Unit Transfrormer Earthing

What should be the best earthing arrangement for the Generator and the Transformer neutrals.

That which is specified in your local electrical standards, regulations and wiring codes applicable to your country and specific application! If this is outside what you are capable of then you need to talk with either the generator company or hire a consultant or engineer to do the work for you.

Please bear in mind that if this is for a project or job, then your employer (and possibly you too) could be liable for any illegal works, property damage, loss of life (including yours!), etc if a potentially unqualified individual tries to perform said electrical specification and/or installation.

This is not a project someone should be undertaking without proper engineering training (34MW is more a grid power station than, say an industrial backup generator), please leave it to the professionals.

Alternatively please elaborate on your question (including if possible - country, application, temporary/fixed generator arrangement, how many generators, electrical codes and standards you are working to, etc), as someone here may be able to offer you some guidance (but you will still need to verify your installation is compliant for safety and legal requirements).

Excellent response... a GA point from me.

Local standards, codes, regulations has nothing to do with the type of neutral earth for generator and transformer you are going to carry out.

Operating time of modern CB can be 0.02 seconds that means fault can be interrupted without dammage to the equipment under consideration even if earthed solidly.

Practical limitations besides reliabilty of power; In a system you have to take into account that down stream (feeder) relays are time graded to isolate the faulty section only, and in consideration thereof the set time of the relays to trip the power house will be larger which can cause excessive fault current to flow.

Standard practice is that for HT generators and transformers some device in the neutral is incorporated to limit the fault current to less than half the FL, the device can be rated to 0.5 second time with proper heat disipation.

For the proper selection of the device one needs to have complete knowlede of the system and protection, standard formulas are there for sizing but for sure it is not a guess work