16 Oct 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. 30 Jan Sometimes the induction motor starts to run at one seventh speed of synchronous speed, it is called as crawling in the induction motor. When a. 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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Sometimes, squirrel cage induction motors exhibits a tendency to run at very slow speeds as low as one-seventh of their synchronous speed. This action is due to the fact that, flux wave produced by a stator winding is not purely sine wave. Welcome to Electrical Engineers Guides!

Cogging And Crawling of Induction Motor

Recieve free updates Via Email! Why does the induction motor performance phenomena known as “cogging” and “crawling” occur and how can motors can be designed to minimize them? About Terms Sitemap Contact. This characteristic of the induction motor is called cogging. If the total load torque assume remain constant, the resultant torque may fall below load torque.


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

Yes helloworldi craaling the author. Acceleration can also be limited by the torque output of the motor relative to the load torque at that speed.

A common problem is with the seventh harmonic where the seventh harmonic creates a forward rotating torque field at one seventh of the synchronous speed. 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. The shapes of the slots can also be optimized to reduce flux wave distortion. Cogging of Induction Motor This characteristic of induction motor comes into picture andd motor refuses to start at all.


Newer Post Older Post Home. Thus, a locking is created between the stator and rotor teeth. This action is due to ,the fact that the AC winding of the stator produces a flux wave which is not pure sine wave.

When a three phase supply to given to induction motor, it produces rotating magnetic flux which rotates at synchronous speed. This phenomenon is called as crawling in induction motors. Instead, it is a complex wave consisting a fundamental wave and odd harmonics like 3rd, 5th, 7th etc. This will cause a modulation in the current flow in the motor and this in turn can modulate the commutation angle of the SCRs. Where the phase modulation of the commutation angle causes an amplitude modulation of the motor current, and there is o current control loop, it is possible that the response time of the loop can further amplify the modulation.

This phenomenon is called cogging or magnetic locking of induction motor. 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. Anr of Electric Drives.

Cogging Induction motors have a series of slots in the stator and in the rotor. It is also helpful to design the motor so that the torque vs. Why not share it? If we neglect all the higher harmonics, the resultant torque will be equal to sum of fundamental torque and 7th harmonic torque. The slots will align like a stepper motor. Manoj are you sure you are crawlinf trying to increase traffic to your blog! Induction motors have a series of slots coggibg the stator and in the rotor. Induction motors that cog or crawl will not accelerate to full speed.


The seventh harmonic is the best known and documented crawl speed, but others can exist due to the total interaction of all harmonic sources. Constructing the rotor with skewed slots and providing more or fewer rotor slots than indduction slots is the remedy for both cogging and crawling.

Apart from this, there is one more reason for cogging. When a motor is started with a soft starter, the crawing harmonics are increased by the harmonic currents produced by the phase controlled SCRs of the soft starter. If the harmonic frequencies coincide with the slot frequency due to the harmonics present in the supply voltage then it causes torque modulation.

Skewing of the rotor slots, that means the stack of the rotor is arranged in such a way that it angled with the axis crzwling the rotation. The slots are skewed to keep an overlap on all slots to reduce this problem. Manoj Sahu 25 1 2 5. Another characteristic of induction motors, is crawling. Crawlihg this reason, there are an unequal number of slots in the rotor and in the stator, but there can still be situations where the slot frequencies coincide with harmonic frequencies and this can cause torque modulations.

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. If the motor crawls just below inxuction of these speed, there is a definite interaction between the motor and the harmonics produced by the soft starter.