Three-phase asynchronous motor: principle of operation
Asynchronous motors have found great use in the economy. They convert up to seventy percent of electricity into mechanical. Among all electric motors, this type is the simplest, reliable and cheap to manufacture. The most common is a three-phase asynchronous motor, the principle of operation of which is discussed briefly in this article.
General about asynchronous motors
The motors do not have a brush-collector or sliding collector units, thereby achieving minimal costs during their operation. The low cost and high degree of reliability have made these engines widespread in various fields.
- single phase;
- three phase.
Single-phase mechanisms operate in fans, machine tools, washing machines, various electric tools and water supply pumps. Three-phase types have found their application in various mechanisms operating in the industrial, agricultural, construction sectors. They are also widely used for domestic needs.
A three-phase asynchronous motor, the principle of operation of which is performed in a standard manner, is an electrical unit consisting of:
- fixed stator;
The stator includes a frame where the electromagnetic core is pressed in, consisting of a magnetic wire and a three-phase distribution winding. The nucleus serves to magnetize the aggregate or the appearance of a rotating magnetic field. The magnetic circuit consists of thin, stamped, separated from each other sheets, when bonded, which form teeth and grooves. It is a small magnetic resistance for the flow that forms the stator winding. As a result, magnetization occurs, which enhances the flow.
The three-phase stator winding fits into the grooves, which in its simplest version consists of three coils with axes shifted to each other by 120 degrees. Phase coils are connected in the form of a star or a triangle.
In more detail, the principle of operation of an asynchronous electric motor in terms of connections is clearly revealed below through a simple experiment.
The rotor consists of a magnetic core, which also has stamped steel sheets with grooves where the winding is located. The latter happens:
- phase, similar to that in the stator, which is connected in a star;
- short-circuited, the most used, which is a form of "squirrel cage".
The principle of operation of the asynchronous motor
It has already been said that the three-phase stator winding is necessary for magnetization or the formation of a rotating magnetic field. It is not difficult to guess that the law of electromagnetic induction is driven by an induction motor. The principle of its operation is as follows: a rotating stator magnetic field intersects the rotor short-circuited winding, which causes an electromotive force and the flow of alternating current. This current forms its own magnetic field, and interacting with the stator rotating field, it starts the rotor rotation. As far back as the eighteenth century, this principle was demonstrated through a simple experiment: a horseshoe magnet was rotated at a constant speed near a metal disk, which was loosely fixed on the axis. The disk began to rotate for a magnet, but at a lower speed.
If you know the law of electromagnetic induction, then the phenomenon becomes clear. When the magnetic poles move, an electromotive force is induced near the surface of the disk below them.Because of it, currents are created that form a magnetic disk field.
The same phenomenon for simplicity can be thought of as a wheel (instead of a disk), in which there is a large number of spokes connected by a sleeve and a rim. They conduct current. Elementary contour are two spokes connecting their rim and bushings. The disk field is coupled with a pole magnetic field, and the disk is addicted to it. It is clear that the largest electromotive force will act in a stationary state, and the smallest, on the contrary, when it approaches the speed of disk rotation.
If you take an asynchronous motor, the principle of operation of a short-circuited rotor winding is similar to a disk, and the stator - to a rotating magnet. However, in a stationary stator, the rotation of the magnetic field is realized through a three-phase current system, passing in the winding with a phase shift.