Electrical Output power in Train for Light and Fan (Three Brush Generator)

Method of Obtaining Constant Electrical Output power in Train

The most important requirement of train lighting is to obtain constant output irrespective of locomotive speed.
To achieve this there are three methods of obtaining constant output. They are as follows :

1. Belt Driven Generator2. Three Brush Generator :

To make the output of the generator self regulating, the conventional generator is modified.
In this, instead of two brushes three brushes are used.
The brushes A, B and C are placed at right angles to each other as shown in the Figure
The brushes A and C are used to excite the field winding and the output across brushes A and B is given to the load.
As the speed of the train increases, the EMF across the brushes A and B also increases. This will further increase in the load current.
This increase in load current will cause increase in the armature reaction a.
This makes more and more distortion in the main flux. This further reduces the induced EMF across brushes AC, which helps in reducing the field excitation.
This will cause the reduction in the EMF generated across main brushes AB.

3. Rosenberg Generator