How asynchronous machines work and who invented them

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

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 power range, ease of changing the direction of rotation - all this makes them indispensable as drives for a wide variety of devices, including machine tools and conveying systems.

The essential advantage that asynchronous machines have is their high efficiency.

The most common electric motors are kilowatt, their use is very wide, in almost every industrial enterprise they make up the majority of drive devices.

Asynchronous electric machines got their name because their angular velocity depends on the magnitude of the mechanical load on the shaft. Moreover, the higher the resistance to torque, the naturally it spins more slowly. The lag 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 slip. It is calculated, as a rule, as a relative value:

S=(ωn-ωp)/ ωn

Where:

ωn - magnetic field rotation speed, rpm;

ωp - rotor speed, rpm.

The dependence of the relative amount of slip on the load on the shaft is manifested in particular in the fact that in the idle mode S is practically equal to zero.

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

In the case of a squirrel-cage rotor due to inductive pickup from the stator currents, an EMF occurs in the rotor windings according to the right hand rule. Further, everything is simple: two frames through which an electric current passes begin to interact with each other, and a torque appears.

Asynchronous machines, the rotor of which is equipped with slip rings, work even easier: the power to the rotating windings is supplied directly through the 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 spin the rotor to a working angularspeed. These motors are used where a three-phase network is not available, for example, to drive the rotating parts of household appliances.

In addition to motors, machines with opposite purposes, generators, are asynchronous. Their device is almost the same. To the credit of Russian electrical engineering, we can confidently speak about the priority of our country in the field of electric motors of this type. M. O. Dolivo-Dobrovolsky back in 1889 was the first in the world to use a three-phase power supply and obtain 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.