A new single-end current based whole-line quick-action protection for VSC-HVDC transmission lines

It is discovered in the research on the structure and boundary characteristic of VSC-HVDC transmission system that large capacitors configured at both ends of VSC-HVDC transmission line appear as low impedances for high-frequency signals, and it affects the protections installed at both ends of HVDC transmission line so that there are frequency differences among the current components sensed by the protections. Using such a feature a new single-end current based quick-action protective principle to protect the whole length of VSC-HVDC transmission line is proposed: the amplitude ratio of high-frequency component of fault current to its low-frequency component amplitude is used to distinguish the fault occurred inside the protection zone from the fault occurred outside the protection zone. The value of this amplitude ratio is smaller for the fault occurred outside the protection zone and lager for the fault occurred inside the protection zone. Using the proposed protective principle, whether the fault is inside or outside the protection zone can be effectively recognized and there is no strict requirement on sampling frequency. The PSCAD based simulation of the proposed protection is performed and simulation results show that the proposed protection is quick-action and slightly affected by transition resistance.