Working Principle of AC Generator - How AC Generator Works?

Working Principle of AC Generator – How AC Generator Works?

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As a matter of fact, the working principle of ac generator is the same to direct-current generator. The basic working principle of ac generator is to convert motion into electricity. Providing this motion requires that either a magnetic field is generated and a wire coil is rotated within it, or a magnetic field is rotated within a stationary coil.

The turning of a coil in a magnetic field produces motional EMFS in both sides of the coil which add. Since the component of the velocity perpendicular to the magnetic field changes sinusoidally with the rotation, the generated voltage is sinusoidal or AC.

Working Principle of AC Generator – How AC Generator Works?

An AC generator or an Alternator works on Faraday’s law of electromagnetic induction, which states that when a conductor is rotated in a magnetic field, an emf is induced in it.

An Alternator has 2 sets of windings, namely main field findings and exciter windings. The exciter field winding is supplied with DC. When the exciter armature is rotated an emf is induced in it, which is rectified by a rotating diode disc assembly and this DC is supplied to the main field winding(rotor).

When this main field winding is rotated inside the stator (main armature winding) and emf gets induced in the armature winding. And when a load is connected to this armature a current flows.

Basic Working Principle of an AC (Alternating Current) Generator

Requirements: wire, magnets, steam engine. Generating AC: The wire is looped for creating several coils known as the armatures. The steam engine forwards the wire by means of magnetic fields with the help of magnets, which will enable in creating an alternating current.

Further more to explain… Here is the mechanism…

The moving coil produces motional emfs on both sides of the coil.

This follows Faraday’s Law in which the rotation/movement of the coil continuously changes the magnetic flux and thereby generating voltage.

The turning of a coil in a magnetic field produces motional EMF in both sides of the coil which add. Since the component of the velocity perpendicular to the magnetic field changes sinusoidal with the rotation, the generated voltage is sinusoidal or AC.

This process can be described in terms of Faraday’s Law when you see that the rotation of the coil continually changes the Magnetic flux through the coil and therefore generates a voltage.

Construction of AC generator (Alternator)

Main parts of the alternator, obviously, consists of stator and rotor. But, the unlike other machines, in most of the alternators, field exciters are rotating and the armature coil is stationary.

Stator: Unlike in DC machine stator of an alternator is not meant to serve path for magnetic flux. Instead, the stator is used for holding armature winding. The stator core is made up of lamination of steel alloys or magnetic iron, to minimize the eddy current losses.

Why armature winding is stationary in an alternator?

  • At high voltages, it easier to insulate stationary armature winding, which may be as high as 30 kV or more.
  • The high voltage output can be directly taken out from the stationary armature. Whereas, for a rotary armature, there will be large brush contact drop at higher voltages, also the sparking at the brush surface will occur.
  • Field exciter winding is placed in rotor, and the low dc voltage can be transferred safely.
  • The armature winding can be braced well, so as to prevent deformation caused by the high centrifugal force.

Rotor:  There are two types of rotor used in an AC generator / alternator:

Salient Pole Type

Salient pole type rotor is used in low and medium speed alternators. Construction of AC generator of salient pole type rotor is shown in the figure above.

This type of rotor consists of large number of projected poles (called salient poles), bolted on a magnetic wheel. These poles are also laminated to minimize the eddy current losses. Alternators featuring this type of rotor are large in diameters 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 havingg slots along its outer periphery. Field windings are placed in these slots.

Working Principle of AC Generator Conclusion

After going through the above portion of ac generator we can now establish basic working principle of ac generator. I hope you enjoy when reading this article, thank you.