GATE Electrical Engineering (EE) 2016 Shift 1 Solved Paper

A $30\mathit{M}\mathit{V}\mathit{A}$, 3-phase, $50\mathit{H}\mathit{z},13.8\mathit{k}\mathit{V}$, star-connected synchronous generator has positive, negative and zero sequence reactances, $15\%,15\%\mathit{a}\mathit{n}\mathit{d}5\%$ respectively. A reactance (${\mathit{X}}_{\mathit{n}}$) is connected between the neutral of the generator and ground. A double line to ground fault takes place involving phases ${}_{}^{\prime }{\mathit{b}}_{}^{\prime }\mathit{a}\mathit{n}\mathit{d}{}^{\prime }{\mathit{c}}^{\prime }$, with a fault impedance of $\mathit{j}0.1\mathit{p}.\mathit{u}.$ The value of ${\mathit{X}}_{\mathit{n}}$ (in $\mathit{p}.\mathit{u}.$) that will limit the positive sequence generator current to $4270\mathit{A}$ is _________.