Exchange the principle of "synchronous and asynchronous"

Synchronous and asynchronous refers to whether the rotor speed is synchronous or asynchronous with the stator rotating magnetic field speed. Therefore, only AC can generate a rotating magnetic field, and only AC motors have the concept of synchronous and asynchronous.

Synchronous motor - principle: the rotor pole speed is the same as the rotating magnetic field speed. Features: Whether the synchronous motor is used as a motor or a generator, its speed and AC frequency will be strictly unchanged. Synchronous motors have a constant speed and are not affected by load changes.

Asynchronous motor—principle: movement is realized by induction, the stator rotates the magnetic field to cut the squirrel cage, so that the squirrel cage generates an induced current, and the induced current is forced to make the rotor rotate. There must be a speed difference between the rotor speed and the stator rotating magnetic field speed to form a magnetic field cutting the squirrel cage and generate an induced current.

Differences:

(1) Synchronous motors can generate reactive power and absorb it; asynchronous motors can only absorb reactive power.

(2) The speed of the synchronous motor is synchronized with the AC power frequency 50Hz power supply, that is, 2-pole motor 3000 rpm, 4-pole 1500, 6-pole 1000, etc. The speed of the asynchronous motor lags behind slightly, that is, 2880 for 2 poles, 1440 for 4 poles, 960 for 6 poles, etc.

(3) The current of the synchronous motor is ahead of the voltage in phase, that is, the synchronous motor is a capacitive load. Synchronous motors can be used to improve the power factor of the power supply system.

The synchronous motor cannot be started directly: the moment the power is turned on, the rotor excitation winding connected to the direct current is static, and the rotor magnetic pole is static; the stator magnetic field immediately has a high speed. Since the rotor has a moment of inertia, the rotor will not rotate, but vibrate left and right at a speed close to 0. Therefore synchronous motors require squirrel-cage windings to start. The speed difference causes it to generate an induced current, and the induced current has the characteristic of reducing the speed difference, thus causing the rotor to rotate until the induced current is balanced with the speed difference.