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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If the cogying frequencies coincide with the slot frequency due to the harmonics present in the supply voltage then it causes torque modulation. A transmission line has four constants R, L, C and shunt conductance. This condition is known as Cogging or Magnetic locking.

The total motor torque now consist three components as: Induction Motor Photo Credit – www.

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. This is an oc and free to study website for Electrical Engineering students, Professionals and everyone who wants to learn.

Crawlibg the rotor with skewed slots and providing more or fewer rotor slots than stator slots is inductiob remedy for both cogging and crawling. Construction and Working of Induction Motor.

If we neglect all higher order harmonic, total torque is sum of fundamental torque and seven harmonic torque. 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.


Instead, it is a complex wave consisting a fundamental wave and odd harmonics like 3rd, 5th, 7th etc. Connects Facebook Youtube Videos. These harmonics create additional torque fields in addition to the synchronous torque.

Hence 3rdd harmonics do not produce rotating field and torque. Hence, the net forward torque is equal to the sum of the torque produced by 7 th harmonic and fundamental torque.

The content on this website is copyrighted and may not be reproduced. Welcome to Electrical Engineers Guides! By my electrical Reaction: Your the link’s author? How are induction motors designed to minimize cogging and crawling? The answer to this related question may be helpful.

Crawling and Cogging in Induction Motors

Crawling of Induction Motor It has been observed that squirrel cage type induction motor has a tendency to run at very low speed compared to its synchronous speed, this phenomenon is known as crawling. Would you please elaborate it in more details.

If the mechanical load on the shaft involves constant abd torque, the torque developed by the motor may fall below this load torque. 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 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. 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.

Sometimes the induction motor starts to run at one seventh speed of synchronous speedit is called as crawling in the induction motor. Classification of Electric Drives. How to minimize this effects? Ane Globe All about Electrical and Electronics.


Crawling and cogging both are particularly related to squirrel cage induction motors. This characteristic of the induction motor is called cogging.

Crawling and Cogging of Induction Motor

The rotor tends to remain fixed in this condition and causes serious problem in starting. When the stator and the rotor teeth faces each other, the reluctance of the magnetic path is minimum. See the How to Ask page for help clarifying this question. Effect of Crawling The problem of Cogging is overcome by making the number of rotor slots prime to the number of stator slots. Apart from this, there is one more reason for mmotor. Why not share it? This action is due to the fact that harmonics fluxes produced in the gap of the stator winding of odd harmonics like 3 rd5 th7 th etc.

Hence total motor torque has there components. The 5 th harmonic produces small torque in the reverse direction but it is neglected.

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Read articles related to various Electrical Engineering topics. This is known as crawling of induction motor. Yes helloworldi am the author. But generally, three constants R, L and C are considered and the The basic cause of crawling is a stator magnetic flux wave that is distorted rather than purely sinusoidal.