Show us your mains waveform!

[tautech]

Wow, ocw, that's interesting. By emergency generator do you mean one of those tiny 5kW things, or a big industrial Caterpillar-type thing?

That was from a 40 kVA three phase generator.  Some UPS's still have problems accepting that generator waveform as "clean power" and will not pass it.  Many home generators have a much worse output--not that far from square wave.  The commercial power comes from a sub-station not much more that an kilometer away which translates to clean power.

Dirty exciter slip rings and brushes perhaps ?

[engrguy42]

Wow, I stumbled on this site that shows some waveform comparisons between pure sinewaves and those with varying degrees of THD. Assuming the data is correct, it seems to confirm what coppice said and I've been presuming about waveforms in the 5% THD range looking very clean, as opposed to the waveforms folks are showing here.

Which again begs the question:

Why are folks seeing waveforms with such apparently high THD's, when the utility and (presumably) most equipment is designed to meet IEEE 519?

It would be nice if someone could identify some actual equipment that is actually causing these distortions and do a before and after to see why it's happening.

http://diyaudioprojects.com/mirror/members.aol.com/sbench102/thd.html

[engrguy42]

Okay, for those playing at home, I dumped the memory from my scope to USB to grab 1 million+ samples of about 30 cycles of my mains waveform (screenshot posted previously), and that gave me a monster CSV file.

I went into Matlab and entered the following lines of code:

A = readmatrix ('thd.csv', 'ExpectedNumVariables', 1000000)

R = thd(A)

And the result was about -26dB. If you convert that to THD % it gives almost exactly 5%.

I haven't double-checked anything so this may be somewhat bogus, but at least it's one way to analyze your waveforms for THD if anyone is interested. 

[2N3055]

Or you can do this if you have it..

I also tried Picoscope, ti was pretty much the same..

[engrguy42]

So I did an FFT for my mains, and here's what I got. Curious.

3rd and 5th harmonics, but also some in-betweens of 200, 280, and 320 Hz. Not sure what that's all about. I assume it's electronic, not electrical in origin.

[engrguy42]

Wow, go figure....

I did a hand calc of THD based on the FFT results, and it matches what I got in Matlab. 

Matlab said 5% and my hand calc said 5.5%.

[MarkL]

So I did an FFT for my mains, and here's what I got. Curious.

3rd and 5th harmonics, but also some in-betweens of 200, 280, and 320 Hz. Not sure what that's all about. I assume it's electronic, not electrical in origin.

I don't know the inner workings of Rigol's FFT, but it looks like it might be aliasing.  You could try several different horizontal sweep speeds, or maybe select the FFT to be computed from memory (if not already set that way), and see if the unexpected harmonics change.

[Jay_Diddy_B]

Hi group,

All those people who have posted their waveforms so far must live in "impure neighborhoods" 

Here is what the mains should look like:




This is almost 'Audiophile grade'




The THD is 0.115% measured with an HP 35665A DSA.

Of course this didn't come out of the wall. It came from an Elgar 251 AC Power Source with a home made oscillator. The oscillator is a DDS design using a PIC16F876 and a DAC.



If I measure the wall coming out of the wall with a Fluke 41 Power Harmonic Analyzer:





The third harmonic is the largest at 0.7%

The THD is 2.1%

If I measure between two phases:



I get 248V. In my home you do this in the kitchen like this:



Regards,
Jay_Diddy_B

[bdunham7]

Solar could be contributing. I should measure mine while I am at full power. Solar is constant power so come the peaks there is less current to give unless they are storing it and managing the output carefully over the cycle.

My computers ATX supply is PFC and that is 10 years old.

I don't know the UK regs, but here any solar inverter from this century would be required to have a clean output and they do indeed have input capacitors to store the required energy.  Newer ones from the past few years even have to comply with Rule 21, which requires them to also provide the necessary recirculating current to serve a load with a power factor down to 0.85, IIRC--just like a generator would have to do.  Mine predate Rule 21, so when my AC is running and the sun is fully out at noon, I'm drawing near zero billable power but the utility is supplying all of the imaginary part of my ancient AC compressor's load. 

And as far as whether small devices are PFC, the vast majority are now, although how clean they are at lower loads can be questionable.  This is not expensive to implement because the same chip and system that gives you PFC also gives you multi-voltage functionality.  ATX power supplies became PFC right about the time the 110/220 voltage switch disappeared.

[engrguy42]

Solar could be contributing. I should measure mine while I am at full power. Solar is constant power so come the peaks there is less current to give unless they are storing it and managing the output carefully over the cycle.

My computers ATX supply is PFC and that is 10 years old.

I don't know the UK regs, but here any solar inverter from this century would be required to have a clean output and they do indeed have input capacitors to store the required energy.  Newer ones from the past few years even have to comply with Rule 21, which requires them to also provide the necessary recirculating current to serve a load with a power factor down to 0.85, IIRC--just like a generator would have to do.  Mine predate Rule 21, so when my AC is running and the sun is fully out at noon, I'm drawing near zero billable power but the utility is supplying all of the imaginary part of my ancient AC compressor's load. 

And as far as whether small devices are PFC, the vast majority are now, although how clean they are at lower loads can be questionable.  This is not expensive to implement because the same chip and system that gives you PFC also gives you multi-voltage functionality.  ATX power supplies became PFC right about the time the 110/220 voltage switch disappeared.

Rule 21?? Wow, you must be in California 

[engrguy42]

Anyway, FWIW, if you look at many of the waveforms posted, including mine, you might start to see a similarity. The up slope looks like a sine wave, and the down slope looks more linear. My hunch is that's due to everyone having CFL and LED and other lighting loads. The THD's are within the 3-5% limits, and the distortion is slight or noticeable.

If you look at papers on voltage distortion due to various lighting loads you'll probably see similar waveforms.

I'm guessing all the neighbors have a lot more lighting operating than other fancy stuff, so it seems like the most likely cause. Maybe that's why when I turned off everything in the house, the distortion remained due to neighbors' lights.

And the really distorted ones with the flat tops? Hell, I have no clue. But something doesn't look right.

[tautech]

Ask yourself what might clip/limit/distort the peak of voltage in a sinewave and you have your answer to what we see on the mains.
Yes, it's really that simple !

[Simon]

I'm not going to believe that every phone charger and tiny device is PFC. OK they are small loads, but they take all of that power at peak so they appear like 10-20 times greater which is the whole point of PFC, if you add up all of the small devices that may have an inductor at best you may be surprise at how much unclean power is being drawn.

Last time i looked PFC required another stage of SMPS, a recent industrial unit I looked at showed a seperate block and was only 90% efficient but looking at a DC/DC that is 96% efficient because it does not need two stages.

[ahbushnell]

Wow, I stumbled on this site that shows some waveform comparisons between pure sinewaves and those with varying degrees of THD. Assuming the data is correct, it seems to confirm what coppice said and I've been presuming about waveforms in the 5% THD range looking very clean, as opposed to the waveforms folks are showing here.

Which again begs the question:

Why are folks seeing waveforms with such apparently high THD's, when the utility and (presumably) most equipment is designed to meet IEEE 519?

It would be nice if someone could identify some actual equipment that is actually causing these distortions and do a before and after to see why it's happening.

http://diyaudioprojects.com/mirror/members.aol.com/sbench102/thd.html

519 is called:

IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems. In section 1.2 it says it is a recommended practice.  It is used in industrial situations.  Like a manufacturing plant.  It's not a residential or office standard. 

[ahbushnell]

Solar could be contributing. I should measure mine while I am at full power. Solar is constant power so come the peaks there is less current to give unless they are storing it and managing the output carefully over the cycle.

My computers ATX supply is PFC and that is 10 years old.

I don't know the UK regs, but here any solar inverter from this century would be required to have a clean output and they do indeed have input capacitors to store the required energy.  Newer ones from the past few years even have to comply with Rule 21, which requires them to also provide the necessary recirculating current to serve a load with a power factor down to 0.85, IIRC--just like a generator would have to do.  Mine predate Rule 21, so when my AC is running and the sun is fully out at noon, I'm drawing near zero billable power but the utility is supplying all of the imaginary part of my ancient AC compressor's load. 

And as far as whether small devices are PFC, the vast majority are now, although how clean they are at lower loads can be questionable.  This is not expensive to implement because the same chip and system that gives you PFC also gives you multi-voltage functionality.  ATX power supplies became PFC right about the time the 110/220 voltage switch disappeared.

Rule 21?? Wow, you must be in California 

This describes rule 21.  Double and you get 42. 
https://www.scoop.solar/blog/understanding-rule-21-california-and-beyond/

[engrguy42]

Wow, I stumbled on this site that shows some waveform comparisons between pure sinewaves and those with varying degrees of THD. Assuming the data is correct, it seems to confirm what coppice said and I've been presuming about waveforms in the 5% THD range looking very clean, as opposed to the waveforms folks are showing here.

Which again begs the question:

Why are folks seeing waveforms with such apparently high THD's, when the utility and (presumably) most equipment is designed to meet IEEE 519?

It would be nice if someone could identify some actual equipment that is actually causing these distortions and do a before and after to see why it's happening.

http://diyaudioprojects.com/mirror/members.aol.com/sbench102/thd.html

519 is called:

IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems. In section 1.2 it says it is a recommended practice.  It is used in industrial situations.  Like a manufacturing plant.  It's not a residential or office standard.

Right. Because we're talking about service from the utility. The equipment people put in their residence or office is somewhat irrelevant to the rest of the world pretty much. And of course people buy cheap junk that couldn't care less about harmonics and power quality. What people care about is whether the utility is providing good power quality, and that's why IEEE is referenced. And of course if people are connnecting their generators to the grid, which might affect others.

[engrguy42]

BTW, I assume it goes without saying, but many/most/all utilities and other organizations require compliance with IEEE 519 (as well as other ANSI, etc., stuff), even though it's a "recommended practice". If someone's operations cause other customers problems, and they don't comply with IEEE 519, that's bad.

So I recommend when people make these waveform measurements they disconnect/turn off all relevant electrical equipment in their house/whatever first, so they can measure only what the utility is providing. That way they can clearly judge whether an ugly waveform is the fault of the utility, or something in their own house. If what they measure doesn't meet IEEE 519, then they have a pretty good idea they utility is not meeting their own requirements, or else a neighbor is causing a problem.

Otherwise, the ugly waveform is nobody's fault but your own. 

[bdunham7]

I'm not going to believe that every phone charger and tiny device is PFC. OK they are small loads, but they take all of that power at peak so they appear like 10-20 times greater which is the whole point of PFC, if you add up all of the small devices that may have an inductor at best you may be surprise at how much unclean power is being drawn.

Last time i looked PFC required another stage of SMPS, a recent industrial unit I looked at showed a seperate block and was only 90% efficient but looking at a DC/DC that is 96% efficient because it does not need two stages.

The typical small power supply PFC/multivolt section additional parts are exactly one each of a suitable power mosfet, inductor and diode, plus of course the power supply controller chip must be a PFC model--but those likely cost 0.10 or less in bulk.  Obviously a small amount of power is dissipated, but I'm not sure an efficiency comparison between PFC and non-PFC is apples-to-apples because the non-PFC just shifts the inefficiency elsewhere.  I've seen exactly one 'efficient' non-PFC ATX supply, by Antec, that I used in a build about 8 years ago--every other non-PFC unit has been total crap for efficiency compared to any newer models.  And even that Antec isn't as good as the better PFC models.

Now if you are talking wall warts, although I suspect many except the very cheapest are actually PFC, I've no proof.  I suppose I should tear one down.  But almost everything recent I've stuck in my Killawatt device has shown a pretty good power factor.

As for what causes all that harmonic distortion, I don't really know but if you look in the list of exceptions to the CE power factor requirement, there's a whole list of suspects like cheap LED lights under 25W, heating controls under 200W, large arc welders, etc.  In addition, some requirements only specify a power factor >0.7, which is pretty bad.  Then there's the whole issue of the legacy installed equipment.

[NiHaoMike]

What gets interesting is that grid tie inverters can be more efficient at part load if they supply more power near the peaks. If it can read the load current (as those that support zero export do), it wouldn't be too difficult to have it try to follow the load current waveform and effectively do PFC on all of them. Even grid tie inverters that are not aware of the load current can analyze the voltage waveform and then shape the current to push the waveform to look more like a sine wave.

A lot of loads do very badly with a square power waveform. Many power supplies will go up in smoke, because high enough harmonics will put a huge current through the front end filter caps.

Few power supplies have problems running on modified sine.

That distortion looks high enough that it might cause problems, for example with a large induction motor. The harmonic currents generate no torque, only heat, and the impedance of the motor may be much less at harmonic frequencies.

As an inductive load, the impedance goes up with frequency. Hence why motor VFDs often don't have output filters. In fact, if a motor is inductive enough (e.g. Prius motors), it will run well on square waves.

[ahbushnell]

BTW, I assume it goes without saying, but many/most/all utilities and other organizations require compliance with IEEE 519 (as well as other ANSI, etc., stuff), even though it's a "recommended practice". If someone's operations cause other customers problems, and they don't comply with IEEE 519, that's bad.

So I recommend when people make these waveform measurements they disconnect/turn off all relevant electrical equipment in their house/whatever first, so they can measure only what the utility is providing. That way they can clearly judge whether an ugly waveform is the fault of the utility, or something in their own house. If what they measure doesn't meet IEEE 519, then they have a pretty good idea they utility is not meeting their own requirements, or else a neighbor is causing a problem.

Otherwise, the ugly waveform is nobody's fault but your own. 

Is that a UL requirment in the US?

[BravoV]

Curious how the mains wave will look like when using hair dryer like this condition below where it generated a DC offset at the mains line. Did this measurements many years ago as I didn't have HV diff.probe yet at that time.

It was Philips 1600 watts hair dryer, more details -> HERE

[Tomorokoshi]

Mains power and Abacus supply. Also measured on HP 35665 DSA.

Mains THD: 7.332%

Abacus THD: 1.052%

Measured using a 67 dB attenuator off the power line for around 60 mV into the DSA.

[srb1954]

I not looked at the current waveforms of individual items but have looked at building power installations with large air conditioning plant machinery using PFC. I have not seen the major current waveform distortion, as you describe, from such devices but rather the opposite. PFC equipped rectifier circuits simultaneously reduce the current waveform distortion and improve the power factor.

When you say PFC moves the current waveform to be centred on the voltage waveform I think you are incorrect. In a normal rectifier feeding directly into a capacitor input filter, the current waveform peak is already closely aligned with the voltage waveform peak but the current waveform, due to its spiky non-sinusoidal shape, is very high in harmonics. It is these harmonics that cause the poor factor not a minor phase shift between the peak of the current waveform and the peak of a voltage waveform. In fact, it is not mathematically possible to have a good power factor if there is significant distortion on the current waveforms.

[Simon]

BTW, I assume it goes without saying, but many/most/all utilities and other organizations require compliance with IEEE 519 (as well as other ANSI, etc., stuff), even though it's a "recommended practice". If someone's operations cause other customers problems, and they don't comply with IEEE 519, that's bad.

So I recommend when people make these waveform measurements they disconnect/turn off all relevant electrical equipment in their house/whatever first, so they can measure only what the utility is providing. That way they can clearly judge whether an ugly waveform is the fault of the utility, or something in their own house. If what they measure doesn't meet IEEE 519, then they have a pretty good idea they utility is not meeting their own requirements, or else a neighbor is causing a problem.

Otherwise, the ugly waveform is nobody's fault but your own. 

You just won't listen will you. Industrial users are probably making more of an effort as anything high power will be made properly. But pitch against those all of the tiny non compliant devices and you see where there in the problem. I reapeat again as you insist on playing ignorant that turning stuff off in your own house WILL MAKE NO DIFFERENCE. unless your the only guy at the end of a 1000km supply line

[engrguy42]

BTW, I assume it goes without saying, but many/most/all utilities and other organizations require compliance with IEEE 519 (as well as other ANSI, etc., stuff), even though it's a "recommended practice". If someone's operations cause other customers problems, and they don't comply with IEEE 519, that's bad.

So I recommend when people make these waveform measurements they disconnect/turn off all relevant electrical equipment in their house/whatever first, so they can measure only what the utility is providing. That way they can clearly judge whether an ugly waveform is the fault of the utility, or something in their own house. If what they measure doesn't meet IEEE 519, then they have a pretty good idea they utility is not meeting their own requirements, or else a neighbor is causing a problem.

Otherwise, the ugly waveform is nobody's fault but your own. 

You just won't listen will you. Industrial users are probably making more of an effort as anything high power will be made properly. But pitch against those all of the tiny non compliant devices and you see where there in the problem. I reapeat again as you insist on playing ignorant that turning stuff off in your own house WILL MAKE NO DIFFERENCE. unless your the only guy at the end of a 1000km supply line

Simon,
First of all, chill with the personal attacks. You're a moderator, you should know better.

Second, are you saying that an electrical device in your home can have no effect on the voltage waveform you see when measuring the mains in your home?