Connected Neutral

Any imbalance current would flow in the neutral.

Thanks PWSlack.

Then, which one is better, solid grounded both of neutrals or just one of them?

The purpose of ground/earth is to operate the circuit protective device(s) in the event of a fault. A current in the neutral conductor does not constitute a fault, so the question is unanswerable.

Follow the wiring codes applicable to the country of installation. In the UK it is British Standard 7671.

Don't forget to check the electrical properties of the soil were you have those machines, before close any of the circuit´s (Neutral and Ground)

That makes a very big difference in all aspect´s.

Thwere is no reason to run a neutral to the transformer from the generator.

You will need an equipment grounding conductor. Do you have a connection on the secondary for a neutral?

What I see right know, they have an N-CT on solid grounded transformer, while the Y on the generator is left open

That would make it an IT system; pretty immune to earth faults. "They" know something. "They" can see it. Why not ask "them" what it is, instead of trying to change it willy-nilly by asking a bunch of strangers who can't?

Not really, an IT system has an earth connection for generator/transformer, while in this case the generator connection is left open.

So the only reason I can think of is the supply continuity.

You did not say how the generator is connected to the transformer.

A) generator (Y) to Transformer (Y) the secondary as (D) ?

If Yes: Generator Neutral to Ground makes sense, while the transformer Neutral is kept isolated. Then the Transformer's metal Body can be grounded. This way, any protective device can operate to protect the generator and the cables supplying the transformer. Also, protection for the people nearby etc.

In this case, a virtual Neutral can be created for the secondary .... for protection. (but that is not your enquiry).

B) generator (Y) to Transformer (D) the secondary as (y) ?

If Yes: Same as above exactly for the same reasons stated. BUT now the Neutral of the secondary should be grounded to a separate ground pit from the first one. this will now be suitable to operate protective devices to protect the transformer secondary (and also primary + Generator etc).

Thanks for your comments LAA Lucke, maybe I didn't explain it clearly.

Like in the 1st posting, the output of the Y Generator is connected to the Primary of a step up Y transformer. They left the neutral open at the generator, but solid ground on the Y transformer.

Therefore, in my comment, the A) paragraph fits for an answer.

- The Solid Ground at the transformer Neutral point will not help to properly action a protection device if a fault develops in the cable run to the transformer. It will even make things worse by bringing the leaky(faulty) phase to the neutral point of the transformer Y primary.=> Higher voltage will be experienced on the secondary.Also, no differential C.B. will function at the generator side (supply side, if fitted).

- Therefore, it is better that the neutral is grounded at the generator side only, while the transformer Y neutral point be kept isolated. If not, you will be shorting the 3 phase outputs from the generator, VIA the ground return! Since the ground resistance will be in the OHMs range, this is a real short circuit!

- The transformer metal outer body must be grounded separately. This will permit you to detect any leaks from the primary winding, to the ground (as afault), and trip the protection system at the generator side or ON the transformer side if fitted to the primary.

[if you draw a schematic circuit showing the 3 phase 'Y' of the generator, connected to the transformer primary 'Y', and do the different Neutral to ground wiring, this will help you visualise the problems I am trying to explain above].