Working Principle of Alternator

The working principle of alternator is very simple. It is just like basic principle of dc generator. It also depends upon Faraday's law of electromagnetic induction which says the electric current is induced in the conductor inside a magnetic field when there is a relative motion between that conductor and the magnetic field.

For understanding working of alternator let's think about a single rectangular turn placed in between two opposite magnetic pole as shown below.

Say this single turn loop ABCD can rotate against axis a-b. Suppose this loop starts rotating clockwise. After 90° rotation the side AB or conductor AB of the loop comes in front of S - pole and conductor CD comes in front of N - pole. At this position the tangential motion of the conductor AB is just perpendicular to the magnetic flux lines from N to S pole. Hence rate of flux cutting by the conductor AB is maximum here and for that flux cutting there will be an induced current in the conductor AB and direction of the induced current can be determined by Flemming's Right Hand Rule. As per this rule the direction of this electric current will be from A to B. At the same time conductor CD comes under N pole and here also if we apply Fleming Right Hand Rule we will get the direction of induced current and it from C to D.

Now after clockwise rotation of another 90° the turn ABCD comes at vertical position as shown beside. At this position tangential motion of conductor AB and CD is just parallel to the magnetic flux lines, hence there will be flux cutting that is no current in the conductor. While the turn ABCD comes from horizontal position to vertical position, angle between flux lines and direction of motion of conductor, reduces from 90° to 0° and consequently the induced current in the turn is reduced to zero from its maximum value.