Phase voltage is the voltage across each phase of a three-phase power supply or a three-phase load. In the star connection method (set the neutral point to N) to be the relative neutral point voltage, the phase voltages of the A phase, B phase and C phase are UAN, UBN, UCN, respectively; in the delta connection, the phase and phase The voltage between the phases, the phase voltages of phase A, phase B and phase C are UAB, UBC and UCA, respectively.
Wiring
The star connection of the three-phase voltage is to connect one end of each phase power supply or load to one point, and the other end of the phase is used as a lead line, which is respectively three phase lines of three-phase voltage. For the star connection method, the midpoint (called the neutral point) can be taken out as a neutral line to form a three-phase four-wire system.
It can also be omitted, forming a three-phase three-wire system. Of course, whether or not there is a neutral line, ground lines can be added to become three-phase five-wire or three-phase four-wire systems.
The delta connection of the three-phase voltage is to connect the power supplies or loads of each phase end by end, and draw each connected point as three phase lines of the three-phase voltage. The delta connection has no neutral point and cannot lead to the neutral line, so there is only a three-phase three-wire system. After adding the ground wire, it becomes a three-phase four-wire system.
The three-phase voltage of the star connection, the line voltage is 
times the phase voltage, and the line current is equal to the phase current. When the three-phase load is balanced, even if the neutral line is connected, no current flows through it. When the three-phase load is unbalanced, the neutral line should be connected, otherwise the load of each phase will be divided.
The three-phase voltage of the delta connection, the line voltage is equal to the phase voltage, and the line current is equal to times the phase current.
