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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 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 is a cogging mill?
: a pair of heavy rolls through which heated steel ingots are passed.
What are the types of induction motor?
Types of Induction Motors
- Split Phase Induction Motor.
- Capacitor Start Induction Motor.
- Capacitor Start and Capacitor Run Induction Motor.
- Shaded Pole Induction Motor.
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.
What is the need of starter in induction motor?
Such a device which limits high starting current is called a starter. Let us study in detail why starter is required for an induction motor. At starting time, the speed of the motor is zero and slip is at its maximum i.e. unity. So magnitude of the rotor induced emf is very large at start.
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 cogging and crawling explain with their effects over the performance of an induction motor how these effects can be removed or reduced?
The crawling and cogging of an induction motor will not go faster because the cogging characteristic of the motor will not go faster at all & the crawling characteristic of this motor will stop accelerating at a particular speed. This acceleration can be controlled through the torque in the motor.
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 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 are the effects of harmonics in 3 phase induction motor?
Voltage unbalance and harmonics present in 3-phase supply, affects the output parameters of induction motors which include output torque, current, oscillations. this cause the vibrations and temperature rise in 3-phase induction motor which increases the losses and reduces the efficiency.
Which starting method is the best method in induction motor?
Starting of an Induction Motor
- Direct on-line starter. The direct on-line starter method, of an induction motor, is simple and economical.
- Star delta starter. The star delta starter method of starting three-phase induction motors is very common and widely used among all the methods.
- Autotransformer starter.
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 do you mean by cogging?
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 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.
Why Cannot an induction motor run at synchronous speed?
Due to this difference in flux, the rotor will experience a torque and will start to rotate at speed less than synchronous speed due to lagging. So, theoretically, the Induction motor can never run at synchronous speed. This will result in no torque on the rotor, and it will stop moving due to this.
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 are the effects of harmonics in 3phase induction motor?
EFFICIENCY & TEMPERATURE RISE : A major effect of harmonic voltage and current in an induction motor is increased heating due to increased iron and copper losses at the harmonic frequencies. This affects the machine efficiency and temperature rise.
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 are the advantages of induction motor?
Induction Motor Advantages:
- Induction motors are simple and rugged in construction.
- Induction motors are cheaper in cost due to the absence of brushes, commutators, and slip rings.
- They are maintenance free motors unlike dc motors and synchronous motors due to the absence of brushes, commutators and slip rings.
What are the applications of induction motor?
The single-phase induction motors are used in low power applications. These motors are widely used in domestic and industrial applications.Three-Phase Induction Motor:
- Lifts.
- Cranes.
- Hoists.
- Large capacity exhaust fans.
- Driving lathe machines.
- Crushers.
- Oil extracting mills.
- Textile and etc.
