage losses in Electric 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 energy expenditure, which is called windage loss. It represents a loss of power.

Windage loss in rotatory machines occurs due to air resistance to the armature. Therefore, in order to even start a motor, the machine needs to overcome friction, 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.

windage loss in electrical machines

The windage loss depends on the design and shape of the rotating object. In synchronous machines, salient pole rotors have more windage loss than non-salient or cylindrical rotors. If the fan is used in motors for cooling, the windage loss occurs in the fan as well.

The higher-speed electrical machine has more windage loss. Therefore, it is specially designed to minimize windage loss.

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 the theoretical equation.

windage loss formula

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