Earthing Transformer

Actualy we have used NGT ( Neutral Grounding Transformer ) for Alternator Neutral grounding to limit the current , which flow through Earth at the time of system fault.

A 'zigzag transformer' is there to provide a neutral from a 3-phase supply where no neutral exists.

When the transformer or generator are delta connected or if the neurtral points are not accessible then artificially the neutral earthing point can be created with the use of star connected earthing transformer. Such transformer has no secondary . Each phase of primary has two equal parts. There are three limbs and each limb has two windings providing opposite flux during normal condition.

These transformers are of short time ratings in the range of 10 seconds to 1 minute. Hence the size of these transformers is small as compared to power transformers of same rating.

If the earthing transformer is not available then a star-delta transformer is used.