How to speed the AC motor?
The speed of three-phase asynchronous motor is expressed as:N= (60 * f / P) * (1s) =n1 (1s),N - motor speed (R / min, revolutions per minute); F - power frequency (Hz);P - the polar logarithm of an electric motor;S - slip ratio of motor, s= (N1 - n) / n;Synchronous speed n1 motor, n1= (60 * f / P) (R / min).There is a way to change the speed of an electric motor:1, change the power frequency;2, change the number of poles of the motor;3, change the speed difference.
Rated speed n=60f/p (1-s) = synchronous speed N1 (1-S) f, power frequency P, motor pole logarithmic s slip1. use frequency changer to change power frequency speed regulation, speed range is wide, stability smoothness is better, mechanical characteristic is hard. That is, with the rated load, the speed drops much less. Stepless speed regulation. It is suitable for most three-phase squirrel cage asynchronous motors.2., change the magnetic pole logarithmic speed regulation, belong to level speed regulation, speed adjustment smoothness, generally used in metal cutting machine tools. 3. change slip speed regulation.
There are about three speed regulation methodsOne is to use the frequency converter to change the frequency of the power supply.The two is to change the number of poles of the motor (the motor itself has the conditions).Three is the slip speed regulator. This method is not to change the motor speed. Instead, it changes the clutch of the slip clutch that is connected with the motor shaft, and changes the speed of the clutch output shaft to adjust speed.
(1) rotor circuit series resistance: used in AC winding asynchronous motors. The range of speed regulation is small, the resistance consumes power, and the motor efficiency is low. Used of cranes.(2) change the speed of power supply voltage, the speed range is small, the torque decreases greatly with the voltage drop, and the three-phase motor is usually not used. Used for single-phase motor speed regulation, such as fan.(3) cascade speed regulation, in essence, is the introduction of additional rotor electromotive force, change its size to speed. It is also only used in wound motors, but the efficiency is improved.(4) electromagnetic speed regulation. Used only for slip motors. By changing the exciting coil current, stepless smooth speed regulation, the mechanism is simple, but the control power is smaller. Not suitable for long term low speed operation.
