Earthing of multiple generators
Earthing of multiple generators
(OP)
Hi
I have a situation where two diesel generators operated in parallel (1MW each, 11kV) only have one of them earthed at any one time. I was told this was to prevent circulating currents. Can anyone tell me where these currents come from and how one can calculate them?
Thanks in advance.
I have a situation where two diesel generators operated in parallel (1MW each, 11kV) only have one of them earthed at any one time. I was told this was to prevent circulating currents. Can anyone tell me where these currents come from and how one can calculate them?
Thanks in advance.






RE: Earthing of multiple generators
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RE: Earthing of multiple generators
I don't know what the winding pitch is but I do know the generators are identical so I would assume same pitch. I am curious to know why you ask?
Thanks
RE: Earthing of multiple generators
RE: Earthing of multiple generators
Use this link:
bmcoi.com/CatLit/Power/.../GEN. WINDINGPITCH - LEKX3115.PDF
It will explain how winding pitch realtes to circulating neutral harmonics.
RE: Earthing of multiple generators
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Earthing of multiple generators
Is the link correct or complete as I get an error if I paste it into my browser as it is? Really looking forward to what this document has to say.
dpc - yes, this is what I have heard as well. Thanks for this. I am curious to know where the 3rd harmonic currents come from though and how to quantify them. Trosepe's winding pitch appears to be the answer.
Kind regards.
RE: Earthing of multiple generators
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Earthing of multiple generators
The generators I have are two 11kV ones connected directly to an 11kV network (no trfr in between). They are also identical sets. Thus from what you say it should be okay to earth both of them directly?
Also, would the introduction of neutral earthing resistors not help as they would suppress the 3rd harmonic currents even further? I know there are other issues that arise if you do this like is the EF sensitivity on the protection devices sufficient for an impedance earthed system, etc.
RE: Earthing of multiple generators
You can provide each generator with its own grounding resistor and ground each one. This is commonly done in the US,maybe less commonly elsewhere. This does reduce any third harmonic circulating current.
You do need to consider the continuous third harmonic current that could flow in this situation when rating the grounding resistors. A grounding resistor with an 10-second rating does not have an official continuous current rating, at least in IEEE/ANSI land. You would need to make sure the resistor could handle whatever continuous current may flow.
Generator manufacturer should be able to provide expected third harmonic voltage. If generators are identical, resulting circulating currents should be pretty small.
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Earthing of multiple generators
Im second with Dave.
It is not good idea solidly grounding of industriaul MV generators. Low or medium, is OK.
Veritas, are those generators will operated in co-generation with grid?
RE: Earthing of multiple generators
Try this one:
http