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NEUTRAL GROUNDING RESISTOR (NGR) is employed in AC distribution networks to limit the fault current which would flow from the transformer or generator neutral star point to a safe value, in the event of an earth fault in the systems, without exceeding specified temperature limits.
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NGR & NIS PANEL normally consist of two separate cubicles attached to each other. The Resistance cubicle consists of number of Resistance Assemblies (Tiers) mounted one atop other and supported on HT Post Insulators. The enclosure is fitted with covers, provided with louvers and wiremesh. A Space Heater is provided to prevent condensation of moisture.
The NIS Cubicle houses the Isolating Switch (Manual or Motorised Isolator / Vacuum Contactor) and CTs, as desired. |
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A gland plate is provided in the NIS cubicle for the Incoming Neutral, or for the Three Phase Incoming Cables, where star is formed inside the NIS Cubicle.
A Single Pole Isolator is provided in the Neutral Circuit and the other end is connected to the NGR. The HT Bushings, to connect the NGR Terminals are mounted on the partition wall of the NGR & NIS Cubicles.
LT Terminal Box for housing Thermostat and MCB, ON / OFF indicating lamps & LT terminals of Isolator & CTs etc. are provided in the NIS Cubicle.
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NIS Panel with Motorised
Isolator and CTs |
Typical Electrical Schematic for
NGR with CTs and Isolator |
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