Asynchronous single-phase motor, its device and connection

An asynchronous single-phase motor is a machine that converts electrical energy into a mechanical one, taken as a torque on its shaft. It got its name because with increasing load on the shaft its speed decreases, lagging behind the rotation frequency of the magnetic field. The difference in these velocities is called slip.

An asynchronous single-phase motor, like all electric machines, consists of two main parts - a stator and a rotor. Inside the terminal box fixed to the body, the terminals are marked, indicated in different ways. There are four of them, and in order to properly connect them, it is necessary to understand the purpose of each of the two pairs of wires.

From an ordinary three-phase electric motor, an asynchronous single-phase motor is distinguished by the number of windings and their configuration. There are two, and they are not the same. The main winding is designed to create a rotating magnetic field of elliptical shape.

At right angles to it is an auxiliary or auxiliary inductor generating the starting torque necessary to impart the initial rotation to the rotor. The necessity of this element is due to the fact that one electric winding excites a magnetic field, the axis of symmetry of which remains stationary, and therefore an additional force is required to move the rotor from its place. Its form is elliptical, and it can be represented as the sum of two circular fields with opposite directions, one of which promotes rotation, and the other prevents it. The characteristics of such a machine are, for this reason, significantly worse than those of a three-phase machine, but in an apartment or house you have to put up with this disadvantage.

Typically, an asynchronous single-phase motor is a machine of low power, used most often for household electrical appliances. An example is a hair dryer, a vacuum cleaner, a coffee grinder or a food processor. Electric motors of this type can cope with their task, especially as there are practically no alternatives to them.

Connection single-phase asynchronous motor has its own characteristics, due to the specific design. The fact is that the starting winding is not intended for long-term operation. The machine is started in a short time. After the set operating angular velocity, the excitation circuit of the additional field must be opened, otherwise there will be its dangerous overheating and, possibly, failure. The starting time, as a rule, does not exceed three to five seconds. The opening can be done manually (by simply releasing the "Start" button) or automatically (with the help of a time switch). The most advanced devices use centrifugal systems designed to disconnect the accelerating winding at the moment when the asynchronous single-phase motor reaches the nominal speed of rotation.

In addition to the additional winding and the start button, there is another element necessary to make a single-phase induction motor rotate. The connection scheme provides a series connection with the inductance of the circuit, providing a phase shift. As a rule, it is a capacitor, when passing through which the vector of electric current changes direction relative to the voltage vector.