# Relevant highest order harmonics in power systems

i am learning about harmonic analyzers and i have a couple of questions concerning them that need some sort of practical experience to answer them ( and i have none :) ) :

1-can harmonic analyzer analyze up to any harmonic? or is there a maximum ? if there is no maximum what's the highest order harmonic that is relevant to us in power systems ? i read somewhere online that when calculating THD they normally include up to the 15th -17th harmonic, and a friend told me that no one cares about what's beyond the 55th or so because these high frequencies are attenuated by the inductance of transformers or motors, so i need a practical opinion on this .

2- when i was reading about THD literally everyone was ignoring the even harmonics, i read it's because the half-cycle symmetry and it was mentioned " which is very common in power applications", so my question is there any common application where there is half cycle symmetry ( i am not speaking of dc offset which can easily be removed) i couldn't think of any tbh.

3- how do harmonic analyzers deal with different power quality problems that can affect their readings like frequency and voltage fluctuations? does the input has to be a steady periodic wave to get accurate answers?

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berkeman
Mentor
Are you asking about harmonic distortion from the AC Mains power source, or from equipment that is hooked to the AC Mains?

If the latter, one applicable standard is EN 61000-3-2:

https://en.wikipedia.org/wiki/IEC_61000-3-2

It does look like they are not checking the even harmonics of the power waveform. I end up having to test to this standard for some of the products we design because of Power Factor quality issues with some simple switching power supplies. You pretty much have to use a Power Factor Corrected switching power supply to pass this Harmonics test.

so according to this standard they are checking and including in the THD up to the 40th harmonic
Are you asking about harmonic distortion from the AC Mains power source, or from equipment that is hooked to the AC Mains?
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i am asking in general , either it's the mains voltage or inverter ouput or line current to some motor

Tom.G