This is known as crawling of induction motor. This action is due to,the fact that the AC winding of the stator produces a flux wave which is not. It can also be reduced by using the skewed rotor. Cogging and Crawling are less eminent in wound rotor motors because of the higher starting. Induction motors will not accelerate to full speed if they cog or crawl. Cogging motors do not accelerate at all, and crawling induction motors stop accelerating.

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But generally, three constants R, L and C inxuction considered and the In addition, it is helpful to select a skew angle for the rotor slots. If the harmonic frequencies coincide with the slot frequency due to the harmonics present in the supply voltage then it causes torque modulation. Home Questions Tags Users Unanswered. Would you please elaborate it in more details. See the How to Ask page for help clarifying this question. There may be a bit more risk with electronic reduced-voltage starters.

It can also be reduced by using the skewed rotor. This action is due to the fact that, flux wave produced by a stator winding is not purely sine wave. As a result in addition to mktor fundamental torque ,harmonics torques also developed whose synchronous speed for fundamental torque. P Please frame your question properly, include as much information as possible! What is meant is to arrange the stack of rotor laminations so that the rotor slots are “skewed” or angled with respect to the axis of rotation.

Crawling and cogging both are particularly related motoe squirrel cage induction motors. It is also helpful to design the motor so that the torque vs. In your link, you wrote “This can be easily overcome by making number of rotor slots more than crawlng number of stator slots inductjon by giving slightly slop to the rotor slots to the rotor slots skewed. Here is a bit more detail on the reason that distorted flux waves cause problematic torque variations.


Constructing the rotor with skewed slots and providing more or fewer rotor slots than stator slots an the remedy for both cogging and crawling.

Crawling and Cogging Effect in the Induction Motor | Electrical Revolution

If we neglect all higher order harmonic, total torque is sum of fundamental torque and seven harmonic torque. Crawling Sometime the squirrel cage induction motor refuses to start particular at low voltage, it is known as crawling effect.

About ,otor Sitemap Contact. Thank you Charles Cowie. Read articles related to various Electrical Engineering topics. Why not share it? Apart from this, there is one more reason for cogging. Note that the acoustical noise related to this phenomena can also be problematic.

The basic cause of crawling is a stator magnetic flux wave that is distorted rather than purely sinusoidal. This torque produced by fifth harmonic which works as a braking action is small in quantity, so it can be neglected. But the main reason for starting problem in the motor is because of cogging in which the slots of the stator get locked up with crawlin rotor slots.

Even after applying full voltage to the stator winding, the rotor of a 3 phase induction motor fails to start. Connects Facebook Youtube Videos. Instead, it is a complex wave consisting a fundamental wave and odd harmonics like 3rd, 5th, 7th etc. What is meant is to arrange the stack of rotor laminations so that the rotor slots are “skewed” or angled with respect to the axis of rotation.


This phenomenon is called as crawling in induction motors. Newer Post Older Post Home. The rotor tends to remain fixed in this condition and causes serious coging in starting. If the motor is well designed, it should not experience crawling with any reasonably acceptable commercial power waveform or PWM VFD waveform.

This condition is known as Cogging or Magnetic locking. Classification of Overhead Transmission Line.

However the stator flux is not pure sinusoidal, it consists of fundamental and harmonics. This phenomenon is called cogging or magnetic locking of induction motor.

Cogging in Induction Motor

I would inductkon to know what are the various causes behind this. Manoj are you sure you are not trying to increase traffic to your blog!

Distortion can be caused by stator windings that are not well distributed among the slots, an insufficient number of stator slots, a poor relationship between the number of stator slots and rotor slots, or distortion of the voltage supplied to the cofging. When the stator and the rotor teeth faces each other, the reluctance of the magnetic path is minimum.

Methods to overcome Cogging This problem can be easily solved by adopting several measures.

Yes helloworldi am the author. I have mentioned one or two in my blog post. Induction Motor Photo Credit – www.

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