How are the asynchronous machines constructed and who invented them

The reason why asynchronous machines are widely used is the simplicity of their design, reliability and manufacturability. Applicability for a three-phase and single-phase network, a wide range of capacities, ease of changing the direction of rotation - all this makes them indispensable as drives for a wide variety of devices, including machines and transport systems.

The essential advantage that an asynchronous machine possesses is its high coefficient of efficiency.

The most common electric motors are kilowatts, their application is very wide, practically at every industrial enterprise they make up the bulk of the drive devices.

Their name is given to asynchronous electric machines because their angular velocity depends on the magnitude of the mechanical load on the shaft. In this case, the higher the resistance of the torque, the more naturally, it rotates more slowly. Lagging of the angular velocity of the rotor from the frequency of rotation of the magnetic field created by the current passing through the stator windings is called slipping. It is calculated, as a rule, as a relative quantity:

S = (ωn-ωp) / ωn

Where:

Ωn - rotation speed of the magnetic field, rpm;

Ωp - rotor speed, rpm.

The dependence of the relative magnitude of the sliding on the shaft load is manifested in particular in the fact that in the idle mode S is practically zero.

The device of an asynchronous machine is the same as that of any other electric motor or generator. The internal surface of the stator is equipped with special grooves in which windings are laid (in the case of three-phase power supply there are three, and for single-phase motors there are two). The rotor is also uncomplicated, its design resembles a squirrel cage, and the windings are short-circuited or have contact rings.

In the case of a short-circuited rotor due to inductive interference from the stator currents, an EMF arises in the windings of the rotor according to the rule of the right hand. Further all is simple: two frames on which there passes an electric current, start to interact with each other, and there is a rotational moment.

Asynchronous machines, whose rotor is equipped with contact rings, work even easier: power to the rotating windings is fed directly through graphite brushes. Such rotors are also called phase rotors.

Single-phase asynchronous motors have two windings, working and starting, designed to create an initial torque and unwind the rotor to the working angular velocity. These motors are used where a three-phase network is unavailable, for example, to drive the rotating parts of household appliances.

In addition to engines, there are asynchronous machines of the opposite purpose, generators. Their device is almost the same. To the credit of Russian electrical engineering, we can confidently talk about the priority of our country in the field of electric motors of this type. M.O. Dolivo-Dobrovolsky as early as 1889 was the first in the world to apply three-phase power and received a rotating magnetic field. Modern asynchronous machines are fundamentally no different from the first three-phase electric motors of the great Russian inventor and scientist.