Note: The 3 phases of current are displaced from each other by 120 degrees and all three currents use a common return line. Therefore if the magnitude of all three phase currents are balanced (made equal) then the net current in the return conductor is equal to zero.
(i1 sin 0`) + (i2 sin 120`) + (i3 sin 240`) = return conductor Amps. Therefore the closer the amplitudes of i1, i2. and i3 are to each other the smaller the amplitude of the return conductor current will be.
One reason is to reduce the current flowing in the neutral return conductor. The amount of current flowing in the neutral creates a voltage drop which results in power loss.
In a balanced 3 phase system the currents flow between the phases.
If it is unbalanced, the out of balance current has to return to the source via the neutral, which is the star (wye) point of the supply transformer, which is also normally earthed (grounded).
to maintain balance in three phase
Reduce losses to neutral currents.
