Line voltage is the difference that you calculate between two phases in a three-phase system. It is denoted as V (L-L). The phases are the red phase, the yellow phase, and the blue phase. These are shortened as R, Y, and B which is the first letter of the colour.

So what is Line Voltage vs Phase VoltageLine voltage in simple terms is the voltage difference between the two phases and phase voltage is the difference in voltage between one phase and the neutral point junction. This is denoted with a V. A line current is the current in one particular phase and the phase current is the current in the neutral three-phase system.

The two connections

There are two kinds of connections. These are the star connection and the delta connection

Star connection

A star connection is like a combination of wires that join at a common point. These are usually three-wire coils that go from the centre to the end resembling a star. The phases are the conductors. The neutral wire is present in the middle and this is shared. At times it could be a four-wired connection too.

You need to know the relation between the line voltage and the phase voltage.

Vline=3–√Vphase

Vline=3Vphase

So as you see in the above formula the line current is √3 times the phase current.

The delta connection

The second type of connection is the delta connection. Here all the three ends of the phases are connected to form a triangle. This is a completely closed circuit. It does not have a central neutral point as you see in the star connection.

The equation that you need to know here is:

Vline=Vphase

Thus you see that the line current and the phase current are equal.

Line voltage and phase voltage

• When the line voltage increases then this leads to an increase in the phase voltage.
• When the phase voltage increases then this shows as an increase in the line voltage.

Line voltage and phase voltage – Difference

Here are the differences between the line voltage and the phase voltage.

• In the star connection, the line voltage is always higher than the phase voltage.
• Line voltage is the difference between any two phases or lines. The phase voltage is the difference between the phase and the neutral junction.
• The line voltage is √3 times the phase voltage in a star connection. The line and the phase voltage are the same in a delta connection.

Things to know

• If the question does not mention the voltage type then it is a line voltage. In the case of a phase voltage, it will be mentioned. In case nothing has been mentioned then it is a line voltage.
• The voltage supply in our home is a three-phase supply and it is 440 volts. This is a line voltage. In the case of a single-phase, it is a 230 volts AC supply. This is the voltage difference between the phase junction and the neutral phase. This is a more polyphase system and here the line voltage and the line current is the same.
• In case the loads are not symmetrical then the system is not balanced.
• When you find the emf between the two phases then this is the phase voltage. When you find the emf between the phase and neutral phase then this is a line voltage.
• You use a phasor diagram to present the differences in the phases between the signals. These are sinusoidal. With the help of the phasor diagram, it is possible to analyze the signals that have the same frequency.
• Any star connection has a 60-degree angle between two of its phases. The difference in phase between any two of the phases is a star connection. When you do the calculation then you will have to consider a 60 degree. The reason for this is that the resultant is drawn between one negative axis and one real axis.

Solved examples

Explain line voltage.

The voltage difference between the two phases in a line voltage. The voltage difference between one phase to another is the line voltage. In the case of a star connection, the line voltage is equal to 1.732 times the phase voltage. In the case of line voltage and in the case of a delta connection, the line and the phase voltage are the same.

The line current is the measurement of the current in a single-phase system. It is denoted by I (L) and it is measured in ampere. In a star connection, the phase and the line current are equal. In a delta connection, the line current is 1.732 times the phase current.

Explain phase voltage.

The voltage phase is the difference between one phase and the neutral put in any three-phase system. In the case of a star connection, the phase voltage is the same as the line voltage divided by 1.732. In a delta connection, the phase and the line voltage are the same.

The phase current is the measure of the current that lies in the delta and star connection in any three-phase system. It is measured as Iph.

The phase and the line current are the same. In the delta connection, the phase current is the line current divided by 1.732.

Conclusion

The line voltage is the difference between any of the two phases in a polyphase or three-phase system. The phase system is the difference in the voltage between the neutral point and one of the phases in a three-phase or polyphase system. The line and the phase voltage are proportional to each other.

The three-phase power system is widely used. It is different from a single-phase system. In the alternating current, there is a sine wave because the current varies in direction and amplitude. A single phase has only one wave. However when you consider a three-wave system then this has three phases and three components. Every component moves in the opposite direction but all of them have the same magnitude.