The figure shows the single line diagram of a power system with a double circuit transmission line. The expression for electrical power is $1.5 \sin \delta$, where $\delta$ is the rotor angle. The system is operating at the stable equilibrium point with mechanical power equal to $1$pu. If one of the transmission line circuits is removed, the maximum value of $\delta$, as the rotor swings, is $1.221$ radian. If the expression for electrical power with one transmission line circuit removed is $P_{\max} \sin \delta$, the value of $P_{\max}$, in pu is ______. (Give the answer up to three decimal places.)
