Neutral Connection For Balanced Load

According to BS 7671 means shall be provided for the main earthing terminal of the installation to be connected to the earthing point of the source of energy.

That means you need a conductor between Y secondary transformer point [earthed] to connect these two points. In a fault phase-to-ground case the short-circuit through earth is not sufficient to start the protection

You need to add an insulated conductor between the transformer neutral connection and the panel neutral. That is how all three phase 4 wire systems are designed and operated. It was omitted in your case because it was not necessary at the time. Use the same gauge wire as used for the phase conductors, for compatibility, or use a reduced size protected by the breaker rating for the spring charging motor. Or purchase a transformer and derive the voltage you need to run the spring charging motor.

You should have a ground conductor that is separate from the neutral conductor. That is used to carry the earth connections from your motors and equipment to the ground connection that your transformer is earthed to.

Of course, doing such a thing will unbalance the phases.

https://www.tutorialspoint.com/star-star-connection-of-transformer-three-phase-transformer-connection#:~:text=The%20star%2Dstar%20connection%20of,out%20as%20the%20line%20terminal.

Do you have a tertiary winding in the transformer?

https://www.linkedin.com/pulse/winding-one-talks-tertiary-peter-salerno-ncso-coss

No Sir it hasn't tertiary winding, it is simply two winding Transformer 1250Kva 6.6/0.451kv dyn11.

I agree with the solution to install one Control/Auxiliary Transformer 400/230Vac on the incoming of the ACB/Trafo. This is more economical then installing a bunch of cables from Tr. Neutral to panel Neutral. Output side. Instead of bring.

Suggestion about keeping ground conductor separate from the neutral conductor is complying to IEC Standard. Surely will take into consideration.

Thanks for responding to my enquiry.

Seems like a delta wound transformer would trap the harmonics....

Yes that's right, Harmonic current keep circulating in delta winding and does not reflect to utility. Its overheating effect is obvious. But our TR is already very much over sized.

NEC [NFPA 70] in USA recommends a grounding conductor between the source [of the power] grounding and the consumer grounding in any case [grounded system and ungrounded system]. The earth shall not be considered as an effective ground-fault current path. See NEC art.250.4 A and B.

IEC 60364-1 , BS 7671 or BS 7430 permits [IT system] only local grounding if the source system is ungrounded or grounded through an impedence.

Simpler solution could be using a small 400/230V single phase transformer connected between two phases on primary side, with secondary feeding the ACB motor.

We had 3-phase (and no neutral) LV switchboards in one of the power plants.

All the single phase loads like lighting and small power are supplied using 3-phase, Dyn connected, 415/433V ratio transformers through 3-phase, 4-wire Distribution boards.

Simpler solution could be using a small 400/230V single phase transformer connected between two phases on primary side, with secondary feeding the ACB motor.

Yes this is the most economical solution and time saving keeping the rest system integrity as it is. Neutral and Ground bus will remain isolated. We will surely go for this option.

Later I dig more and found in this system for single phase loads one 20KVA single phase 400/230Vac is used. But I must use another aux. TR. around 500/600VA 400/230Vac only for ACB spring charging motor. Whose primary must come from TR output.

Thanks for valuable input.

Of course, doing such a thing will unbalance the phases.

Can anybody help me how to upload doc/pdf file to this forum. Asking to insert link??

The best way is to upload it to the cloud and put the link in a reply to the original poster, which is Anonymous Poster #1.

https://www.pdf2go.com/pdf-to-text

https://cloudconvert.com/doc-to-txt

Thanks all for your technical expertise shared. Please see attached report I have finally submitted. Client intension to go with Inverter option. Kindly advice how much watt inverter would be enough for spring charging motor of ACB. I have proposed 1000W I believe it very much oversized.

https://drive.google.com/file/d/1A2jOqv-JZBvYEA9SggABYPWrGWsQhBAr/view?usp=sharing

<...how much watt inverter would be enough for spring charging motor of ACB...>

The forum cannot see either the label on it or the manufacturer's instructions for it, which are where the answer can be read.

Yes you are right, I am waiting issue of WO to take spring charging motor name plate data. But so far I have seen in common range of 200W to 600W.

If <...in common range of 200W to 600W...> is true then <...believe it very much oversized...> would be false.

The absence of as-built documentation and maintenance manuals and procedures for this piece of kit would raise a very loud alarm here.