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Question
Synchrounous motor is three phase motor,but its not self 
starting .why?
 Question Submitted By :: A.balakrishnan
I also faced this Question!!     Rank Answer Posted By  
 
  Re: Synchrounous motor is three phase motor,but its not self starting .why?
Answer
# 1
low starting tarque 
Is This Answer Correct ?    19 Yes 32 No
Vinod
 
  Re: Synchrounous motor is three phase motor,but its not self starting .why?
Answer
# 2
it does not having revolving field
because it works on 2 powersuplys ac & dc
 
Is This Answer Correct ?    11 Yes 35 No
Vamsi
 
 
 
  Re: Synchrounous motor is three phase motor,but its not self starting .why?
Answer
# 3
Synchronous motor Three phase motor but it two winding
which are connected to rotor after 70% it'll be connected.
In the intial time Synchronour motor are not three Phase
but after about 70% speed it'll make Three phase. In the
starting Condiction, it is working as 2phase. it has zero
slip under usual operating conditions. Contrast this with
an induction motor, which must slip in order to produce
torque
 
Is This Answer Correct ?    9 Yes 23 No
Guru101
 
  Re: Synchrounous motor is three phase motor,but its not self starting .why?
Answer
# 4
synchronous motor stator has 3 ph winding n rotor s suplied
by a dc suply to form a north n south pole..supose two
magnets are aligned axialy. now rotate one of them slowly.
the other one also starts rotating with dat. thatz how the
working of syn motor can be xplained in a very simple way.
if we rotate the magnet fastly the other one cant move with
that much speed becoz of its inertia. when 3 phase suply s
given to the stator winding, a rotating magnetic field is
created with syn speed. but the rotor cant rotate. so at
first the rotor s rotated by some external means to the syn
speed n then give suply to the stator.so that the rotor
continues to rotate with syn speed
 
Is This Answer Correct ?    53 Yes 5 No
Ashli
 
  Re: Synchrounous motor is three phase motor,but its not self starting .why?
Answer
# 5
Synchronous motor is not self starting. Because to develop
torque motor has to run at synchronous speed. the motor
needs some type of device to bring rotor to synchronous
speed.
 
Is This Answer Correct ?    4 Yes 14 No
Sangeetha
 
  Re: Synchrounous motor is three phase motor,but its not self starting .why?
Answer
# 6
because of the rotor inertia it is unable to rotate in the
anticlockwise direction as the energy supplied is
insufficient to make it to spin because it is very
heavy....so a prime mover is required to produce a
unidirectional torque.
 
Is This Answer Correct ?    4 Yes 11 No
Vidhya
 
  Re: Synchrounous motor is three phase motor,but its not self starting .why?
Answer
# 7
sync motor has no self starting torque this is bcaz its
high inertia prevents it from rotating in either of the
direction,so it is not self starting
 
Is This Answer Correct ?    4 Yes 10 No
Tulsi_lotus@yahoo.com
 
  Re: Synchrounous motor is three phase motor,but its not self starting .why?
Answer
# 8
becoz in synchronous machine uni-directional torque not
produce.
 
Is This Answer Correct ?    3 Yes 9 No
Rahul
 
  Re: Synchrounous motor is three phase motor,but its not self starting .why?
Answer
# 9
let assume the stator field as Ns and Ss..the rotor field as
Nr and Sr..when the given to supply to stator windings,which
cause rmf may occur..assume Ns is repel Nr..as the direction
of rotor is clock wise..(in first half cycle)..in next cycle
Ss is attract Nr(anti clk wise direction)..so the rotor cant
able to rotate in same direction.... so having only low
torque ...so that provides resudual magnetism at
innitialy..(ie dc excitation like alternator)
 
Is This Answer Correct ?    25 Yes 5 No
Saravana Babu
 
  Re: Synchrounous motor is three phase motor,but its not self starting .why?
Answer
# 10
the essential requirement for starting a synchronous machine
is that in the initial stages the rotor( which houses d.c
excited field windings) must be rotated at the synchronous
speed(determined using(120*f)/p where'f'is the supply
frequency and 'p' is the no. of poles) so that the rotor
poles may lock on to the stator rotating poles( created by
three phase balanced excitation given to the stator armature
windings) following which the rotor will rotate
synchronously with stator field at that speed. hence without
the use of an external prime mover in the beginning, the
syn. motor cannot self start....
 
Is This Answer Correct ?    9 Yes 1 No
Arnab Choudhury
 

 
 
 
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why we use star connection on the primary side of a transformer? DRDO 4
 
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