KWH meter discrepancy [RE-wrenches]

Matt Lafferty mlafferty at universalenergies.com
Sat May 20 11:27:54 PDT 2006


Wrenches,

Joel D said:

> a survey of calibated and certified electromechanical
> revenue grade kWh meters showed over 1% inaccuracy
> forward and over 3% inaccuracy backward.
 
There have been numerous "surveys" over the years. As with any "survey" and
"statistics", there can be a huge disparity in what the published results
mean and the intent of the survey in the first place... 

What you are most likely to find when you pull back the curtain is this:
Most revenue grade kWH meters account for power factor losses to some
degree. 

The key words in the above statement are: "to some degree."  

I base this on my own observation including interviews with Meter Shop
personnel, research of data comparisons for "what left the substation" vs.
"what is metered at the customer site", Power Factor & Harmonics on the
Distribution sections, transfomer & wire losses, etc.  I really should have
said "power quality" instead of power factor to embrace the overall effects.


The utilities have recognized these issues for years.  Harmonics and Power
Factor are increasingly large issues for our grid. In many Distribution
sections, the harmonics issue is really bad.  The primary cause for this is
the growing quantity of electronic equipment in homes and businesses that is
not filtered at a very high level.  (Hint: You can't trust the "FCC
Compliant" sticker on a whole lot of stuff that is manufactured in certain
parts of the world.)  They have established protocols to recover a portion
of the revenue losses associated with this. What this boils down to is that
the "acceptable" meter accuracy tolerances have been modified to meet this
need. It is not always easy to get to the bottom of this and get the actual
documentation in most cases. 

There are generally two ANSI standard levels for acceptable utility metering
tolerance... One is at "+/- .5%" and the other is at "+/- 2%".  This seems
like a huge difference and it is if "all things were perfect and equal on
our grid at all times".

A meter that reads within the +/- .5% accuracy range at 1.0 PF on a
low-harmonic system will not necessarily meet that standard when the power
quality is lower.  The utilities deal with this by picking a "system
average" power quality and making sure their meters are within the +/- 2%
range at this level. They have to have this approved by the regulatory body
that they answer to.  For those of you who are already thinking "those
scumbags must be gaming the system", and I know you are out there, I have to
say that they take this seriously and "err on the side of most customers" in
every case I've seen.  Hard to believe, but true.  They are "losing kWH"
overall.

Folks, our grid is not healthy. For any of us who are connected to the grid,
we are affected by it and it is affected by us.  Every time you plug in
another computer, tv, stereo, microwave, battery charger, compact
flourescent (yes, compact flourescent)... Plugging in anything with with an
electronic clock or electronic circuit, you are affecting the local power
quality.  Fact.  

We all need to understand this and work to ensure that our "demands" and
expectations related to incentives and the needs of utilities are reasonable
and helpful.  Anything short of that is irresponsible and un-sustainable.
We are not the "only ones who matter!"     

I'm not a "utility apologist" by any stretch of the imagination.  Just a
poor solar janitor who has worked hard to understand what is real and try to
make sure that right and fair things happen.

This whole thing is a true iceberg and, unlike our polar icebergs, it is
growing. 

2 Cents, 


Matt Lafferty 
Universal Energies Institute 
mlafferty at universalenergies.com 
(415) 252-0343 Phone 
(916) 914-2247 Fax
 


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