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

If the fault current is $$2000$$ A, the relay setting is $$50$$% and CT ratio is $$400:5,$$ the plug setting multiplier will be

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

For an unbalanced fault, with paths for zero sequence currents, at the point of fault