This that famous harmonic distortion?

[Behemot]

Been playing with my chinese 2kV O-scope probe for the first time so I thought, hey, why not look in the power grid? So I got this Rigol DS2072 with the chinese probe, separated from grid by 2kVA transformer. It is connected to one wall-plug also with passive-PFC'd Fortron and Fujitsu PA19-2.

This is what came from the grid, that it, the famous distortion? Forgive the stupid question but I am looking at grid, with modern O-scope, after like 10 years from school where I've seen historic Tesla O-scope only, once

[Kiriakos GR]

Re: This that famous harmonic distortion?

I am unable to imagine of what you are doing over there, you better post pictures of all your setup.

[Behemot]

Re: This that famous harmonic distortion?

Just looking at 230 V AC from wall?

[T30M31]

Re: This that famous harmonic distortion?

Checking AC wall power with an oscilloscope is a tricky and potential dangerous task if the scope is AC powered.

Is your scope AC powered and if so are you using an isolation transformer?

I have seen waveforms similar to yours when the scope was not isolated, the probe tip was connected to one side of the AC main, and the probe reference lead was left floating (not connected).

If you are using an AC powered scope and you connect the probe reference lead to the AC main it will probably destroy the probe and may damage the scope. I have seen this done and it doesn't turn out well.

[budm]

Re: This that famous harmonic distortion?

Show us the setup, your scope shows 1.5V P-P.

[rievax_60]

Re: This that famous harmonic distortion?

That waveform and amplitude is likely to be normal for the Neutral phase.

[Kiriakos GR]

Re: This that famous harmonic distortion?

Ok I think that I got it, 2KV probe = 100X one.

[tom66]

Re: This that famous harmonic distortion?

Be aware that a mains transformer is a pretty good low pass filter, so you should understand it might filter out some of the harmonics you otherwise expect to see.

Real mains waveform typically looks like a sine wave with flattened tops, the flattened tops are because most non-APFC devices draw power at the peaks and there are so many of these (every CFL bulb does this, most laptop supplies do, most standby supplies do.)

[budm]

Re: This that famous harmonic distortion?

Hi Tom, that is 3V P-P, are you using some kind of step down and xx probe? That is about the same wave form shape I get in typical US power line here as well, about 2.5% HD.

[Behemot]

Re: This that famous harmonic distortion?

The probe I have indeed is x100 or 100 Mohm, 2kV. I bought it primarily for checking transformer primaries and inverter secondaries as there is higher voltage, mains is probably OK even with x10 300V probe. As for transformer, I wrote in the first post. Measured phase against ground.

[tom66]

Re: This that famous harmonic distortion?

Hi Tom, that is 3V P-P, are you using some kind of step down and xx probe? That is about the same wave form shape I get in typical US power line here as well, about 2.5% HD.

I just nicked that photo off the internet - I'm too much of a coward right now to test my own mains (that, and I don't have a 100X probe.)

[Kiriakos GR]

Re: This that famous harmonic distortion?

Real data and fresh from Greece.

Yes it is wise if you do not have the proper tools to step back, and move forward only when you have them.

[budm]

Re: This that famous harmonic distortion?

Is your electrical system in CZ has one side of the power tied to the breaker panel safety ground like in the US?
What AC reading do you get when measure from that phase and ground? Since you are using 100X probe (100 x attenuation), the scope is showing 1.5V P-P, that means the souRce is 150V P-P which is odd if you power line is 230V R.M.S. (648.6 V P-P).

[Kiriakos GR]

Re: This that famous harmonic distortion?

It does not need much of imagination he is not in position to set his scope properly yet.
Either way by this thread his own curiosity is now solved.
When he will get some experience with his box, he will improve.

[budm]

Re: This that famous harmonic distortion?

Well that is the scarcely part, luckily he did not electrocute himself.

[Kiriakos GR]

Re: This that famous harmonic distortion?

By watching my pictures just realized that its impossible to make an phase to phase measurement at 380V RMS by this probe.

Single phase measurement is rather easy if you not make the mistake to connect the phase wire with the ground lead of the scope.

But these diferencial probes is up to 300 EUR, and for now I am avoiding them.

[Behemot]

Re: This that famous harmonic distortion?

Well that is the scarcely part, luckily he did not electrocute himself.

I told ya several times already, I am no idiot. That's probably why I have survived all those tens of repairs working with hazardous voltage sources and I tend to do the same with next hundreds at least. I am not saying my methods look nice, but as usually, I don't care about the appearance, it works while safe enough.

Anyway, I am not interested in the Vp-p value right now, will start with the waveforms itself, mostly looking after what's coming out from all those al cheapo UPSes. And it must be something, my cheap multimeter can only make like 160 V from it

And oh, I got 20MHz limiter on but somethings tells me it won't make much difference

[japlytic]

Re: This that famous harmonic distortion?

An appropriately rated high voltage differential probe should be used for this application, which means that the oscilloscope ground is maintained for safety.
To measure mains harmonics, you would need an FFT option for your oscilloscope - there is a project for an Arduino-powered mains harmonics meter out there (although you would need to adapt the program to suit the particular LCD display).

[tom66]

Re: This that famous harmonic distortion?

Most modern DSOs have powerful FFT features.

[Kiriakos GR]

Re: This that famous harmonic distortion?

Anyway, I am not interested in the Vp-p value right now, will start with the waveforms itself, mostly looking after what's coming out from all those al cheapo UPSes. And it must be something, my cheap multimeter can only make like 160 V from it

New glossary terms for you.
what's coming out from all those al cheapo UPSes.
Modified sine wave with passive PFC.

my cheap multimeter can only make like 160 V from it
Average measuring meter = Non - True RMS