In a thyristor $$dc$$ chopper which type of commutation results in best performance?

For a $$500$$ Hz frequency excitation, a $$50$$ km short power line will be modeled as

For equilateral spacing of conductors of an untransposed $$3$$-phase line, we have

During a disturbance on synchronous machine, the rotor swings from A to B before finally settling down to a steady state at a point C on the power angle curve. The speed of the machine during oscillation is synchronous at point(s)