Why do we use grounding transformer?

Grounding transformers are sometimes used on distribution systems. A grounding transformer provides a source for zero-sequence current. Grounding transformers are sometimes used to convert a three-wire, under grounded circuit into a four-wire, grounded circuit.

 The grounding transformer is used to provide a path to an ungrounded system or when the system neutral is not available for some reason, for example, when a system is delta connected. It provides a low impedance path to the neutral and also limits the transient overvoltage when the ground faults occur in the system. The grounding of the system can be done in the following way

• By using a delta-star grounding transformer.
• By using a zig-zag grounding transformer

Ground transformer is used to provide aground path to either an ungrounded wye or a delta-connected system. They are typically used to:

1. Provide a relatively low-impedance path to ground, thereby maintaining the system neutral at or near ground potential.
2. Limit the magnitude of transient overvoltages when restriking ground faults occur.Provide a source of ground fault current during line-to-ground faults.
3. Permit the connection of phase-to-neutral loads when desired.