Earthing txs are used where there is no common or star point, eg on the delta connection of a power tx. It is a 1 to 1 auto tx wound in inter star format. The star point is then earthed.
They are often found in substations. Regards,
Suggestion: The earthing transformer can be delta star with the star grounded. This is governed by the requirement on the system grounding. The zig-zag star winding grounding (earthing) transformer is normally used for the ground fault lasting up to 10 seconds only. Visit