Friends:
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:
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.
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.
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.
This realization was huge to me. Think about it...
William Miller
PS: Just replacing a 3 phase panel with a single phase panel does not give
you 120/240 with 180 degree phase angle.
Wm
At 08:23 AM 10/21/2011, you wrote:
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.
Jason Szumlanski
On Oct 21, 2011, at 11:17 AM, "Allan Sindelar"
<<mailto:al...@positiveenergysolar.com>al...@positiveenergysolar.com> wrote:
Wrenches,
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.
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?
Thank you, Allan
--
A
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches@lists.re-wrenches.org
Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out participant bios:
www.members.re-wrenches.org
