Speed Control of Three Phase Induction Motor (1)

February 25, 2020
Latest company news about Speed Control of Three Phase Induction Motor (1)

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."


3 phase induction motor actual speed

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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