Page 610 - Basic Electrical Engineering

Figure 7.4 (a) A coil is shown rotated in a magnetic field; (b) after half revolution the position of the
coil side along with commutator segments change, the position of brushes remain unchanged; (c)
output dc wave shape of the load current

The function of brush and commutator in a dc machine working as a
generator is to convert ac generated in the armature coils into dc at the output.

7.1.3 Function of Brush and Commutators in Motoring Action

We shall now examine the operation of an elementary dc motor by
considering a single coil (for simplicity) on its armature. In a dc machine,

operating as a motor, electrical energy is converted into mechanical energy.
Fig. 7.5 shows the armature coil fed from a source of dc supply. The armature

having the coil on it is placed in a magnetic field created by the field system
as shown in Fig. 7.5 (a).

In Fig. 7.5 (b) is shown how current will flow from the positive polarity of
the supply source through brush B′ and commutator segment C′ to coil side a′
and then to coil side a, returning through commutator segment C and brush B

to the negative terminal of the supply source. By applying Fleming’s Left
Hand rule to coil-side a′ in Fig. 7.5 (b) we find that the conductor will