Isolation Transformers [RE-wrenches]

[John Berdner]

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mark / Wrenches:
 
Unfortunately, It is up to the individual utilities if you need an
"extra" isolation transformer or not.
The Sunny Boys have one in every unit but some utilities feel this is
not enough.
LIPA is at one extreme requiring one for every install.
A more common utility position is "you need an isolation transformer if
the secondary side of the distribution transformer feeds more than one
service."
This is common in urban areas with underground service where you can
have several services fed from one pad / vault mounted transformer. 
I have also seen it on overhead services in more rural settings. 
It is common in Germnay to have 50 or so houses fed from the secondary
side (230/400 Vac, 3 phase) of a single big transfomer.  It is not an
issue there with over 200k units installed but...
 
The argument given to me as justification was "it is to prevent DC
injection to the neighbors".
While this has some possible merit for some inverter topologies it does
not really apply to the Sunny Boy since we already have the isolation
transformer. 
When I pointed this out the protection engineer said "yes, but what if
someone miswired the PV to the grid".
As that point I realized logical arguements were not going to work so I
gave up since it was clear that this particular protection engineer was
certain that PV is evil and all trout live in trees.
 
Best Regards,
 
John Berdner
 
 


>>> Mark at TheEnergyGrid.com 5/5/2004 07:36:42 AM >>>


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Thanks, Bill.

I've got a 20k installation in California using SMA's. An local 
inspector (who was more familiar with LIPA) asked the CEO of Nextek if

we were going to install an isolation transformer. 
I can explain to him that the SMA's have it built in, but I wanted to 
give him a little more scope, explaining where and when, and under what

circumstances it is needed.



Bill Brooks wrote:
> 
> Mark,
> 
> Are you referring to LIPA's transformer requirement or the basic
design 
> of a
> PV series Xantrex inverter?
> 
> Bill.
> 




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