What is NGR (Neutral Grounding Resistor)?

It can be used for the LV system also.

But it since it is a long time practice we all are used to solidly earthed system in LV.

It is used mainly in the HV system......................because

to protect all the HT motors and other outgoing feeders which are designed to withstand low earth fault current and also in any system most likely fault in the system is earth fault.

with NGR are we are limiting the earthfault current so that all these equipments can be protected

The topic is too large to be explained here. Please visit this website:

www.i-gard.com

They have some very good publications on the subject.

It is already mentioned by sms149 that 'it can be used for the LV system also'. In addition, I would like to clarify one more thing. If you use NGR in a system, you cannot use the single phase (line to neutral) of the system. Generally, the single phase is used in low voltage electrical system, and it is the reason the use of NGR is not common in low voltage. However, in the process industries NGR is used in 3 phase low voltage system and in this case, all single phase loads are provided from the line to neutral of a separate transformer whose neutral is solidly grounded.

See the previous threads:

http://cr4.globalspec.com/thread/56612/Neutral-Grounding-Resistor