Why are star connections mostly used for the stators of high-voltage motors?

For low-voltage motors, they are segmented based on power. For instance, in the basic series motors, a 3kW boundary is set; those not exceeding 3kW are connected in star, while the rest are connected in delta. For variable-frequency motors, the boundary is set at 45kW; those not exceeding 45kW are connected in star, and the rest are connected in delta. As for hoisting and metallurgical motors, star connection is more common, and large-sized hoisting motors may also adopt delta connection.

High-voltage motors are generally connected in a star configuration to prevent the motor windings from being subjected to high voltages. In a star connection, the line current is equal to the phase current, and the line voltage is the square root of 3 times the phase voltage (in a delta connection, the line voltage is equal to the phase voltage, while the line current is the square root of 3 times the phase current). Therefore, the voltage that the motor windings bear is relatively low. In high-voltage motors, the current is often small, and the insulation grade requirements for the motor are high. Thus, the insulation of motors connected in a star configuration is easier to handle and more economical.