Isolation Transformers [RE-wrenches]

Wed May 5 17:45:32 PDT 2004

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John B wrote:

> Unfortunately, It is up to the individual utilities if you need an
> "extra" isolation transformer or not.
<snip>
> 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.

John,

Are you implying that trout don't live in trees, or are you saying that only
some trout live in trees?  Are they easier to catch in trees than other more
well-known environments?  Any recommendations for bait or technique?  Is a
special "tree-trout" license required to be allowed to fish for these?  Is
that license issued by Utilities specifically or do other agencies also
regulate tree-trout?  Please advise soon because I've got a couple of trees
in my backyard that I'd like to try but want to make sure I don't break any
rules.   (One is a lemon tree with the best tasting lemons you can
imagine... The other is a butter tree.... You get the picture!)

I think you gave up too soon.  At the very least I would have told this
particular person that 'Well, the person who miswired the PV to the grid'
would receive the next Darwin Award."

The particular "protection" engineer mentioned aside, two quickies... 

John is only partly right in his statement about "Unfortunately, It is up to
the individual utilities if you need and "extra" isolation transformer or
not."  He got the "unfortunately" and "individual utilities" right, but he
left out the part that says it is "unfortunately up to an individual in most
utilities".  "Company Policies" are often created or at least strongly
influenced by the perspective and opinion of an "individual".  (Virtual
"Micro Kingdom Syndrome".... VMKS.... Can I copyright that?)   Enough
said....????

I must ask: Who's gonna protect me from my neighbor injecting DC into my
service?

I wish I had recorded the times I have measured / tested / witnessed where
there was DC Voltage present on the AC line with ZERO PV connected on the
secondary of the existing Utility Transformer or anywhere within at least a
half mile of the site.  I'll never forget the first time I saw it and didn't
know what it was.  (This particular place was in a suburban, Folsom, CA,
neighborhood with three homes on the same transformer.)

I wasn't looking for it, I just noticed 10+ VDC on my Fluke 41 when I was
looking at the PQ on a home service just for fun.  I thought I had it on the
wrong scale or something.  Nope, clear as day.  I've found it quite a few
times since then because I was looking for it in the course of doing a lot
of things, including PV.  The coolest thing I've seen, without exception, is
that "once you turn on an inverter with an integral iso-tranny", the DC
completely disappears at the Service.  This happens whether or not the
inverter has started or "connected".  My only take is that the iso-tranny
absorbs it somehow.   Of note is that each of the times I've found it,
either the homeowner or a secondary-sharing neighbor is a "gadget freak"
(Not intended to be a slam in anyway)  If any of you have a Fluke 41, 43 or
other equipment capable of measuring this, go out and hook it up to your
Service Panel.  If you have a PV or wind system, test it with the system on
and off.  You might be surprised at what you find, especially if you're one
of those "extra geeks"!  LOL

One case was a "problem customer" who had a 2.5 kWAC Sunny-Boy system
installed.   Anyway, about two weeks after his system was installed, he
started saying the lights were blinking in his kitchen and his 50+ inch
big-screen TV was turning on and off at random.  We did a two-week power
quality study of his service.  One week with the PV completely locked out
and one with it operating normally.  Condition the same either way.  We went
beyond and added additional equipment at various points of his home's
distribution.  Turns out that two things were culprits.  One was a loose
neutral in the Disposal / Dishwasher circuit that "blinked" sensitive loads
on the same phase that were distributed from that sub-panel.  The other was
a 30+ VDCpeak on one 120  VAC circuit and 20+ on another.... One was his ham
radio.  (This guy actually stopped the installation partway through because
he all of a sudden thought that the DC Home Runs in EMT running paralell to
4 feet of his ham antenna wiring in a 3" ABS pipe at about 10 feet away on
the opposite side of a wooden beam would cause coupling or interference...
That one took two weeks and two separate engineering opinions to resolve...
Guess who the janitor was for the whole project.)  The other was his
dedicated office equipment circuit.  All nice brand-name equipment but that
was the source.  Laser Printer, Fax, 3 PC's, etc.  We had to shut off every
circuit in the house except the Main, Sub-Panel Main, and those circuits to
prove it to him, but that was the story.  Haven't heard from him since,
which is a good thing.  Not even a whimper about his ham radio signal.  I
have always believed that the problem was there before the PV and his stuff
was the source of it.  Maybe he thought he'd get something for free or maybe
he was one of those "bad customers".... Happened to be an engineer.... Those
who've heard me lecture on "good customer / bad customer" understand... Wish
I could laugh... One of those cases where I added "BD" as initials behind my
name on all correspondence....

DC injection is not a joke from the perspective of Power Quality... At the
Consumer level and at the Utility Level.  DC injection messes with a bunch
of things and can make a bunch of weird things happen.  Strange sounds,
"ghosts", etc.  DC injection comes from a numerous and growing number of
sources.... Predominately electronics that don't have suitable filtering.
My understanding is that this is "regulated" by the FCC, but I am left to
wonder how much value is in the little sticker on the back of the things,
especially knowing that so many are made "overseas".  I'll leave it there.

Electronic ballasts (CF's, T-8's, etc.), computers, VCR's, TV's, cordless
phones, stereos, clocks on ovens, garage door openers, sprinkler timers,
home automation (X10), battery chargers, etc.  Some are better than others.
You, the consumer, may not think about it and if you do, how do you test it
and how do you know for sure?  

As this dynamic has grown, Utilities, specifically protection and line
quality engineers, are increasingly sensitive to it.  When you say "DC",
they think "No, not that!".  I don't know the answer but I instinctively
have to believe that the level of testing and number of hoops our inverters
must go through should strongly support their adequacy in addressing this
issue.  They must comply with FCC regs, too.  I inherently think personally
that transformer-based inverter platforms are better at filtering DC
injection than non-transformer based platforms.  I don't have data to
support that, but that's what I think based on what I've seen.

I am left to ask.... What, are we all gonna stop using electronics?  You
mean to tell me that Utilities don't insist on micro-control over the
products sold by Good Guys, Circuit City, Wal-Mart, Etc. but they are afraid
of the miniscule number of Grid-Connected PV systems out there?  Get Real
Stupid!  Clean up your own house before you come to mine.  My housekeeper
only comes every other Monday.  

I say, if it's such a big problem, why don't they install filters at each
service or in their own transformers?  INVERTERS AREN'T THE SOURCE OF THE
UTILITIES' DC INJECTION HEADACHE!

Lemon & Butter Trees for All!

Matt Lafferty
Universal Energies Institute
mlafferty at universalenergies.com
(916) 422-9772
(916) 628-7694 Cell
(916) 914-2247 Fax
www.universalenergies.com

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