# Positive Sequence Resistance and Reactance calculation

1. Aug 9, 2016

### 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

2. Aug 12, 2016

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].