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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I would like to know what are the various causes behind this. This is an open and free to study website for Electrical Engineering students, Professionals and everyone who wants to learn. 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 to start.

I really have no idea what you are asking and the link you inductin referring to doesn’t really help.

Crawling and Cogging of Induction Motor

How are induction motors designed to minimize cogging and crawling? If the harmonic frequencies coincide with the slot frequency due to the harmonics present in the supply voltage then it causes torque modulation. It is also helpful to design the motor so that the torque vs. Constructing the rotor with skewed slots and providing more or fewer rotor slots than stator slots is the remedy for both cogging and crawling. Thus, a locking is created between the stator and rotor teeth.

As a result of these forces an alignment torque greater than the accelerating torque with consequent failure of the motor to start. The number of slots in rotor should not be equal to the number of slots in the stator.


Induction Motor Photo Credit – www. Why does the induction motor performance phenomena known as “cogging” and “crawling” occur and how can motors can be designed to minimize them? Hence, harmonic torques are also developed in addition with fundamental torque.

The rotor tends to remain fixed in this condition and causes serious problem in starting. Instead, it is a complex wave consisting a fundamental wave and odd harmonics like 3rd, 5th, 7th etc.

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. However the stator flux is not pure sinusoidal, it consists of fundamental and harmonics.

Cogging in Induction Motor

The answer to this related question may be helpful. This phenomenon is called as crawling in induction motors. Crawling and cogging both are particularly related to squirrel cage induction motors.

Under this minimum reluctance path condition, magnetic locking takes place between the stator and the rotor teeth. There coggibg be a bit more risk with electronic reduced-voltage starters.

The total motor torque now consist three components as: This condition arises when the number of stator and rotor slots are either equal or have an integral ratio. 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. Ineuction addition, it is helpful to select a skew angle for the rotor slots. These characteristics are the result of improper functioning of the motor that means either motor is running at very slow speed or it is not taking the load.


Cogging And Crawling of Induction Motor – Electrical Engineers Guide

Apart from this, there is one more reason for cogging. Welcome to Electrical Engineers Guides! 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 coggijg slots skewed.

By my electrical Reaction: 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. The 5 th harmonic produces small torque in the reverse direction but it is neglected.

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

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

By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms crawlibg Service. This torque produced by fifth harmonic which works as a braking action is small in quantity, so it can be neglected. These harmonics create additional torque fields in addition to the synchronous torque.

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The number of the stator slots equal to or an integral multiple of the rotor slots, strong alignment forces is produced between the stator and the rotor. This phenomenon is called cogging or magnetic locking of induction motor. Your the link’s author? You can also use this website as reference for your Projects, Exams.