Avoiding being overcharged by your smart meter by using AC line filters.

[uer166]

The current transformers should be resonable tolerant to a DC part. With some loads a DC component can happen. A relatively common example are hair dryers on the lower power setting that use a diode to reduce the power to half. AFAIK for hand held use this is allowed in many regions.

I would not expect the CT to saturate under some 100mA, as few materials get saturation under 1 A/m and 10 cm magentic path is still relative small. So it would be hard to make the CT saturate so early. Chances are they would prepare for some DC and intentionally use a material with current needed for saturation / leaving the good range.

None/few of the US meters are designed to tolerate DC, and in my experience you need very little current to saturate, single amps range. For MID metering in europe, they require to be tolerant to a half-wave rectified load of full current rating, and therefore you need to design CTs in weird ways. E.g. you usually have a dual (or even sometimes triple) core CT, where one material is high-permeability for high accuracy for normal loads, and a lower permeability to keep it working in case of 30A DC or whatever, but at slightly degraded accuracy.


Re: even harmonics: for a DC-tolerant CT, I think you're right, they can't measure DC but may be able to measure even harmonics. In general all these edge cases can corrupt, and break:

• RMS measurements of V and I
• Power factor measurements
• Reactive power calculation
• Frequency measurement (e.g. when it's done based on zero-crosses

Does that imply that the active power becomes inaccurate? No, it does not!

OP, I think you're really confused about how conducted EMI works, and how high-frequency stuff can affect metering. All that 10kHz or 100kHz or whatever, gets attenuated to nothing in the input filters, it simply doesn't meter it.

[coppice]

From the website you linked:

Here, the electricity being consumed no longer has a perfect waveform, instead it acquires an erratic pattern. The designers of modern energy meters have not made sufficient allowance for switching devices of this kind.

When they dismantled the energy meters tested, the researchers found that the ones associated with excessively high readings contained a ‘Rogowski Coil’ while those associated with excessively low readings contained a ‘Hall Sensor’. Frank Leferink (Professor of Electromagnetic Compatibility at the UT) points out that

As someone who designs and certifies MID meters, both 3-phase and 1-phase, the above smells of BS, the designers certainly have allowed sufficient allowance for high harmonic content. There are a few cases where a lot of the meters in the field read extremely low when presented with a half-wave rectified load, namely the current-transformer based ones. I don't see how anything can read 582% high unless you're trying to defeat the device in some non-real-world edge case. Also, hall and rogowski? Seriously? The author couldn't have chosen anything more exotic than that, household meters are CT or shunt-based.

I have found the actual paper scihub and going through it now, I suggest you do too to understand how the authors may have been mistaken (or not).

There are some major manufacturers of electrical energy meters who use hall sensors and rogowski coils, especially in Europe. CTs and resistive shunts are more common globally, but there is nothing strange or rare about a domestic tariff meter using either a hall sensor or a rogowski coil.

[uer166]

In that case I stand corrected. Do you know of specific manufacturers/part numbers? I remember doing the math concluding that a class B meter wasn't really possible to do with Hall.

[coppice]

In that case I stand corrected. Do you know of specific manufacturers/part numbers? I remember doing the math concluding that a class B meter wasn't really possible to do with Hall.

Its several years since I worked in metering. I would probably mix up who does what now. A small British company did a lot of work trying to get accurate results from Rogowski coils constructed as PCBs, while limiting their influence from external fields. Their approach has gone into some high volume meters, although the results we found when experimenting with their approach was quirky. One of the European makers used to use Hitachi hall sensors for three phase designs, which I think were only 2% accurate. Very cool designs, though. 100% of the electronics was on a single PCB, that clicked into place, with the hall sensors on it. When clicked in, the sensors were in just the right place above the high current terminals moulded into the case. That's the cleanest meter design I've seen. At least 2 people have their own ASICs, which have the hall probe and all the conditioning electronics within the ASIC. They claim extremely high accuracy. I think L&G are one of the companies that do this.

[Conrad Hoffman]

I tend to be skeptical of any non-rigorous measurement or discussion of power. There are a lot of pitfalls one can stumble into measuring power. Errors in measurement account for most claims of over-unity in free energy scams. I've been measuring low PF gadgets on the job for many years. We're well equipped and some high frequency measurements are still hard and prone to errors. Sometimes we admit that getting a super accurate result isn't worth the time and effort it would take and we just move on. I have a fair amount of faith in the people that design commercial power meters, as the technology is well established and the stakes are high.

[coppice]

I tend to be skeptical of any non-rigorous measurement or discussion of power. There are a lot of pitfalls one can stumble into measuring power. Errors in measurement account for most claims of over-unity in free energy scams. I've been measuring low PF gadgets on the job for many years. We're well equipped and some high frequency measurements are still hard and prone to errors. Sometimes we admit that getting a super accurate result isn't worth the time and effort it would take and we just move on. I have a fair amount of faith in the people that design commercial power meters, as the technology is well established and the stakes are high.

The standards for domestic energy meters focus on their accuracy from power factors of unity, where maximum accuracy is expected, to 0.5, where a relaxed accuracy is expected. Generally the approvals and calibration processes for meters do not check them below +-0.5PF, which I think is weird. Having a very relaxed spec seems appropriate, but not checking if the accuracy goes completely crazy doesn't. Its the same with small currents. Between the creep current (the minimum the meter is supposed to even register as power, so its readings don't accumulate small amounts of noise) and 5% of full scale, they don't generally even do a sanity check of the accuracy.

[Fflint]

Op here, I haven't gotten around to measuring my power use using CTs, because my use as charged did come down significantly after my meter was replaced when I installed my PV system. Previously I fairly routinely got bills between 600 in summer to over 1000  kWh in winter per 2 month billing period. After I installed my PV system (2.3kW only, projected annual production 2500kWh) my bills in the warm period (May-September) I got bills of few bucks per 2 months. So I basically used almost exactly the same as was generated. Now during winter my last 2 bills were on the level of summer use before. This is just anecdotal evidence, but it does seem significantly lower (by a third) than before.

Furthermore, the New meter gives me an hour by hour breakdown on use/generation and as far as I can tell it is accurate. I might actually make a refund claim based on that so the energy company sends the old meter for testing. (I hope they still have it).

This is just anecdotal "evidence". Anyone can say "maybe you're using less now that you have direct visibility of use", but I sure haven't made any extra effort to do that.

[Circlotron]

There are a few cases where a lot of the meters in the field read extremely low when presented with a half-wave rectified load, namely the current-transformer based ones.

Often wondered how accurate are old timey rotating disc watt-hour meters with a half wave rectified load.

[Zero999]

Dave did a video on the power wasted by smoke detectors, the apparent power of a nations worth of smoke detectors was a significant number in the MW.

That's not a problem, because smoke detectors are capacitve loads, which will be more than compensated for by the huge number of inductive loads, especially in industry, where motors are the main load.

[coppice]

There are a few cases where a lot of the meters in the field read extremely low when presented with a half-wave rectified load, namely the current-transformer based ones.

Often wondered how accurate are old timey rotating disc watt-hour meters with a half wave rectified load.

Why would half wave loads give trouble with CT based meters? They are all specified to use CTs with a pretty high DC tolerance. That spec usually comes from the meter's customer (the utility) rather than a standards body. Its there, none the less.

Most of the old disc (Ferraris wheel) meters work well with highly asymmetric load waveforms, unless the load is extremely high. Like the CT based meters, the core in most Ferraris wheel meters is specified to have considerable DC tolerance. I've seen some very lightweight meters, which are a bit suspect in this area, but most are OK.

[uer166]

They are all specified to use CTs with a pretty high DC tolerance.

That is not true of any US meters I've tested, and multiple MID EU certified meters that should have DC tolerance, but don't.