How to plot R-X diagram

[ProtectiveBoy]

Hi,

I want to plot the R-X diagram for distance relay using MATLAB.
I have series of currents and voltages as follows:
1. Current, I
2. Voltage, V

In order to obtain impedance, I should calculate Z, i.e.(Z=V/I)

Question:
1. Should I calculate impedance,Z equal to |V|/|I| ?, or
2. Should I calculate impedance,Z equal to |V/I|

*|V| means magnitude of voltage

3. From my understanding, the function of relay is comparing between 'impedance setting' and 'impedance seen'.If 'impedance seen' less than 'impedance setting', then the relay will pass trip signal to circuit breaker.
But impedance consists of real and imaginary parts, Z=(Real part) + (Imaginary part);
Therefore which part should I compare ?

regards

 

[Eleceng01]

ProtectiveBoy,

Actually you can use the phasors (Z=V/I) since most relays use either a quad or mho impedance/distance element though I haven't used MATLAB in some time so I am unsure if you can do this.

You are somewhat correct that if the value is less than the impedance setting that the relay sends the trip to the breaker, but you might try looking at some of the manufacturer's literature. One that come to mind is "Z=V/I Does Not Make a Distance Element" by J. Roberts, et. all. I believe it is still available on the SEL website.

 

[jghrist]

The best thing is to use the actual algorithm for the relay in question. Check with the manufacturer of the relay.