Resistance speed regulation of three-phase asynchronous motor

The rotor of a wound asynchronous motor is connected in series with an additional resistor, which increases the slip rate of the motor and allows it to operate at lower speeds. The larger the resistance connected in series, the lower the speed of the motor. This method has simple equipment and easy control, but the slip power is consumed in the form of heat on the resistor. It belongs to graded speed regulation and has relatively soft mechanical characteristics.
Stator voltage and speed regulation method
When changing the stator voltage of the motor, a set of different mechanical characteristic curves can be obtained, thereby obtaining different speeds. Due to the fact that the torque of an electric motor is proportional to the square of the voltage, the maximum torque decreases significantly, and its speed range is relatively small, making it difficult to apply general cage type motors. In order to expand the speed regulation range, cage type motors with high rotor resistance values should be used for voltage regulation and speed regulation, such as torque motors specifically designed for voltage regulation and speed regulation, or frequency sensitive resistors should be connected in series with wound motors. In order to expand the stable operating range, feedback control should be used to achieve automatic speed adjustment when the speed regulation is above 2:1.
The main device for voltage regulation and speed control is a power supply that can provide voltage changes. Common voltage regulation methods include series saturation reactors, autotransformers, and thyristor voltage regulation. The thyristor voltage regulation method is the best. Characteristics of voltage and speed regulation:
1. The voltage and speed regulation circuit is simple and easy to achieve automatic control;
2. During the voltage regulation process, the differential power is consumed in the form of heat in the rotor resistance, resulting in low efficiency.
3. Voltage regulation and speed control are generally applicable to production machinery below 100KW.