October 27, 2020 February 24, 2012 by Electrical4U. The important characteristics normally shown by a squirrel cage induction motors are crawling and cogging. 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.
What is meant by crawling in 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). This phenomenon is called as crawling of an induction motor. This action is due to the fact that, flux wave produced by a stator winding is not purely sine wave.
What is cogging and crawling describe briefly?
because of Cogging motors do not accelerate at all, and crawling induction motors stop accelerating at part speed. Acceleration can also be limited by the torque output of the motor relative to the load torque at that speed. Crawling and Cogging is explain for Induction Motor below.
What is cogging in motor?
Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a Permanent Magnet (PM) machine. It is also known as detent or ‘no-current’ torque. … Cogging torque is an undesirable component for the operation of such a motor.
How do you stop an induction motor from crawling?
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. In addition, it is helpful to select a skew angle for the rotor slots. The shapes of the slots can also be optimized to reduce flux wave distortion.
What is crawling in machine?
Q.What is Crawling? A: 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 resultant speed is nearly 1/7th of its synchronous speed.
Where is induction motor used?
Applications of Single Phase Induction Motor
- Small fans.
- High speed vacuum cleaners.
- Electric shavers.
- Drilling machines.
What does cogging mean?
‘Cogging’ is a general term (possibly even a colloquial term) used to describe a brushless motor appearing jumpy or jittery. It is much more prevalent at lower speeds than higher as high speeds tend to smooth out the motor considerably.
What does crawling mean?
1 : to move slowly with the body close to the ground : move on hands and knees. 2 : to go very slowly or carefully Traffic was crawling along. 3 : to be covered with or have the feeling of being covered with creeping things The food was crawling with flies.
What happens if fifth harmonics is given to induction motor?
What happens if fifth multiples of harmonics is given to induction motor? It will rotates in reverse direction. Fail to start. It will rotates in normal operation.
How do you stop cogging?
The most effective way to reduce cogging torque is skewing of stator slots or rotor poles. It means skewing of one side of stator (rotor) core by few degrees in according to the other side of core (Fig. 7). The skewing allows to eliminate the cogging torque or to reduce it to minimum.
What is a induction motor and how does it work?
An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. An induction motor can therefore be made without electrical connections to the rotor.
Is cogging torque bad?
COGGING torque is defined as the attraction/interaction of the magnetic poles (typically on the rotor) to the steel teeth (typically on the stator lamination) within an un-energized motor. … Cogging is a “bad thing”; if the machine will not rotate, it is of no use for a process.
What is speed control of induction motor?
In this method, speed of an induction motor is controlled by injecting a voltage in rotor circuit. … If we inject emf which is in phase with the rotor induced emf, rotor resistance will decrease. Thus, by changing the phase of injected emf, speed can be controlled.
Which method is most suitable to easily stop the motor?
1. DC Injection Braking. DC injection braking is a method of braking in which direct current (DC) is applied to the stationary windings of an AC motor after the AC voltage is removed. This is an efficient and effective method of braking most AC motors.
What is double cage induction motor?
A Double Cage Induction motor is that type of motor in which a double cage or two rotor windings or cages are used. This arrangement is used for obtaining high starting torque at a low value of starting current. The stator of a double cage rotor of an induction motor is same as that of a normal induction motor.