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Mains Harmonics measuring instruments operate unusually?

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treez

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Hello
Why do instruments which measure mains harmonics of SMPS’s , measure the harmonics by considering that the fundamental current sinusoid is the fundamental of the actual mains input current waveform?
As you can see in the attached waveform showing mains input current and voltage to a PFC’d SMPS, the fundamental of the actual current is not quite in phase with the voltage in this case.
As such, the fundamental current sinusoid should be that 50Hz sinusoid component that is in phase with the voltage, do you agree?
Then, for example, for Class C equipment, the 9th Harmonic maximum should be 5% of that fundamental, and so forth.
 

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  • Mains input current and voltage.jpg
    Mains input current and voltage.jpg
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I didn't get what you consider "unusually" and what kind of problems do you expect with the shown waveform? There's nothing special with it, I think. Having a certain reactive current is just normal. Measurement of harmonics is e.g. clearly specified in EN 61000-3-2, what's wrong with it?

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Part of the harmonic current specifications is related to fundamental current, part to real power. Asking why is as pointless as requesting a reasoning for individual harmonic percent numbers, I think. Just take it as granted.
 
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Thanks, i was forgetting that mains harmonics pertain to core losses (ie heating) in mains power system transformers, and so the phase of the current is not relevant in the restriction of the harmonics levels.
 

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