Common NGR Operation in Parallel Genset

It makes a huge difference if all contactors are closed at the same time, an earth fault in any generator will result in all 6 generators feeding the fault instead of just 1. This question gets asked repeatedly here, type NGR into the search box under "Search this Forum" in the upper right hand sideof the screen, and you will see many of the previous answers.

Dear ram sir,

I put this question after all searches in this forum, most of the conclusions are regarding each generator having its own ngr, tht case by adding each resistance in parallel will cause the reduction of resistance hence the current flow increase. but if we use only one common ngr for the all 6gensets it makes no difference. and one more thing since all gensets will feed to the fault during earth fault, so is it possible to isolate the faulty set only? as i under stood even if we use individual CTs and earth fault protecton relays, all cts will read current during fault.

thanks.

You not making a lot of sense with your explination of your problem ....explain better what the problem is because we people that must help you are not on your site where the problem is

Regards and good luck

The problem is,

1)since 6gensets are working one of the neutral is earthed through NGR, so where ever the fault all the 6gensets will be tripped since there is only one CT, after that we have to start one by one to find out the faulty one. is it possible to trip only the fault genset using any scheme?

2) What is the issue if all the nuetral isolators are closed through common NGR, i think circulating neutral current is not a major issue, can be managed with the relay setting.

thanks.

You might benefit from reading chapter 10 from the GE publication "The Art & Science of Protective Relaying" since without knowing details about your company and its protection philosophy it's hard to make any specific suggestions. There are also some excellent IEEE and CIGRE guides that might provide further insight.

thank you,

its informative