NG cubicle is used to install Neutral Grounding Transformer (NGT) and Neutral Grounding Resister (NGR) for grounding/earthing of neutral current during unbalanced three phase load of a generator, essentially required for protection of the generator winding.

The Neutral Grounding Transformer (NGT) steps down the Neutral side voltage of the generator to 110 or 220 Volt level, this stepped down voltage is fed to a Neutral Grounding Resistor and a ground earth Terminal for bringing the voltage level of neutral bus as close as possible to zero voltage level.

Why a Neutral Grounding Resistor/Neutral Earthing Resistor

Neutral Grounding Resistors are used for grounding of industrial power system. They are generally connected between ground and neutral of the transformers, generators and grounding transformers. Neutral grounding resistors are used in order to limit maximum fault current to a value which will not damage the equipment in the power system, yet allow sufficient flow of fault current to operate protective relays to clear the fault. Although it is possible to limit fault currents with high resistance Neutral Grounding Resistor, earth short circuit currents can be extremely reduced. As a result of this fact, protection devices may not sense the fault. Therefore, it is the most common application to limit single phase fault currents with low resistance Neutral Grounding Resistor to approximately rated current of transformer and/or generator.

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