Why do most high-voltage motor stators use star connection?
For three-phase motors, the stator windings have two connection methods: delta and star. The star connection is to connect the tails of the three-phase windings together, and the heads of the three-phase windings are connected to the power supply. The star connection methods include outer star connection and inner star connection. There are two cases of star connection. In the inner star connection motor, the star point connecting the three-phase windings is fixed at the appropriate part of the stator winding, and there are three outlet terminals. The outer star connection is to lead out all the heads and tails of the three-phase windings. , while connections and wiring are made outside the motor.
The delta connection method is to connect the head of one phase winding to the tail of another phase winding, that is, U1 is connected to W2, V1 is connected to U2, W1 is connected to V2, and the connection point is connected to the power supply.
If each phase winding is treated as a line, when the stars are connected, they will look like shining stars, and the triangle connection will look like a triangle, so it is called star connection or triangle connection. We can also connect triangle connection motors into internal angles and external angles.
If it is a single-voltage motor, both internal and external connections are possible, but for a dual-voltage motor, you can only lead out all the heads and tails of the three-phase windings, and then make external connections according to the voltage. High voltage corresponds to star connection, and low voltage corresponds to star connection. Corner joint.
Why do high-voltage motors need star connection?
For low-voltage motors, they will be segmented according to their power. For example, the basic series motors are divided into 3kW, and those that do not exceed 3kW are star-connected, and others are corner-connected. For variable frequency motors, they are divided into 45kW, and those that do not exceed 45kW are star-connected. Others are star-connected. Corner connection is used; for hoisting and metallurgical motors, star connection is more common, and large-size lifting motors will also use corner connection.
High-voltage motors are generally star-connected to prevent the motor windings from being exposed to higher voltages. In the star connection, the line current is equal to the phase current, and the line voltage is 3 times the root of the phase voltage (in the delta connection, the line voltage is equal to the phase voltage and the line current is equal to √3 times the phase current), so the motor windings bear The voltage 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, the insulation of the motor with star connection is easier to handle and more economical.
