Neutral Wire Having Current

https://en.wikipedia.org/wiki/Ground_and_neutral explains all.

Of course the neutral carries current. That is what it is there for. There is nothing to <... be corrected...>.

A current in the neutral merely indicates an imbalance between the phase currents. In the limit, i.e. zero load current on two of the three phases, the neutral current is the same as the phase current as it is the neutral conductor that is completing the circuit.

This sounds like a homework question.

The only way the neutral conductor has current on it is if the vector sum of all three current phases is not zero. The simplest method to force this condition is to not connect the neutral to any load, including wiring leakage paths. Remove the neutral wire. Doing this and nothing else in addition will mean whatever is drawing the imbalanced power will now be without power.

If I did not connect the neutral of the supply before switching on load ,would that correct the anormally ,whereby it can be reconnected again? What about other electric equipment in the load system that is single phase and need the neutral to work?

The <...single phase...equipment...> either wouldn't work or, if spread across more than one phase, would result in some really silly voltages appearing at their inlet terminals.

<...not connect the neutral of the supply before switching on load ,would that correct the anormally...> no, it wouldn't.

The phrase <...one of the phase becomes neutral with no current...> is nonsensical at present.

The thing to be embraced is that there is nothing to be corrected; that is the job of the neutral conductor.

Yes, the neutral is doing its job and there is no stated need to reduce the neutral current to zero.

On the off chance that there is a valid but unstated reason for reducing the neutral current to zero (I have no idea what this reason might be) while still powering something with the lower voltage of phase to neutral then a step down transformer could be added that takes phase to phase power to the desired voltage.

Two reasons come to mind for neutral current in a 3 phase system. The first, of course, is an unbalanced load. The second is if the load is non-linear.

Even with a balanced load, for example, fluorescent lighting will generate neutral current at 3 times the line frequency (180 hz in US). This is because the current conducts at the voltage cycle peaks resulting in a non-sinusoidal waveform containing a large amount of third harmonic content. Each of the three phase currents add in phase for third and multiples of the third harmonic.

Fluorescent Light with Magnetic Ballast

https://www.researchgate.net/publication/319370332_Performance_analysis_of_fluorescent_and_led_lamp_system

And more specifically on the issue of triplens harmonics:

https://electrical-engineering-portal.com/what-are-triplen-harmonics

Data centers with the plurality of the loads being non-linear (before power factor corrected supplies became de rigueur) used to have significant neutral currents.

But the three phase motor are rotating well

One wouldn't expect anything else.

Friend,

A typical 3-phase 4-wire system has three phase (hot or live) wires and one neutral wire which is electrically in the center between the three phase wires. Picture this as an equilateral triangle with the three phase wires at the corners and the neutral in the very center of the triangle. Then draw lines from each corner to the center (and leave the lines between the corners in place). A single-phase load is between any corner and the neutral. A higher-voltage single-phase load (connected to two of the phase conductors without any connection to the neutral) is sometimes called a 2-phase load, but is electrically still a single-phase load. A 3-phase load is only between corners. [2-phase loads are with the phases 90-degrees apart and are drawn with 1-wire in the center and 2 or 4 wires on lines at right angles from the center. These are fairly rare, as are 6-phase circuits!]

So, a 3-phase motor will run if all three phases are energized and is independent of the neutral and the currents drawn on each phase should be equal. When you add single-phase loads, each one puts equal amounts of current on the phase and neutral wires attached to that load. If you have many single-phase circuits divided onto different phase-neutral loads the neutral will carry the sum of all the individual circuits. However since the waveform for each phase's currents are 120-degrees apart, the instantaneous currents in some are going positive while the currents in others are going negative and the actual sum is the imbalance (the vector sum) between all the phase currents, NOT the arithmetic (scalar) sum of them.

As others have pointed out, when you are dealing with loads that are not linear (typically those supplying electronic equipment) the loads impose harmonics (multiples) of the input wave form onto the wires. Certain ones of these harmonics do NOT cancel, so the neutral can carry current even if the non-linear loads are all equal. That is why the codes require the neutral conductor to be larger than the phase conductors for non-linear loads (while allowing it to be smaller otherwise)!

Have fun learning the physics and theory behind electricity, as well as the practical of what you will run into each day. The more you know, the better-equipped you will be to troubleshoot and fix the causes of problems you see in your work. You can reset a breaker that has tripped--that eliminates the symptom, but hasn't looked for and found the cause.

--JMM

It’s possible we don’t understand the question, perhaps a table of the line to neutral voltages and line currents before & after closing the breaker?

https://www.accesstraininguk.co.uk/electrical-courses?adgroup=63720112720&network=s&device=c&keyword=%2Belectrical%20%2Bcourse&adposition=&gclid=EAIaIQobChMIrM2sg67y6wIVWfBRCh2oWgMQEAAYASAAEgIRqPD_BwE

Are you running a "Y" or Delta? I'm assuming Delta, since you're not expecting current on the neutral.

I am deeply thankful to all of your experiences,knowledge and expertise shared here.I was able to resolve this issues from ideas garnered here. Thank you all

So what was the outcome, Mildred?

Harmonics