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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 will happen at the time of CT saturation?and what will be the Relay's function at the time of CT saturation?   1
What are armoured cables? IOCL 2
what is the basic difference between fan and home motor if both have single phase induction motor? Engineers-India-Limited 4
WHY SECONDARY OF CT SHOULD NEVER BE KEPT OPEN CIRCUITED?   7
1> what r different types of fault in cables? How will u locate and test these faults? 2> why earth wire is provided on top throughout the transmission line. why not only on towers? How much area it can protect? 3> what r different types of transmission losses? How power loss can be minimized? 4> what is the % of power loss on transmission lines? IOCL 3
How Many Safety of Transformer   2
what is inverter Bhel 12
plz explain TSM and PSM.with example suppose ct ratio is 4000/5 and tsm is .15 and plug is at 3.75 if fault current is 8000A.so how i find relay oprating time. ME 2
In 3 phase induction motor 1hp current rating is 1.5 amps constant ? is correct or not ? TATA 4
How to select Main CB Rating for 187 KW Load?   6
How do you change an AC motor to DC? why there is only 50 Hz frequency in india & not other? TATA 4
Why induction motor can not be operated at synchronous speed?? what would happen if it is operated at synchronous speed??   5
 
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