Application of NGR

NGR is used for connecting the neutral point of transformers to ground.

This is done in order to limit the ground fault current in the event of ground fault.

For 33 KV feeders you can use overcurrent, distance protection , also you can use pilot wire protection if you wish but it would be costly.

Dear Bhupender NGR's are used to restrict the earth fault currents.Objective is not to allow full fault current to circulate,which is likely to damage the core of motors/trafos etc if left unrestricted. The protection for the 33kV incomer without studying the network would be difficult and to some extent incomplete. By n large u can go in for IDMT O/C,IDMT E/F,Feeder diff,trafo diff (if applicable),distance protection(if applicable),AND Bus differential (the relay will be located in the bus coupler but CT core needs to be considered in the incomer). REF and SEF for the intervening transformer ,if the same is not taken care in the upstream switchgear. Regards Ravipra

Thanks very much sir,

regards

Bhupender

Hi Bhupender,

NGR is used basically to limit the current as mentioned by others above. It is about 1 ohm resistor or so. The purpose of that low resistance is, it does not allow a direct short to ground. If there was no resistor, then a heavy fault current will flow to ground, damaging all the cables and windings. Putting the resistance limits the current, thereby GIVING ENOUGH TIME FOR THE PROTECTION RELAYs to act and trip.