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