Abstract
Voltage source converter (VSC)-based high voltage direct current (VSC-HVDC) interconnectors can realize accurate and fast control of power transmission among AC networks, and provide emergency power support for AC networks. VSC-HVDC interconnectors bring exclusive fault characteristics to AC networks, thus influencing the performance of traditional protections. Since fault characteristics are related to the control schemes of interconnectors, a fault ride-through (FRT) strategy which is applicable to the interconnector operating characteristic of working in four quadrants and capable of eliminating negative-sequence currents under unbalanced fault conditions is proposed first. Then, the additional terms of measured impedances of distance relays caused by fault resistances are derived using a symmetrical component method. Theoretical analysis shows the output currents of interconnectors are controllable after faults, which may cause malfunctions in distance protections installed on lines emanating from interconnectors under the effect of fault resistances. Pilot protection is also inapplicable to lines emanating from interconnectors. Furthermore, a novel pilot protection principle based on the ratio between phase currents and the ratio between negative-sequence currents flowing through both sides is proposed for lines emanating from the interconnectors whose control scheme aims at eliminating negative-sequence currents. The validity of theoretical analysis and the protection principle is verified by PSCAD/EMTDC simulations.
Highlights
Based on self-turn-off devices such as insulated gate bipolar transistors (IGBTs), voltage source converters (VSCs) are capable of independent control of active and reactive power in four quadrants of the P-Q plane [1,2,3]
When a fault happens in an AC network, interfaced distributed generators (IIDGs) only output active power or reactive power, but the fault side converter in the VSC-HVDC interconnector may work as a rectifier or an inverter, which makes the range of the angle of additional impedance measured by the distance relay larger than that in [12,13]
Taking phase-to-phase faults that happen at f1 and f2 as example, the applicability of the phase-to-phase distance protection to the line emanating from the VSC-HVDC interconnector is discussed
Summary
Based on self-turn-off devices such as insulated gate bipolar transistors (IGBTs), voltage source converters (VSCs) are capable of independent control of active and reactive power in four quadrants of the P-Q plane [1,2,3]. The control scheme and post-fault output characteristics of VSCs differ greatly from those of CSCs. The analysis and conclusions that distance protection, directional comparison pilot protection and differential protection are not applicable in [7,8,9,10] cannot be directly applied to the lines emanating from VSC-HVDC interconnectors. When a fault happens in an AC network, IIDGs only output active power or reactive power, but the fault side converter in the VSC-HVDC interconnector may work as a rectifier or an inverter, which makes the range of the angle of additional impedance measured by the distance relay larger than that in [12,13].
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