What Is Cogging Of Rotor - Seniorcare2share

The phenomenon of Magnetic Locking between the stator and the rotor teeth is called Cogging or Teeth Locking. Thus, a locking is created between the stator and rotor teeth. This condition is known as Cogging or Magnetic locking.

What is meant by cogging effect?

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.

What is cogging and crawling effect?

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 measure can be taken for Minimising the effect of crawling?

This tendency of the motor to run at a stable speed as low as one seventh of the normal speed Ns. In this condition the motor is unable to pick up its normal speed is known as crawling of the motor. Crawling can be reduced by reducing fifth and seventh harmonics.

What is no load test of induction motor?

The no-load test of an induction motor is similar to the open-circuit test of a transformer. The motor is not connected from its load, and the rated voltage at the rated frequency is applied to the stator to run the motor without a load. The 2-wattmeter method measures the input power of the system.

How do you stop cogging?

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. 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 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 called cogging?

What happens if 5th harmonics 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 slip in induction motor?

“Slip” in an AC induction motor is defined as: As the speed of the rotor drops below the stator speed, or synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the rotor’s windings and creating more torque. Slip is required to produce torque.

Why skewing is used in induction motor?

The skewing of the rotor reduces the tooth harmonics, and thus prevents the crawling effect. Reduces Magnetic Hum: The skewing helps in reducing the magnetic hum, and the motor runs quieter.

What is a universal electric motor?

A universal motor is a series-wound motor — meaning that the field and armature windings are connected in series — and is mechanically commutated with brushes and a commutator. For proper operation with AC supply, a universal motor incorporates a compensation winding, in series with the armature and field winding.

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.

How does a 3 phase induction motor start?

The three-phase induction motor may be started by connecting the motor directly to the full voltage of the supply. The motor can also be started by applying a reduced voltage to the motor. The torque of the induction motor is proportional to the square of the applied voltage.

What is cogging torque in motors?

Cogging torque is the torque needed to overcome the opposing torque created by the magnetic attractive force between magnets on the rotor and the iron teeth of the stator. There are multiple rotor positions within a revolution where the cogging torque is high.

What is double cage rotor?

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 the same as that of a normal induction motor.

What is cogging crawling?

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 skewing in motor?

Cogging is magnetic locking . When an induction motor refuses to start even if full voltage is applied to it, this is called as cogging. This happens when the rotor slots and stator slots are same in number or they are integer multiples of each other. Skewing the rotor bars prevents the locking thus preventing Cogging.

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 crawling in machine?

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.

How do I stop cogging and crawling?

What are the Methods to Overcome Cogging?

The number of slots within the stator as well as the rotor should not equal.
The arrangement of rotor slots skewing can be done in such a way that it can be angled through the rotation axis.