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

It can also be reduced by using the skewed rotor. Effect of Crawling The problem ccrawling Cogging is overcome by making the number of rotor slots prime to the number of stator slots.

About Terms Sitemap Contact. Leave a Reply Cancel reply Your email address will not be published. Here is a bit more detail on the reason that distorted flux waves cause problematic torque variations. When the stator and the rotor teeth faces each other, the reluctance of the magnetic path is minimum. If we neglect all the higher harmonics, the resultant torque will be equal to sum of fundamental torque and 7th harmonic torque.


If the motor is well designed, it should not experience crawling with any reasonably acceptable commercial power waveform or PWM VFD waveform.

This phenomenon is called as crawling of an induction motor. Sometimes, squirrel cage induction motors exhibits a tendency to run at very slow speeds as low as one-seventh of their synchronous speed. The answer to this related question may be helpful. I have mentioned one or two in my blog post. Welcome to Electrical Engineers Guides! Cogging and Crawling are less eminent in wound rotor motors because of the higher starting torques. This is known as crawling of induction motor.

Crawling and Cogging of Induction Motor

Manoj Sahu 25 1 2 5. Please clarify your specific problem or add additional details to highlight exactly what you need. Circuit Globe All about Electrical and Electronics. Hence 3rdd harmonics do not produce rotating field and torque. The shapes of the slots can also be optimized to reduce flux wave distortion.

Note that the acoustical noise related to this phenomena can also be problematic. This characteristic of the induction motor is called cogging.

Classification of Electric Drives. Classification of Overhead Transmission Line. The rotor tends to remain fixed in this condition and causes serious problem in starting. The primary method of avoiding or minimizing these problems is to select cgging optimum number of stator and rotor slots and an optimum winding distribution scheme. Home Questions Tags Users Unanswered.

However the stator flux is not pure sinusoidal, it consists of fundamental and harmonics. If the harmonic frequencies coincide with the slot frequency due to the harmonics present in the supply voltage then it causes torque modulation.


How are induction motors designed to minimize cogging and crawling? Group Drives Photo Credit – http: 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 coggijg.

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Crawling and Cogging in Induction Motors

Sometimes the induction motor starts to run at one seventh speed of synchronous speedit is called as crawling in the induction motor. Thus, a locking is created between the stator and rotor teeth. The number of slots in rotor should not be equal to the number of slots in the stator.

ACD 2, 6 Your the link’s author? Here crxwling consider only 5 th and 7 th harmonics and rest are neglected.

Crawling and Cogging of Induction Motor

Home Electrical machines Power system Contact electricaleasy. 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.

These solutions are as follows: Hence, harmonic torques are also developed in addition with fundamental torque.