5.4.5 Generators

In 1831, Michael Faraday discovered that changing the magnetic flux passing through a conductive circuit induces an electromotive force (EMF), which drives an electric current in a closed loop. This principle—Faraday's Law of Induction—forms the foundation of modern electrical power generation.

An electrical generator converts mechanical energy into electrical energy by continuously rotating a conductor coil within an external magnetic field, generating a continuously varying induced current.

Principles of AC and DC Generators

As the armature coil rotates at a constant angular velocity (ω) inside a uniform magnetic field (B), the magnetic flux passing through the loop varies sinusoidally (Φ = BA cos(ωt)). According to Faraday's Law, the induced EMF (ε) is proportional to the rate of change of flux:

The fundamental structural difference between alternating current (AC) and direct current (DC) generators lies in how current is extracted from the rotating armature to the external circuit:

• AC Generators (Alternators): Use smooth slip rings connected to carbon brushes. As the coil rotates, the current naturally reverses direction every half-rotation, outputting a smooth sinusoidal alternating current.
• DC Generators: Use a split-ring commutator. The split ring reverses the connection to the external circuit every 180° just as the induced voltage changes polarity, converting the internal alternating current into a pulsating direct current in one direction.