<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;">Hello William,<br><br>It works as long as you tie into just one phase of the three-phase system for the input .. from which you can then derive single-phase output. A 180 degree shift is also do-able with multiple output windings in the transformer.<br><br>Still recovering from SPI. It was a *long* week.<br><br><br>Dan<br><br><br>--- On <b>Sun, 10/23/11, William Miller <i><william@millersolar.com></i></b> wrote:<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>From: William Miller <william@millersolar.com><br>Subject: Re: [RE-wrenches] Three-phase off-grid<br>To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org><br>Date: Sunday, October 23, 2011, 11:30 PM<br><br><div id="yiv841708555">
<div>
<font size="3">Dan:<br><br>
We are not desiring 120 degrees. We are desiring 180 degrees, and
it can be derived, and without a Scott-T. I have done this
recently.<br><br>
William Miller<br><br>
<br>
At 08:26 PM 10/23/2011, you wrote:<br>
</font><blockquote type="cite" class="yiv841708555cite" cite=""><font size="3">Mac,<br><br>
You can't get a 120 degree phase shift from a transformer with windings
on a common core. Two transformers can be combined in a
"Scott-T" configuration" to synthesize a 120 degree shift,
but special transformers are required. Also, a Scott-T
configuration must be used with closely balanced loads between
phases.<br><br>
There's an explanation of how a Scott-T topology works at this
link:<br><br>
<a rel="nofollow" target="_blank" href="http://en.wikipedia.org/wiki/Scott-T_transformer">http://en.wikipedia.org/wiki/Scott-T_transformer</a><br><br>
<br><br>
Dan<br><br>
<br><br>
--- On <b>Sun, 10/23/11, mac Lewis <i><maclewis1@gmail.com></i></b>
wrote:<br>
</font><blockquote type="cite" class="yiv841708555cite" cite=""><font size="3"><br>
From: mac Lewis <maclewis1@gmail.com><br>
Subject: Re: [RE-wrenches] Three-phase off-grid<br>
To: "RE-wrenches"
<re-wrenches@lists.re-wrenches.org><br>
Date: Sunday, October 23, 2011, 9:02 PM<br><br>
Wrenches,<br><br>
Is it a "special" transformer that will give you the 180 deg
phase shift from the original 120 deg shift?<br><br>
Thanks<br><br>
On Fri, Oct 21, 2011 at 5:52 PM, William Miller
<<a rel="nofollow">william@millersolar.com</a>>
wrote:
</font><dl>
<dd><font size="3">Friends:<br>
</font></dd><dd><font size="3">I posted a question here about three weeks ago on the subject of
connecting a dual SW inverter stack to a three phase generator. I
have learned a lot since then. Here are the most important
points:<br>
</font></dd><dd><font size="3">Most large, three phase generators are allegedly field convertible to
be either 208 or 240 three phase. The 208 version is probably wye
configured and the phase angle between any two phases is 120
degrees. If you connect a 120/240 inverter system (even numbers of
Outbacks, two SW's or XWs configured single phase, and maybe other
models) across two of the phases, the 120 degree phasing will cause the
inverters to puke. If you purchase and connect the correct
transformer across two of these phases and you will provide the 180
degree phase angle you need but you will imbalance the generator.
For a large (30KVA or larger) generator, the 10 KVA of imbalance is not a
big issue. Your transformer will cost about $1,000 delivered and
will weigh about 200 pounds.<br>
</font></dd><dd><font size="3">You can swap some connectors and have a 240 configuration which will
probably have a "stinger" leg. If it does, the windings
are probably a delta with one winding center tapped. If so, the
phase angle between the two phases on either side of the neutral is 180
degrees. You can connect your Outbacks (or others) across these two
phases and neutral without a transformer. You'e saved your client
$1,000 and yourself a hernia.<br>
</font></dd><dd><font size="3">If the customer can live with a stinger then you have your cake and
eat it too: Three phase for 240 VAC loads and a 120/240 single
phase inverter system for 120 or 240 VAC loads.<br>
</font></dd><dd><font size="3">This realization was huge to me. Think about it...<br>
</font></dd><dd><font size="3">William Miller<br>
</font></dd><dd><font size="3">PS: Just replacing a 3 phase panel with a single phase panel
does not give you 120/240 with 180 degree phase angle.<br>
</font></dd><dd><font size="3">Wm<br>
<br>
<br>
<br>
</font></dd><dd><font size="3">At 08:23 AM 10/21/2011, you
wrote:</font><blockquote type="cite" class="yiv841708555cite" cite="">
<dd><font size="3">Do they actually have 208v loads? If not, replace with 120/240 panel.
Just a thought... Although a transformer would be required to use an
existing 208v generator. <br>
</font></dd><dd><font size="3">Jason Szumlanski<br><br>
</font></dd><dd><font size="3">On Oct 21, 2011, at 11:17 AM, "Allan Sindelar"
<<a rel="nofollow">allan@positiveenergysolar.com</a>>
wrote:<br><br>
</font><blockquote type="cite" class="yiv841708555cite" cite="">
<dd><font size="3">Wrenches,
</font></dd><dd><font size="3">We have been asked for a design for an off-grid system to reduce
generator runtime for a mountain resort. Initial projections (consumption
measurement results not yet available) suggest 15-20 kW of PV and around
30 kW of inverter capacity. However, the generators and existing wiring
are three-phase 120/208.<br>
</font></dd><dd><font size="3">My assumption is that our only options are a set of six Sunny
Islands, or 9-12 Outback GVFX3648s. Are there any other options or
approaches that I'm missing?<br>
</font></dd><dd><font size="3">Thank you, Allan
</font></dd><dd><font size="3">-- </font></dd></blockquote></dd></blockquote>
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