Amazing three-phase asynchronous motors play a pivotal role in both industrial production and life. But have you ever wondered how its rotational speed is adjusted? Today, we will interpret this problem and take a look at the seven speed regulation methods of asynchronous motors.
The speed of the asynchronous motor is directly related to the frequency of power supply, the number of pole pairs of the motor, and the slip rate. The formula is as follows: n = 60f p(1-s). This means that we can change the rotational speed by changing these three factors.
The purpose of speed regulation for a three-phase asynchronous motor is to change the synchronous speed of the AC motor, or to keep the synchronous speed constant. In actual production, we commonly use the speed regulation methods that do not change the synchronous speed are: rotor string resistance speed regulation, wave speed regulation, cascade speed regulation of wound motors, electromagnetic slip clutch, fluid coupling and oil film clutch, etc. The methods of changing the synchronous speed are: multi-speed motor that changes the number of stator pole pairs, and frequency conversion speed regulation that changes the stator voltage and frequency.
Generally speaking, speed regulation methods are divided into high-efficiency speed regulation methods and inefficient speed regulation methods. The principle of efficient speed regulation is to keep the slip rate constant, so there is no slip loss. Such as multi-speed motors, frequency conversion speed regulation and methods that can reduce slip loss (such as cascade speed regulation, etc.). However, for inefficient speed regulation, such as the rotor string resistance speed regulation method, the energy is lost in the rotor circuit; The speed regulation method of electromagnetic clutch, the energy loss is in the clutch coil; The fluid coupling regulates the speed, and the energy is lost in the oil of the fluid coupling. Generally speaking, the slip loss increases with the expansion of the speed regulation range, so it is necessary to pay attention to the control of the speed regulation range.
Two of these ways are described in detail:
Pole change number speed regulation method: This method achieves the purpose of speed regulation by changing the wiring mode of the stator winding, thereby changing the number of stator pole pairs of the cage motor. It has the advantages of hard mechanical characteristics, good stability, no slip loss, and high efficiency. In addition, it is simple to wiring, easy to control, and inexpensive. However, this method is a step-by-step speed regulation, and the step difference is large, and a smooth speed regulation cannot be obtained. This method is suitable for equipment that does not require stepless speed regulation, such as metal cutting machine tools, lifts, lifting equipment, fans, water pumps, etc.
Frequency conversion speed regulation method: This is a speed regulation method that changes the frequency of the stator power supply of the motor, thereby changing its synchronous speed. This kind of inverter provides inverter power supply, and there are two types: AC-DC-AC inverter and AC-AC inverter. It is characterized by high efficiency and no additional loss; It has a wide range of applications and is suitable for cage asynchronous motors; The speed range is large, the characteristics are hard, and the precision is high. However, the technology is complex, the cost is high, and the maintenance is difficult. It is suitable for occasions that require high precision and good speed regulation performance.
In addition to the above-mentioned methods, there are other speed regulation methods, such as wave speed regulation, cascade speed regulation, fluid coupling speed regulation, etc., they have their own characteristics, and users can choose the appropriate method according to different needs.
It is hoped that through the above detailed introduction, we will have a deeper understanding of the speed regulation method of asynchronous motors. In actual use, it is necessary to choose the most suitable speed regulation method according to the actual situation, so as to make better use of the motor and improve production efficiency.