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A grounding transformer or earthing transformer is a type of auxiliary 
Grounding transformers most commonly incorporate a single winding transformer with a
A grounding transformer or earthing transformer is a type of auxiliary transformer
In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...
used in three-phase electric power
Three-phase electric power (abbreviated 3ϕ) is a common type of alternating current (AC) used in electricity generation, transmission, and distribution. It is a type of polyphase system employing three wires (or four including an optional n ...
systems to provide a ground path to either an ungrounded wye or a delta-connected system. Grounding transformers are part of an earthing system
An earthing system (UK and IEC) or grounding system (US) connects specific parts of an electric power system with the ground, typically the equipment's conductive surface, for safety and functional purposes. The choice of earthing system can ...
of the network. They let three-phase
Three-phase electric power (abbreviated 3ϕ) is a common type of alternating current (AC) used in electricity generation, Electric power transmission, transmission, and Electric power distribution, distribution. It is a type of polyphase system ...
( 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
A zigzag is a pattern made up of small corners at variable angles, though constant within the zigzag, tracing a path between two parallel lines; it can be described as both jagged and fairly regular.
In geometry, this pattern is described as a ...
winding configuration, but may also be created with a (rare case) delta-wye transformer
A delta-wye transformer is a type of three-phase electric power transformer design that employs delta-connected windings on its primary and wye/star connected windings on its secondary. A neutral wire can be provided on wye output side. It can ...
. 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. Martin Heathcote (ed.), ''J & P Transformer Book'', Newnes, 2011 pp. 421-422
References
Electric transformers Power engineering {{Electric-power-stub