A three-phase electric motor is an electric machine designed to operate in three-phase AC networks . Such an engine consists of a stator and a rotor. The stator has three windings shifted by one hundred and twenty degrees. When a three-phase voltage appears in the winding circuit, magnetic fluxes are formed at the poles, the rotor rotates. Electric motors are synchronous and asynchronous. Three-phase asynchronous motors are widely used in industry and in everyday life. Such motors are single-speed, in which case the motor windings are connected according to the "star" or "triangle" scheme, and multi-speed. The last units are switchable, in which case there is a transition from one connection scheme to another.
Three-phase electric motors are divided according to the connection schemes of the windings. There are two connection schemes - connection with a star and a triangle. The connection of the motor windings in the "star" type is the connection of the ends of the motor windings at one point (zero node): an additional conclusion is obtained - zero. The free ends are connected to the phases of the electric current network 380 V. Externally, such a connection resembles a three-pointed star. The following diagram is shown in the photo: “star” and “triangle” connection.
The connection of the motor windings of the "triangle" type is a
series connection of the windings: the end of the first is connected to the beginning of the second winding, the end of the second to the beginning of the third, and the end of the third to the beginning of the first. Three-phase voltage is applied to the winding connection nodes. With this connection of the windings, there is no zero output. Outwardly, it resembles a triangle.
The connection of the "star" and the "triangle" are equally common, they do not have significant differences. To connect the windings in the "star" type (when the motor is operating in the rated mode), the linear voltage must be higher than when connecting in the "triangle" type. Therefore, the characteristics of a three-phase motor indicate the rated voltage as follows: 220/380 V or 127/220 V. If it is necessary to connect an electric motor to a 380 V network with a rated voltage of 220/380 V, the windings must be connected in the form of a "star", and the rated voltage of the motor It will be 380/660 V (of the "triangle" type).
It should be noted that the combination of a star and a triangle is often used. This is done in order to more smoothly start the electric motor. During start-up, a star connection is used, and then, using a special relay, a switchover to the "triangle" occurs, thus, the starting current is reduced. Such schemes are recommended for starting high-power motors requiring a large inrush current. It is important to remember that in this case the starting current exceeds the rated current by seven times.
There are other combinations when connecting electric motors, for example, the connection with a "star" and a "triangle" can be replaced by a double, triple "star", as well as other connection options. Such methods are used for multi-speed (two-, four-, etc.) electric motors.