An asynchronous electric motor is the simplest design device in a family of units that convert electrical voltage into motion energy.
For the first time, an engine of this type was proposed by the inventor Dolivo-Dobrovolsky. The general principle of operation is based on the interaction of a short-circuited winding and a magnetic field in rotational motion. To strengthen the field, the motor windings are placed on a pair of cores assembled from electrical steel (thickness 0.5 mm). At the same time, in order to reduce the eddy current losses, the steel plates are insulated from each other by means of varnish.
Design
The stationary part of the device, or the stator, is a hollow cylinder. Inside it, in the grooves, a winding is laid, designed for a three-phase voltage, which excites a magnetic field. The moving part, the rotor, is also made in the form of a cylinder, but only solid. Its location is the motor shaft. The rotor winding is located on its surface, in the grooves. If you mentally remove the winding from the moving part, you will get something like a cylindrical cage (like a squirrel wheel), in which the role of gratings is played by aluminum or copper rods, bridged at the ends. There is no insulation on the rods inserted into the grooves.
Principle of operation
An asynchronous motor at rest can be compared with a transformer, only here, instead of the primary winding, there are stator wires, and instead of the secondary, there is the rotor winding. The voltage available on each phase stator winding is balanced by the electromotive force induced by the magnetic field. Thanks to him, tension appears in the rotor. According to Lenz's law, the current in the rotor winding will tend to weaken the field that induced it. However, weakening the field will reduce the EMF in the stator, as a result of which the electrical equilibrium is disturbed, which forms an unbalanced overvoltage. The stator current increases, the magnetic field increases, and equilibrium is restored.
The currents in the stator and rotor are proportional. Those. a change in voltage in the stator winding leads to a change in voltage in the rotor winding. When the motor starts to rotate, the magnetic field crosses the rotor winding at high speed, due to which EMF is induced in it. A starting current also occurs in the stator, which exceeds the rated (operating) by approximately 7 times. The starting jolt phenomenon is typical for asynchronous motors. With an increase in the rotor speed, the EMF created by it gradually decreases, respectively, the currents in the rotor and stator windings also decrease. When the motor is at full speed, the current is reduced to the rated current. If the motor shaft is loaded, the current will increase again, thereby increasing the power consumption from the mains.
