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Re: Unique Problem With Standby AC Generator

Posted: Wed Aug 17, 2016 10:18 am
by Larry Milliken
This generator is feeding the same ND-5 transmitter at this site. You have an interesting question about the series verses parallel configuration and I will double check that. The generator does have a neutral and it is not switched. The power company is giving us closed delta, and the generator was supposed to be configured that way. When we moved an electrical contractor did the removal and reinstallation. They said they did not touch the internal wiring of the generator. When I get out there next I will update this post. Thanks a lot fellow techs!

Re: Unique Problem With Standby AC Generator

Posted: Thu Aug 18, 2016 8:51 am
by Kelly
From what I understand, when using a closed delta for generator and utility you aren't supposed to bond the neutrals, but use a transfer switch with a switched neutral. You could easily prove this theory by disconnecting the neutral from your generator from the utility neutral. If the tripplen harmonics on that one phase go away, you've found the problem.

Re: Unique Problem With Standby AC Generator

Posted: Thu Aug 18, 2016 9:32 am
by Larry Milliken
That's a good suggestion and I will try disconnecting the neutral. Thanks, Kelly! I will let you folks know the results.

Re: Unique Problem With Standby AC Generator

Posted: Thu Aug 18, 2016 9:31 pm
by dbuckley
Whether you need a three or four pole switch depends on the generator arrangement. If the generator supplies a ground, ie there is a N/G bond in the generator, then you need a for pole switch. If the genset does not supply a ground, then the N/G bond in the installation does the job, and a three pole switch is required. But in either case then genset frame ground musty be solidly connected to the installation ground.

Its easy to check for; measure resistance, preferably with a low resistance capable tester that tests with several hundred mA or more flowing, from generator neutral connection to frame ground of the genset, but make sure the genset phase and neutral wires are not connected to the installation. If there is very close to zero ohms, then the genset has a N/G bond.

In a simple installation, it doesn't matter whether the genset supplies the ground or not, so generally the genset is configured to not provide ground, as a three pole switch is generally less expensive than a four pole switch. As N/G bonds are generally easily removable, unless manufacturer instructions mandate its use, remove the link and have a three pole switch.

The four pole arrangement is needed when a more complicated arrangement is used, for example a single generator feeding two installations.

Re: Unique Problem With Standby AC Generator

Posted: Tue Aug 23, 2016 5:23 pm
by Larry Milliken
Well, I am about to give up and see if I can find a generator tech. I disconnected the neutral, in fact, isolated the generator completely and still the frequency is too high between E2-E3. Thanks for all the encouragement and suggestions.

Re: Unique Problem With Standby AC Generator

Posted: Mon Sep 12, 2016 12:54 pm
by kcbooboo
Any progress or outcome on this?

Bob M.