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THD Measurements From Electric Company!

Discussion in 'Audio Hardware' started by Soundgarden, Jan 13, 2021.

  1. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    A week ago, my electric company came out and put a tracer at the meter. Today, they removed it and sent back some graphs of THD for voltage and current.

    THD for voltage is easy to interpret. It varies in a fairly constant manner throughout the day as the first chart shows, with lows around 2.4% and highs around 3%. Very similar between the two channels/lines.

    THD for current is more nuanced. Which is not surprising as it's impacted by my own electrical habits which vary widely throughout each day. The second graph shows THD patterns over the same seven days. The third graph shows a single day, Jan 12.

    Looking at the third graph, daytime THD seems to be 5-10% on Ch1 and 15-25% on channel 2. Not only does Ch1 have considerably lower THD (at least on this day) but it's more consistent. (Note the big dip at 4pm on Jan 12. That's when I threw all the sub-breakers and left them off for 10 min. The engineer said current THD at the meter was zero during that time and voltage THD was unaffected.)

    I'm not quite sure what the patterns in current THD correspond to. The regular spikes are probably the fridge right? And if I zoomed in on the day I did laundry... I imagine I could make that out pretty clearly. No AC this time of year. But lots of heater use. Those seem like the biggies in terms of regular patterns and use.

    I'm also not sure how to interpret these patterns to determine which side of panel is Ch1 and which is Ch2. I'm asking for additional graphs.

    Why did I do this? I'm getting a dedicated 20A audio circuit installed soon. I had this test performed (for free!) to help determine which channel to use and also what my power conditioning needs might be. Seems to me I want to put the dedicated circuit on Ch1 but I'm not 100% confident in that. And I have no reference point for THD on voltage or current for a single family home. So I don't know what's low and what's high. Also it's worth noting that the ten single family homes on my block all share a common transformer

    So is my power clean? Or is it dirty?

    [​IMG]

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    bajaed likes this.
  2. Ingenieur

    Ingenieur Forum Resident

    The voltage is ok imo, below the standard of 5%., average of <3%

    The current is strange, one ch good, the other bad. I assume by ch they mean line 1 and 2.
    Ch 1 ~10%
    Ch 2 ~20%
    Are you home during the day?

    The stuff overnight is likely changing xfmr taps and switching capacitors due to decreased load.
     
  3. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Yes, channel 1 = line 1 and channel 2 = line 2. Do you think based on these readings that I've got a problem with the "bad" channel?
     
  4. Oelewapper

    Oelewapper Plays vinyl instead of installing it on the floor.

    That third graph looks funny, quite a large difference between the channels.
    Everything else looks fine imo.
     
  5. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Yeah, in the third graph you can see clearly that Ch2 has higher and more variable distortion than ch1. This trend seems to be evident in other days as well. Waiting for graphs for other days. Any idea what it could be? In my head I'm not correlating it to anything in particular.

    What's a reasonable level of THD for current in a residential unit?
     
  6. rpd

    rpd Senior Member

    Location:
    Nashville
    What’s the advantage of a dedicated 20 amp circuit for the audio system?
     
  7. Ingenieur

    Ingenieur Forum Resident

    Here's info on IEEE standards.
    Your current THD seems within limits.
    It's caused by non-linear loads.
    The loads in your home (or those on the same xfmr) most likely are responsible for the majority of it since your service xfmr will filter most out.

    The I chart is short ckt I/load I
    If SC I is say 10,000 and load is 10 A, look in the 1000 column, 20%.
    The lower the load, the higher the THD.
    Looks like ch 1 has more load and ch 2 has computers, etc. Newer furnace fans are 1 ph vfd's, which are non-linear devices.
    An amp can do that since it charges the caps in 'slugs'.

    It looks normal imo.


    [​IMG]
     
    Shawn and Soundgarden like this.
  8. Uglyversal

    Uglyversal Forum Resident

    Location:
    Sydney
    If the display on a conditioner I had on trial is to be trusted, the voltage THD in my place also moved between 2 and 3%, (there was no measurement of current), still the conditioner made an impact on the sound. Not huge, but it could be noticed.
     
    TarnishedEars and Soundgarden like this.
  9. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    A circuit just for the audio. Otherwise I just have one 15A/14AWG circuit for my entire living room.
     
    jusbe likes this.
  10. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    If I knew which channel corresponded to the left side of my breaker box and which to the right side I could get a better sense of why the differences between the two...
     
  11. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    what type of residence? Mine is a single family detached.
     
  12. rpd

    rpd Senior Member

    Location:
    Nashville
    But what’s the advantage of having this?
     
  13. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Are you of opinion that a dedicated 20A/12AWG circuit offers no benefits over a crowded 15A/14AWG circuit?
     
  14. Uglyversal

    Uglyversal Forum Resident

    Location:
    Sydney
    Same here but I have no idea how many houses would be connected to the first transformer in the area. There are generally no flats or industrial facilities nearby.
     
  15. Ingenieur

    Ingenieur Forum Resident

    On the 24 hour chart it looks like a fan turning on and off. But the ch's are at different times.
    I'm guessing you share a xfmr with another residence.
     
  16. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    I had no idea either. But the power company was able to tell me.
     
  17. rpd

    rpd Senior Member

    Location:
    Nashville
    Not necessarily. This is a legit question from me. That being said, I am a guy who does think fancy cables and power cords are complete and total nonsense and snake oil. But I’m still curious about what a dedicated circuit does
     
  18. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Yeah I share a transformer with nine other residences...
     
  19. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    You can't measure current when there is no current. That is what turning off the breaker shows. It still shows the distortion coming into your house via voltage.
     
  20. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Yeah, I know. If the results were otherwise I would have been puzzled. Not a major finding. Just something to do.
     
  21. Ingenieur

    Ingenieur Forum Resident

    What stuff cycles over night?
    Fan?
    Humidifier?
    Heater?
     
  22. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    In my house, during the winter, just the heating / fan and the fridge. Can't think of anything else with a cycle. I have a very small fish tank with a heater and pump, but it doesn't cycle. Sometimes I run a small air purifier in my bedroom but again, no cycling. Water heater is gas powered.
     
  23. Ingenieur

    Ingenieur Forum Resident

    So 9 single detached homes on 1 xfmr?
    Must be pretty big. Large fault current/low load equal high I THD, and the others contribute.
     
  24. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Yeah, ten homes is a lot... Nothing I can do I about that I suppose :)
     
  25. Ingenieur

    Ingenieur Forum Resident

    I assume gas heat?
    So it's the fridge and fan.
     

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