Grounding parallel generators

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mohammadfawaz

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Hello 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 you

Mohammad
 
mohammadfawaz said:
...grounding parallel generators.

... connect each one of them to ground,
That will give multiple ground current paths.
"multiple grounding of the neutral circuit conductor may cause stray currents that are likely to be objectionable and will cause ground-fault current to flow in paths that may adversely affect the operation of round-fault protection equipment."
... connect all of them to one neutral bus and connect that bus to ground,
This is a good method. One drawback is the available short circuit current increases to where it may be more than one gen can stand.

... simply ground one of them to avoid any ground loops.
Not a good method. How do you take that gen out of service for repairs?

... Can someone please provide some good references?
IEEE 446 (Orange) has a section on gens and grounding
Click to expand...

I'm partial to impedance grounded systems. That gets rid of a lot of evils associated with parallel operation.

cf
 
This one also addresses some of your questions

IEEE 142 (green) Recommended Practice for Grounding of Industrial and Commercial Power Systems

cf
 
Thank you for your reply
Concerning the third method, I noticed that the common practice is to allow all generators to be grounded (through circuit breakers), or at least some of them, while grounding only one at at time. In that case, the system is always grounded. The only drawback I can see here is that the grounded generator should be able to withstand the possible high ground fault current alone. But overall, the total current caused in the first two method (all generators are grounded) is much higher (according to "the electrical transmission and distribution reference book.

Do you see any other drawback?

Thanx
 
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