AC output analysis using what equipment you have

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Joined: 13/10/2014
Location: Australia
Posts: 1479
Posted: 03:58am 21 Jul 2023      

Hi Peter, a bit late on posting, I've been fighting the dreaded bad Influenza going around for over 4 weeks and finally back to almost normal in the past few days

This subject is timely as I was asked to fix a HIOKI 3197 Power Quality Analyzer, got it all going and I have a loan of it for a few months as reimbursement.

The NO Load AC voltage THD is around 1.5% to 2% on my inverter, this then varies with load, as the load increases the THD goes down, with 2kW + of load, mainly induction motors and heating elements, THD is around 1%.

Interestingly the higher unloaded THD is due to a 27th and 29th harmonics suddenly appearing. So a quality common mode HF Ferrite choke of 2 or 3 turns should remove those.

The Mains AC has almost the same THD with various loads. Obviously it does not have the higher order harmonics.

I was able to test the Inverter AC with a Hair dryer that uses a Diode for low Heat, as previously posted, the inverter is now almost silent with that load. The interesting thing is the THD went up to 3% but the cause is the Even harmonics were now showing with the same levels as the Odd harmonics, with content out to around the 27th harmonic.

With the Hair Dryer, the AC waveform has that sharp Kink in the side of the Waveform (no ringing) and this is obviously causing a lot of nonliterary in the Toriod, but IMHO perfectly acceptable considering the load.

I was able to compare the HIOKI waveforms and harmonic levels to my new RIGOL and while not as neat a display, it was still close to the HIOKI with THD levels and total Harmonics.

When I get a chance I will compare it to the Free Software you posted, not to pick on it, but to get a more accurate reference point for the information it displays.  

I hope to get the HIOKI set up with it's Current clamp(s) and do some serious testing on THD and other variables with respect to other distortion products and test some good HF filters I've wound for the Lower HF bands.

BTW: I forgot to add, when the Hair Dryer is placed very close to the inverter AC output, the THD goes up to 11.2%, the Mains AC with that load is 2.6%, IMHO totally meaningless comparison information, but it highlights the roll that the length of AC power wiring, combined with the loads on, and between the Bad load and the inverter,  can have on how the inverter reacts to those loads.

What I'm trying to say is: Builders have reported that sometimes the Inverter works fine with all the loads for weeks or more, then one day it just goes bang, so many ways for the loads to find any weakness in an inverter over time.  

Fortunately Mikes (Wiseguy) design appears to be virtually unbreakable when set up correctly - baring a component failure  
Edited 2023-07-21 14:24 by KeepIS