Wednesday, 24 January 2018

Commutator And Commutation - Mostly Needed Part In The DC Generator !!

Commutator And Commutation - Mostly Needed Part In The DC Generator  

Description About Commutator And Commutation Which is Mostly Useful Parts In DC Generator And How The Commutator Convert AC Current DC Current Using Commutation Process. 

We all know that The Current induced in Armature conductors of a d.c. generator are alternating. 

To make their flow unidirectional in the external circuit, we need a Commutator.

Over, these Current Flow in one direction when armature conductore are under N-pole and in the opposite direction when they are under S-poles. 

As conductors pass out of the influence of a N-poles and enter that of S-poles, the current in them is reversed.

This reversal of current takes place along Magnetic Neutral axis or brush axis.

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i.e. when the brush spans and hence short-circuit that perticular coil undergoing reversal of curremt through it.

This process by which current in the short-circuited coil is reversal while it crossres the M. N. A.  Is called Commutation.

The brief period during which coil remains short-circuted is know as Commutation period Tç.

  • If the current reversal i.e. the change from +I to zero and then to -I is completed by the end of short circuit or Commutation period. Then the Commutation is ideal. 

  • If current reversal is not complete by that time, then sparking is produced between the brushes the brush and the Commutator which results in progressive damage to both. 

Methods of improving Commutation
There are two practical ways of improving Commutation.

i.e. of making current reversal in the short-circuite coil as sparkless as possible. These methlds are know as

(1) resistance Commutation and

(2) e.m.f. Commutation( which is done with the help of either brush lead or interpoles, usually the later).

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