[RE-wrenches] Buck/Boost transformer for phase conversion, 3 phase generator to outback split phase quad stack

William Miller wrmiller at charter.net
Wed Jan 14 21:43:56 PST 2009


Nick:

I just finished the first phase of a large project for the state of 
California using a quad stack.  The generators are three phase but the 
campus is all split phase.  They were able to center tap one winding of the 
generators and use the two phases on either side.  I was skeptical, 
thinking that the phase angle would be 120 degrees, not 180 degrees as 
required for the quad stack, but an oscilloscope proved the 180 degree 
phase angle.  The quad stack is happy with the two phases of the three 
phase.  Let me repeat that this is only possible because the winding on the 
generator between the two phases we are using was center tapped and bonded 
to create a neutral.

I was told that many large three phase generators have a 12 winding 
configuration.  I belive that this configuration will allow the center tap 
to be made.  You should verify this will not void any warranties or damage 
the generator.

The down side is that there is some loss of generator capacity, but it was 
far less than I predicted, somewhere about 80% of name plate.

I have pictures of the PV and inverters on our web site, but not of the 
generators.  I think they are 30 KVA Kohlers.  As a side note, the 
generator system is very unique.  There are three generators and they can 
run one, two or three in synchronization, as needed.  Also, the inverter 
system does not through-put power.  The generator control system switches 
the generators off the main buss moments before switching the inverters 
onto the main buss.  To further complicate things, the generators must be 
loaded at close to capacity at all times to reduce emissions.  There is a 
load bank that switches in and out to accomplish this.  It took Kohler 
Corporate many trips to get this working, and I'm not sure I really belive 
they have all of the bugs out yet.

Good Luck,

William Miller


At 09:03 PM 1/14/2009, you wrote:
>Hi Nick,
>
>Why you want the change from single to 3 phase?
>Pretty big difference that.
>
>
>jay
>
>peltz power
>
>
>On Jan 14, 2009, at 4:56 PM, Nick Houser wrote:
>
>>Has anybody done  (or even TRIED) this?  The Quad stack is exactly
>>like page 20 of the manual. Owner
>>refuses to let me convert the Quad panel to three phase as he won't
>>give up the forth inverter' contribution.
>>Ditto repacing or converting the generator. Related question:  If
>>the transformer is a viable option, how do
>>I size it? Help. please, I'm running out of options. Nick Houser,
>>Off Grid Services, Powell River, BC
>>offgridnick at telus.net    604-483-4898  Fell free to contact me off
>>list, and Happy New Year. ALL!!!!!
>>
>>--
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