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Question
what is cogging and crawling
 Question Submitted By :: Guest
I also faced this Question!!     Rank Answer Posted By  
 
  Re: what is cogging and crawling
Answer
# 1
When rotor bars are made to run parallel with stator , the
torque rises & falls correspondingly causing more
pulsations. This is termed as cogging in other qords
magnatic locking. This is reduced by making the rotor bars
run at an angle to the stator ie crawling in order to make
the torque uniform.

Crawling on the other hand signifies running of motor at
almost one seventh of the rated spped due to interference
of seventh harmonics.
 
Is This Answer Correct ?    127 Yes 34 No
Sukhjeet Saini
 
  Re: what is cogging and crawling
Answer
# 2
cogging means magnectic locking, when the speed of the
stator flux is equal to rotor flux that time it will happen
due to imprpper design of rotor.



motor runs at one seventh of the rated speed is known as
crawling
 
Is This Answer Correct ?    64 Yes 41 No
Suresh
 
 
 
  Re: what is cogging and crawling
Answer
# 3
when an induction motor refuses to start even if full
voltage is applied to it, this is called as cogging. this
happens when the rotor slots and stator slots are same in
number or they are integer multiples of each other. due to
this the opposite poles of stator and rotor ome in front of
each other and get loked.
on the other hand when an IM runs at a very low apeed
(precisely speaking 1/7th of synchronous speed)even if full
rated voltage is applied to it,then it is called at
crawling. this happens due to harmonic induction torques.
in which torques due to 7th harmonic overpower the driving
torque(fundamental component torque).
 
Is This Answer Correct ?    223 Yes 12 No
Heramb Mayadeo
 
  Re: what is cogging and crawling
Answer
# 4
The cogging effect is the attraction between the magnets and
the stator poles when at rest; this attraction and cogging
is easily felt when trying to turn an electric motor by
hand. The rotor resists the turning, the magnets attempting
to stay bonded to the current poles, until just over halfway
through the air gap, where the attraction to the next pole
is stronger than that of the previous pole, resulting in a
"clunking" or jumping effect at low Speed (such as when
trying to turn by hand). This is the cogging effect,
resulting in a large torque required to begin rotation.
 
Is This Answer Correct ?    10 Yes 12 No
P.puhalendhi
 
  Re: what is cogging and crawling
Answer
# 5
The cogging effect is the attraction between the magnets and
the stator poles when at rest; this attraction and cogging
is easily felt when trying to turn an electric motor by
hand. The rotor resists the turning, the magnets attempting
to stay bonded to the current poles, until just over halfway
through the air gap, where the attraction to the next pole
is stronger than that of the previous pole, resulting in a
"clunking" or jumping effect at low RPM (such as when trying
to turn by hand). This is the cogging effect, resulting in a
large torque required to begin rotation.
The motor runs at one seventh of the synchronous speed if
the full rated supply voltage is applied is known as
crawling. This is happens because of 7th harmonic induction
torque
 
Is This Answer Correct ?    7 Yes 4 No
Pugezhenthi.p
 
  Re: what is cogging and crawling
Answer
# 6
when the full voltage applied to the stator winding ,the
rotor of 3-phase cage induction motor fails tostart.This
happenes whe the no. of stator and rotor slots are equal
or an integral ratio.so due to strong alingment of forces
are produced between stator and rotor at the instant of
starting. these forces create an alingment torque greater
than the accelarating torque.The phenomenon of magnetic
locking between stator and rotor teeth is called cogging or
teethl ocking.
 
Is This Answer Correct ?    10 Yes 6 No
Mohd.rizwan Qureshi
 
  Re: what is cogging and crawling
Answer
# 7
what u mean by cogging it is nothing but it is depend upon
the current when we never give the load cogging is not
happen in the motors to avoid the cogging just switchoff
the supply THANK YOU.

Crawling means muttil ezhayuva this is not a problem it is
a habit............veendum thank you
 
Is This Answer Correct ?    3 Yes 39 No
Vsanth Palkaran
 
  Re: what is cogging and crawling
Answer
# 8
cogging---the no. of stator slots is equal to the rotor
slots and due to 5th harmonic rotor fails to start and
causes magnetic locking this is called cogging....to
troubleshoot this scked rotor is used.and it require large
torque to overcome this strogr alignment

crawling---the speed of the motor is 7th time that of the
synchronous speed ie.Ns/7 is called as crawling
 
Is This Answer Correct ?    7 Yes 8 No
Sunil Parmar
 
  Re: what is cogging and crawling
Answer
# 9
When the voltage is low, the rotor of Squirrel-Cage motor
refuses to start at all. This happens when the number of
stator teeth S1 is equal to the number of rotor teeth S2
and is due to the magnetic locking between the stator and
rotor teeth.This is why this phenomenon also known as teeth-
locking or cogging.

The Squirrel- Cage type motor sometimes exhibit a tendency
to run stably at speeds as low as one-seventh of their
synchoronous speed Ns. This phenomenon is known as Crawling.
 
Is This Answer Correct ?    9 Yes 2 No
Shweta Gupta
 
  Re: what is cogging and crawling
Answer
# 10
if the no. of stator poles are been equal to the no. of
rotor poles in an induction motor then the machine refuses
to start. then that reason is called as cogging.this is due
to the failure of machine elements(i.e,bearings) of an
electrical machine.
 
Is This Answer Correct ?    3 Yes 3 No
Kiran
 

 
 
 
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