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Can I use a simple oscilliscope to see powerline harmonics?

Discussion in 'Electrical Engineering' started by Frank White, Jan 15, 2005.

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  1. Frank White

    Frank White Guest

    Wondering if I could measure the power quality on a 3ph 600V service
    like this?


    To send me e-mail remove the sevens
    from my address.
     
  2. operator jay

    operator jay Guest

    That's a broad question. I would expect that you would use CTs /
    transducers and PTs and measure those with your oscilloscope. You would
    probably want some software that did data logging, triggering on certain
    events (high / low amperages ... significant amperage changes ... harmonic
    level thresholds ... imbalance ... transients ... etc.) and processing
    (Fourier spectra, sequence values, imbalance, RMS values, data trending)
    depending which aspects of 'power quality' you want to 'measure'. There are
    PQ loggers available that have stuff like this built in, and have software
    available for analysis. Those I'm aware of are expensive and typically
    sample at a relatively low rate (say, 128 samples per cycle or stuff like
    that, as opposed to oscilloscopes which might be sampling as high as
    millions of samples per cycle).

    I hope that helps. If you have something specific in mind, though, post it.

    j
     
  3. Something to keep in mind, some transformers have horrible frequency
    responses at frequencies other than 60hz. Also, in the real world a
    transformer does not simply act like a lowpass filter. So, unless you know
    the frequency response of the transformer, you really can't be sure of what
    you are measuring. Most magnetic transformers will perform good enough to
    see 13th harmonic or so. Above that it depends on a lot of factors. If you
    do see something at a high frequency, it may or may not really be there and
    if it is really there, you cannot be sure of its actual amplitude.


    Charles Perry P.E.
     
  4. Roy Q.T.

    Roy Q.T. Guest

    you know it's good you posted this,

    I have trouble with this,

    Conventionally you should be able to get measurements from it but
    according to the manufacturer and the way they teach this in school you
    have to bridge a circuit of a known value to reference from.,

    I Hate That .," for the sake of pete"

    if we're going to design a scope and tell people it can measure upto
    thousands of volts & mega hertz in different scales, then why not design
    one you can just Plug and Play to obtain the measurements of available
    equipment with common or known waveforms.

    I am just a bit of a procrastinator i guess, or i wouldv'e had a better
    response for you };-) lost interest right after i got the eliptical egg
    shape waveform, lot of good learning that did.....
     
  5. If you are taking spot measurements, I would recommend buying/renting a
    Fluke 43. I think they can be had for less than $2k. They are meant to
    measure harmonics, and other power quality phenoma, at 600V. It is a single
    phase device, but this is not a problem for spot measurements. Fluke now
    makes a three phase version, but I am not familiar with the pricing.

    Charles Perry P.E.
     
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