Experience with 3 Phase High Leg Delta? [RE-wrenches]

jberdner at sma-america.com jberdner at sma-america.com
Fri Apr 26 08:40:23 PDT 2002


Jeff:

In a high leg open delta you will get 240 Vac on the line - line
connections.
The Sunny Boy has an isolation transformer in it so you can hook it up
line - line in either Delta or Wye configurations.
The neutral is normally tied in half way between two of the phases to
give you two 120 volt legs.
I think you also get one 208 Vac connection between one of the lines and
neutral - I don't remember.

As you mentioned, it is a really good idea to take some quick voltage
measurements on line to line and line to neutral before you plan out the
job.
Helps eliminate those extra trips back to the shop and all those little
pieces you forgot to include in the bid ;-)

For this job, just wire the inverter up to across the 240 Vac line to
line connections.
In ASCII cad:

3 pole 30 Amp breaker in main panel >> 3 pole utility disconnect >> 
small 3 phase sub-panel >> 2 pole 15 amp breaker (1 of 4) >> 
Sunny Boy (1 of 4).

I like to take a quick line to line voltage measurement and figure out
which pair of phases have the lowest voltage.
Usually it is not very much lower - a few 10ths of a volt or so.
Connect the "extra" Sunny Boy to the pair with the lowest voltage.
While it is not a big deal it will help to balance out the loading on
the transformer.

If you have any questions, or if I can be of any further assistance,
please do not hesitate to contact me.

Best Regards,

John Berdner

SMA America, Inc.
20830 Red Dog Road
Grass Valley, CA  95945
530.273.4595 (voice)
530.274.7271 (fax) 

 
-----Original Message-----
From: Jeff Clearwater [mailto:clrwater at earthlink.net] 
Sent: Friday, April 26, 2002 7:21 AM
To: RE-wrenches at topica.com
Subject: Re: Experience with 3 Phase High Leg Delta? [RE-wrenches]


Hi Matt,

Yes you are absolutely right, should have caught it earlier but 
fortunately nothing was committed or ordered yet.  The face plates of 
all the panel equipment says 208 volt and much of the 3 phase loads 
say 208 and the campus electrician had referred to 208 volt many a 
time.  I do always check but I wasn't at the site for most of the 
design process.  Exactly the reason for this visit, to double check 
things before final design.

So as Matt says, heads up to all 3 phase installations out there.  Do 
not in any way assume 208 VAC on a 3 phase system!  Check it out 
first thing no matter what name plates say!.  (A High Leg Delta will 
show 120 V to N on two of the legs but on the third leg you'll see 
between 190-208 VAC).

Not withstanding I'm still looking for any experience on this.

Thanks!

Jeff

>
>The immediate thing this brings to mind is, from experience here, why 
>are you in the "final stages of design" before you found this out?  (We

>have had various contractors and, yes, even SMUD personnel design 
>systems like this, only to find out at the time of install or just 
>prior what the actual Voltage Configuration is at the site.  Kinda 
>embarrassing!)  At least you caught it now!
-- 
~~~~~~~~~~~~~~~~~~~
Jeff Clearwater
Ecovillage Design Associates
Home, Community and Village Scale Renewable Energy Systems

2525 Arapahoe Ave, Suite E4, #280
Boulder, CO 80302
1-800-440-2523 PIN7071
Fax:  720-528-7813
clrwater at earthlink.net
jeffc at ic.org

Council Member - Ecovillage Network of the Americas -
http://www.ecovillage.org
Founder:  Ecovillage Research, Development, and Demonstration Program:
http://www.home.earthlink.net/~clrwater/RDD/rdd.html
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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