It is a more convenient arrangement because it does not need a commutator. The rotor is fed with DC through slip-rings and the brushes last much longer. The main current is generated in the static winding enclosing the rotor.
1) Rotating armature alternator, rotates in stationary magnetic field. 2) Rotating field alternator, the magnetic field is rotating.
If you are asking why most a.c. generators (alternators) use a rotating field, rather than a rotating armature, then the answer is that a rotating armature would require slip rings to carry huge currents and be insulated for high voltages, which is not practicable.
Armature is a rotating part of the machine, the coil which wound in the core of that rotating part.
type 1: single phase tree phase poly phase type 2: rotating armature rotating field type 3: salient pole machine non salient pole machine type 1: single phase tree phase poly phase type 2: rotating armature rotating field type 3: salient pole machine non salient pole machine
The stator is the stationary winding assembly that makes the magnetic field inside the alternator. It is this magnetic field that the armature rotates in generating the electricity.
One of the role of the armature in the DC motor is to carry the current that is crossing the field. By carrying the current crossing the field, it creates the shaft torque in the rotating machine.
Advantages of Rotating Field with Stationary Armature1. Rotating field is comparatively light and can run with high speed.2. High voltage can be generate due to high speed and there is very little difficulty in providing high voltage on a stationary part than a moving part.3. It is easier to insulate armature coils for high pressure usually generated (6.6 to 11 kV). Since the stator is outside the rotor, so more space is available for greater insulation required for armature winding.4. Very little difficulty is experience in supplying the field magnet current as it is very low in comparison with the armature current
Field coils and armature
An emf is induced in a coil as a result of (1) a coil cutting through a magnetic field, or (2) a magnetic field cutting through a coil. As long as there is relative motion between a conductor and amagnetic field, a voltage will be induced in the conductor. That part of a generator that produces the magnetic field is called the field. That part in which the voltage is induced is called the armature. Forrelative motion to take place between the conductor and the magnetic field, all generators must have two mechanical parts - a rotor and a stator. The ROTor is the part that ROTates; the STATor is the part that remains STATionary. In a dc generator, the armature is always the rotor. In alternators, the armature may be either the rotor or stator. ROTATING-ARMATURE ALTERNATORSThe rotating-armature alternator is similar in construction to the dc generator in that the armature rotates in a stationary magnetic field as shown in figure 3-1, view A. In the dc generator, the emf generated in the armature windings is converted from ac to dc by means of the commutator. In the alternator, the generated ac is brought to the load unchanged by means of slip rings. The rotating armature is found only in alternators of low power rating and generally is not used to supply electric power in large quantities.
In an alternator, there are two main parts, one is stationary part and other is rotating part. Field winding may be placed on fixed part(stator) as in case of DC generator and on rotating part(rotor) as in case of AC genarators. Armature winding may be placed on rotating part(rotor) in case of DC generator and on stationary part (stator) in case of AC generator. In AC generators, for all practical purposes you have rotating filed system.
This part forms the field circuit. It is a rotating part with a magnetic field that induces current into the stator
This part forms the field circuit. It is a rotating part with a magnetic field that induces current into the stator