小学一年级英语作文:Good friend

高级词汇使用较丰富，拼写做的很棒；句式变化多样，句法方面做的很棒；过渡词和衔接词不饱和，文章行文较为流畅。

Protction for MMC-HVDC Transmission Lines Under Single Line to Ground Fault Based on Current Waveform Recognition NING Lian-ying (School of Electronic Information and Electrical Engineering,Shanghai Jiao Tong University, Minhang District, Shanghai 200240,China) ABSTRACT: Through the theory analysis, this paper discovers that the fault current of modular multilevel converter HVDC(MMC-HVDC) transmission lines oscillates rapidly under single line to ground fault and does not oscillate rapidly under other types of fault. Based on this different fault characteristic, this article presents a new single line to ground fault discriminant method for MMC-HVDC transmission lines through one-terminal current waveform recognition. A double-end MMC-HVDC simulation model is put up by using real time digital system(RTDS) and the simulation results verify the correctness of the analysis results and the proposed method. The proposed method is able to identify single line to ground fault quickly and reliably and mal-operation of the proposed protection does not occur when other types of fault happen. KEY WORDS：MMC-HVDC ；fault transient current characteristics；high frequency damped oscillation；one-terminal current waveform recognition；RTDS simulation