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Trend of resistance & reactance values in fault signal

  1. Jul 25, 2014 #1
    Hi,
    What I have been trying to achieve is learn about signal processing ,particularly filters. Newbie to DSP,so far!
    I have 2 signals with me.Voltage and current signals. Both are unfiltered. I have managed to filter out these two signals to remove most of the noise. Now,I want to find the impedance in the signals before the fault occurs and after the fault occurs. This is the algorithm that I have used (Link to the image has been attached)

    http://s1284.photobucket.com/user/sandycook9211/media/Screenshot101_zpse9cf445d.png.html

    While I have managed to get peak current and peak voltage values correctly,(I verified by finding maxima of data signals) the trend of resistance and reactance values is bothering me.

    For starters, can someone confirm the above algorithm to calculte Ipeak,Vpeak,R and X for "before fault" (input is filtered V and I signals) and "after fault" (unfiltered V and I raw signals) ? My data window is 60 and I run through 60 samples for each iteration. Ie,1st iteration from 1 to 61st, 2nd iteration ,from 2 to 62nd etc until I traverse the entire data.

    Moreover, I just assumed "before fault" to mean filtered signal and "after fault" to mean unfiltered input signal. Is this correct?

    Any help will be appreciated,thanks in advance!
     
  2. jcsd
  3. Jul 25, 2014 #2

    Baluncore

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    Welcome to PF.

    I see no attachment. Here is some stock advice.

    To attach a file, when posting “Quick Reply”, or an “Edit” of a recent post, click “Go Advanced”,
    then scroll down to “Additional Options”, “Attach Files”, click “Manage Attachments”.
    Click “Browse”, select your file, then click “Upload”. Wait till done, then “Close this window”.
    “Preview Post” and you will see your file attached.
     
  4. Aug 27, 2014 #3
    It appears you are doing TDR (time domain reflectometry). If so this might answer your question; if not, simply ignore this.

    For TDR the voltages vs. time are proportional to reflection coefficient vs. distance. Reflection coefficient is related to effective resistance and reactance of the line at distance (effective because the lumped model isn't strictly valid in transmission lines). This is based on transmission line theory and RF.

    The before fault and after fault are simply points in time in the time series if this is TDR. A fault will cause a numerical discontinuity in the voltage/reflection coefficient, because the resistance/reactance is discontinuous at a fault - transmission lines (cables) are required/intended to be constant characteristic impedance but faults change that impedance at the fault.

    Some of the best references for TDR are published by Agilent/Keysight:

    http://literature.cdn.keysight.com/litweb/pdf/5966-4855E.pdf
     
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