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one NGR only
3

one NGR only

one NGR only

(OP)
We have 03 offshore 6 kV generators work parallel, if only there is 1 generators NGR connect to the ground be to obtain neither

RE: one NGR only

Sorry, that sentence is gibberish. Would you mind trying again?
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: one NGR only

I think he mean to say that he has 3 generators running in parallel but only one NGR is there and at one time only one of the generator is connected to the NGR. The remaining two generators run ungrounded.

I have seen the same situation in one of the Power Plant for a fertilizers industry in Pakistan. This was designed by BBC.

RE: one NGR only

(OP)
Dear undervoltage,
Sorry for my English, do you know why they design like that. Doing so can benefit

RE: one NGR only

Well, I would like dpc any other senior member to reply to this.

 

RE: one NGR only

But I believe, by keeping one generator grounded at one time, you keep the other two in operation even if there is ground fault on the distribution side since all the generators are synchronised.

 

RE: one NGR only

Is the NGR connected to the main panel so that when any generator breakers is open that generator is running ungrounded?  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: one NGR only

2
If the generators are connected to a common bus, as long as one generator's grounding resistor is in service, all the generators are referenced to ground through that resistor.

Using only one grounding resistor keeps the maximum ground fault current down and eliminates circulating third harmonic currents between the units.  The typical 10 second grounding resistor normally have no (official)continuous current rating, so harmonic currents can pose a heating problem in the resistor, although this is generally not a major concern if the generators are well matched.

Switching the grounding resistors adds additional cost and complexity, so there are tradeoffs.  It is not too common in the US, in my experience, but apparently it is routinely done in other parts of the world.   

David Castor
www.cvoes.com

RE: one NGR only

(OP)
Thanks dpc, may you score 2 system (system has 1 grounding NGR and system has all grouding NGRs)  

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