Positive Sequence Resistance and Reactance calculation

[asela115]

Hi,

I have following two parameters with me

a) Maximum three phase fault current in amperes (A) and phase angle in degrees (B).

I want to calculate the positive sequence resistance (R) and reactance (X) from above two variables for a symmetric system. I couldn't figure out a way to find R and X values using just these two parameters. However I noted somebody has calculated them using following formula for same purpose (unfortunately couldn’t verify who did this in my workplace).

R = A * COS ( PI()*B/180 ) X = A * SIN ( PI()*B/180 ) where A is the three phase fault current and B is the phase angle

If someone can assist me to figure out the correct formula and the relation above, please

Thanks

 

[Babadag]

In my opinion, if you intend to calculate the impedance in ohm-not in p.u.-then you’ll need the voltage.

A=V/(R+Xi)=V(R-Xi)/(R^2+X^2) then:

Iactiv=V*R/(R^2+X^2) Ireact=-V*X/(R^2+X^2) TAN(B)=Ireact/Iact=-X/R

A=SQRT(Iactiv^2+ Ireact^2)

A=V*SQRT(R^2+X^2)/(R^2+X^2)=V/SQRT(R^2+X^2)

X=TAN(B)*R

Then:

A=V/R/SQRT(1+TAN(B)^2) and from here:

R=V/(A*SQRT(1+TAN(B)^2)

(1+TAN(B)^2)=1+SIN^2(B)/COS^2(B)=1/COS^2(B)

R=V/A*COS(B) X=V/A*SIN(B)

B has to be radians then if B it is done in degrees then B[rad]=pi()/180*B[degrees].