Speed Control of Three Phase Induction Motor
How to control the speed of the three-phase induction motor? The speed control method includes: changing the number of poles, stator voltage control, stator frequency conversion, cascade speed control, double-feed speed regulation, hydraulic coupler, electromagnetic slip clutch, etc.
The actual speed of the three-phase asynchronous motor is given by n=ns (1 - s) =120f /p (1-s). It can be seen from the formula that you can change the speed of 3 phase induction motor using changing the number of induction motor’s poles "p," the slip "s," and the frequency of power supply"f."
Pole-changing speed control
As shown in the formula ns=120f/p, it can change the motor's synchronous speed by changing the number of poles of the stator winding, thereby changing the running speed. Pole-changing speed control is mostly used in a squirrel-cage induction motor. The pole-changing speed control has the following characteristics:
- Harder mechanical characteristics and good stability
- No-slip loss and high efficiency
- Simple wiring, convenient control, and low price
But it cannot get a smooth speed regulation by this method due to its large grade difference. Therefore, you can use it with voltage speed control and electromagnetic slip clutch to obtain a higher-efficiency smooth speed regulation characteristic.
This method is suitable for production machinery without step-less speed control, such as metal cutting machines, lifts, cranes, fans, water pumps, etc.
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