A novel pilot protection scheme for LCC-HVDC transmission lines based on smoothing-reactor voltage

This paper proposes a novel pilot protection scheme for LCC-HVDC transmission lines based on smoothing reactor voltage (SRV). The proposed scheme is derived taking into consideration transient capacitance current and fault resistance. The polarity characteristics of SRVs are theoretically analyzed under internal and external faults in the fault transient period. And for internal fault, the polarities of SRVs at both sides are positive; when an external fault occurs, the polarity of SRV is negative at faulted side and positive at the other side. Based on these characteristics, a new back-up protection scheme is proposed. Moreover, a fault pole selection criterion is proposed. A +/- 800 kV LCC-UHVDC test system is established to verify the accuracy and validity of the proposed protection scheme under different fault conditions. Comprehensive simulations show that the proposed method can identify internal and external faults reliably, with high sensitivity and selectivity, and its performance is inspiring under different fault locations and fault resistances. Furthermore, the proposed protection needs a lower sampling frequency and does not require data synchronization, making it valuable for applications in HVDC transmission system.