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 mechanical energy into electrical energy and so it acts as a generator. If electrical energy is supplied to the machine, it works as a motor and it converts electrical energy into mechanical energy.

Types of dc generators

DC generators are classified according to the method of excitation of their field windings. The production of the magnetic flux in the generator by circulating current in the field winding is called excitation.

Separately excited dc generator

In this type of machine, the field winding is excited by a separate dc source. The schematic diagram of separately excited dc machines is shown in figure 7.9.