On what basis are the stator windings joined into stars or triangles?

   A: The three-phase winding of the three-phase asynchronous motor has a total of six terminals, connected to the six wiring of the junction box, and marked with the symbols D1, D2, D3, D4, D5, D6, where D1 and D4, D2 and D5, D3 and D6 are each one phase, called A, B, C three-phase winding, as shown in Figure 3-2.

Figure 3-2 Layout of the six wires in a junction box

Figure 3-3 Triangle or star connection of the motor winding
      There are two kinds of connection methods for three-phase asynchronous motor, one is triangle connection, represented by the symbol "△"; The other is the star connection, which is represented by the symbol "Y". The so-called triangle connection is to connect the upper and lower two of the six terminals of the junction box with metal sheets, and then connect the power supply respectively, as shown in Figure 3-3 (a). The so-called star connection is to connect the top three terminals with metal strips, and the bottom three terminals are connected to the power supply respectively, as shown in Figure 3-3 (b).

Diagram of arrangement of six wires in junction box
    Figure 3-2 Layout of the six wires in a junction box
Motor winding triangle or star connection
    Figure 3-3 Triangle or star connection of the motor winding
    The three-phase winding of the motor is connected in what way, depending on the voltage and wiring mode indicated on the nameplate, if the nameplate is marked with voltage 220/380V, the connection △ / Y, indicating that the motor has two kinds of wiring methods, to adapt to two different voltages. If the power supply voltage is 220V, it should be connected into a triangle. If it is mistakenly connected into a star shape, the voltage connected to each phase winding will drop from 220V to 220/√3=127V, and the motor will not start because the voltage is too low, if it still bears the rated load, it is easy to cause overload and burn. If the power supply voltage is 380V, it should be connected into a star shape, such as mistakenly connected into a triangle, each phase winding will bear 380V voltage and cause the stator current to increase and burn the winding. Therefore, the correct wiring mode should be able to make the motor in normal operation, the power supply voltage must be equal to or close to the rated voltage of the motor.