Working principle of alternator
An alternator **is a synchronous machine which converts mechanical power into AC electric power through the process of electromagnetic induction.
As alternator consists of two main parts viz.
- Stator – The stator is the stationary part of the alternator which carries the armature winding and where voltage is generated. The armature winding of the alternator is star connected .
- Rotor – The rotor is the rotating part of the alternator. The rotor produces the main field flux.
An alternator works on the principle of electromagnetic induction, i.e., when changing flux is cut by a conductor, an EMF is induced in the conductor. When the armature winding of alternator is subjected to the rotating magnetic field, the voltage is generated in the armature winding.
When the rotor field winding of the alternator is excited by providing dc supply, the alternate N and S poles are developed on the rotor. When the rotor is rotated by a prime mover, the armature conductors placed on the stator are cut by the magnetic field of the rotor poles. As a result, the EMF is induced in the armature conductors due to electromagnetic induction.
the frequency of it is given by,
f=NsP/120
NsNs is the synchronous speed in RP
P is the number of rotor poles
The magnitude of the generated voltage depends upon the speed of rotation of the rotor and the DC field excitation current.
Construction of an alternator
- Stator or Armature (stationary) :
- Stator frame: The stator frame is the outermost part of the alternator. It is made up of cast iron or cast steel. It gives mechanical protection to the entire machine.
- Stator core: It is the inner part of the stator which is bounded by the stator frame. There are slots on the core in which armature windings are placed.
- Stator winding: Armature winding is made up of insulated copper conductor placed in stator core slots. These stationary conductors when cut by the magnetic field emf get induced in them.
- Rotor (rotating) :
- Magnetic poles and field winding: The magnetic poles and field winding are placed on the rotor. The rotor shaft is driven by the prime movers connected to the turbine. Thus a rotating magnetic field is produced.
- Slip-rings: slip-rings. It is in a circular shape object whose purpose is to supply excitation current to the rotating field from the stationary brushes.
- Brush and brush holder:
- Exciter: The field current required to excite field poles is usually provided from a small dc shunt or compound generator known as exciter mounted on the same shaft of the prime mover ..
- Shaft and bearings: The brushes are made up of carbon placed over the surface of slip-rings to supply the dc exciting current to the field winding.
Difference between alternator and generator
| Basis for Comparison | Alternator | Generator |
| Definition | A machine that converts the mechanical energy into AC electrical power. | A machine that changes mechanical energy into electrical energy (AC or DC). |
| Current | Induces alternating current | Generate both AC & DC. |
| Magnetic Field | Rotating | Stationary |
| Input Supply | Takes from stator. | Takes from rotor. |
| Armature | Stationary | Rotatory |
| Output EMF | Alternating | Constant |
| RPM (Rotation per minute) | Wide Range | Narrow Range |
| Dead Battery | Do not charge | charge |
| Output | Higher | Lower |
| Size | Alternators are generally smaller in size. | Generators are larger and require more space to fit in |
| Uses | Alternators are mainly used in the automobile industry as a charging system for the battery. | Generators are widely used to produce large-scale electricity. |