Transformer Body Earth & Neutral Ground Earth

The transformer tank [or frame] has to be grounded [earthed] at least once but all metallic parts which could be energized in case of insulation break down have to be bonded together and connected to grounding. The neutral of transformer has to be grounded close to transformer. In the main switchgear you have to ground the neutral once again if the switchgear is located in separate building. NEC Art.250.24(A)(2).

For different transformer secondary connections see also IEEE-142/2007 ch.1.6 Location of system grounding points.

BS7430 recommends different systems to connect the neutral to earth. See fig.1 for TN system, fig.2 for TT and IT Systems.

You will have to read the appropriate standard as it depends on the standard you are working to and the application (for the minimum required earthing).

For example (from memory), the AS/NZS substation transformer and switchgear standard calls for two independent parallel runs of rated earth cable for 100% protective earthing redundancy for transformers and switchgear.

Have a look in the standards you are working to, the information should be clearly indicated. The end customer may possibly require more extreme earthing protection above what the standards say is recommended, so also consult them (as I once found out in the middle of a project).

As per usual, not enough information.

It depends upon the country of installation, as that country's electrical standards would be immediately applicable to the installation and would determine the answer the Original Poster's question.

Theoritically ONLY one idea connection to earth is sufficient for body as well as for neutral. But practically you shopuld have atleast two for a back up and earth resistance data required. In practice three pits are made in a delt form - joined together and are used for two connection fron two different pits. In many cases standards and guidelines also demand this. I am not sure which are of glob , you are talking about. SO go by standards of the area for legal/ mandatory compliances.

In all the cases while earthing body please note that the sections connected with bolts e.g. Terminal bloc covers , tank cover etc need to be bonded tegether.

We generally use 2 body earthing and 2 neutral earthings for transformer.

common knowledge and depending the standard and the area of application. where are you installing that transformer, matters most. as for the switchgear it is as simple as ABC, unless you are assembling or manufacturing.

With two or more connections it is possible to disconnect one of them for the purposes of testing while maintaining a safe installation, from the point of view of the individual doing the testing.