Why High-voltage Motors Mostly Adopt Star-connected Stator Windings

Three-phase high-voltage motors' stator windings have two standard connection configurations widely used in industrial manufacture, namely star connection and delta connection. Each wiring method carries distinct electrical characteristics and applies to different voltage classes, power ranges and operating conditions.

In star connection, all tail terminals of three-phase windings are interconnected to form a neutral point, and the head terminals are separately connected to three-phase power supply. This mode is divided into internal and external star connection. The internal star connection fixes the neutral point inside the stator structure, with merely three external terminals reserved for power access. By contrast, external star connection leads out all winding head and tail ends, allowing wiring assembly outside the motor casing.

As for delta connection, each phase winding connects end to end in sequence. Specifically, U1 connects with W2, V1 connects with U2 and W1 connects with V2, and all connecting junctions serve as power access points. The two connection types get their names from their geometric shapes. Similarly, delta connection also contains internal and external wiring structures to meet diverse installation demands.

Single-voltage motors can work steadily with either internal or external connection. For dual-voltage motors, all winding terminals must be drawn out for on-site switching. Normally, star connection matches high voltage operation, while delta connection fits low voltage working scenarios.

Wiring selection of low-voltage motors is classified based on rated power. Ordinary motors under 3kW adopt star connection, and higher-power ones choose delta connection. Variable frequency motors set 45kW as the classification boundary. Hoisting and metallurgical motors prefer star connection in most cases, and oversized units occasionally apply delta connection.

Virtually all high-voltage motors adopt star connection primarily to decrease voltage load on windings. Electrically, line current is identical to phase current in star connection, and line voltage is √3 times phase voltage. In delta connection, line voltage equals phase voltage, yet line current reaches √3 times phase current.

High-voltage motors runs with relatively small current and rigorous insulation standards. Star connection effectively cuts down actual voltage endured by windings. It simplifies insulation design and production processing, helps enhance operational safety and stability, and achieves more economical manufacturing and maintenance costs for heavy-duty high-voltage motors.