Monday, February 6, 2017

Electric generator

An electric device which converts mechanical energy into electric energy is called an electric generator.


Principle:  Electric generator works on the principle of electromagnetic induction. When the coil of electric generator rotates in a magnetic field, the magnetic field induces a current in this coil. This induced current then flows into the circuit connected to the coil.

Types of electric generators:
1.       AC Generator
2.       DC Generator

1.       AC Generator:  A generator which converts mechanical energy into electric energy in the form of alternating current is called AC Generator.

Construction:

The main components of AC generator are as shown in figure.
1. Armature    2. Strong magnets   3. Slip rings and     4. Brushes.
    Armature, strong magnets and brushes are the same as used for electric motors.

Slip rings:

The two ends of the armature coil are connected to two brass slip rings R1 and R2. These rings rotate along with the armature coil.

Working:

a.        When the armature coil ABCD rotates in the magnetic field provided by the strong magnets, it cuts the magnetic lines of forces.
b.       Thus the changing magnetic field produces induced current in the coil. The direction of induced current is determined by the Flemings right hand rule.
c.        The current flows out through the brush B1 in one direction in the first half of the revolution and through the brush B2 in the next half revolution in the reverse direction, this process is repeated.
d.       Therefore, the induced current produced is of alternating nature. Such a current is called as alternating current.

2.       DC Generator:

A generator which converts mechanical energy into electrical energy in the form of direct current is called as DC generator.



Construction:



The main components of D.C. generator are:
1.       Armature coil 2. Strong magnets 3. Split rings or commutator 4. Brushes 5. Bulb.

The components such as armature coil, strong magnet, brushes are the same which are used for AC generators. Slip rings or commutator is the same as used in electric motor.

Working of DC generator:

(a)     When the coil of DC generator rotates in the magnetic field, potential difference is produced in the coil. This gives rise to the flow of current. This is shown by glowing of the bulb.
(b)     In D.C. generator, the flow of current in the circuit is in the same direction as long as the coil rotates in the magnetic field.

(c)     This is because one brush is always in contact with the arm of the armature moving up and other brush is in contact with the arm of the armature moving downward in the magnetic field.