The reason why asynchronous machines receivedwide distribution, consists in simplicity of their arrangement, reliability and manufacturability of manufacturing. 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 kilowatt, their application is very wide, practically at every industrial enterprise they make up the majority of the drive devices.
Its name is asynchronous electric machinesreceived because their angular velocity depends on the magnitude of the mechanical load on the shaft. At the same time, the higher the resistance to the torque, the more naturally, it rotates more slowly. The lag of the rotor angular velocity from the rotation frequency 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 slip on the load on the shaft is manifested in particular in the fact that in idle S is practically zero.
The device of an asynchronous machine is the same asany 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 - 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 toInductive stalling from stator currents in the rotor windings, an EMF occurs according to the rule of the right hand. Further everything is simple: the two frames, through which an electric current passes, begin to interact with each other, and a torque appears.
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 twowinding, 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 not available, for example, to drive the rotating parts of household appliances.
In addition to motors, machines are asynchronousthe opposite destination, 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. MO Dolivo-Dobrovolsky back in 1889, the first in the world used 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.
