Table of Contents
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 cogging and crawling?
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 crawling in 3 phase induction?
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 in machine?
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 cogging of an 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. This characteristic of the induction motor is called cogging.
Why does crawling occur?
Reasons for Crawling in Induction Motor It can be caused due to the presence of space harmonics within the air gap flux. Air gap harmonics can be occurred because of the uneven sharing of the Stator winding. The difference in air gap reluctance can be occurred due to the slots in Stator & Rotor.
What is meant by cogging?
The permanent magnets produce an attraction force to all magnetic materials. Cogging is an result of the iron core motor design. The iron core has “preferred” positions relative to the magnets, and the motor must vary its thrust force to overcome these positions.
What happens if 5th harmonics is given to induction motor?
It will rotates in normal operation. Either short circuit or open circuit occurs. The sinusoidal components having frequency five times of fundamental are known as fifth harmonics. Hence induction motor will rotates in reverse direction because of reverse phase sequence of fifth harmonics.
What is the reason of crawling in an induction motor?
Crawling is a phenomenon in which Induction Motor operates at very low speed. Crawling is caused by the presence of space harmonics in the air gap flux.
What is crawling in website?
Website Crawling is the automated fetching of web pages by a software process, the purpose of which is to index the content of websites so they can be searched. The crawler analyzes the content of a page looking for links to the next pages to fetch and index.
How do you reduce 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 cogging how cogging effects can be reduced?
To reduce cogging in Iron Core linear motors, Tecnotion has taken two measures. First, the magnet plate is constructed with a skewed magnet arrangement that smooths out the movement of the iron core. Second, Tecnotion Iron Core motors use a proprietary coil laminate that is specifically designed to reduce cogging.
How do you calculate cogging torque?
The cogging torque is calculated by assuming that the flux density distribution on the side of the tooth is the same as the flux density calculated at the stator bore radius at the slot opening and multiplied by the relative permeance of the assumed circular flux path.
Which is more efficient DC or AC motor?
AC motors are generally considered to be more powerful than DC motors because they can generate higher torque by using a more powerful current. However, DC motors are typically more efficient and make better use of their input energy.
How does a universal motor work?
The universal motor is a type of electric motor that can operate on either AC or DC power and uses an electromagnet as its stator to create its magnetic field. It is a commutated series-wound motor where the stator’s field coils are connected in series with the rotor windings through a commutator.
What causes motor cogging?
One common cause of cogging is that the startup current settings are not set appropriately. This is especially true in applications where startup occurs under load. Increasing the power going into the motor at startup can give the motor the ‘extra kick’ that it needs to avoid cogging.
How do I stop cogging and crawling?
This problem can be easily solved by adopting several measures. These solutions are as follows: The number of slots in rotor should not be equal to the number of slots in the stator. 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.
What is the slip?
Slip is the differentiation between synchronous and asynchronous speed. The difference between the synchronous speed of the electric motor magnetic field, and the shaft rotating speed is slip – measured in RPM or frequency. Slip increases with increasing load – providing a greater torque.
At which condition the rotor and supply frequency is same?
i.e., Rotor current frequency = Fractional slip x Supply frequency (i) When the rotor is at standstill or stationary (i.e., s = 1), the frequency of rotor current is the same as that of supply frequency (f’ = sf = 1× f = f).
What is torque slip?
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.
Is cogging a word?
1. to manipulate or load (dice) unfairly. 2. to cheat, esp. at dice.
What is cogging in forging?
Cogging, or open die forging, is a process used to convert a cast ingot into a forged billet. The material is locally compressed between two dies which “bite” their way along the length of the ingot. As a result, the cross section is reduced and the length increases.
