AC Electric motor

1、 AC asynchronous motor

AC asynchronous motor is a leading AC voltage motor, which is widely used in electric fans, refrigerators, washing machines, air conditioners, hair dryers, vacuum cleaners, range hoods, dishwashers, electric sewing machines, food processing machines and other household appliances, as well as various electric tools and small-scale electrical equipment.

AC asynchronous motor is divided into induction motor and AC commutator motor. Induction motor is divided into single-phase asynchronous motor, AC / DC motor and repulsion motor.

The speed of the motor (rotor speed) is less than the speed of the rotating magnetic field, so it is called asynchronous motor. It is basically the same as induction motor. S = (ns-n) / NS. S is the slip rate,

NS is the magnetic field speed and N is the rotor speed.

Basic principle:

1. When the three-phase asynchronous motor is connected to the three-phase AC power supply, the three-phase stator winding flows through the three-phase magnetomotive force (stator rotating magnetomotive force) generated by the three-phase symmetrical current and generates a rotating magnetic field.

2. The rotating magnetic field has relative cutting motion with the rotor conductor. According to the principle of electromagnetic induction, the rotor conductor generates induced electromotive force and induced current.

3. According to the law of electromagnetic force, the current carrying rotor conductor is affected by electromagnetic force in the magnetic field to form electromagnetic torque and drive the rotor to rotate. When there is a mechanical load on the motor shaft, it will output mechanical energy outward.

Asynchronous motor is a kind of AC motor, and the ratio of speed under load to the frequency of connected power grid is not constant. It also changes with the size of the load. The greater the load torque, the lower the rotor speed. Asynchronous motor includes induction motor, doubly fed induction motor and AC commutator motor. Induction motor is the most widely used. It can generally be called asynchronous motor without causing misunderstanding or confusion.

The stator winding of ordinary asynchronous motor is connected to AC power grid, and the rotor winding does not need to be connected to other power sources. Therefore, it has the advantages of simple structure, convenient manufacture, use and maintenance, reliable operation, low quality and low cost. Asynchronous motor has high operating efficiency and good working characteristics. It runs at a constant speed from no-load to full load, which can meet the transmission requirements of most industrial and agricultural production machinery. Asynchronous motors are also easy to generate various protection types to meet the needs of different environmental conditions. When the asynchronous motor is running, the reactive excitation power must be absorbed from the power grid to deteriorate the power factor of the power grid. Therefore, synchronous motors are often used to drive high-power and low-speed mechanical equipment such as ball mills and compressors. Because the speed of asynchronous motor has a certain slip relationship with its rotating magnetic field speed, Its speed regulation performance is poor (except AC commutator motor). DC motor is more economical and convenient for transportation machinery, rolling mill, large machine tool, printing and dyeing and papermaking machinery requiring a wide and smooth speed regulation range. However, with the development of high-power electronic devices and AC speed regulation system, the speed regulation performance and economy of asynchronous motor suitable for wide speed regulation are comparable to that of DC motor 。

Post time: Dec-27-2021