TG DG Synchronization

Not necessary for synchronization if that's what you mean.

If you have any type of systems which are not fed from DG but are fed from TR (as I do in my facility) there may be some PQ issues which would create neutral currents. If the load matches exactly, there is no issue and no neutral contactor is needed.

These systems are both contained in the same facility, right? Since you said the neutrals were linked before...it would be logical. That would be a major deciding factor. In this instance the neutral would be bonded, not switched, by convention.

This is not an IS reference, but it seems to cover your situation in a conversational manner: https://workspace.imperial.ac.uk/capitalprojects/Public/Engineering/E7EarthingRequirments.pdf

While I do not believe you need a neutral breaker, I think that a current transformer on the neutral to ground circuit tied to appropriate relaying to trip the 3 phase breaker might be desirable. This is a common practice in co-generation, which applies for the time both generators are tied together. Normally, as long as the 3 phase is balanced and you are looking at minor circulating currents through linked neutrals you will not be in trouble but if a failure occurs in either generator, a ground current can exist that could take out both generators. The cost may be proportionately high for your system to do this, I worked only on larger systems, but the cost of failures escalating beyond the point of failure is very high also. A good relay study of your system would be valuable. What you want to protect from is current going to ground and bypassing the neutral link. Particularly a fault current.

Yes, Definitely. You have 2 MVA transformer and 1250 KVA generator, Which mean on generator you are not running complete load, which you are running on transformer.

So, please check following things,

1. Whether load transformer is balance in individual phase...?

2. Load on generator is balance in individual phase...?

it is 100 % sure that load is not at all balance....!

Even if it is synchronizing but sometime due to abnormal/ single phase / transient load condition it will reflect on Neutral. But we are connected neutral together It will transfer the issue with one with other.

It is always advisable to have separate 4 pole ACB for tranformer and Generator.