Three-phase motors.

Each electric motor consists of a fixed part, called the stator, located in the engine block, and the moving part, called the rotor, seated on a shaft resting in bearings.

Induction motor parts: 1- stator core, 2 - stator winding, 3 - hull, 4 - squirrel cage rotor 5 - cage rings, 6 - motor shaft, 7 i 8 - bearing shields;

In the stator casing there is a core made of thin steel sheets mutually insulated, the inner surface of which is grooved; a three-phase winding is placed in the slots. The compact squirrel-cage rotor consists of a cylindrical core, made of insulated steel sheets.

The rotor winding is placed in slots on the outer surface of the cylinder. This winding consists of several copper or aluminum rods, short-circuited at both ends (copper or aluminum), located on both sides of the rotor.

Heat is generated in the motor by current flow in the stator and rotor windings and by friction in the bearings. This heat is dissipated by a fan. Operation of a three-phase induction motor (asynchronous) is based on the use of the phenomenon of a rotating magnetic field. If we connect the stator terminals to the network, it is in its winding that current will flow, which creates a rotating magnetic field in the stator. The magnetic lines of this field during its spinning will cut the bars of the rotor cage, producing in them the electromotive force of induction, under the influence of which induced currents will flow in compact bars. The interaction of the magnetic field of these currents and the rotating magnetic field will generate forces, acting on individual rods, under the influence of which the rotor will rotate in the direction of rotation of the stator magnetic field, but at a slightly lower speed.

The figure shows the cross-section of the stator and rotor parts of the induction motor with the marked sense of the force lines of the magnetic field rotating at the rotational speed ns. Because the rotational speed nw is lower than the rotational speed of the rotating field, therefore the magnetic lines of the rotating field will cut the rotor bars, inducing an electromotive force in them. The return of that strength, and thus also electricity, it is opposite to the direction of rotation of the magnetic field (the rotor is lagging behind the rotating magnetic field). The ratio of the difference in the rotational speeds of the rotating field ns and the rotor nw to the rotational speed of the rotating field is called motor slip s.

There is little engine slip during idling (ok. 0,5%), as the engine is loaded, the slip increases and it comes to high power engines 2%, and in engines with lower power up to 4%.

Three-phase motors have six terminals for connection to the mains and for switching the internal windings into a star or delta.

Ways of connecting a compact asynchronous motor: a) stator windings star connected, b) stator windings delta connected. Attention: the ends of the windings formerly marked X, Y, Z are now designated U2, V2, W2.

Regardless of this, special "zero - star - delta" switches are used to switch the motor windings at the time of start-up in order to reduce the current drawn from the network.

Three-phase motors used to drive gastronomic machines usually have a protected housing, hooded or closed, depending on conditions and rooms, in which they work.