3-Phase Power

A 3 phase system is a symmetrical power supply system in which 3 conducting lines carry alternating current with identical levels of frequency and voltage with respect to a common reference level, but with an angular phase shift difference of 120 degrees.

Usually the reference point is established through a common line connected to the ground and is normally called the neutral point.

The difference in the phase voltage between the 3 AC lines attains a peak value at 1/3rd of a cycle after one of the neighboring phase lines, and 1/3rd cycle prior to the other neighboring phase lines.

Due to this uniformly shifting phase difference between the 3 lines, the connected 3 phase linear load is able to work in an ideally balanced manner.

The phase difference across the 3-phase also helps to produce a rotational magnetic field in 3 phase motors armatures, thus enabling easy rotational configuration in them.

And it also helps to configure additional 3rd phase arrangements in transformers, such as in a 2 phase system using Scott-T transformer.

We can express the difference in voltage across two phases as the amplitude of the voltage difference between two phases which is √3 times the amplitude of the voltage of the individual phases.

In all three phase electrical systems that are used for operating balanced linear loads, we find the added total of the instantaneous currents of the three lines to be equal to zero.

Alternatively, we can say that in any three phase load, the current passing through any one of the lines at any instant will be equal in magnitude to the sum of the currents of the other two lines.

As far as the return path of the current is concerned, it is always via the other two lines for any of the individual phases.

In this category we discuss many important three phase related circuits, which complement the 3 phase AC system to create a healthier control environment for the various loads.