For three-phase motors , there are two stator winding connections: delta and star. In the star connection, the tails of the three-phase windings are connected together, and the heads of the three-phase windings are connected to the power supply.
For three-phase motors, stator windings can be connected in two ways: delta and star. In a star connection, the tails of the three-phase windings are connected together, and the heads of the three-phase windings are connected to the power supply. There are two types of star connections: external star and internal star. In an internal star connection, the star point connecting the three-phase windings is fixed at an appropriate position on the stator winding, with three lead-out terminals. In an external star connection, both the head and tail of the three-phase windings are led out, and the connections and wiring are performed outside the motor.
The delta connection is to connect the head of one phase winding to the tail of another phase winding, i.e., U1 to W2, V1 to U2, W1 to V2, and the connection point is connected to the power supply.
If each phase winding is considered as a line, the star connection resembles a shining star, while the delta connection resembles a triangle, hence the names star connection or delta connection. A delta-connected motor can also be connected in two ways: internal and external angles.
For a single-voltage motor, both internal and external connections are acceptable. However, for a dual-voltage motor, only the beginning and end of the three-phase windings can be brought out, and then external connections should be made according to the voltage conditions: star connection for high voltage and delta connection for low voltage.
Why do high-voltage motors use a star connection?
For low-voltage motors, they are segmented according to power. For example, basic series motors are divided into segments based on 3kW. Motors not exceeding 3kW are star-connected, and others are delta-connected. For variable frequency motors, the segment is based on 45kW. Motors not exceeding 45kW are star-connected, and others are delta-connected. For hoisting and metallurgical motors, star connection is more common, and large-size hoisting motors may also use delta connection.
High-voltage motors are generally connected in a star configuration to avoid subjecting the motor windings to higher voltages. In a star connection, the line current equals the phase current, and the line voltage is √3 times the phase voltage (in a delta connection, the line voltage equals the phase voltage, and the line current equals √3 times the phase current). Therefore, the voltage across the motor windings is relatively lower. In high-voltage motors, the current is often relatively small, while the insulation requirements are high. Therefore, a star connection makes insulation management easier and is more economical.
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