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Commutator

Definition:

It is defined as the rotating electrical device connected to motor or generator through which an electrical connection can be made  to the load such that it always reverses the current that flows between the motor or generator and the load.

In other words, commutator is defined as the splitting device used to keep torque in DC motor from reversing every time, when the coil moves to the plane perpendicular to the magnetic field.

Application of commutator:

  It is used in :

  • DC motor
  • DC generator
  • Universal motors

Use of commutator in motor:

In motor, commutator applies the electrical current to the windings, then it reverses these current flow for each half cycle in the rotating windings, thus a steady rotating force called torque is produced to rotate the load

Use of commutator in generator:

 In generator, commutator picks off the current from the windings and reverses these current for every half cycle such that it converts current from AC to unidirectional current DC

Construction of commutator:


It consists of cylindrical multiple metal contact segment placed on the rotating armature winding of machine. It consists of Two or more electrical contacts called Brushes. Brushes are made up of soft conductive material called copper.
These copper are made to press against commutator to make sliding contact so the armature will be connected to the commutator segment. Copper is used in early motors where spring loaded carbons are in use now.

Commutator

Dead Spot:
In practical commutator three segments are provided to reduce dead Spot. So the brush is always made greater than insulated gap,t to make the brush to be in contact with the armature coil all the time. Such that if the rotor steps in a position where two commutator segment touch one brush, it will de-energise one of the arms whole other still functions and cope up with motor to produce torque.

Practical commutator

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