Talk about the star and triangle connection of the motor

1. Winding connection method

1. The star connection method of the motor is to connect the three-phase ends of the motor winding together, and the first end of the three-phase is the power supply end;

2. The triangle connection method of the motor is to connect the three-phase windings end to end, and the three endpoints are the power supply ends.

2. Voltage and Current

1. Star connection

The line voltage of the power supply is √3 times the phase voltage of the motor, that is, U line = √3U phase, and the line voltage phase leads the phase voltage phase by 30°. The line current of the power supply is equal to the phase current of the motor, that is, I line = I phase.

2. Triangle connection

The phase voltage of the motor is equal to the line voltage of the power supply, that is, U phase = U line, the line current of the power supply is equal to √3 times the phase current of the motor, that is, I line = √3I phase, and the line current phase lags the phase current phase by 30°.

3. Supplementary Notes

1. When the motor is connected in star, there is a neutral point. The motor is generally a three-phase symmetrical load, so the neutral line is not led out. The specific method is to connect the three tails of the three-phase winding of the motor together, and the three heads are connected to the power supply. At this time, there are two voltage levels, namely line voltage and phase voltage, and the line voltage is equal to √3 times the phase voltage, and the line current is equal to the phase current.

2. There is no neutral point when the motor is connected in a triangle. The specific method is to connect the head and tail of the three-phase winding of the motor separately. At this time, there is only one voltage level, the line voltage is equal to the phase voltage, and the line current is equal to √3 times the phase current.

3. The star-connected motor cannot be connected in a triangle, otherwise the voltage at the winding end will increase by √3 times, and the motor will inevitably burn out if it runs for a long time.

4. The motor connected in triangle cannot be connected in star shape, otherwise the voltage at the winding end will be reduced to 1/√3 of the original value, the power will be reduced, and if it carries the rated load, it will be in an overload state, which will inevitably burn the motor over time.

5. In my country, motors below 3-4KW are generally required to be connected in star shape, and motors with higher power are required to be connected in triangle shape.

6. The advantage of connecting larger power motors in a triangle is that it is convenient for Y-△ step-down starting when starting with light load, reducing the starting current to 1/3 of the original.

4. Advantages and Disadvantages

1. Star connection

The advantage is that the starting current is reduced, the winding withstand voltage is reduced, and thus the insulation level is reduced. The disadvantage is that the motor power is reduced.

2. Triangle connection

The advantage is that it increases the motor power, but the disadvantage is that the starting current is large and the winding is subjected to a large voltage, thereby increasing the insulation level.

5. Y-△ step-down starting

The motor with the stator winding connected in triangle during normal operation can adopt Y-△ step-down starting. When starting, the stator winding is first connected in star shape, so that the voltage of each phase winding is 1/√3 of the normal operation. After starting, it is restored to triangle connection, and the motor runs normally under full voltage. Although the star starting current is reduced to 1/3 of the full voltage starting current, the starting torque is only 1/3 of the rated torque, so this method is mostly used for light load or no-load starting.