The relationship between star connection and delta connection of three-phase motors and how to convert them

The wiring method of three-phase motors varies according to the motor type and operating voltage. Generally, there are two methods: star connection and triangle connection.

Star connection method: connect the three cables of the motor to the endpoints of the three symmetrical windings of the motor respectively, and then connect the three phase lines in an interlaced manner. That is, one end is connected to U1, one end is connected to V1, one end is connected to W1, and the other end is connected to U2, V2, and W2. This method is suitable for three-phase motors with a voltage of 380V.

Triangle connection method: Connect the three cables of the motor to the endpoints of the three symmetrical windings of the motor respectively, and then connect the three phase lines in pairs. That is, U1 is connected to V1, V1 is connected to W1, W1 is connected to U1, and the other end is connected to U2, V2, and W2. This method is suitable for three-phase motors with a voltage of 220V.

The star connection and delta connection of three-phase motors are two different circuit connection methods. The difference between them lies in the different flow directions of voltage and current in the motor windings, which affects the operating parameters and performance of the motor.

In the star connection, the center points of the three symmetrical windings of the motor are connected together to form a star shape, and the three outer phase lines are connected to the ends of each winding. In this way, the phase voltage of the motor will be distributed to each winding, and the difference between the voltages generated at both ends of the winding is the phase voltage, so the voltage of each winding is lower. On the other hand, the line current of the motor is equal to the phase current divided by the square root of 3, because in each winding, the current first flows into the center point, and then flows out from the center point, flowing through the two branches of the winding, the current will be dispersed, so the current flowing through each branch will be reduced. Therefore, the star connection is suitable for low-power, low-voltage three-phase motors.

In the delta connection, the ends of the three symmetrical windings of the motor are connected in pairs to form a triangle, and the three outer phase lines are connected between each winding. In this way, the phase voltage of the motor will all appear between the windings, and the line voltage of the motor is equal to the phase voltage multiplied by the square root of 3, so the voltage of each winding is higher. On the other hand, the line current of the motor is equal to the phase current, because in each winding, the current starts from one winding and flows through the other two windings. The current will not be dispersed, so the current flowing through each winding will remain unchanged. Therefore, the delta connection is suitable for high-power, high-voltage three-phase motors.

In actual use, the choice of star connection and triangle connection depends on the rated voltage and power of the motor. It is usually necessary to select the appropriate wiring method according to the actual situation of the motor to ensure the normal and safe operation of the motor. The essential difference between star connection and triangle connection is that the current and voltage are distributed differently in the motor winding, resulting in different operating parameters and performance characteristics. In actual use, the appropriate wiring method should be selected according to the actual situation of the motor, and the wiring should be correctly connected in strict accordance with the wiring method on the circuit diagram or motor identification to ensure the normal and safe operation of the motor.

The star connection and triangle connection of a three-phase motor can be converted to each other. Usually, it is necessary to select the appropriate conversion method according to the actual situation of the motor and connect the wires correctly in strict accordance with the conversion process to ensure the normal and safe operation of the motor.

The following takes the conversion of a triangle connection to a star connection as an example to introduce the conversion steps:

In the triangle connection, record the connection points of the three phase lines and the winding ends, denoted as A, B, and C, as shown in the figure:

Connect phase B and phase C to form a new connection point N, recorded as A, N, B = C, as shown in the figure:

Lead out a new phase line at the new connection point N and connect it to the center point of each winding to form a star connection, as shown in the figure:

After the above three steps, the triangle connection can be converted into a star connection.

It should be noted that the phase sequence of the motor must remain unchanged during the conversion process, that is, the phase sequence of the three phase lines A, B, and C remains unchanged after the conversion, otherwise it will cause motor damage or safety accidents. Therefore, when converting the motor star connection and delta connection, it is recommended to use professional electrical tools and instruments to operate, or ask a professional electrician to operate.