Novel travelling wave directional pilot protection approach for LCC-MMC-MTDC overhead transmission line

Abstract

Currently, line commutated converter (LCC) and modular multi-level converter (MMC) based hybrid high voltage direct current (HVDC) transmission technology is utilized in actual power grid. Aiming to acquire large transmission capacity and avoid commutation failure, LCC and MMC converters are applied in rectifier and inverter stations in multi-terminal direct current (MTDC) topology structure, respectively. Generally, LCC-MMC-HVDC transmission line adopts travelling wave (TW) protection principle based on one-ended signals. However, it cannot identify fault direction and exists threshold issue. Besides, the different structures of LCC and MMC stations have not been considered. In order to overcome these shortcomings, the paper proposes a novel TW directional pilot backup protection for hybrid LCC-MMC-MTDC transmission line. First, TW propagation process in hybrid multi-terminal transmission system is analysed. Afterwards, fault direction identification criterion is proposed. Eventually, using PSCAD/EMTDC, a ±400 kV hybrid three-terminal LCC-MMC-MTDC simulation model is established. And the simulation results prove that the novel protection is not affected by different fault locations, different fault resistances and different fault types.