What Is a Three-Phase Circuit?

A three-phase circuit is a circuit composed of a three-phase source, a three-phase load, and a three-phase transmission line. The most basic structural feature of this circuit is that it has one or more sets of power supplies. Each set of power supplies is composed of three sinusoidal power supplies with the same amplitude, the same frequency, and the same phase difference between each other. The power supply and the load adopt a specific connection method. ^[1] Three-phase circuits are widely used in power systems such as power generation, transmission, distribution, and high-power electrical equipment.

symmetry

In a three-phase circuit, as long as there is some asymmetry, it is called

symmetry

One watt method can only be used for

Loads of star and delta connection in three-phase circuits. The three-phase winding terminals of load star connection: X, Y, and Z loads are connected to one node and started one, and B and C are connected to the power line respectively, which is called load star connection, or Y connection.

If you ignore the impedance line, the line voltage is equal to the line voltage terminal and the load power terminal. The neutral line is not connected to the two stars of the neutral line. The neutral low-voltage power network is called a four-phase three-wire system, and wireless is called a three-phase three-wire system.

(1) The phase of the line voltage is 30 ° ahead of the phase voltage.

(2) The effective value of line voltage is the effective value voltage multiplication.

(3) The line current is equal to the phase current.

The delta connection of the load: the winding of the three-phase load, the end-to-end closed loop connected in turn, and then the first end, the B and C leads are connected to the power supply, which is called the delta connection of the load, or the delta connection.

Its engineering has the following characteristics:

(1) The phase voltage is equal to the line voltage.

(2) The line current is several times the phase current. ^[3]