D.C. Generator Components and Working Principle

A D.C. generator is a type of electrical machine designed specifically to generate direct current (D.C.) electric power using mechanical energy. Here's how they work and their key components:

Principle

A D.C. generator converts mechanical energy into electrical energy by transforming kinetic energy from rotating parts into chemical potential energy stored in a battery's electrolyte water molecules. This process involves three main steps: commutation, excitation, and collection.

Commutation

Commutation is the process whereby brushes make contact with the spinning armature passing through stationary field coils, completing a circuit between the rotator and external load without short-circuiting the field winding. In simple terms, it ensures that electricity flows out of the armature only when it's facing towards the load instead of flowing back and forth like AC generators do.

Excitation

Excitation refers to the interaction between the magnetic fields generated by both the DC generator windings and the permanent magnets on the rotator (or rotator poles). It creates a torque which can drive the rotation mechanism and produce electricity.

Collection

Collection of the output voltage occurs when the brushes come into contact with the commutator, which separates the individual coils so that only one set is connected to the output at any given time. This prevents cross interactions and allows proper transfer of current to the external load.

Key Components

The core components of a D.C. generator are:

• Armature - consists of multiple electromagnetic coil windings wrapped around a cylindrical shaft called the rotator. As the armature turns due to mechanical input, its movement induces an electromotive force (EMF) in each coil, producing alternating current.

• Field Coils - these are stationary electromagnetic components made up of wire wound around iron cores. They create a strong constant magnetic field that interacts with the rotating armature, generating a significant amount of electric current.

• Brush Assembly - this includes two sliding contacts (brushes), insulated from each other but conductive to the metal body of the rotator, which connects to the external load. These brushes ensure continuous communication between the rotator and the external load.

• Commutator - a ring-shaped piece of material with segments separated from each other, allowing brushes to selectively contact specific segments based on position relative to the field coils.

In summary, the principle behind a D.C. generator is fundamentally different from those used in AC machines because it relies upon mechanical commutation rather than natural line frequencies found in household circuits. While more complex than AC systems, D.C. generators offer steady voltage levels unaffected by phase shifts during periods of rapid change in speed.