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

Matt Lafferty pvpro at attbi.com
Fri Apr 26 07:04:55 PDT 2002


Jeff / Wrenches:

Interesting.  We've dealt with this a couple of ways (Nice to be the Utility
sometimes).

On Customer-side connections we have installed transformers to correct the
voltage configuration to a 120/240 Straight Delta.  This reduces the kWH
production due to the transformer losses and raises the installation costs,
offsetting any savings you may have been counting on related to using the
Sunny-Boy versus another Hi-Volt DC, 3-Phase AC Inverter. Yes, SB has remote
metering/monitoring capability which may be a good thing to have in this
application.... (No angry phone calls please.....John B, Kent S!)

On Utility-Side connections at Customer Sites we have dropped in a new
service and connected to the 240 legs only. (Not exactly balanced but it's
not connected to anything besides the Grid.....Another topic)

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!  Whew!

I, personally, verify the voltage configurations and interconnectivity at
all sites on the first visit and strongly urge those I work with to do the
same.

The voltage configuration and interconnection are factors that should be
considered in any system design so your options are open.

Pray for Sun!

-Matt Lafferty
pvpro at attbi.com


----- Original Message -----
From: "Jeff Clearwater" <clrwater at earthlink.net>

> I'm in the final stages of designing a 10KW system using Sunny Boys.
> However we just found out that our 3 phase service is not the normal
> Wye 208/120 VAC but 240/120 VAC High Leg Delta (and possible High Leg
> "Open" Delta as there are two transformers on the pole).

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