Talking about the connection of three-phase AC power

Through three wires, each wire acts as the other two circuits, and the phase difference of the three components is sequentially one-third of a cycle or a phase of 120° phase angle. Three-phase power connections are commonly used with a star connection (ie, a Y-shape) and a delta connection (ie, a delta shape).

Star (Y) connection

Connect the ends of the three windings of the three-phase power supply, X, Y, and Z together to form a common point O, and lead three end lines from the beginning ends A, B, and C. This connection is called "star connection method" or "Y-shaped connection method".

Figure 1 Star connection

The voltage between any two end lines is called the line voltage. The voltage between any one phase and the neutral line is called the phase voltage. The three power supplies form a loop. Only when the three-phase power supply is symmetrical and connected correctly, there is no internal power supply. Circulation.

Figure 2 Relationship between phase voltage and line voltage

As can be seen from the above figure: line voltage = 1.732 phase voltage (leading or lag 30 °), commonly known as 380V is the line voltage, 220V is the phase voltage. In this connection, the phase current and the line current are equal.

2. Triangle (Δ) connection

Figure 3 triangle connection

In the delta connection, the power or load of each phase is connected end to end, and each connected point is taken out as three phase lines of three-phase electricity. At this time, phase voltage = line voltage, line current = 1.732 phase current.

3. Comparison of star and delta connections

The phase current formula of the two connections is: Δ: phase current = power ÷ 3 line voltage Y: phase current = line current = power ÷ 1.732 line voltage star connection method due to small output power, often used for low power, high torque The motor, or the motor with higher power, is used when starting, so the loss to the machine is small, and the triangle connection is used after normal operation.

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