The positive, negative and zero sequence impedances of a three-phase generator are Z1, Z2 and Z0 respectively. For a line-to-line fault with fault impedance Zf, the fault current is If1 = kIf, where If is the fault current with zero fault impedance. The relation between Zf and k is

• A. \({Z_f} = \frac{{\left( {{Z_1} + {Z_2}} \right)\left( {1 - k} \right)}}{k}\)
• B. \({Z_f} = \frac{{\left( {{Z_1} + {Z_2}} \right)\left( {1 + \;k} \right)}}{k}\)
• C. \({Z_f} = \frac{{\left( {{Z_1} + {Z_2}} \right)k}}{{1 - k}}\)
• D. \({Z_f} = \frac{{\left( {{Z_1} + {Z_2}} \right)k}}{{1 + k}}\)