Connection of three-phase motor

In electrical engineering there are two simple ways to connect a three-phase motor. They differ significantly among themselves, and their choice depends on the operating conditions and the type of engine.

The first type uses a three-phase motor connection called the "triangle". It involves joining the stator windings in series. In fact, the end of the first starting motor winding is connected to the second one. This type of connection assumes the occurrence of high starting currents and allows the engine to give out full passport power.

The second type of connection is called a "star". When using it, the ends of the windings are connected together, and power is fed to their start. This connection of the three-phase motor is more sparing, but the engine produces one and a half times less power than when connected with a "triangle".

The most correct is the combined connection. It is used mainly on high-power engines, but it is also suitable for domestic conditions, because it protects the engine from unnecessary overloads, and at the same time it gives out the full power claimed in the passport. The engine starts using a star connection. At the same time, it will not experience heavy loads from high currents. After the revolutions reach their nominal value, a switch to the "triangle" winding takes place, which continues until the end of the work. This connection of a three-phase motor involves the use of a time relay or a special starter.

Separately it is worth noting that most engines react negatively to voltage drops or short circuits. Therefore, when developing projects for connecting a three-phase motor, usually the circuit includes fuse-links or whole protective mechanisms.

Quite often, many people are faced with a situation where there is a three-phase motor, and the electrical network has only one phase. In such cases, a three-phase motor is connected to a single-phase network using capacitors. They are connected through a free winding terminal and connected to the network. It should be borne in mind that the capacitance of capacitors should vary with the engine speed. Therefore, they are connected in parallel to each other in such a way that, when switched on, both capacitors are in the network, and when reaching the operating speed, the second capacitor should be switched off.

Therefore, when a three-phase motor is connected to a single-phase network, a capacitor, constantly working, is called a working one, and the one that is disconnected is called a starting one. In this case, the capacity of the start capacitor should be approximately three times that of the working capacitor. The starting capacitor is connected via a separate button, which is held until the engine reaches the set speed.

It is worth noting that with this connection, the engine loses more than 60% of its power, and if it is connected using the "star" scheme, then such a loss can increase by another half. Therefore, in such cases it is recommended to use the "triangle" scheme, so that power losses are minimal.