All generators operate on the principle of dynamically induced electromotive force (e.m.f.), which is based on Faraday’s law of electromagnetic induction. This law states: “Whenever the number of magnetic lines of force, or flux, linking with a conductor or coil changes, an electromotive force is induced in that conductor or coil.”
For the flux associated with the conductor to change, there must be relative motion between the conductor and the flux. This relative motion can be achieved by either rotating the conductor relative to the flux or rotating the flux relative to the conductor. As long as this relative motion exists, a voltage is generated in the conductor.
This type of induced e.m.f., caused by the physical movement of the coil or conductor with respect to the flux, or vice versa, is known as dynamically induced e.m.f.
Key Point: The generating action requires the following essential components:
i) A conductor or coil
ii) Relative motion between the conductor and the flux
In a generator, conductors are rotated to cut the magnetic flux while the flux remains stationary. To produce a large output voltage, multiple conductors are connected in a specific configuration to form a winding, known as the armature winding of a d.c. machine. The component on which this winding is mounted is referred to as the armature of the d.c. machine.
The rotation of conductors is achieved using an external device called a prime mover. Common prime movers include diesel engines, steam engines, steam turbines, and water turbines. The required magnetic flux is generated by a current-carrying winding known as the field winding.
The direction of the induced e.m.f. can be determined using Fleming’s right-hand rule.