Page 33 - Basics of Electrical, Electronic and Communication

138 Chapter 7. DC machines

will flow through the load resistor from M to L. In the next half revo-
lution, the direction of induced current will be from D to C and from
B to A as shown in the figure. The current will again flow from M to
L through the load resistor.
In a dc generator the emf induced in the coil is alternating. In order
to get a unidirectional current an arrangement known as commutator is
used. The function of commutator in a dc generator is to convert the
alternating current produced in the armature (coil) into direct current in
the external circuit. In the figure the ends of the armature are connected
to a split ring which acts as commutator.

7.4 Constructional details of dc Machine

A direct current machine can be used as a generator or as a motor.
When the dc machine is driven by a prime mover, it converts mechan-
ical energy into electrical energy and so it acts as a generator. If elec-
trical energy is supplied to the machine, it works as a motor and it
converts electrical energy into mechanical energy.

Field winding

Pole shoe Yoke or frame
Commutator

Shaft Commutator
Armature segments
conductors Interpole

Figure 7.4: Construction of a dc generator

The constructional features of a dc machine are given below.

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