What Is Line Voltage?

Line voltage is the voltage between two wires of a multi-phase power supply system. Taking three phases as an example, the three-phase lead wires of A, B, and C are also called line voltage. The magnitude of the line voltage of the star connection is three times the root of the phase voltage. The phase voltage of the triangular power supply is equal to the line voltage.

In three-phase circuits, the voltage between A, B, and C three-phase lead wires is also called line voltage. Regardless of star wiring or delta wiring, the three line voltages are U _AB , U _BC, and U _CA , as shown in the figure.

Line voltage of three power supplies

The relationship between the line voltage and phase voltage of a three-phase power supply is (take the power supply side as an example):

For delta wiring, the line voltage is equal to the phase voltage;

For star wiring, the relationship between line voltage and phase voltage is U _AB = U _AN -U _BN , U _BC = U _BN -U _CN and U _CA = U _CN -U _AN .

If the phase voltage of the three-phase power supply is a positive-sequence (negative-sequence) symmetrical group, the three-phase line voltage is also a positive-sequence (negative-sequence) symmetrical group. This pair of triangular power supplies (or triangular loads) is self-evident. For a star power supply (or star load), taking a positive sequence symmetrical group as an example, there are:

U _AB = U _AN -U _BN = 3U _AN

U _BC = U _BN -U _CN = 3U _BN

U _CA = U _CN -U _AN = 3 U _CN

It can be seen that in a symmetrical three-phase circuit, regardless of the three-phase power supply or three-phase load, U _l = U _p when the delta connection is used, and U _l = 3U _p when the star connection is used. Here, U _l and Up These are the rms values of the line and phase voltages. ^[1]