Alternator in Automobile Engineering

Table of Contents

All alternators work on the principle of electromagnetic induction. According to this act, conductor, magnetic field and mechanical energy are required to generate electricity

The main parts of an alternator are, apparently, a stator and a rotor. But, unlike other machines, in most alternators, the field exciter rotates and the armature coil becomes stationary.

Stator

The DC machine of the alternator is not to serve the route for the opposite magnetic flux in the stator. Instead, the stator armature is used for rotation. The stator core is made of steel alloy or lamination of magnetic iron, to reduce the AD current loss.

Why is the armature winding fixed in the alternator?

At higher voltages, static armature windings are easier to insulate, which can be 30 kV or more.

The high voltage output can be extracted directly from the static armature. Where for rotary armature, there will be a large brush contact drop at high voltages, as well as sparking on the brush surface.

The field exciter is mounted on a rotating rotor, and the low DC voltage can be safely transferred.

The armature winding can be braced well to prevent deformation caused by high centrifugal force.

Rotor

There are two types of rotors used in AC generators/alternators:

(i) main and (ii) cylindrical type

Main pole type: The main pole type rotor is used in low and medium speed alternators. This type of rotor has a large number of projected poles (called main poles), bolted in a magnetic cycle. These poles are also laminated to reduce AD current losses. Alternators characteristic of this type of rotor are large in diameter and short in axial length.

Cylindrical type: Cylindrical type rotors are used in high-speed alternators, especially in turbo-alternators. This type of rotor consists of a smooth and solid steel cylinder with slots on the outer circumference. These slots have field windings.

Working principle

The working principle of an alternator is very simple. This is like the basic principle of a DC generator. It also depends on Faraday’s law of electromagnetic induction which states that the relative motion between the conductor and the magnetic field occurs in the conductor within the electromagnetic field.

DC supply is provided for rotor rotation through slip ring and brush arrangement. Having understood the basic principles of alternators, let us now take a look at the basic operating principles of practical alternators.

In discussing the basic functions of alternators, we have considered that the magnetic field is constant and the conductors (armature) are rotating. But generally in the practical construction of alternators, the armature conductors are stationary and field magnets rotate between them.

The rotor of an alternator or asynchronous generator is mechanically connected to a shaft or turbine blade, which is designed to rotate at synchronous speed Ns under some mechanical force resulting in cutting off the magnetic flux of the static armature conductors placed on the stator.

As a direct result of this flow, an induced emf cut and the current begins to flow through the armature conductors which flow in one direction for the first half cycle and then for the second half cycle in each direction with a fixed time delay for each winding.

These special events result in a 3φ power flow from the alternator which is then sent to distribution stations for domestic and industrial use.