In electrical engineering, there are two simple ways to connect a three-phase motor. They vary 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 a “triangle”. It involves connecting the stator windings in series. In fact, the end of the first starting motor winding is connected to the second. This type of connection assumes the occurrence of high inrush currents and allows the engine to issue full rated power.
The second type of connection is called a “star”. When using it, the ends of the windings are connected together, and power is supplied to their beginning. Such a connection of a three-phase motor is more gentle, but at the same time the motor gives out one and a half times less power than when connected with a “triangle”.
The most correct is considered a combined connection. It is used mainly on high power engines, but it is also suitable for domestic conditions, as it protects the engine from unnecessary overloads, and at the same time it gives out the full power stated in the passport. The engine starts using a star connection. However, he will not experience large loads from high currents. After the revolutions reach the nominal value, there is a switch to the “triangle” type winding, which continues to work until the end of the work. Such a 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 fuses or entire protective mechanisms are included in the circuit .
Quite often, many people are faced with a situation where there is a three-phase motor available, 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 terminal of the winding and connected to the network. In this case, it should be borne in mind that the capacitance of the capacitors must vary depending on the engine speed. Therefore, they are connected in parallel to each other in such a way that when turned on, both capacitors are in the network, and when reaching the operating speed, the second capacitor must be disconnected.
Therefore, when a three-phase motor is connected to a single-phase network, a capacitor that is constantly working is called a working one, and the one that is turned off is called a starting one. In this case, the capacitance of the starting capacitor should be approximately three times greater than the working one. The starting capacitor is connected via a separate button, which is held until the engine reaches the specified speed.
It is worth noting that with such a connection, the engine loses more than 60% of its power, and if it is connected using the “star” scheme, such a loss can increase by one and a half times. Therefore, in such cases, it is recommended to use the “triangle” scheme so that power losses are minimal.