Three phase induction phases
For many industrial applications, three phase induction motors are used and these motors are most popular in the market . For choosing this type of motors can have a number of reasons:
- Non-complex construction – these don’t require permanent magnets, windings or brushes on the motor.
- These run directly off of the electric distribution grid.
- Low cost.
- Rough and suitable for uncertain environment.
- Due to not having brushes, they are long lasting and required less maintenance.
However, the main drawback of 3 phase induction motor is that they have small, load-dependant speed range. Do you know what causes is to be a drawback for induction motors?
Where ‘ns’ is the synchronous speed
‘f’ is the supply frequency
‘p’ is the number of motor poles.
The motor speed will slightly less than the synchronous speed and that will dependent on the motor load.
For example, for the given motor – if the number of poles is fixed , then the only way to change speed is to change the frequency of the power supply to the motor. This is because the electrical grids run at fixed frequency. Normally “induction motors run at a constant speed” with slight variation in the load changes.
There are so many methods have been developed for the speed control of AC induction motors but one of the most cost effective one is the ‘ open loop’, ‘v/f’ control.
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