For three-phase motors, there are two connection methods for the stator winding: triangular and star. The star connection method connects the tail of the three-phase winding together, and the head of the three-phase winding is connected to the power supply; There are two types of star connection methods: alien connection and inner star connection. The inner star connection motor fixes the star points connected to the three-phase winding at the appropriate parts of the stator winding, with three output terminals leading out. The outer star connection method leads out all the heads and tails of the three-phase winding, and connects and connects them outside the motor.
The triangular connection method is to connect the head of one phase winding to the tail of another phase winding, that is, U1 to W2, V1 to U2, W1 to V2, and connect the connection point to the power supply.
If each phase winding is treated as a line, and the stars are connected, it looks like a glowing star, and the triangle connection method looks like a triangle, so it is called the star connection method or the triangle connection method. We can also connect the triangular connection motor into two types: inner and outer angles.
If it is a single voltage motor, both internal and external connections can be used, but for a dual voltage motor, only the head and tail of the three-phase winding can be led out, and then external connections can be made according to the voltage situation. High voltage corresponds to star connections, and low voltage corresponds to corner connections.
For low-voltage motors, they will be segmented according to their power. For example, basic series motors are divided by 3kW, with star connections for motors up to 3kW and corner connections for others. For variable frequency motors, they are divided by 45kW, with star connections for motors up to 45kW and corner connections for others; For lifting and metallurgical motors, star connections are more commonly used, and corner connections are also used for large-sized lifting motors.
High voltage motors are generally connected in a star configuration to avoid the motor winding being subjected to higher voltages. In the star connection method, the line current is equal to the phase current, and the line voltage is three times the root of the phase voltage (in the triangle connection method, the line voltage is equal to the phase voltage and the line current is three times the phase current √), so the voltage borne by the motor winding is relatively low. In high-voltage motors, the current is often small and the insulation level of the motor is required to be high. Therefore, using the star connection method for motor insulation is better and more economical.