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Thread: non Linear loads

  1. #21
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    Quote Originally Posted by Jraef View Post
    It's a safe bet that it's single phase.

    99% of single family residences only get a single phase service here. It takes a lot of money and cajoling to get a utility to run 3 phase out to a residential service, often including you having to pay the full cost for them to run the third wire from the nearest 3 phase connection point, which can be miles away.
    On a farm though there can be high leg delta systems supplying the farm - three phase is run to structures that need three phase, like a feed mill or grain storage/handling area. If there is a larger water system there may be a three phase well. If there is a house on the property it still normally just gets 120/240 supply run to it but originates at the high leg delta supply and not a separate supply, same for other outbuildings with minimal power requirements.

  2. #22
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    Quote Originally Posted by Carultch View Post
    They are only "additive on the neutral", when the harmonic multiplier of the fundamental frequency is divisible by the number of phases. So your fifth harmonics are not additive on the neutral, but your even harmonics in split phase, and your multiple of 3 harmonics in 3-phase, are.


    A matter of physics often overlooked due to published works covering 3Ø only. The question is, do these power supplies generate these additive harmonics?
    I will have achieved my life's goal if I die with a smile on my face.

  3. #23
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    If you take two identical waveforms, invert one relative to the other, and add these together, then no matter what the harmonic content is the result is zero.

    .

  4. #24
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    Quote Originally Posted by gar View Post
    170810-1246 EDT

    If you take two identical waveforms, invert one relative to the other, and add these together, then no matter what the harmonic content is the result is zero.

    .
    Fair enough. But what we are arguing is that if there are line to neutral loads there is no guarantee that the phase relationship between fundamental and harmonic will be the same on both legs. That invalidates your premise that they are inverses of each other.
    If the loads are in fact symmetric, then your point is valid.

    Sent from my XT1585 using Tapatalk

  5. #25
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    Quote Originally Posted by GoldDigger View Post
    Fair enough. But what we are arguing is that if there are line to neutral loads there is no guarantee that the phase relationship between fundamental and harmonic will be the same on both legs. That invalidates your premise that they are inverses of each other.
    If the loads are in fact symmetric, then your point is valid.

    Sent from my XT1585 using Tapatalk
    From my post #17:
    If the computers are all the same and are distributed equally on each half with a common neutral back to the supply then you might reasonably assume that, for the non-linear loads on each half, their input current waveforms would the same magnitude but in antiphase and cancel even if they are not sinusoidal
    Dennis mentions that they are computers. I think it was in his opening post. Maybe 50 or so of them. My response, including the caveat, was based on that.
    Si hoc legere scis nimium eruditionis habes.

  6. #26
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    Quote Originally Posted by Besoeker View Post
    From my post #17:

    Dennis mentions that they are computers. I think it was in his opening post. Maybe 50 or so of them. My response, including the caveat, was based on that.
    FWIW identical does not imply symmetric.
    One example is the half wave rectifier supply. There will be a DC component in the neutral. (Not a "harmonic", of course.)

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  7. #27
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    Quote Originally Posted by GoldDigger View Post
    FWIW identical does not imply symmetric.
    One example is the half wave rectifier supply. There will be a DC component in the neutral. (Not a "harmonic", of course.)
    Think it will be AC if the 120-0-120 are antiphase.
    Si hoc legere scis nimium eruditionis habes.

  8. #28
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    Quote Originally Posted by Besoeker View Post
    Think it will be AC if the 120-0-120 are antiphase.
    Think again. If a half-wave rectifier is used, with the neutral as, for example, the negative side of the DC output, then the direction of the current in the neutral will be the same from both legs, just 180 degrees out of phase.

  9. #29
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    Quote Originally Posted by GoldDigger View Post
    Think again. If a half-wave rectifier is used, with the neutral as, for example, the negative side of the DC output, then the direction of the current in the neutral will be the same from both legs, just 180 degrees out of phase.
    Brain fade. It happens at my age.
    But I think we are drifting off the original topic.
    Si hoc legere scis nimium eruditionis habes.

  10. #30
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    GoldDigger:

    Identical means identical. That does not include a time shift.

    .

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