Current Transformer Meters - AKA Digital kWH Meters [RE-wrenches]

[Matt Lafferty]

All:

Speaking from the Utility side (not the Obfuscationist type, here)....Ditto
on Bill's comment below, but wait, there's more!

Beware: Most meters used by utilities for the past 20 years or so may run
"backwards" but the kwh indicators run forward.  This is the utilities'
attempt to prevent "upside down meter" theft.  Our meter shop identified a
series of one manufacturer's meters last year that did this, but just
informed us about a month ago that it, in fact, affects virtually all
customers.

We've had a couple of the situations mentioned below....Our Meter Shop
bought "special" meters that were ostensibly supposed to read both ways
($600+....no charge to our customer).  Upon further review, they weren't
calibrated correctly when running "backwards".  We are working to get to the
bottom of it and find a solution.  We think the only way to do this with
currently available meters is to purchase "dual register" meters.  This
would require a modification to the handheld data capture units in use by
our meter readers and a new process set up in billing to "do the math"
(simple subtraction).  While this sounds simple, there are many people,
data-caps, computer programs, etc. "in the loop".  A similar situation will
be encountered in virtually every Utility, whether they realize it yet or
not.

This affects Time of Use meters that are not 400 Amp as well.  I have been
told that, essentially, any digital display kWH meter (Current Transformer)
reads as described by Bill, below.

I have stories, yet to be written for the enjoyment of all.  One case:
Customer was taken off the TOU rate but the meter was left in place.  For
reasons too long to mention here, the time between system start-up and
Customer Net Meter set was about 7 weeks.  Anyway, this customer ended up
with a $68 higher bill for the one full month of billing.  We have made
adjustments, manually and issued the appropriate credits.

The issue to all this is that the customer's bill will reflect consumption
anytime the meter is spinning "backwards".  If there is a time delay between
system initialization and changeout to a true bi-directional meter,
depending on the rate class involved (i.e. TOU), this could equate to a
significant $$$ amount.  Remember, the primary reason residential customers
go to a TOU rate is so they can manage their consumption by not using during
the peak times.  This happens to be when most PV is producing at peak.
Bummer for them if the metering hasn't been changed prior to starting the
system.

Watching the disc spinning backwards is fun.  That is why I do this, too.
Just be aware that your customer may be paying for that fun!

Stand there for awhile and watch the dials if you don't believe me.

-Matt Lafferty
-pvpro at attbi.com


----- Original Message -----
From: "Bill Brooks" <billb at endecon.com>
To: <RE-wrenches at topica.com>
Sent: Friday, May 10, 2002 12:32 PM
Subject: RE: [RE-wrenches]


> Dave,
>
> My experience with current transformer meters (my previous house had one)
is
> that most of them only read the absolute value of current and will read
> reverse current flow as energy usage not energy production. That meter
will
> almost certainly need to be replaced.
>
> Bill.
>
>
> -----Original Message-----
> From: David Palumbo, Independent Power & Light [mailto:ipl at sover.net]
> Sent: Friday, May 10, 2002 7:10 AM
> To: Wrenches
> Subject: [RE-wrenches]
>
>
> I just had a call from an electrician who has a customer interested in a
> net-metered pv system.
> One question he had concerned the current transformer on the 400 amp
service
> and if the meter will spin backwards on this
> one. He says the meter is wired differently than on a system without the
> current transformer. It is a single phase 240 volt supply.
>
> Thanks,
> Dave

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