The function of a commutator in DC generator
The function of a commutator? Yes, why wonder? When we talk about the construction of the DC generators we speak in detail about the commutator, so what is new? that’s very good and you are perfectly right.
We speak about the commutator because we consider it as the rotor. It’s the most important in DC generator because:
- It connects between the rotating armature conductors and stationary external circuits by the brushes.
- It converts the alternating current produced in armature conductors to a unidirectional current in the external load circuit.
- Sequentially it also converts the alternating torque to continuous torque in the armature in motor action.
The commutator of DC generator
Now we will deal with the commutator as a mechanical rectifier or a rotary electrical switch.
This mechanical rectifier commutate the alternating current produced in the armature winding of the Dc generator into a direct current. It also keeps the torque from reversing its direction and that happens by the commutator.
Similarly, with the help of the stationary brushes, we simply can say that the commutator works like a bridge rectifier.
We need alternating current in electric light bulbs, electric heating elements, small electric motors like food mixers, vacuum cleaners, and so on.
So why do we commutate the alternating current? That’s a good question which takes us to very large electric motors. For instance, locomotives, ships, diesel motors, electric razors, producing aluminum, chlorine, and other industrial applications. These only work perfectly with direct current.
It is important to keep a continuous moving contact between the commutator segment and the brushes to ensure the continuous transformation of current from the rotating armature to the brushes.
Working of DC generator with the commutator
Firstly, when the armature starts to rotate, the coil rotates between a positive brush and its consecutive negative brush.
So the current flows through the coil in a direction inward to the commutator segments.
Then with the help of a brush and for the commutation period which is approximately (1/500 sec), the coil is short-circuited.
And after this period the armature coil re rotates between the negative brush and its succeeding positive brush.
So it is axiomatic that the current direction is reversed away from the commutator segments. This reversing process of direction is the commutation.
The commutation process completed by the end of the commutation period to avoid any damage to the commutator surface due to overheating or due to sparking.