Grounding transformer

A grounding transformer

A grounding transformer or earthing transformer is a type of auxiliary transformer used in three-phase electric power systems to provide a ground path to either an ungrounded wye or a delta-connected system.<ref>"Grounding Transformer" (PDF). Swedish Neutral.</ref><ref name=":0">Dickinson, Mike (August 19, 2011). "Grounding Transformers". Pacific Crest Transformers. Retrieved September 4, 2017.</ref> Grounding transformers are part of an earthing system of the network. They let three-phase (delta connected) systems accommodate phase-to-neutral loads by providing a return path for current to a neutral.

Grounding transformers are typically used to:

• Provide a relatively low-impedance path to ground, thereby maintaining the system neutral at or near ground potential.<ref>"Floating Neutral Transformer". Neutral Transformers.</ref>
• Limit the magnitude of transient overvoltages when restriking ground faults occur.
• Provide a source of ground fault current during line-to-ground faults.
• Permit the connection of phase-to-neutral loads when desired.<ref name=":0"/>

Earthing transformer with a zig-zag

Grounding transformers most commonly incorporate a single winding transformer with a zigzag winding configuration, but may also be created with a delta-wye transformer.<ref name=":0"/><ref>"Grounding Transformer FAQs". Pacific Crest Transformers. November 8, 2013. Retrieved September 4, 2017.</ref> Neutral grounding transformers are very common on generators in power plants and wind farms.<ref name=":0"/> Neutral grounding transformers are sometimes applied on high-voltage (sub-transmission) systems, such as at 33 kV, where the circuit would otherwise not have a ground; for example, if a system is fed by a delta-connected transformer. The grounding point of the transformer may be connected through a resistor or arc suppression coil to limit the fault current on the system in the event of a line-to-ground fault. <ref>Martin Heathcote (ed.), J & P Transformer Book, Newnes, 2011 ISBN 0080551785pp. 421-422 </ref>