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    harmonic currents

    If I wanted to check the harmonics of a generator backup system, what type of oscilloscope do you recommend that is Reasonably priced? Pref. a usb for my laptop.

    Single family dwelling 120/240V. 1P.

    #2
    Re: harmonic currents

    Harmonics don't cause problems on 120/240 single phase systems.
    Ryan Jackson, Salt Lake City
    Inspector, Instructor

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      #3
      Re: harmonic currents

      Harmonics do not cause neutral overheating problems on a 120/240V system, but do cause power quality problems when it is a result of non sinusoidal voltage and current waveforms from a generator.
      Fluke has several good scopes.
      Ron

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        #4
        Re: harmonic currents

        If measuring below 130.VAC the SureTest St-1THD can find voltage harmonics, but purchasing the seperate cl/amp-probe atachment is needed for accurate current harmonics.

        There are cheeper and cruder ways of detecting harmonics.

        1) ShureTest manuals claim 3d harmonic computer loads will drop the peak voltage faster than the RMS voltage. One crude indication of a distorted waveform, if your true-RMS DVM has a seperate peak-voltage measurement, would compare how close that peak is to 1.414 times the measured RMS line voltage.

        2) ShureTest manuals claim common-mode voltages (N-G) > 2.0vac can result from harmonics, amoung other things, and CMV > 4.0vac is overloaded. If your DVM can resolve fractions of a volt, one crude indicator is to see if this CMV increases with proximity to the suspected-harmonic source.

        The manual claims, "the SureTest ST-1THD is the only hand held instrument available that can provide full load testing and wave form analysis in one cost effective instrument."

        But without data logging, unless you stand there taking notes for a long time, the SureTest can't record transient-power spikes, power sags/swells, and loading peaks, such as more expensive wave-form analyzers that cost more than a few days wages just to rent or calibrate.

        So, crude harmonic indicators can be had cheeply, but hiring someone with the right equipment may be the shiznit for a precise and quick measurement.
        Roger Ramjet NoFixNoPay

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          #5
          Re: harmonic currents

          If this is just a one-time deal just rent an analyzer.

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