[RE-wrenches] Connecting Two Grid-Battery Backup Inverters to 120/208

[William Miller]

Chris:

I am surprised that the SW inverters connected to this service.  They may 
not have been synced properly.  Was there a ribbon cable between the two 
inverters?  Maybe this is why they failed...

Are there 240 VAC loads in the system?  If not, you can configure the 
inverters in parallel to provide 120 VAC only.  You also feed them 120 VAC 
only, therefore the 120 degree phase angle between phases is not an 
issue.  You must be careful not to imbalance the feeder.  Ask if you need 
more information about this.

You could also install the proper transformer on the input to the inverters 
to convert two phases of 3 phase to 120/240 split phase.  Here is a link to 
a small version of this transformer:

http://www.alliedelec.com/search/productdetail.aspx?sku=70191805

As an aside, we purchased one of these transformers and the windings were 
mislabelled.  After we sorted this out, the transformer later failed.  The 
temporary mis-connection may have been the cause.  Always ohm your 
transformer windings before you connect.

Lastly, if you ever encounter a center tapped delta three phase, the phase 
angle on either side of the neutral is 180 degrees so that service will 
connect directly to an Outback inverter system in single phase mode.

Good luck,

William Miller

At 10:06 AM 11/28/2012, Christopher Warfel wrote:
>We were asked to replace two failed Trace SW4048 inverters with two 
>Outback GT3048 inverters. Upon start up the slave inverter would not 
>connect.  We did not realize that the building service is 208, 3 phase. 
>The bypass is 120/240 which the SW4048s could connect to without a 
>problem. Outback says their inverters will not connect to this system 
>because of the phase angle of 120 and their software.
>
>The phases are always going to be at this rotation, so I don't see a 
>transformer helping solve the problem, but this is something I am really 
>unfamiliar with.
>
>So the input at the inverter panel is two 120 volt phase at 120 degrees. 
>The output to the EP is 120/240.
>
>I am asking if anyone has an idea of how to fix this problem? The goal is 
>to have a grid interconnected system with battery backup.
>
>Chris