Question

Describe the working of an AC generator with the help of a labeled circuit diagram. What changes must be made in the arrangement to convert it to a DC generator?

Answer 1

Principle of AC Generator:

1. It is based on the principle of electromagnetic induction.
2. It can be used to convert mechanical energy to electrical energy.

Working:

1. Initially, at t=0 the armature ABCD is vertical with arm AB up and CD down. During the motion of armature between t=0 and t=T/2, the arm AB moves down and CD moves up.
2. Using Fleming's Right-hand rule, the current in the armature will flow in the direction of DCBA.
3. During the motion of armature between t=T/2 to t=T, the arm CD moves up and AB moves down. During this interval, the current will flow in the direction of ABCD.
4. Whenever the armature is vertical, its arms AB and CD momentarily move parallel to the field. So the rate of change of magnetic flux becomes zero which means that the induced e.m.f. corresponding to the vertical positions of the armature is zero. Thus at t = 0, T/2, and T induced e.m.f. produced is zero.
5. When the armature is horizontal, the arms AB and CD move normally in the direction of the magnetic field. At t=T/4 and t=3T/4 the induced e.m.f. produced is maximum.
6. For converting an AC generator to a DC generator; replace split rings with slip rings for a DC generator. The split ring commutator makes the current change direction every alternate half rotation.

Using this the direction of the current changes every alternate half rotation, it essentially converts the current direction in every half-cycle to positive.