Discuss the Principal of A.C Generator by labelled diagram.

Principle :

A.C. generators or alternators (as they are usually called) operate on the same fundamental principles of electromagnetic induction as D.C. generators.

Alternating voltage may be generated by rotating a coil in the magnetic field or by rotating a magnetic field within a stationary coil. The value of the voltage generated depends on-

The number of turns in the coil
Strength of the field.
The speed at which the coil or magnetic field rotates

An Electrical Generator is a device that produces an Electromotive Force (e.m.f.) by changing the number of Magnetic Flux Lines (Lines of Force), Φ, passing through a Wire Coil. When the Coil is rotated between the Poles of the Magnet by cranking the handle, an AC Voltage Waveform is produced.

Operation principle of a Generator is based on Electromagnetic Induction, which is defined by Faraday’s Law, which states:

The Electromotive Force, Eemf, induced in a Coil is proportional to the number of turns, N, in the Coil and the Rate of Change, dΦ / dt, of the number of Magnetic Flux Lines, Φ, passing through the surface (A) enclosed by the Coil.

An Induced Effect is always such as to Oppose the cause that produced it.

Working:

In the Generator, the Coil is under a Stationary Magnetic Field. The Magnetic Flux Density, B, is constant and Φ = B x Aeff, so Φ is proportional to the Effective Area, Aeff, of the Loop. As the Loop rotates at different angles, there is a change in Aeff.

The Rate of Change of Φ, dΦ / dt, is the largest at the zero points of the Waveform and is the smallest at the peaks of the Waveform, therefore the Induced Eemf is maximum at the zero points and minimum at the peaks is shown in figure below.