This paper focuses on the inverter station of ultra-high voltage direct current(UHVDC)transmission sys-tem with a hybrid cascaded structure.Based on its primary topological structure,adhering to the principles of protec-tion without dead zones and easy fault location,and considering the installation position of measurement transform-ers,a protection partition suggestion and configuration plan are proposed.According to the location and severity of faults in inverter station,hierarchical block strategies including line-commutated converter(LCC)block,single modular multilevel converter(MMC)block,overall MMC block,sequential pole block,and step pole block are proposed,aiming to quickly eliminate faults and reduce the outage range.Finally,a real-time closed-loop simula-tion system is established based on the actual control and protection devices of the Baihetan-Jiangsu hybrid cas-caded UHVDC transmission project and a real-time digital simulation(RTDS)model established according to the complete set of engineering parameters.The feasibility and effectiveness of the proposed protection scheme and block strategies are verified through simulation.
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