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Question
Why we use Carbon & graphite mixxed brushes in the DC motor?
 Question Submitted By :: Electrical-Engineering
I also faced this Question!!     Answer Posted By  
 
Answer
# 1
Grafite For Lubrication Carbon for current collection
purpose.
 
Is This Answer Correct ?    13 Yes 2 No
Virendra Ku Mallah
 
Answer
# 2
According to the periodic table carbon lies in the list of
semiconductor having valency of 4 thus semiconductors have
the property that with increase in temp. their resistance
decreases. Thus when carbon brushes rub against the commutator
due to friction their temp. increases and resistance falls.
Thus they are used for collection of current in DC machines.
In AC systems slip rings are used.
 
Is This Answer Correct ?    8 Yes 0 No
Sahil Joseph
 
 
 
Answer
# 3
THE PURPOSE OF CARBON BRUSHES ARE TO POLISHING THE SURFACE
OF THE COMMUTATOR AND TO REDUCE THE REACTENCE AT THE
COMMUTATOR.
 
Is This Answer Correct ?    6 Yes 3 No
Prasad
 
Answer
# 4
it has good peripheral speed and current density, self lubricating 
Is This Answer Correct ?    4 Yes 1 No
Karthik Raman.b
 
Answer
# 5
carbon is hard material compared to graphiate so it will
give a stainsail strength of graphite at the time of full
load runing condition.and graphite use for the just collect
the current and passing.
 
Is This Answer Correct ?    4 Yes 4 No
Guest
 
Answer
# 6
this wil reduce th sparking in the commutator 
Is This Answer Correct ?    4 Yes 5 No
Vinod Kumar T
 

 
 
 
Other Electrical Engineering Interview Questions
 
  Question Asked @ Answers
 
what do you mean by synchronous speed of a three phase induction motor? FlexPoint 5
What is the BS(British Standard)code for 11kv motor   1
Which type of moter is used in trains, what is the ratting of supply used explain Working principal?   2
what is electricity   4
why star connected transformers used in tneb?   1
1)Why V cross Arm is used in transmission lines? 2)Why H cross Arm are not used in single poles?   1
why are the transmission lines operated at 220 kv nly... nt les dan dat...   3
why transformers not work at d.c.-   3
figure of phasor diagram of transformer when full load or no load ? TCS 1
what is L.T?specify the range?   7
Why 11KV PT Secondaries [(11000/1.732)/(110/1.732)/ (110 / 3)]are in star connection ? And why the same should not be in delta ?   1
How do we calculate the out Put voltage of generator, after excitation being given?   1
 
For more Electrical Engineering Interview Questions Click Here 
 
 
 
 
 


   
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