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Most of alternator have
Rotating field
Rotating armature
Either of above
None of above
Rotating field
Most alternators use a rotating field design where the magnetic field is produced by the rotor and the armature windings are placed on the stationary stator. This configuration is preferred for large power ratings because it simplifies insulation and connection requirements.
Most alternators use a rotating field design where the magnetic field is produced by the rotor and the armature windings are placed on the stationary stator. This configuration is preferred for large power ratings because it simplifies insulation and connection requirements.
EphтАЛ=4.44f╬жTphтАЛKwтАЛ тАФ EMF equation of an alternator where KwтАЛ is the winding factor.
f=120PNтАЛ тАФ Frequency relation where P is poles and N is speed in RPM.
In a rotating field alternator, the DC excitation is supplied to the field windings on the rotor via slip rings or brushless exciter, creating a moving magnetic flux. This flux links with the stationary armature windings on the stator, inducing an EMF according to Faraday's law of electromagnetic induction. Because the armature is stationary, high-voltage generated power can be extracted directly from the stator terminals without the need for high-voltage slip rings.
Stationary armature allows for better cooling and easier insulation of high voltage windings.
The rotor only requires low voltage DC excitation, which is easily managed by slip rings.
Rotating field alternators minimize the size of sliding contacts (slip rings/brushes).
Mechanical strength of the stator is higher than that of a rotating armature at high speeds.
Improved insulation of stationary high-voltage windings.
Easier output connection to the load without brushes.
Reduced sparking and maintenance associated with high-voltage collection.
Better cooling due to the stationary nature of the armature.
Requires high-quality low-voltage slip rings for DC excitation.
Rotor construction is complex due to field windings and mechanical balancing.
Power generation in thermal, hydro, and nuclear power plants.
Synchronous generators used in industrial AC supply systems.
| Feature | Rotating Field Type | Rotating Armature Type |
|---|---|---|
Armature Position | Stationary | Rotating |
Insulation | Easier for HV | Difficult for HV |
Almost all commercial alternators rated above a few kVA utilize the rotating field configuration.
Rotating armature is only found in very small, low-voltage alternators where power collection via slip rings is acceptable.
A is correct тАФ Most modern alternators employ a rotating field construction to facilitate easier insulation and output collection of high-voltage power.
Always remember: Rotating Field = Stator carries armature windings. Rotating Armature = Stator carries field windings. Modern large-scale machines always use Rotating Field.