Answer / p.puhalendhi

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.

Answer / dharm veer verma

Induction motors have a series of slots in the stator and in the rotor. These slots should not be equal in number because if they are, there is a good chance that the motor will not start at all due to a characteristic known as cogging. The slots will align like a stepper motor.
For this reason, there are an unequal number of slots in the rotor and in the stator, but there can still be situations where the slot frequencies coincide with harmonic frequencies and this can cause torque modulations. The slots are skewed to keep an overlap on all slots to reduce this problem.

Answer / santhosh s

Sometimes, squirrel cage induction motors exhibits a tendency to run at very slow speeds (as low as one-seventh of their synchronous speed). This phenomenon is called as crawling of an induction motor.
Sometimes, the rotor of a squirrel cage induction motor refuses to start at all, particularly if the supply voltage is low. This happens especially when number of rotor teeth is equal to number of stator teeth, because of magnetic locking between the stator teeth and the rotor teeth. When the rotor teeth and stator teeth face each other, the reluctance of the magnetic path is minimum, that is why the rotor tends to remain fixed. This phenomenon is called cogging or magnetic locking of induction motor.

Answer / pawan kumar

cogging means fails to start .when rotor and stator slots are same and opposite poles are interact which each other they will be locked by magnetic locking and fails to start to avoid this problem we use skewing of rotor bars or have not same rotor and stator slots..

Answer / kiran

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.

Answer / soughata kanu electrical engin

Cogging means when the stator teeth s1 and the rotor teeth s2 faces each other respectively on the sam time.And due to this is called magnetic locking or cogging. It is found that the reluctance path is minimum when the stator and rotor teeth face one opposite to each other...

On the other side crawling of an induction motor is not but when the squirrel cage rotor exhibits to run very slow speed as low as 1/7 of their synchronous speed. This phenomena is known as crawling of an induction motor..

Answer / shruti mistry

Cogging
When no.of slots of rotor and stator are equal , then a magnetic interlocking takes place and motor does not start. lt occurs during starting of motor.

Crawling
In this phenomenon motor starts to run stably at speed lower than the rated speed due to presence of harmonics. It occurs during running of motor.

Answer / michel j. discouz

Cogging torque take place due to equal no of stator and rotor pole which will cause inter locking between the stator and rotor and cause mechanical locking. To avoid cogging we use different pole of stator and rotor and taking more pole arc of stator so that avoid cogging.

Answer / sunil parmar

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

Answer / vsanth palkaran

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

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