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 crawling in induction motor & how it will be reduced?
Crawling of Induction Motor
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.
How do I stop cogging and crawling?
In order to reduce or eliminate the process of Cogging, the number of stator slots is never made equal to the rotor or has an integral ratio. It can also be reduced by using the skewed rotor. Cogging and Crawling are less eminent in wound rotor motors because of the higher starting torques.
How can you reduce the speed of an induction motor?
There are several ways to control the speed of an induction motor.
- Reduce the voltage applied to the motor. …
- Control the current to the motor. …
- Use a wound-rotor motor and control the resistance applied to the rotor windings. …
- Control the frequency and voltage applied to the motor.
How can we reduce motor starting torque?
A variable frequency drive (VFD) can control the torque of the induction motor by changing the applied frequency. By doing this, the motor can start at a low frequency, corresponding to the slip frequency of the motor. This allows full torque at zero, or any, speed. This is an expensive but most elegant solution.
What is crawling in an induction motor?
The crawling in the induction motor is caused by harmonics developed in motor. Crawling is the tendency of particularly squirrel cage rotor to run at speeds as low as one-seventh of their synchronous speed. This phenomenon is known as the crawling of an induction motor.
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.
How do you solve motor cogging?
Check current settings. 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.
What is V f control of induction motor?
V/F is abbreviated from voltage/frequency. V/F control is an induction motor control method which ensures the output voltage proportional with the frequency, so it maintains a constant motor flux, preventing weak magnetic and magnetic saturation phenomenon from happening.
What do you mean by cogging and crawling of 3ph induction motor?
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. Instead, it is a complex wave consisting a fundamental wave and odd harmonics like 3rd, 5th, 7th etc. … 3rd harmonics are absent in a balanced 3-phase system.
How do gears reduce speed?
The basic gear changing rule is ‘brakes to slow – gears to go’. As the car increases speed, change up through the gears. When you want to slow down, use the foot brake. You need only change to a lower gear when you need the accelerator again to ‘drive’ the car.
How can we reduce the starting current of a single phase induction motor?
Some of the techniques used to reduce the starting current of a squirrel induction motor:
- Soft starting (voltage control)
- Variable Frequency Drives (Voltage and frequency control)
- Star/Delta Starting.
- Stator impedance and/or resistance starting.
- Autotransformer Starting.
How does induction motor increase torque?
An induction motor develops torque by inducing current to the rotor, which is proportional to the differential speed of the rotor and the rotating magnetic field in the stator. For NEMA design B motors the differential speed (called slip) is between 1% and 2% at full load.
How will you improve the starting torque of a three phase induction motor?
Starting torque of an induction motor can be improved by using following methods.
- Increasing Internal Rotor Resistance.
- Increasing External Rotor Resistance.
- Variable Voltage/Frequency.