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Apparent Impedance Plot

Apparent Impedance Plot

Apparent Impedance Plot

(OP)
I am trying to calculate and plot apparent impedance from wavefom data captured by a substation relay. Where for Phase A the apparent impedance would be Va / (Ia + k*Ir). K would be a known value related to the zero and positive sequence line impedances.

A bit lost. Given that I have all phase voltage and current waveforms sampled at 32 points per cycle... how would I would I calculate and plot the apparent impedance points per cycle?

RE: Apparent Impedance Plot

I believe the values of impedance you are looking for can only be calculated from RMS values, not instantaneous points on the cycle.

RE: Apparent Impedance Plot

Take the square root of the average of the squares of 32 data points at a time. If your relay captures the data, the vendor probably has software that will do the calcs.

RE: Apparent Impedance Plot

Electrotek has a very good package called TOP which reads COMTRADE waveform records and allows you to calculate the RMS values.  Plus a whole heap of other useful stuff.  Wouldn't be without it!  You can shift in time, add waveforms, multiply, do FFTs etc.  I haven't tried, but it could probably be persuaded to do the impedance calcs for you, and give you a plot of the impedance changing with time.  But it wouldn't plot the change in the R-X plane.

Bung
Life is non-linear...

RE: Apparent Impedance Plot

As stated above you must first calculate values for phasors from sampled data, this can be done using FFT but beware these approach fails for highly distorted waveforms.

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