Grounding Transformers, also called Earthing Transformers, or Neutral Couplers are used to create a neutral point in a three phase system which provides possibility for neutral earthing.

Grounding Transformers are used to provide a relatively low impedance path to ground. They also limit the magnitude of transient over voltages when re-striking ground faults occur.

Grounding Transformers likewise provide a source of ground fault current during line to ground faults which. It permit the connection of phase to neutral loads is desired.

Grounding Transformers can either be a transformer with just one winding that is zig zag connected, or a star/ delta connected winding.

Grounding Transformer Specifications usually consist of the following paramaters:

Primary Voltage - the system voltage to which the grounded winding is to be connected.

Rated KVA - the grounding transformer must be sized to carry the rated continuous primary phase current without exceeding its temperature limit

Continuous Neutral Current - three times the phase to current, or the zero sequence current.

Impedance - should be chosen so that the un-faulted phase voltages during a ground fault are within the temporary over-voltage capability of the transformer and associated equipment

Primary winding connection - Specify the type of primary connection, either Zig-Zag or grounded Wye.

Secondary connection - specify the secondary voltage and connection when applicable.

What Is a Grounding Transformer
Grounding is clearly one of the most important aspects of electrical design, but it steadfastly continues to be misinterpreted and misunderstood. Millions of dollars in liability and loss can be attributed to ground-fault arcing; thus, grounding-related issues should top the checklists of any electrical contractor. Continue Reading...

Neutral Grounding Transformer
Resistance grounding resistor systems protect power transformers and generators from damaging fault currents. Low resistance grounding of the neutral limits the ground fault current to a high level (typically 50 amps or more) in order to operate protective fault clearing relays and current transformers. These devices are then able to quickly clear the fault, usually within a few seconds. The limited fault current and fast response time also prevent over-heating and mechanical stress on conductors. Continue Reading...

Zigzag Transformer
The Zigzag grounding transformer is a commonly used option. It is a three-phase, dry-type, air- cooled auto-transformer with no secondary winding. Each phase has two identical windings, which are wound in opposite directions to give the high impedance to normal phase currents. The windings are connected in a Wye configuration. The neutral point is then connected either directly or through a neutral grounding resistor (NGR) to ground. Continue Reading...

Difference Between Grounding Transformer and Distribution Transformer
Grounding transformers (GT) differ from "standard distribution transformers" (DT) because they are used to establish a return path for ground fault currents on a system which is otherwise isolated or effectively un-grounded. This differentiates the construction in a couple of ways. Continue Reading...

Grounding Transformer Specification Sheet Sample
A specification sheet sample provided by Pacific Crest Transformers.

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