A 30MVA, 3-phase, 50Hz, 13.8kV star-connected synchronous generator has positive, negative and zero sequence reactance. 15%, 15% and 5% respectively. A reactance  is connected between the neutral of the generator and ground. A double line to ground fault takes place involving phase ‘b’ and ‘c’, with a fault impedance of j0.1 p.u. The value of  (in p.u.) that will limit the positive sequence generator current to 4270 A is______________.