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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Crawling and Cogging of Induction Motor
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. The total motor torque now consist three components as: Thus, a locking is created between the stator and rotor teeth. Now the question arises why this happens?
But generally, three constants R, L and C are considered and the Hence, harmonic torques are also developed in addition with fundamental torque. As a result, of it cogging occurs.
This phenomenon is called cogging or magnetic locking of induction motor. Cogging Magnetic locking or teeth locking Sometimes, the rotor of a squirrel cage induction motor refuses to start at all, particularly if the supply voltage is low.
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.
Crawling and Cogging in Induction Motors |
ACD 2, 6 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.
Group Drives Photo Credit – http: Crawling and cogging both are particularly related to squirrel cage induction motors.
If we neglect all higher order harmonic, total torque is sum of fundamental torque and seven harmonic torque. This phenomenon is called as crawling in induction motors. Circuit Globe All about Electrical and Electronics. As we know that there is series of slots in the stator and rotor of the induction motor. You may also like: 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.
Hence total motor torque has there components. Instead, it is a complex wave consisting a fundamental wave and odd harmonics like 3rd, 5th, 7th etc. Connects Facebook Youtube Videos. This torque produced by fifth harmonic which clgging as a braking action is small in quantity, so it can be neglected.
Read articles related to various Electrical Engineering topics. If the mechanical load on the shaft involves constant load torque, the torque developed by the motor may fall below this load torque. Thank you Charles Cowie. About Terms Sitemap Contact. The shapes of moyor slots can also be optimized to reduce flux wave distortion.
Methods to overcome Cogging This problem can be easily solved by adopting several measures. If this question can be reworded to fit the rules in the help centerplease edit the question. Manoj are you sure you are not trying to increase traffic to your blog! 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. What is meant is to arrange the stack of rotor laminations so that ihduction rotor slots are “skewed” or angled with respect to the axis of rotation.
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.
Crawling and Cogging in Induction Motors
Note that the acoustical noise related to this phenomena can also cogfing problematic. This condition is known as Cogging or Magnetic locking. Yes helloworldi am the author.
Sometimes it happens because of low supply voltage. Under this minimum reluctance path condition, magnetic locking takes place between the stator and the rotor teeth. There may be a bit more risk with electronic reduced-voltage starters. I really have no idea what you are asking and the link you are referring to doesn’t really help. When a three phase supply to given to induction motor, it produces rotating magnetic flux which rotates at synchronous speed.
This condition arises when the number of stator and rotor slots are either equal or have an integral ratio. See the How to Ask page for help clarifying this question.
This is an open and free to study website for Electrical Engineering students, Professionals and everyone who wants to inductioon. Sometimes, squirrel cage induction motors exhibits a tendency to run at very crawking speeds as low as one-seventh of their synchronous speed. But the main reason cofging starting problem in the motor is because cgoging cogging in which the slots of the stator get locked up with the rotor slots. This can be easily overcome by making number of rotor slots more than the number of stator slots and by giving slightly skew to the rotor slots skewed.
This phenomenon is called as crawling of an induction motor. It can also be reduced by using the coggging rotor. 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 cogging.