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Positive Sequence Resistance and Reactance calculation

  1. Aug 9, 2016 #1
    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. jcsd
  3. Aug 12, 2016 #2
    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].
     
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