Asynchronous electric machines are widely used to solve various problems of the national economy, industrial sector and household needs of the population. Such popularity of this type of electric motors is due to their technical features. And in this article we will tell you about the device and the principle of operation of an asynchronous motor.
What is an induction motor?
In accordance with clause 60 of GOST 27471-87, an asynchronous machine should be understood as such a brushless unit in which the ratio of the rotor speed to the frequency of the electric voltage in the supply network will depend on the connected load. And the arising difference of motion is described by the slip function, as the ratio:
S = (n-n1) / n
Where
- n1 is the rotor speed of the induction motor;
- n is the rotation speed of the stator magnetic field;
- s - slip, calculated as a percentage.
Asynchronous motor device
Several types of asynchronous electrical machines are produced on an industrial scale. They may differ in the location of the windings, the way they are laid, power, type of rotor, etc. As an example, we will consider the most typical device. Structurally, an asynchronous motor consists of the following components:
- shaft (1) - designed to transmit rotational force;
- stator (10) - is made of laminated steel, has a cylindrical shape, the winding is placed in the stator slots;
- squirrel-cage rotor (9) - used for electromagnetic interaction with the stator field;
- borno (11) - contains winding leads and terminals for their connection;
- bearings (2 and 6) - are installed to fix the rotating parts and end shields (3 and 8) to connect the bearing to the motor housing;
- case (5) - performs the function of protection against mechanical damage, can be equipped with radiator fins to remove heat energy;
- paws (4) - are used to attach an induction motor to building and structural elements;
- fan (7) - installed only on powerful units where there is a need for forced cooling.
But, it should be noted that this is only one of the types of such motors, in practice you can find electric machines with a squirrel-cage or phase rotor. Also a common design is a squirrel cage in aluminum.
Operating principle
In a three-phase asynchronous motor, the phase windings are offset in space relative to each other by 120 °. In the classic version, they are installed on the stator and induce an EMF of mutual induction in the rotor.
When power is applied to the electric motor, the following will occur:
- An electric current will flow in the windings of the unit, which will induce an EMF of mutual induction in the rotor gland.
- Due to the closed conducting circuit, its own currents will arise in the rotor, and, as a result of their flow, an electromagnetic field.
- After that, the stator magnetic field will begin to drag the rotor along with it as the intensity and value at each pole change.
As an example, consider this process in several positions of sinusoids on the motor windings.
As you can see in Figure 2, at this point the maximum of the magnetic field will be at pole 2 - positive and 5 - negative. The rotor will begin to be attracted to them, then the voltage curve will move to the next point and the picture of the magnetic field distribution will look like this:
As you can see in Figure 3, here the maximum magnetic flux falls on poles 1 and 4, to which the rotor of the electric motor is attracted. Further, depending on the change in voltage in time, a rotational movement of the shaft will occur.
For more information on the induction motor, see the video:
Or read in the article: https://www.asutpp.ru/asinhronnyj-elektrodvigatel.html