Owing to its rapidity in detecting faults

non-unit traveling wave protection is usually used as one of the main protection schemes of flexible DC transmission lines. But it has problems such as low sensibility when the high transition resistance faults occur and false tripping due to noise interference. Therefore

this paper utilizes singular entropy analysis to characterize the dynamic changes of time-domain signals and proposes a novel principle of non-unit traveling wave protection based on singular entropy. Firstly

based on the differences in the waveforms of the one-mode traveling waves in the case of internal and external faults

the fault traveling waves are embedded to form a Hankel matrix

and then the magnitude and distribution of the singular values of the matrix are analyzed. Secondly

by introducing singular entropy to characterize the singular value features of the traveling wave matrix and utilizing the significant differences in singular entropy values obtained in the case of internal and external faults

a non-unit protection criterion for flexible DC transmission line is developed. Finally

the proposed principle and the complete protection scheme are verified and compared with existing protection methods via the simulation model of four-terminal flexible DC transmission system. The simulation results indicate that the proposed principle can be adopted to quickly and accurately identify line faults. It has low sampling frequency requirements while demonstrating strong tolerance to transition resistance and high noise immunity

thereby ensuring its high reliability.