Classification And Working Principle of Alternator
Working principle and classification of Alternator is provided in this article, this theory is very basic and useful to learn operation of alternator and also electrical machine.
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| Classification And Working Principle of Alternator |
Alternators, according to their construction, are divided into the following two classifica-
tions:
1.Revoluing-armature type
2.Revolving-field type.
1.Revolving-armature type alternator
It has stationary field poles and revoluing armature.
It is usually of relatively small kVA capacity and low-voltage rating.
It resembles a D.C. generator in general appearance except that it has slop-rings instead of a commutator.
The field excitation must be direct current and therefore, must be supplied from an external direct current source.
2.Revolving-field type alternator:
It has a stationary armature or stator,inside of which the field poles rotate.
Most alternators are of the revolving-field type, in which the revolving-field structure or rotor has slip rings and brushes to supply the excitation current from an outside D.C.source.
The armature coils are placed in slots in a laminated core called the 'stator'which is made
up of thin steel punchings or laminations securely clamped and held in place in the steel
frame of the generator.
Usually the field voltage is between 100 and 250 volts and the amount of power delivered to the field circuit is relatively small.
The following are the principal aduantages of the revolving-field type alternators:
✓The armature windings are more easily braced to prevent deformation under the mechanical stresses due to short-circuit currents and centrifugal forces.
✓The armature(stator)winding must be insulated for a high voltage, while the voltage of field circuit is low(100 to 250 volts). It is much easier to insulate the high-voltage winding when it is mounted on the stationary structure.
✓Only a small amount of power at low voltage is handled by the slip ring contacts.
✓It is easier to build and properly balance high-speed rotors when they carry the field...
structure.
✓The armature winding is cooled more readily because the stator core can be made large
enough and with many air passages or cooling ducts for forced air circulation.
Operating Principle
When the rotor rotates, the stator conductors
(being stationary)are cut by the magnetic flux,hence they have induced e.m.f.produced in them.
