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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
 
If 440 V supply has given at the secondary winding of transformer at that time if we apply 11 KV at primery then what will happen???????   4
If 3-Ph motor of same rating connected in Delta & Star for same load one by one then which connection take more current in running (not in starting)for full load.(eg 8.5 KW,3-Ph 400 V) GE 1
i Have 1000kva 11/.4 kv voltemp make t/f Its a 2 year old. i wants to known how much iron losses & copper loses during no load condition.   2
Whats the use of earth pits? and it will function? whats the natural earth value? How to improve ur earth resistance?   1
For which purpose the temp. rise test of transformer is conducted?   2
what s the differenc between electrical &electronis , how to define them   9
if u want to buy a motor than what will be the configuration of that motor?   2
which motor used in electric train ans how much volt. Trimax 3
1. What does mean of "PS" stand for Diff. CT class? 2. What is the formula of KW for 1Phase load inturms of voltag,current & P.F.? Hero-Honda 4
why the weight of oil in transformer is specified (on the nameplate) in litres as well as kilo grams? Reliance 2
how many types of cbs?with pcific ratings? Bhel 1
will we have to design the UPS differently for both i.e. if we want to connect the two batteries in parallel and/or we want to connect the two batteries in series ?   4
 
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