Why High Voltage Motor Stators Mostly Adopt Star Connection?

For three-phase motor, there are two connection methods of stator winding: △ and Y. The star connection method connects the tail of three-phase winding together, and the head of three-phase winding is connected with the power supply; There are two cases of star connection: external star connection and internal star connection. The internal star connection motor fixes the star point connected with the three-phase winding at the appropriate part of the stator winding, and has three outgoing terminals. The external star connection is to lead out all the heads and tails of the three-phase winding, and connect and connect them outside the motor.
 
The delta connection method is to connect the head of one phase winding with the tail of the other 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 with the power supply.
 
If each phase winding is regarded as a line, after the stars are connected, it looks like a luminous star, and the triangle connection law looks like a triangle, so it is called star connection law or triangle connection law. We can also connect the motor with triangle connection into two cases: internal angle and external angle.
 
If it is a single voltage motor, it can be connected internally and externally, but for a double voltage motor, it can only lead out the head and tail of the three-phase winding, and then connect externally according to the voltage. The high voltage corresponds to star connection and the low voltage corresponds to corner connection.
 
Why do high voltage motors use star connection?
 
For low-voltage motors, it will be treated in sections according to power. For example, the basic series motors are divided according to 3KW, star connection for motors not exceeding 3KW, corner connection for others, and 45KW for variable-frequency motors, star connection for motors not exceeding 45KW, corner connection for others; For lifting and metallurgical motors, there are many star connections, and large-size lifting motors will also adopt angle connection.
 
High voltage motors are generally star connected in order to avoid high voltage on the motor winding. In the star connection method, the line current is equal to the phase current and the line voltage is 3 times the root of the phase voltage (in the triangular connection method, the line voltage is equal to the phase voltage and the line current is equal to √ 3 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 requirements for the insulation grade of the motor are high. Therefore, the insulation of the motor with star connection method is better and more economical.