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Question
In Swinburne's Test on D.C.machines, why the efficiency  is 
more when the machine runs as generator than when it runs as 
motor???
 Question Submitted By :: Electrical-Engineering
I also faced this Question!!     Answer Posted By  
 
Answer
# 1
The total loss Pl= constant loss(Pk) + variable loss(Pv)
for any DC machine.
For generator, since Ia=Il+If, the efficiency = 1-Pl/
(VtIl+Pl)
For motor, Ia=Il-If , the efficiency =1-Pl/VtIf.

Its obvious that the efficiency value for generator will be
higher than motor, since Pl is not a negligible value.
 
Is This Answer Correct ?    27 Yes 4 No
Lakshmi Devadas
 
Answer
# 2
because of high currents obtained when it is placed as motor & 
Is This Answer Correct ?    43 Yes 22 No
Dharani
 
 
 
Answer
# 3
in motor the supply voltage isopposed by the back emf .soit
draws more current to run the load
but in generator the whole generated emf supplied to the load
 
Is This Answer Correct ?    15 Yes 5 No
Hema
 
Answer
# 4
the output of a generator is more and also the input to the generator will be less and so the efficiency will b more 
Is This Answer Correct ?    15 Yes 8 No
Chaitanya
 

 
 
 
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