<html><body><span style="font-family:Verdana; color:#000000; font-size:10pt;"><div>Marco,</div>
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<div>I believe some of the discussions in the past had to do with the old 6kW imbalance limit that is used by several utilities on a 120/240 small residential single phase transformer. (don't remember the CA utility that came up with this)<BR></div>
<div>I had this discussion with our local utility (FPL) recently and they look at it on a case by case basis due to the many variables involved with 3 phase power distribution, such as the size and type of transformer(s), 3 phase loads on the premises, the harmonic distortion if any on a shared 3 phase transformer, core saturation, load balancing, etc.</div>
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<div>If you install a system in the FPL service area that is not balanced and either the harmonics or voltage is out of spec as a result (yes, they do test them), then you basically have 2 choices, balance the system or pay to upgrade the service drop and transformer.</div>
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<div>There has been talk of testing various 3 phase transformer(s) to determine the maximum/safe out of balance configuration by our local utility, however, again there are a lot of variables, so it would be difficult to cover every scenario. And this usually is only an issue on small 3 phase transformer(s).</div>
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<div>I think that the 8,9,10TL 208v inverter has a load limiting ability that is incorporated in the inverter when you install 2 or more inverters, and it is programmable to limit the output of a single inverter to 6kW. I believe you have to purchase the additional communication cables from SMA (cables available after the first of the year? or so I have been told). Also, the design parameters seem a bit limited on the TL's.</div>
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<div>Jamie</div>
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<DIV id=wmQuoteWrapper>-------- Original Message --------<BR>Subject: [RE-wrenches] feed-in imbalance<BR>From: "Marco Mangelsdorf" <<a href="mailto:marco@pvthawaii.com">marco@pvthawaii.com</a>><BR>Date: Fri, December 10, 2010 2:00 pm<BR>To: "'RE-wrenches'" <<a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>><BR><BR>
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<div class=MsoNormal style="font-size:12pt;">Now that SMA has come up with their new 8, 9 and 10 kW transformerless line of single-phase 120/208V inverters, it brings up the question once again about how practical and wise it is to have one or two of these inverters feed into a three-phase service. That is, is such an unbalanced feed much, if any, of a big deal?<o:p></o:p></div>
<div class=MsoNormal style="font-size:12pt;"><o:p> </o:p></div>
<div class=MsoNormal style="font-size:12pt;">I spoke to my consulting E.E. about this and he said that the large majority of utility-provided transformers are so large these days that an unbalanced feed of, say, a 10 kW inverter that only has output power through L1 and L2 should not present a problem.<o:p></o:p></div>
<div class=MsoNormal style="font-size:12pt;"><o:p> </o:p></div>
<div class=MsoNormal style="font-size:12pt;">Any other thoughts out there on this matter?<o:p></o:p></div>
<div class=MsoNormal style="font-size:12pt;"><o:p> </o:p></div>
<div class=MsoNormal style="font-size:12pt;">Thanks,<o:p></o:p></div>
<div class=MsoNormal style="font-size:12pt;">marco <o:p></o:p></div>
<div class=MsoNormal style="font-size:12pt;"><o:p> </o:p></div></DIV>
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