How are load currents balanced in a distribution system?

Question

Below I drew a simplistic view of a distribution transformer which supplies a particular public area for example some households and shops ect.:

Va, Vb and Vc are three phases(line voltages) of the transformer.

In my previous question I've asked about why balancing the line currents i.e making Ia, Ib and Ib close is important.

Now imagine Z1, Z2 and Z3 are initially same. Let's say they represent same type of electric owens. And we can say Ia, Ib and Ic are initially equal.

And now imagine one of the electric oven Z3 is plugged of from the mains.

In this case, will the system automatically equalize Ia, Ib and Ic again for the sake of a balanced system? Where and how is that done practically? Is there a control mechanism unit for that purpose?

Answer 1

In this case, will the system automatically equalize Ia, Ib and Ic again for the sake of a balanced system?

No it won't automatically balance and, as a result there will be some current passing down the neutral wire to the 3 phase power source. Previously, with all three loads balanced, neutral current would have been zero.

How are load currents balanced in a distribution system?

Statistically, with many households and factories, the currents are reasonably balanced in full load scenarios but nothing is perfect and current imbalances do take place.

Answer 2

Nothing is done to balance the loads actively. Balance relies on statistically having equal current draw.

While line balance is good, it's not essential. The neutral conductor is sized according to the expected degree of worst case balance.

For public single phase distribution, where it's possible to lose one line, the neutral is as big as the line conductors, so it can cope with 100% imbalance.

For power to a single well balanced 3 phase load, the neutral may be omitted altogether.