Brother for a balance 3 phase ac system the current through neutral is zero if there is unbalance in the three phases as the unbalance will be accomplished by the neutral I want you to visualize you practically our distribution system as

1 Whatever transmission scheme 3 phase 4 wire or 3 wire it end our house with distribution transformer.

2 After distribution transformer 3 supply from secondary are taken of same potential and the neutral wire can be taken or can be taken from earth of houses giving each house a single phase supply.

3 In normal condition circuit is completed by the live wire and the neutral.

4 The current flow from live wire to neutral to complete the circuit and yes current flow through the neutral of the house.

5 The fact is the current in the transformers primary neutral which is linked with the power system has no flow of current during the normal operation I mention above as there is no unbalance.

6 As the any unbalance short circuit occur the unbalanced current will flow through the neutral to balance it.

And please do not ask that how the circuit of power system is completed without the flow of current in neutral of the system, there are numerical expression to visualize it but for understanding “The summation of all balanced 3 phase current to neutral cancel out each other”