What is the role of earthing Transformer in neutral grounding?

Answer: In case where the neutral point of a three phase system are not accessible or where transformer or generators are delta connected, an artificial neutral point is required to be created. This is accomplished by means of a zigzag transformer called the earthing transformer.

As compared to the power transformer the rating of Zig Zag transformer is quite different. A grounding transformer is usually specified by the single phase fault current that it handle the two most common interval specified for the fault current are 30 and 60 s. A 60 s grounding transformer will be more expensive as compared to a 30 one.

Grounding transformers are sometimes used on distribution systems. A grounding transformer provides a source for zero sequence current. Sometimes they are used to convert a 3-wire, ungrounded circuit into a 4-wire, grounded circuit.