Answer / hemanshu

beacause carbon contact resistance is too low 0.7 ohm. so its use for exitation of motor & generator.

Answer / kawsar ahmed

We use carbon brush with commutator and slip ring, because carbon has negative coefficient of heat. That means when heat increase carbon brush resistance do not increase.
Another reason is carbon friction loss is less then other element.

Answer / ramesh

Brushes are used in Exciter to facilitate current in
revolving rotor where Field winding is placed. In generators
for Rotor earth fault and as earth to remove any static
current induced in the rotor.

Answer / raul

brushes r the means of supplying the direct current from
the commutator to the external load ........n the contact
resistance is an important factor which plays an important
role. in dc generators, carbon brushes also helps in
improving commutation

Answer / sreeknp

normally brushes are of carbon it is a semiconductor its
resistance decreases with temperature, then self lubricant
this is the reason

In a transformer ,when voltage decreases current increases. but this is a violation of oms law.why?

15 Answers  

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