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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This action is due to the fact that, flux wave produced by a stator winding is not purely sine wave. This phenomenon is called as crawling in induction motors. A transmission line has four constants R, L, C and shunt conductance. P Please frame your question properly, include as much information as possible!

By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. 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 the rotor slots.

This condition arises when the number of stator and rotor slots are either equal or have an integral ratio. Constructing the rotor with skewed slots and providing more or fewer rotor slots than stator slots is the remedy for both cogging and crawling.

Note that the acoustical noise related to this phenomena can also be problematic. Leave a Reply Cancel reply Your email address will not be published. These harmonics create additional torque fields in addition to the synchronous torque. In your link, you wrote “This can be easily overcome by making number of rotor slots more than the number of stator slots and by giving slightly slop to the rotor slots to the rotor slots skewed. When the crawlinf of stator teeth is equal to number of rotor teeth, there is possible locking tendency of the stator and rotor teeth.


Sometimes the induction motor starts to run at one seventh speed of synchronous speedit is called as crawling in the induction motor. Your the link’s author?

It is also helpful to design the motor so that the torque vs.

Skewing of the rotor slots, that means the stack of the rotor is arranged in such a way that it angled with the axis of the rotation. Constructing the rotor with skewed slots and providing more or fewer rotor slots than stator slots is the remedy for both cogging and crawling.

Home Electrical machines Power system Contact electricaleasy. Why does the cgoging motor performance phenomena known as “cogging” and “crawling” occur and how can motors can be designed to minimize them?

Cogging And Crawling of Induction Motor

I have mentioned one or two in my blog post. Classification of Electric Drives. When the slots of the rotor are equal in number with slots in the stator, they align themselves in such way that both face to each other and at this stage the reluctance of the magnetic path is minimum and motor refuse crawlng start.

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.


Hence, the net forward torque is equal to the sum of the torque produced by 7 th harmonic and fundamental torque. How are induction motors designed to minimize cogging and crawling?

Further elaboration ckgging comment: Home Questions Tags Users Unanswered. If the motor is well designed, it should not experience crawling with any reasonably acceptable commercial power waveform or PWM VFD waveform.

How to minimize this effects? This phenomenon is called cogging or magnetic locking of induction motor. The number of slots in rotor should not be equal to the number of slots in the stator.

What is Cogging in Induction Motor? – Magnetic Locking – Circuit Globe

Cogging can be caused by the number of stator and rotor slots being equal to each other or perhaps one being an integral multiple of the other.

Methods to mptor Cogging This problem can crawlinf easily solved by adopting several measures. Induction Motor Photo Credit – www. Would you please elaborate it in more details. This is an open and free to study website for Electrical Engineering students, Professionals and everyone who wants to learn. There may be a bit more risk with electronic reduced-voltage starters.

What is meant is to arrange the stack of rotor laminations anr that the rotor slots are “skewed” or angled with respect to the axis of rotation. Manoj Sahu 25 1 2 5.

The primary method of avoiding or minimizing these problems is to select an optimum number of stator and rotor slots and an optimum winding distribution scheme.