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<TITLE>Re: [RE-wrenches] 3 Phase Answers</TITLE>
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<FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>Jeremy,<BR>
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You might find the information on electrical service types in John Berdner’s article useful:<BR>
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<a href="http://solarprofessional.com/article/?file=SP1_1_pg32_Berdner&search=">http://solarprofessional.com/article/?file=SP1_1_pg32_Berdner&search=</a><BR>
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Also, here’s the link to the 3-phase line currents article that Rebekah Hren mentioned:<BR>
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<a href="http://solarprofessional.com/article/?file=SP3_1_pg66_Hamon&search=">http://solarprofessional.com/article/?file=SP3_1_pg66_Hamon&search=</a><BR>
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This sounds to me like an issue with an inexperienced utility that doesn’t know what to require or expect. It is not at all uncommon for first time projects to elicit requests of this nature. For example, I’ve worked on small PV pilot project designs—like solar for schools projects—with registered professional electrical engineers who want to specify a 3 or 4kW 3-phase inverter. Because the site has a 3-phase service, right? <BR>
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It makes perfect sense from their point of view. But that inverter product isn’t out there & doesn’t need to be. There are single-phase appliances on 3-phase electrical systems, after all. <BR>
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A small grid-tied PV system is basically a dedicated appliance circuit, only it exports current. It is a load reduction appliance with anti-islanding protection...and maybe even backup power capabilities. While a battery backup system might raise more flags with the utility, the system may still be small enough to interconnect at 120Vac without creating or exacerbating any existing phase imbalance issues. Typically the phase imbalance limit is set at 6kW by the utility. If you are backing up 3-phase loads, well then you need 3-phase power from the system.<BR>
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BTW: Did you know that there are three power stages in those 3-phase Fronius IG Plus inverters? Sounds an awful lot like stacking single-phase inverters onto a 3-phase service, doesn’t it? I suspect that these units still output 3-phase power even with only one power stage operating, which the units will do to reduce tare losses. But the product platform is primarily single-phase and only the 3-stage units are available with 3-phase output. The smaller units don’t need to have a 3-phase output. You can configure them granularly as needed to avoid phase imbalance.<BR>
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Of course, the AHJ can set their rules however they see fit, but you can also educate them about national industry standards with line diagrams and case studies or by bringing in a professional engineer with PV systems expertise. You shouldn’t have to use a 11.4kW 3-phase inverter just to interconnect a small array at a facility with 120/208 service. Similarly, you shouldn’t have to scrap plans for a utility-interactive battery backup system just because none of the available inverters offer 3-phase power in a single box. They don’t have to. If the system size is small enough, you’re not creating any meaningful phase imbalance. If the system is larger, you can stack inverters to achieve a 3-phase output from the inverter system.<BR>
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If this is a real project, you might want to start monitoring the line currents at the site. Show the utility the existing load profile. It’s probably not nearly as simple and balanced as they think it is. If one phase always (or usually) has a higher current than the others, you may be able to use your load reduction appliance to improve an existing phase imbalance. <BR>
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Hope this helps.<BR>
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Best regards,<BR>
</SPAN></FONT><FONT SIZE="2"><FONT FACE="Consolas, Courier New, Courier"><SPAN STYLE='font-size:10pt'><BR>
</SPAN></FONT></FONT><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>David Brearley, Senior Technical Editor<BR>
<I>SolarPro</I> magazine <BR>
NABCEP Certified PV Installer ™<BR>
<a href="david.brearley@solarprofessional.com">david.brearley@solarprofessional.com</a><BR>
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On 2/16/10 10:49 AM, "All Solar Inc. Jeremy Rodriguez" <<a href="allsolar@scswifi.net">allsolar@scswifi.net</a>> wrote:<BR>
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</SPAN></FONT><BLOCKQUOTE><SPAN STYLE='font-size:11pt'><FONT FACE="Arial">Thanks to all for the help. Its going to have to be an IG Plus. 208V Delta: 120V WYE config. <BR>
Wait til June for it...................<BR>
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</FONT><FONT FACE="Arial">Jeremy<BR>
</FONT><FONT FACE="Calibri, Verdana, Helvetica, Arial"> <BR>
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</FONT><FONT FACE="Arial"> <<a href="mailto:allsolar@live.com">mailto:allsolar@live.com</a>> </FONT><FONT FACE="Calibri, Verdana, Helvetica, Arial"> <BR>
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