Generator Pitch
Generator Pitch
(OP)
I design a lot of installations with multiple emergency generators connected in parallel (typically 480 volt diesel engine units). For many years, Caterpillar has always promote an "optimum pitch" generator, which is usually around 4/5 pitch. Other manufacturers have claimed that in order to parallel, especially with a utility source, the generators should be 2/3 pitch. Does anyone have more knowledge on this subject that they could share?






RE: Generator Pitch
One of the first hits is a CAT technical paper.
Steve
RE: Generator Pitch
RE: Generator Pitch
I have designed and commissioned a number of paralleling gen plants, ironically mostly CAT, exclusively with 2/3rd pitch. Had no issues.
A case of a site (not engineered by us, and even that engineer was not at fault) where someone installed Six(6) 2MW gensets with some other pitch, even when 2/3rd pitch was specified, there was so big an issue with the circuilating currents that the mfr ended up having to replace all six alternators without added cost to the Owner!
RE: Generator Pitch
We have paralleled a number of non-2/3 pitch machines with both the utility and other machines of different pitch, usually requires a neutral grounding reactor installed.
There have been more than a couple of times when an expansion or new project forgot to take that issue into consideration. Most of the local engineers I deal with where I live are famiilar with DG know the issues and account for them. But quite a few people aren't and it can cause some headaches, everything from complete unit changeouts to floating neutrals, depends on the site and application.
Cummins and Marathon also have excellent papers on generator winding pitch, the current Cummins info is probably the most up to date of any of the US manufacturers I know of.
Hope that helps
RE: Generator Pitch
I could see how that might happen if there is no isolation of zero-sequence current. I would be surprised that was a problem if there was a Dy transf between the gens and utility. Do you remember any details of the transformer connections?
RE: Generator Pitch
I have found no reason to deviate from 2/3 pitch so I stick to it.