One cannot find a person who has not heard the name of a generator, motor, alternator, or transformer. Alternators and generators are like brothers. Even though they are two brothers, there are some differences between them. Alternator/AC generator and DC generator, basic principals are almost the same. But there is an important difference. This article discusses all the topics:
What is Alternator?
A device that converts mechanical energy into electrical energy is called an alternator.
Generally, the voltage generated in an alternator is variable or alternating. But in the case of a DC generator, AC generated is converted to DC through a commutator and supplied to load and electrical power is supplied to load through a slip ring in the alternator.
Two of the main parts of an alternator are the armature and the magnetic field. According to Farad’s principle of electromagnetic induction, when a conducting magnet cuts the field of force, it produces an E.M.F. In small alternators and DC generators, the conductor or armature is rotated while keeping the magnetic field constant, but in larger alternators, the field is rotated while the armature is stationary. As a result, the armature conductor cuts the field flux and AC voltage is produced.
The rotating field of the alternator is called the rotor and the stationary armature is called the stator.
Working Principle of an Alternator or Generator
Alternator or AC generator is made based on the principle of electromagnetic induction (dielectromagnetic induction). Like a DC generator, an alternator has an armature and a field. In large alternators the field rotates and the armature is stationary.
The armature winding of the alternator is housed in a fixed frame slot. It is called the stator and the field coil of the machine is mounted on a rotating structure. It is called a rotor. The following figure shows the position of stator and rotor.
The armature or stator core is attached to a cast iron frame. The windings of the armature are placed in the grooves cut in the inner periphery of the core. The rotor looks a lot like a flywheel. On the outside (Outer rim) North (N) and South (S) poles are placed alternately. 125 or 250 volts current flows from the DC supply through coils wound on the poles.
In most cases a small shunt generator is used along the rotor shaft for DC supply. It is called an exciter. The current from the exciter passes through brushes and slip rings to the field coil. Since this current is low and is supplied at low voltage, relatively thin brushes and slip-rings can be used.
When the rotor starts rotating, the magnetic field also rotates. When the rotating magnetic field intersects the conductors in the stator slots, an emf is induced in each conductor according to the law of electromagnetic induction. The direction of induced emf is known from Fleming’s right hand rule.
Applying this rule, it can be seen that when the north pole (N) is placed in front of a conductor, both the EMF and the current act in the same direction, while the south pole (S) acts in the opposite direction. As a result, the emf induced in the armature is And with that the current is alternating.
Different between alternator and DC generator
| Alternator | DC Generator |
|---|---|
| 1. It generates AC-voltage and is supplied to the load through the slip ring. | 1. It initially produces AC voltage but later through commutator produces DC and supplies it to the load. |
| 2. Alternators have slip rings. | 2. A DC generator consists of a commutator. |
| 3. It may have field or armature both stationary or rotating. | 3. In this the field is fixed and the armature rotates. |
| 4. Armature winding is open. | 4. Armature winding is closed. |
| 5. DC supply is to be provided by the exciter in the field. | 5. No need for separate DC supply. |
| 6. The field core is made of laminated sheet. | 6. The field core is made of cast iron. |
| 7. Distortion occurs in the generated voltage due to the effect of harmonics. | 7. Free from the effects of harmonics. |
| 8. Eddy current loss is very high. | 8. Eddy current loss less. |
| 9. It can generate voltage up to 33.2KV. | 9. It can produce a maximum voltage of 1.5KV. |
Related Terms:
- Ring Distributor with Interconnector
- Advantages and Disadvantages of AC & DC Transmission
- Limitations of AC Transmission