Amigo Bill, What I understand from your words below: under most circumstances, there should not be a problem with having, say, a single 7 kW inverter feeding power (two hot conductors for 120/208 or one hot conductor for 277/480) into a three-phase service. Or, for that matter, two such inverters feeding into a three-phase service. Correct? To play this out one step further, assuming that the Fronius 12 kW inverter has a two hot conductor ouput and is three-phase compatible, would that be pushing it since the possible imbalance could be more than 10 kVA?
Marco Jeff and Ryan, The 6kVA value comes from the California Rule 21 that I worked on. It only applies to split-phase 240V systems (6kVA on 120V). There is no specific limit for imbalance on a 3-phase service. A basic rule for single phase generation on a 3=phase service is to rotate among the phases in a balanced manner. This means the largest imbalance possible right now is 7kVA because of the SMA SB7000US. There is a single-phase SatCon that is 30kVA, but it would be silly to buy a single-phase Satcon when the major on 3-phase units. The best way to place the imbalanced single-phase generators on the service is to test the current on all three phases and put the inverter(s) on the most heavily loaded phase(s). This reduces the site imbalance by reducing the imbalance on the serving transformer (lowering current on the most heavily loaded phases). It is common for 3-phase services to have imbalances of 10 kVA or more, so single-phase inverters can reduce the problem rather than make it worse. Make any sense? Bill. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ryan Mayfield Sent: Friday, August 08, 2008 3:40 PM To: 'RE-wrenches' Subject: Re: [RE-wrenches] Imbalanced Legs in 3-Phase systems Jeff, My memory also recalls something about a 6kW value. I've talked to one of our local utilities about this as well and they base the accepted imbalance by the size of the transformer serving the building. I have never read their white paper on the subject though. When I described a similar situation for an install we were working on, the engineer acknowledged that he would not have any concern with such an arrangement. You may approach your utility and see if they have a standard protocol you could follow for your system. Ryan -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jeff Clearwater, Village Power Design Sent: Thursday, August 07, 2008 10:14 AM To: RE-wrenches Subject: [RE-wrenches] Imbalanced Legs in 3-Phase systems Hi Wrenches, How does one determine how much imbalance can be tolerated on a 3 phase system? I'd like to feed 2 SMA SB5000s at 277 VAC into a 480 VAC panel instead of 1 13 KW Solectria at 480VAC as the PV system is only 9500 Watts STC. The main on the backfed service panel is 600 A. But I'm not that sure of the loads as it's new construction and hasn't been characterized. What are the appropriate calcs to do here? Thanks! Jeff C. -- ~~~~~~~~~~~~~ Jeff Clearwater Village Power Design Sustainable Energy & Water Solutions for Home & Village http://www.villagepower.com [EMAIL PROTECTED] NABCEP (tm) Certified Solar PV Installer Voice: 413-259-3776 Fax: 413-825-0703 65 Schoolhouse Rd Amherst, MA 01002 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~ _______________________________________________ List sponsored by Home Power magazine RE-wrenches@lists.re-wrenches.org http://lists.re-wrenches.org/listinfo.cgi/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus Database: 270.5.12/1597 - Release Date: 8/7/2008 5:54 AM _______________________________________________ List sponsored by Home Power magazine RE-wrenches@lists.re-wrenches.org http://lists.re-wrenches.org/listinfo.cgi/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org _______________________________________________ List sponsored by Home Power magazine RE-wrenches@lists.re-wrenches.org http://lists.re-wrenches.org/listinfo.cgi/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org _______________________________________________ List sponsored by Home Power magazine RE-wrenches@lists.re-wrenches.org http://lists.re-wrenches.org/listinfo.cgi/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
