Speed control circuit of multi-speed machine

The synchronous speed of the motor n = 60 f / P. When the grid frequency f is fixed, n is inversely proportional to the number of pole pairs P. If the number of pole pairs P can be changed, then n will also change. Pole-changing speed regulation is only applicable to cage asynchronous motors. Multi-speed motors are generally divided into two-speed, three-speed, and four-speed. Two-speed motor stators are equipped with one set of windings, and three-speed and four-speed are two sets of windings.

  (A) It is a triangle (four pole, low speed) and double star (two pole, high speed) connection method, which belongs to constant power speed regulation;

  (B) is a star (four-pole, low-speed) and double-star (two-pole, high-speed) connection method, which belongs to constant torque speed regulation. When the directional "low speed" position, the motor is connected to a triangle and runs at low speed; when the S directional high speed position, the contactors KM1 and KM2 work, and the motor is connected to a double star for high speed operation. The role of the time relay is: when the motor starts directly at high speed, the low-speed contactor KM3 is first turned on. After the KT delay, it automatically switches to the contactor KM1 and KM2 to work and the motor runs at high speed. The purpose is to limit the starting current.

  The advantage of two-speed motor speed regulation is that it can adapt to the requirements of different load properties. When constant power speed regulation is required, a triangle-double star motor can be used. When constant torque speed regulation is used, a star-double star motor can be used. The circuit is simple and the maintenance is convenient. The disadvantage is that there is a stepped speed regulation and the price is more expensive. Multi-speed machine speed regulation has a certain use value, usually used in conjunction with mechanical speed change to expand its speed regulation range.