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 crawling and cogging in induction motor?
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.
How can an induction motor be overcome crawling?
Cogging and crawling are less in slipring induction motor due to it’s high starting torque . In cage rotor motors cogging and crawling can be reduced by proper choice of coil span and skewing (slightly twisting the rotor teeth). By chosing proper combination of stator and rotor slots we can minimize crawling.
What is cogging and crawling how it can be eliminated?
Cogging is the magnetic locking between the stator slots and rotor slots. When the no. of Rotor slots is equal to the no. of stator slots or integral multiple of rotor slots then there is a possibility of minimum reluctance. … By making rotor slots are skewed, we can eliminate this effect.
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.
What happen if 5th harmonic is given to induction motor?
What happens if fifth multiples of harmonics is given to induction motor? It will rotates in reverse direction.
What is the induction motor used for?
AC induction motors are the most common electric motors in the world. These simple, reliable and economical motors are found in refrigerators, washing machines and furnaces, as well as conveyors, pumps, winders, wind tunnels and other industrial equipment.
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 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.
What is Torque slip characteristics of induction motor?
Torque Slip Characteristics of Three Phase Induction Motor. The torque slip curve for an induction motor gives us the information about the variation of torque with the slip. The slip is defined as the ratio of difference of synchronous speed and actual rotor speed to the synchronous speed of the machine.
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 synchronous speed?
: a definite speed for an alternating-current machine that is dependent on the frequency of the supply circuit because the rotating member passes one pair of poles for each alternation of the alternating current.
What is a slotless motor?
Slotless motors are designed to optimize smoothness and create predictable torque output with minimal non-linear effects. Commonly referred to as slotless motors when rotary and air core motors when linear, slotless motor designs place only copper phase coils in the air gap of the motor.
How do you reduce cogging torque?
Cogging torque can be reduced by skewing the stator stack or skewing the magnet pole. Skewing the stator stack is to spatially skew one end of the stator stack a few degrees with respect to the other end of the stack. Usually a full skew of one slot pitch is implemented to reduce the cogging torque.
What is cogging in RC cars?
‘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.