Electronics > Beginners
AC Line Waveform Distortion
spiff72:
Thanks for all the responses. I do have a lot of LED bulbs scattered around the house. I might have to repeat the experiment with all the lights in the house turned off and see if that makes a difference. I did actually try turning lights off in just my office (where the scope is located) and it didn't make a difference.
Also, thanks to rstofer for the clarification of the FFT numbers. It does make more sense that the peaks are the 3rd and 5th and my logic was flawed on the counting of the divisions.
Thanks!
joeqsmith:
If I want to run a test with a clean wave, I have to generate it. Link showing the incoming voltage at our house.
https://youtu.be/04I7nHA_HxM?t=731
radiolistener:
The same waveform on my mains :)
I think this is because of switching power supplies in the computer and other home electronics.
bdunham7:
How is the scope connected to the mains? Direct, voltage divider, transformer?
3rd, 5th and 7th harmonics are common. 3rd would be mostly generated locally, typically an unloaded transformer will generate some 3rd due to hysteresis. However, even though industrial loads and distribution systems do generate a lot of 3rd, you don't see them much because in a 3-phase system, they cancel out.
5th is generated by induction motors and certain generator configurations.
What you have looks like an unloaded transformer to me, although rectifier/capacitor systems could be contributing as well. THD is supposed to be under 5% and it looks like you may be approaching that.
B/T/W, that is a nice clean FFT, especially as a freebie add-on to an entry level scope. What exact settings (window type, etc) did you use?
radiolistener:
In my case, I connected mains to oscilloscope through toroidal transformer. Secondary coil is unloaded.
But when I load it with resistor, the waveform shape is the same, just a little smaller amplitude.
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