A.C Generator- Principle, Working, Application and Uses

A.C generator or dynamo is a device which converts mechanical energy into electrical energy. Actually, the name generator is a misnomer because it does not generate any energy. It converts mechanical energy into electrical energy.

Definition of A.C Generator  

An a.c generator is the one which produces a current that alternates or changes its direction regularly after a fixed interval of time, i.e., it is a device which converts mechanical energy into alternating form of electrical energy.

The present form of a.c generator is due to Nikola Tesla, The great Yugoslav scientist who built it in the year 1888.

Working principle of A.C Generator

The working of an a.c generator is based on the principle of electromagnetic induction. When a closed coil is rotated in a uniform magnetic field with its axis perpendicular to the magnetic field, the magnetic flux linked with the coil changes and an induced EMF is produced and hence a current is set up in it.

Components of A.C Generator

1. Field magnet 

It is a permanent magnet of the horse shoe shape in a small dynamo (magneto) or it is a powerful electromagnet in a large dynamo. It produces a strong magnetic field in the region between its pole-pieces.

2. Armature

It consists of a rectangular coil ABCD having a large number of turns of insulated copper wire wound on a soft iron cylindrical core. The core is laminated one to avoid losses due to Eddy Currents. The soft iron core concentrates the lines of force to increase the flux density B. The armature can be rotated in the magnetic field pf the field magnet about an axis perpendicular to field B.

3.Slip rings

The two ends of the armature coil are connected to two coaxial brass rings R1 and R2 called slip rings. The rings are rigidly fixed to same shaft which is used to rotate the coil. The slips are insulated from each other as well as form the shaft. As the armature coil rotates, the slip rings also rotate about the same axis of rotation.

4. Brushes

Two graphite or flexible metallic rods called brushes are lightly presses against the two slip rings. The brushes B1 and B2 remains fixed in their positions and maintain sliding contacts with the rotatable slip rings R1 and R2 respectively. It is through these brushes that the current induced in the armature coil is fed to the external circuit by means of line wires.

5. Source of energy

The armature coil is rotated about its axis with the help of turbine or any other device connected to it. It is the rotational kinetic energy of the turbine which is ultimately converted into electrical energy by the a.c generator.

Working of A.C Generator

Refer above diagram for better understanding!

1. As the armature coil rotates, the magnetic flux linked with it changes and so an induced current flows through it. Suppose initially the coil ABCD be in the vertical position and it is rotated in the clockwise direction.

2. The side AB moves downward and DC moves upward. According to Fleming's right hand rule., the induced current flows in the direction DCAB, with brush B1 acting as positive terminal and brush B2 as negative terminal. During the second half-rotation, the side AB moves upward and DC moves downward.

3. The direction of induced current is reversed , i.e., it flows along ABCD, so that the brush B2 now function as the positive terminal and brush B1 as the negative terminal. Thus the direction of current int he external circuit is reversed after every half cycle.

4. Hence alternating current is produced by the generator. Such a generator which generates alternating current is called an a.c generator or an alternator.

Applications of A.C Generator 

1. Hydroelectric power station

In a hydroelectric power station, water is stored in a dam at a height, from where it falls into giant waterwheels or turbines. These turbines are connected to the loops of wire in ac generators. The kinetic energy of the falling water thus gets converted into rotational energy of the turbines and ultimately into electrical energy supplied by the generator.

2. Thermal power station

In a thermal power station, steam is produced by boiling water using coal or oil as fuel. The turbines coupled to the loops of ac generators are rotated by steam rushing past them and thus electrical energy is generated.

3. Nuclear power plant

In a nuclear power plant, a nuclear fuel is used instead of coal to generate electrical energy.

Advantages of A.C over D.C

• The generation of A.C is more economical than D.C.

• The alternating voltage can be easily stepped up or stepped down by using a transformer.

• The alternating currents can be transmitted to distant places without any significant line loss.

• Also ac can be easily converted into D.C by using rectifiers.

• A.C machines are simple and robust and do not require much attention during their use.

Disadvantages of A.C over D.C

• Peak value of a.c is high. It is dangerous to work with A.C.

• In phenomena like electroplating, electro-refining, electrotyping, etc; A.C cannot be used.

• A.C is transmitted more from the surface of conductor than from inside. This is called skin effect. Therefore, several fine insulated wires (and not a single thick wire) are required for transmission of A.C.

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