The positive, negative and zero sequence impedances of a three phase generator are $Z_1, Z_2$ and $Z_0$ respectively. For a line-to-line fault with fault impedance $Z_f$, the fault current is $I_{f1}= kI_f$, where $I_f$ is the fault current with zero fault impedance. The relation between $Z_f$ and $k$ is
- $Z_f=\frac{(Z_1+Z_2)(1-k)}{k} \\ $
- $Z_f=\frac{(Z_1+Z_2)(1+k)}{k} \\ $
- $Z_f=\frac{(Z_1+Z_2)k}{1-k} \\$
- $Z_f=\frac{(Z_1+Z_2)k}{1+k}$