Optimal frequency to capture a 50Hz peak signal

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WingNut
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Re: Optimal frequency to capture a 50Hz peak signal

Post by WingNut »

Mostly thats true. These days though, more and more power is drawn by high speed switching power supplies. Tvs, led lghts etc all use non linear power. Which means that true RMS meters are more accurate, esp at lower power consumption. If your house is full of led lights and you measure the amps its more important to measure true rms, switch an immersion on or the kettle and the power waveform is primarily linear and rms is fine as the non linear element is much smaller.
As an example in work, I work at an airport, the AGL lighting is controlled by CCR's - constant current regulators which pump out 6.6A or 12A to hundreds of airfield lights at various wattages. The lights are isolated by unity ratio transformers which are in series. The power side of the CCR is controlled by thyristor in older CCR's and by IGBT (insulated gate bipolar transistor) stacks in more modern CCR''s. You cant mearue that current with an rms clamp meter only true rms as the power is non linear - soem lights are led others halogen lamps. Saying that, thats not what I'm trying to achieve. I appreciate what your circuit does and love the wireless iot type capability.
Getting back to the home measurement of power, I wonder how accurate the energy companies system of measurement really is?

steve001
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Re: Optimal frequency to capture a 50Hz peak signal

Post by steve001 »

WingNut wrote:
Sat Jan 08, 2022 9:54 pm
Getting back to the home measurement of power, I wonder how accurate the energy companies system of measurement really is?
Without getting too into it as it starts to get beyond me .

Most electrical energy meters bill from kVAR's and look at THd to calculate a K factor (1.0 - liner load) HIgher K factors indicate higher harmonics / none liner loads and higher equivalent loadings on your transformer they also look at power factor and take this into the calculations

Even the power quality analyser's i.e fluke and pel's only have a sample time of 1 second. I know they do offer "wave form capture" put this is a one shot test and cannot monitor all the time - these are also looking at THD and voltage / current waveforms to calculate k

typically your max demand on your electric meter (domestic or industrial / commercial) is biased on a 5 - 15 min window

have a look at MID Approval - for more information on the accuracies of metering for invoicing from

https://en.wikipedia.org/wiki/Measuring ... _Directive

LED lighting is not as green as people think ! lovely crunchy wave forms that result in high k factors, and equally high bills (electric companies wont tell you of this as they make money from it ;) - invest in some good active filters ) same goes with low Power Factors

I have seen a 1000kVA transformer with around 300 - 400 kVA load but because of the high k ( around 13 if i remember correctly ) the transformer was in fact overloaded.


hope this helps

Steve

WingNut
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Re: Optimal frequency to capture a 50Hz peak signal

Post by WingNut »

Steve yes. It is a very complex matter. Back when they decided to use A/c instead of DC power distribution they wouldnt have been considering that a hundred years later we would be in this situation.
Thankfully my own electricity meter is a simple aluminium disc spun by eddy currents.
For this circuit i will have to sample at a high rate and capture the peak voltage from the ct multiply it by 1.414 as it will be rms. The challenge is to get the circuit to keep the measurement within the 5v operating voltage of the micro and as I intend to use this over a range of currents and applications I need to make it configurable and that to be done simply by an other user. But I'm getting there


Edit* correction rms voltage is 0.7071* Peak voltage
Last edited by WingNut on Tue Jun 28, 2022 6:55 am, edited 1 time in total.

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Re: Optimal frequency to capture a 50Hz peak signal

Post by steve001 »

DC has its on very real issues believe me .. even worse than AC

you mentioned that your CT has a 100 Ohm resistor fitted (this is a typical value fitted by the CT manufactures to prevent again an open circuit CT.
I would normally expect a lot lower value for the burden resistor. back in my DC Drive / Soft Start days they where typically between 1.5 - 5.6 ohms

with 100 Ohms the CT may be saturating and clipping the top of the wave form as it's voltage cannot rise any more to provide the required current output.

Microchip have some reference designs for electricity meters have you see those ?

https://www.microchip.com/en-us/solutio ... ce-designs

WingNut
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Re: Optimal frequency to capture a 50Hz peak signal

Post by WingNut »

No the CT has a 10Ohn burden resistor and 2000 turns - 1v at 60 Amps. I looked at the mcp603 op amp but you cant get them, prob due to electronic shortage so Im trialling uA 741 which will operate at 5v

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Re: Optimal frequency to capture a 50Hz peak signal

Post by WingNut »

For anyone else interested in the subject. This is a scope measurement from the ct with a few led lights on and a tv
6.png
6.png (14.23 KiB) Viewed 2414 times
switch on a heavier linear load (kettle)
5.png
5.png (14.08 KiB) Viewed 2414 times
Although the kettle is almost 100% linear you can still see the affects of the non linear load at the peak of the waveform

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