ngr

Your Neutral Grounding Resistor should be connected between your star point of your transformer or winding to ground to limit the phase to ground fault current.

Can you explain your question in more detail as I am not sure what your 'second source' is (is this a delta/star transformer connected to the output of the gen set)?

we have 2MVA DG GEN (11kv HT DG )set in which Neutral Grounding Resistor connected between star point of transformer or winding to ground to limit the phase to ground fault current.This is right .But in our case the Neutral Grounding Resistor bank has one breaker .this breaker is fed from the UPS power of 230V ac i.e the second source . the first source or the primary source is the DG out put .so My Q is why the power fed to NGR taken from diffrent source though the power is also available at DG output. If the DG set of LT (415V) used then too the NGR power taken from different source.

thaks for your valuable reply.

From what you are describing it sounds like your second source is being used as a control power supply independent of the DG output (ie- the control electronics can run off this second supply while the DG is being powered up/syncronised with the line if being used in a grid-tie application, etc). This is common (as I have designed and built one very similar), what I believe your breaker is doing is acting as a series protection element protecting the transformer output, not the star to earth point of the NGR (with the breaker trip and possibly breaker close functions being powered by this remote 230V supply).

Can you confirm if this is correct?

Dear I got answer from my Senior that the different source for NGR protect the dg set as well as the NGR equipment because if fault occur in NGR cable OR any other fault in NGR the NGR breaker will trip and not effect the running of DG set . If the power taken from the DG then IF the fault occur which may stop the DG .

An interesting approach, but if the breaker operates to disconnect the NGR from the dg set then it is also disconnecting the earth from the star point of the equipment (generator output or transformer), in either case the dg will be running with the star point floating. This is not how I would ever do it (for safety reasons, and the fact that the dg should stop in the event of an unlikely NGR cable fault), but there may be special circumstances that haven't been clearly explained which would make this a good idea.

Thanks for coming back and explaining the reason, that's how we learn a new thing each day.

Dear sir,

This can be due to the need for a backup supply(DC), if such a condition arises that there is absolutely no power in the plant.

Regards

Jithin