Neutral Grounding Resistor(NGR):
NGR is employed in AC distribution networks to limit the fault current which would flow from the transformer or generator neutral star point in the event of an earth fault in the systems. It is used when the neutral of supply transformer is accessible and its own impedance is not enough to limit fault current. The rating of the protection relays within the required time.
For Grounding Neutral of Transformer or Generator, Resistors upto 33 KV are offered for fault of short duration like 10 sec., 30 sec., 60 sec., continuous etc. Material of resistor is normally Stainless Steel, FeCrAl, Cast Iron, Copper Nickel or Nichrome.
Temperature rise is normally 375oC/760oC or as required by customer.

Features:

The metallic NGRs are designed for specific resistance values and voltages specially for shorter time ratings. The Metallic NGRs have the following advantages over a liquid type:
Their resistance value is precise and determined at the manufacturing stage remaining constant throughout their life.
Their temperature Time constant is shorter allowing a resistor of shorter time rating to be used.
They are easily to install on site.
They require virtually no maintenance and have a longer useful life.
No anti frost heating is required nor anti condensation heaters generally.
Because of problem resulting from the evaporation of gel and electrolyte the liquid resistor require constant maintenance.
Invariably the type of cooling will be natural air-cooling.