A new method for avoiding overvoltages when clearing DC-line faults with a low SCR HVDC station

Two promising variants for avoiding AC-side overvoltages at DC, line faults of low-SCT (short-circuit ratio) HVDC systems have been presented. Both use commutation switches. The first one has moderate demands on the mechanical speed of the switches, but requires further investigation on the arc extinction. The second one uses the converters to extinguish the arc, requires almost no commutation duty by the switches, but does demand fast acting switches (20-30 ms). The residual current references to be set at a monopolar fault in a bipolar system must be carefully precalculated and tested dynamically at the simulator. The authors conclude that only the current of the faulty pole should be manipulated. It is based on a comparison by a simple calculation