Apparent Impedance Plot

[cayjay]

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?

 

[DanDel]

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

 

[stevenal]

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.

 

[Bung]

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...

 

[charlierod]

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.