AC Generator — Principle, Diagram and Working

An AC generator works on the principle of Electromagnetic Induction.

"When a closed coil is rotated in a uniform magnetic field, the magnetic flux linked with the coil changes continuously. This changing magnetic flux induces an electromotive force (EMF) and an induced current in the coil."

The direction of this induced current is determined by Fleming's Right-Hand Rule.

1. Strong Magnetic Field (N, S): Provided by powerful permanent magnets or electromagnets with concave poles to create a radial magnetic field.
2. Armature (ABCD): A rectangular coil of insulated copper wire wound over a soft iron core to increase the magnetic flux.
3. Slip Rings (R₁, R₂): Two hollow metallic rings connected to the ends of the armature coil. They rotate along with the coil.
4. Carbon Brushes (B₁, B₂): Two stationary carbon rods that press lightly against the slip rings to pass the induced current to the external circuit.

1. Let the coil ABCD be rotated clockwise in the magnetic field.
2. As arm AB moves upwards and CD moves downwards, they cut the magnetic lines of force.
3. By Fleming's Right-Hand Rule, induced current flows from A to B and C to D. Thus, current flows in the direction ABCD. In the external circuit, current flows from brush B₂ to B₁.
4. After half a rotation, arm CD comes to the left and AB to the right. Now CD moves upwards and AB downwards.
5. The induced current reverses and flows in the direction DCBA. In the external circuit, current now flows from B₁ to B₂.
6. Because the current changes its direction every half-rotation, it is called an Alternating Current (AC).

The primary structural difference between an AC generator and a DC generator is the rings:

• AC Generator uses two full Slip Rings. This allows the current to alternate in the external circuit.
• DC Generator uses a Split Ring Commutator (one ring cut in half). This reverses the internal connections every half turn, keeping the external current flowing in only one direction.