$6\mathrm{.}25$ A $1$ MVA, $3$$,2300$ V$,60$ Hz$,10$ pole, star$-$connected cylindrical$-$rotor synchronous motor is connected to an infinite bus. The synchronous reactance is $0$:$8$ pu$.$ All losses may be neglected. The synchronous motor delivers $1000$ hp$,$ and the motor operates at $0\mathrm{.}85$ power factor leading. $($a$)$ Determine the excitation voltage Ef$.($b$)$ Determine the maximum power and torque the motor can deliver for the excitation current of part $($a$).($c$)$ The power output is kept constant at $1000$ hp$,$ and the field current is decreased. By what factor can the field current of part $($a$)$ be reduced before synchronism is lost?