Earth Test Reports

Do you mean transformer insulation resistance test report (measurements of internal resistance of transformer phase to transformer metalwork for the purpose of checking transformer creepage and clearance along with transformer oil insulation properties)?

Or do you mean actual tests of the transformer earth resistance (either the transformer itself or the transformer installed on site testing its site protective earth path resistance)?

Please provide more information.

I assume that you want to know about the testing of Earth Resistance Values for various systems (HT, LT, Transformer, etc.) Right? If you are talking about system (neutral) earthing, then no standard in the world specifies a minimum or maximum value for system earth resistance. It is only said that the system earth resistance should be low enough (in IS, IE Rules, IEC, IEEE, etc.).

But, as far as equipment earthing is concerned, the National Electric Code (India) 1985, prescribes a maximum permissible value of 5 Ohms for equipment earthing.

Also, it is suggested that the measurement of earth resistance be done only after linking all the earth pits in the plant. That would be real scenario during an actual earth fault. There is no meaning in mesauring individual earth pit resistance.

Further reading can be made at Megger.com website. They have some wonderful publications on earthing & measurement of earth resistance.