My understanding is that utility meters measure instantaneous voltage and c urrent (simultaneously) at a rate much higher than the AC period and use th e sum of the products over a time period (typically a multiple of the AC pe riod) to measure power. Then apparent power is calculated (if needed) by c alculating the RMS of each the voltage and current over the same time perio d and calculating the product. From these two the reactive power and power factor can be calculated.
Did I leave out anything important? Or did I completely misunderstand what is going on?
Rick C.
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current (simultaneously) at a rate much higher than the AC period and use the sum of the products over a time period (typically a multiple of the AC period) to measure power. Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time per iod and calculating the product. From these two the reactive power and pow er factor can be calculated.
The ADCs used in power metering need not have high sample rates nor low noise; a few LSBs of noise are actually good. We are trying to gather statistics on millions of samples of the E*I product, not reproduce the waveforms. The Sampling Theorem doesn't apply here.
I sold hundreds of thousands of channels of AC power metering that used single-slope ADCs sampling at around 27 Hz.
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John Larkin Highland Technology, Inc
lunatic fringe electronics
Not required; those products ARE the instantaneous power, and they sum to reach the real goal, the energy-delivered (kWh) reading. The meter just accumulates and scales according to its time-calibration of the measurement period.
Most utility meters don't display such detail. Whether they calculate/record/report it, though, is uncertain. My (new, digital) meter is less forthcoming than the old moving-dials one, you cannot see the power (energy use rate) spinning a disk, you have to watch, capture two digital measurement energy displays, use a stopwatch...
nd current (simultaneously) at a rate much higher than the AC period ...
of the AC period) to measure power.
reach the
es and scales
each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calcul ated.
ecord/report it, though,
moving-dials one,
.
here I think they all have an LED that flashes once per Wh
current (simultaneously) at a rate much higher than the AC period and use the sum of the products over a time period (typically a multiple of the AC period) to measure power. Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time per iod and calculating the product. From these two the reactive power and pow er factor can be calculated.
at is going on?
Most are electromagnetic followed by a mechanical gear train adder. They ar e insensitive to imaginary power.
It may matter. When the current is far from sinusoidal, the computed power may be much more when the calculation is not done carefully, or when there are problems with the filtering.
A while ago there was some local coverage here in the Netherlands on a consumer tv programme about the fact that so many customers observe an increased energy consumption when they have a "smart meter" installed. Usually before that, they had an electromechanical meter of the "Ferraris" type, and now it is replaced with an electronic meter with remote readout capabilties (called "smart meter" here).
Of course the difference is not related to the remote readout but to the electronic measurement technology.
I studied the relevant regulations for an electricity meter and also mailed with the responsible person at the authority. It turns out that nowhere in the regulations the non-sinusoidal current problem is discussed. The only thing appearing in the standards is the handling of Cos-Phi. The meter should indicate kWh, not kVAh.
However, in today's households there tends to be a non-sinusoidal current due to small switchmode powersupplies (that are not mandatory to have powerfactor correction), LED lamps, etc. The result is that the electronic meter registers more than the Ferraris meter. How much more, that depends on the exact make and model of meter.
But that is all within spec, because THERE IS NO SPEC. When you claim the meter is wrong, it is being checked with a resistive load and of course that is metered correctly...
The difficult problem of course is: what is reasonable. One could also argue that the Ferraris meter displayed a too-low value, as the electricity companies have to deal with the non-sinusoidal current which causes them all kinds of problems. The customer should pay for that or stop doing it.
The last word has not been said about it, but for now I have deferred the change to a smart meter, and so have many others.
and current (simultaneously) at a rate much higher than the AC period ...
ple of the AC period) to measure power.
to reach the
lates and scales
of each the voltage and current over the same time period and calculating t he product. From these two the reactive power and power factor can be calc ulated.
e/record/report it, though,
ld moving-dials one,
o
h...
afaiu quite a few of those used have also have an IR serial port and with a reasonable easy to guess code you can read out all the instantaneous and a ccumulated values
Here (UK) even my Siemens, non-smart-but-digital, meter has a blink-per-wH LED (orange) which you could monitor externally with a sensor without tampering.
It has the split-IR port too (TX, RX halves) for setup/reading (never used since install).
Elektor ran a project for this, with details of the coding/electronics for the IR port. Some features are behind an encrypted/password wall, presumably stuff like "reset counter" and "change tarriff settings" :)
Found it: Elektor (UK) 2002 March, "IEC 1107 Electricity Meter Interface" (although Wikipedia refers to it as IEC *6*1107, later renamed to IEC
Silver Spring Networks has meters around here for several PoCos. Some are set to just display KWH. Others cycle through voltage, KVA, KW, and KWH.
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& no one will talk to a host that's close..........................
Unless the host (that isn't close).........................pob 1433
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It's getting hard to find linear/sinusoidal loads...
Lighting: LED/SMPS Heat: Heat pump with VFD or gas burner with VFD fan Computers: SMPS Oven: VFD/SMPS for temp-controlled heat and so forth.
What's left?
--
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& no one will talk to a host that's close..........................
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Thus it is very attractive for metering companies to register
2*Vpeak*Ipeak*Cos(phi) instead of integrating V*I at a sample time sufficient to see all harmonic components of the current.
And depending on standards and regulations, they may actually be allowed to do that. In the relevant standards here, there is no mention at all about the handling of non-sinusoidal current so meters only need to be tested on a pure resistive load and on inductive and capacitive loads.
No. That works when you have inductive load and are charged for VA instead of Watts. That is not what I am talking about.
Here we are charged for Watts (kWh) but it is only specified that it must take the Cos(phi) into account (so your capacitor does nothing). However, it is not specified how the effective values of voltage and current have to be measured/calculated, and to what upper frequency.
So a load with non-sinusoidal current could be measured to true RMS, or to Ipeak*Sqrt(2), and as a consumer you cannot claim the meter is faulty as long as it works OK on standard resistive loads or loads having some phase angle. Because that is all that is specified.
On Sunday, January 6, 2019 at 2:10:39 PM UTC-5, snipped-for-privacy@gmail.com wro te:
current (simultaneously) at a rate much higher than the AC period and use the sum of the products over a time period (typically a multiple of the AC period) to measure power. Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time per iod and calculating the product. From these two the reactive power and pow er factor can be calculated.
at is going on?
The latter. Utility metering measures energy, not power.
and current (simultaneously) at a rate much higher than the AC period and u se the sum of the products over a time period (typically a multiple of the AC period) to measure power. Then apparent power is calculated (if needed) by calculating the RMS of each the voltage and current over the same time period and calculating the product. From these two the reactive power and power factor can be calculated.
what is going on?
153a.pdf
Right. There are two ANSI standards governing meter performance. They don't care how you do it. Just pass the specified testing they call out. Apparen tly they have three accuracy classes: 0.1, 0.2, and 0.5%, used to determine pass/fail criteria, and they have more than several test waveforms they us e, including pulse AFAICT. Of course, the standards are overpriced and not accessible any other way.
And only people who are stupid enough to be early-adopters of first- generation electric cars need worry about it. :->
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