NGTR

Hello Guest,

NGTR = Neutral Grounding Transformer and Resistor.

The NGTR system allows monitoring of Neutral to Earth Currents, and also limits that current to a safe value.

The NGTR system also allows protection relays to operate, if current increases past the pre-set point of the protection relays, thus limiting the current to a safe value, or totally disconnecting the supply voltage to the Transformer, as needed.

Summary:

NGTR's are installed in the neutral of the distribution power system transformers to limit the ground fault current.

The failure of NGTR's may cause the distribution system to be ungrounded.

The existence of any phase to ground failure in the ungrounded power system generally leads to phase to ground voltage build-up in the other two healthy phases which can result in insulation breakdown plus failures of other electrical equipment.

This failure may also be hazardous to persons in the vicinity.

In other words, a good NGTR system is essential in every 3 phase generating situation, and much more so in dry soil conditions.

Practical Failures:

There have been some spectacular and dangerous failures over the past several years, in the Middle East, where the NGTR system was not used correctly, and because of very high soil (desert sand) resistivity, along with insufficient earth mats and bonding of exposed metal, has caused great damage, both personal and to equipment, not just electrical equipment.

These failures were caused by a poor understanding by the installers of the generating equipment, of incorrectly installing Earth Mats/bonding all exposed metal, plus incorrect settings on the protection relays.

The above failures have not generally been published in the Newspapers or TV.

Hope that assists you.

Kind Regards....