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.[1][2] 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.[3]
  • 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.[2]
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.[2][4] Neutral grounding transformers are very common on generators in power plants and wind farms.[2] 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. [5]

References

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


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