[RE-wrenches] Three-phase off-grid

[mac Lewis]

Wrenches,

Is it a "special" transformer that will give you the 180 deg phase shift
from the original 120 deg shift?

Thanks

On Fri, Oct 21, 2011 at 5:52 PM, William Miller <william at millersolar.com>wrote:

>  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" <
> allan at 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*
>
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-- 



Mac Lewis

*

"Yo solo sé que no sé nada." -Sócrates
*
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