SMA and transformer [RE-wrenches]

[Christopher Freitas - OutBack Power]

Using a T-240 or a X-240 (which are remarkably similar ;) is an option 
for this situation.  The fact that there is high impedance to the 
utility grid distribution system is a benefit when it comes to the 
operation of an autotransformer.  If you want a diagram of how an 
autotransformer works look at the latest OutBack Power Catalog 3rd 
edition on page 20 for more information and a diagram. You can download 
the catalog as a PDF from www.outbackpower.com if you don't have a copy. 
  

Simply connect the autotransformer "across" the two 120 VAC legs with 
the neutral connected to the other two wires of the autotransformer - 
just like when balancing a generator.  This maximimzes the efficiency of 
the autotransformer and inverter as the only "thru" losses on the 
transformer will occur with only 1/2 the power (in an ideal world).  The 
idle of the X-240 is about 10 watts - so thats not terrible - especially 
when compared to a system not working during part of the day.  

Using the balancing configuration may also improve the power quality 
during the day and night - it will make the start up of large 120 VAC 
loads less noticeable on both 120 vac legs.  It is the impedance that 
both causes the problem and that allows the autotransformer to solve it. 
 

You also can use the 120-to-240 configuration as well - but that might 
not be as effective.  Its easy to try either however. 

The ability of an autransformer to correct the fluctuations will be 
dependant upon not only the impedance to the utility distribution system 
but also will be impacted by the magnitiude of other local AC loads.  I 
think it is worth a try however.  

Let us know the results if you try it!

Christopher Freitas
OutBack Power Systems, Inc.
cfreitas at outbackpower.com  www.outbackpower.com
Tel 360 435 6030  Arlington WA USA

 
> Daryl:
>  
> The utility is supposed to keep the voltage within 95 to 105% of
> nominal at the Point of Common Coupling (PCC).
> The location of the PCC may be critical here since they will not be
> responsible for voltage drop in the customer's wiring.
> They are allowed "infrequent excursions" outside this range (ANSI Range
> A).
> Every time the air conditioner comes on is not infrequent.
> If they will not fix it then ask them for a letter that allows the
> inverter to operate outside of the IEEE 929 limits.
> If you can get a letter then we can adjust the inverter's set points.
>  
> Adding a transformer will add losses to the system and should be
> avoided if possible.
> It sounds like the sag is occurring only on one side of the split
> phase.
> Using the transformer to connect the 1800 to 240 Vac will help to some
> degree if the other half of the split phase is staying up.
> I am not sure if it will solve the problem though because it sounds
> like the utility impedance is pretty high.
>  
> 
> >>> daryl_solar at yahoo.com 9/5/2003 05:45:43 PM >>>
> Thanks to all for response
> Several asked why do I care, and here is more of the
> story; the customer lives on a back road. his power
> will drop to 109 volts with the room air conditioner
> on. Or toaster or whatever. I made the mistake of
> selling him a SB1800 when I should have sold a SB2500
> but I did not come up with this 120 volt vs 240 volt
> problem. He has a 1200 watt solar system, that is all
> that he had money for and his good exposure was for
> only 1200 watts. He is willing to work to maximize
> the solar for his live style. Using electricity
> during peak sun. 
> 
> My choice is to put as much of the heavy loads on one
> leg? My voltage would really sag on coincidence. He
> is served by a REA-Coop, who say the power is fine?
> 
> But in the end the customer is King. And I want to
> serve this percieved need. So does anyone know, will
> a T-240 or a X240 help or even work?
> 
> Thanks again.
> And I am pursuing the utility problem, and will send
> what I come up with. 
> Daryl 

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