A Location Method for AC Fault in LCC-HVDC System Based on Virtual Conduction Width Characteristics

When an AC fault occurs in HVDC transmission system, the transient response change in the rate of change of current and voltage, which may lead to the unexpected action behavior of converter protection. This is attributed to the electrical quantity similarities between internal and external faults, leading to difficulties in fault location identification and reducing the sensitivity in protection measure activation. To realize internal and external fault identification and quickly deal with external faults, an AC fault detection method for LCC-HVDC systems based on virtual conduction width characteristics is proposed. First, by utilizing the ratio integral of the three-phase AC current on the valve side to the reference current, the virtual conduction width flowing through each valve in the sampling window is calculated. Second, according to the size relationship among virtual conduction widths, internal and external faults are identified. Third, after determining the external faults, the difference in the virtual conduction width for each valve branch in the sampling window is calculated to locate the fault phase. Finally, the simulation results based on EMTDC/PSCAD show that the proposed method can quickly identify internal and external faults and locate fault phases and is not affected by fault moment and fault resistance.