Alternators

An alternator is an electrical machine, which is used for generating alternating current. The term A.C. generator is also frequently used, in place of alternator. High-speed alternators driven by steam turbines differ considerably in their construction from the slow-speed types and are distinguised by the terms turo-generator or turbo-alternator. Slow engine-driven machines are often described as being of the flywheel-type.

DC Generators vs AC Generators

DC Generators	AC Generators
In DC generators, the field poles are stationary and the armature conductors rotates.	In AC generators or alternators, the armature condutors are stationary and field poles rotates.
The alternating voltage induced in armature conductors is converted to a direct voltage at the brushes by means of the split-ring commutator.	Alternator uses slip ring commutator as they required to supply electrical energy with an alternating voltage.

Working Principle of an Alternator

The alternators works on the principle of electromagnetic induction. Whenever there is a relative motion between the conductors and the flux, e.m.f gets induced in the conductors. The DC generator is, in an alternator the conductors are stationary and field is rotating i.e) construction of alternator is the inverse of DC generator.

How AC signal is produced by an Alternator

For Better understanding we can consider a relative motion of a single conductor under the magnetic field produced by two stationary poles.

Let us split the rotation of a condutor in four quadrant operation for better understanding, let the conductor starts rotating from position 1. At this instant, the total flux cutting the conductor will be zero and hence induced emf in the condutor is also zero.

1^st Quadrant:

In first quadrant operation, the conductor starts moving from position 1 towards position 2, as it moves the flux cutting the conductor gradually increases from zero to positive maximum as the conductor reaches 90⁰ to the flux cutting it.

2^nd Quadrant:

In second quadrant operation, the conductor starts moving from position 2 towards position 3, as it moves the flux cutting the conductor gradually decreases from positive maximum to zero as the conductor reaches 180⁰ to the flux cutting it.

3^rd Quadrant:

In third quadrant operation, the conductor starts moving form position 3 towards position 4, as it moves the flux cutting the conductor gradually decreases from zero to negative maximum as the condutor reaches 270⁰ to the flux cutting it.

4^th Quadrant:

In fourth quadrant operation, the conductor starts moving from position 4 towards position 1, as it moves the flux cutting the conductor gradually increases from negative maximum to zero as the condutor reaches 360⁰ to the flux cutting it.

Thus one sinusoidal singal is produced per revolution of a conductor, thus this process is repeated to get simultaneous AC singal.