NGR Vs NGT

http://www.google.com/search?sourceid=navclient&aq=hts&oq=&ie=UTF-8&rlz=1T4GZAZ_enUS396US396&q=Neutral+Grounding+Resistor+Vs.+Neutral+Grounding+Transformer

The Neutral Grounding Resistor (NGR) and Neutral Grounding Transformer (NGT) are two different things and are used for different purposes. One is not the comparable to or substitute of other. See these threads for the detail about NGR and NGT:

For NGR, see

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

http://cr4.globalspec.com/thread/51653/Neutral-Ground-Resistor-NGR

For NGT, see

http://cr4.globalspec.com/thread/36828/What-is-Earthing-Transformer

- MS

I have some comparison for NGR vs. Earthing Transformer (connected to HV switchboard, not generator or transformer neutral)

Consider if you have a plant that powered from several parallel generators on HV network, by using NGT, you will fix the resistance for your HV system to a certain fix value.

If you use NGR connected to generator star-point, everytime you add a new generator for plant expansion, the total effective resistance value will be modified, to which you may need to re-work on the protection setting on entire HV system. (unless you can ensure only one NGR is connected to the system at one time)

your NGR is an impedance inserted between your neutral and the ground..this is to minimize the amount of current entering the neutrals of your grounded source eg. generators, transformers...

a grounding transformer is applied to a floating ground system...the ussual approach is to connect the primary into a wye bank in order to create a neutral which is then grounded to earth and leaving the secondary open...