Asynchronous motor is an electric motor that runs on alternating current. This electric machine is called asynchronous because the frequency with which the moving part of the engine rotates - the rotor, does not equal the frequency with which the magnetic field rotates, which is created due to the flow of alternating current through the winding of the immovable part of the engine - the stator. The induction motor is the most common of all electric motors, it has received the widest popularity in all industries, mechanical engineering and more.
Asynchronous motor in its design necessarily has two of the most important parts: the rotor and the stator. These parts are separated by a small air gap. The active parts of the engine can also be called windings and magnetic circuit. Structural parts provide cooling, rotor rotation, strength and rigidity.
The stator is a cast steel or cast iron body of a cylindrical shape. Inside the stator housing there is a magnetic circuit, into special cut grooves of whichstator winding installed. Both ends of the winding are brought out to the terminal box and are connected either by a triangle or a star. From the ends, the stator housing is completely closed by bearings. The bearings on the rotor shaft are pressed into these bearings. The rotor of an induction motor is a steel shaft, on which a magnetic circuit is also pressed.
Structurally, the rotors can be divided into two main groups. The engine itself will bear its name in accordance with the design principle of the rotor. The squirrel-cage induction motor is the first type. There is also a second one. This is an asynchronous motor with a phase rotor. Aluminum rods are poured into the grooves of an engine with a squirrel cage rotor (it is also called a “squirrel cage” due to the similarity of the appearance of such a rotor with a squirrel cage) and close them at the ends. The phase rotor has three windings available, which are interconnected into a star. The ends of the windings are attached to the rings fixed on the shaft. When starting the engine, special fixed brushes are pressed against the rings. Resistances are connected to these brushes, designed to reduce the starting current and smoothly start the induction motor. In all cases, a three-phase voltage is applied to the stator winding.
The principle of operation of any induction motor is simple. It is based on the famous law of electromagnetic induction. The magnetic field of the stator, created by a three-phase voltage system, rotates under the influence of a current passing through the windingstator. This magnetic field traverses the winding and conductors of the rotor winding. From this, an electromotive force (EMF) is created in the rotor winding according to the law of electromagnetic induction. This EMF causes an alternating current to flow in the rotor winding. This rotor current itself subsequently creates a magnetic field that interacts with the stator magnetic field. This process starts the rotation of the rotor in magnetic fields.
Often, to reduce the starting current (and it can be many times higher than the operating current for an asynchronous motor), starting capacitors are used, connected in series to the starting winding. After starting, this capacitor turns off, keeping the performance unchanged.
