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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. 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.
• Limit the magnitude of transient over voltages 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.

Grounding transformers most commonly incorporate a single winding transformer with a zigzag winding configuration, but may also be created with a (rare case) delta-wye transformer. Neutral grounding transformers are very common on generators in power plants and wind farms. 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.

References

1. "Grounding Transformer" (PDF). Swedish Neutral.
2. ^ Dickinson, Mike (August 19, 2011). "Grounding Transformers". Pacific Crest Transformers. Retrieved September 4, 2017.
3. "Floating Neutral Transformer". Neutral Transformers. 14 August 2021.
4. "Grounding Transformer FAQs". Pacific Crest Transformers. November 8, 2013. Archived from the original on August 13, 2018. Retrieved September 4, 2017.
5. Martin Heathcote (ed.), J & P Transformer Book, Newnes, 2011 ISBN 0080551785pp. 421-422

v t e Transformer topics
Topics	Balun Buchholz relay Bushing Center tap Circle diagram Condition monitoring of transformers Electrical insulation paper Growler High-leg delta Induction regulator Leakage inductance Magnet wire Metadyne Open-circuit test Polarity Pressure relief valve Quadrature booster Resolver Resonant inductive coupling Severity factor Short-circuit test Stacking factor Synchro Tap changer Toroidal inductors and transformers Transformer oil Dissolved gas analysis Transformer oil testing Transformer utilization factor Vector group
Types	Autotransformer Buck–boost transformer Distribution transformer Pad-mounted transformer Delta-wye transformer Energy efficient transformer Amorphous metal transformer Flyback transformer Grounding transformer Instrument transformer Current transformer Voltage transformer Isolation transformer Austin transformer Linear variable differential transformer Parametric transformer Planar transformer Rotary transformer Rotary variable differential transformer Scott-T transformer Solid-state transformer Trigger transformer Variable-frequency transformer Zigzag transformer
Coils	Hybrid coil Induction coil Oudin coil Polyphase coil Repeating coil Tesla coil Trembler coil
Manufacturers	ABB General Electric Mitsubishi Electric ProlecGE Schneider Electric Siemens TBEA WEG

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