Generator Neutal Earthing.Manoj SharmaElectrical Design Engineer at WorleyParsonsHello all,

I have a small question concerning grounding parallel generators. I found three ways to do it: either connect each one of them to ground, or connect all of them to one neutral bus and connect that bus to ground, or simply ground one of them to avoid any ground loops. Each method has its own advantages and disadvantages. Can someone provide an explanation of when do we use each method? What are the conditions needed to deploy any method of these? Which method is generally better? Can someone please provide some good references?

Thank youManoj Like Comment (2) Share Follow Reply Privately 1 day agoComments2 comments russell ianrussell ian paragosoFreelanceIn my opinion, it has something to do with system protection of generators.

a) If you connect all of them (w/o grounding per generator) and ground only the common bus, (using wye-delta or zigzag transformer) then, the ground fault protection will tend to be not selective, if a ground fault occurs on one of the generators, it will be difficult to distinguish upon where the ground fault on which generator is. But this issue can be overcome using ground 87 on each generator with one CT on the neutral of the grounding transformer.

b) If only one generator is grounded and a ground fault occurs on the grounded generator, and when the generator is isolated, then this will leave the other generator ungrounded, some of this application are applied with switch to change over the NGR.

c) If generator are each grounded, then ground faults can be easily detected. But I think this costs more as you would spend NGR on each generator.

Perhaps there are other best reasons that best answers your query on the subject. This is just in my opinion. Like (1) Reply privately Flag as inappropriate 17 hours agovinit M.likes this DimitriDimitri KuzarevAgronome chez SelectumManoj,

There is an other solution you forgot : inserting a disconnector switch between each generator neutral and ground. This way, you get one generator grounded and only one in any case (operating the disconnector switches).You can not ground too many generators in parallel because this willl induce a high ground fault. That's why I don't recommend to ground each of them if you get more of 4-5 generators in parallel. If you have more tha 5 generators in parallel, I recommend to use an homopolar generator on the busbar to ground the system.Finally, be aware that if you ground several generators in the same time, you need a Restricted Earth Fault protection function to remain selective. Like Reply privately Flag as inappropriate 53 minutes ago