A star connected $400\:V, 50\:Hz, 4$ pole synchronous machine gave the following open circuit and short circuit test results:
Open circuit test: $V_{oc} = 400\: V (\text{rms}, \text{line-to-line})$ at field current, $I_f = 2.3 A$
Short circuit test: $I_{sc} = 10\: A (\text{rms, phase})$ at field current, $I_f = 1.5 A$
The value of per phase synchronous impedance in $Ω$ at rated voltage is __________.