Single-ended protection scheme for three-terminal hybrid DC transmission system based on refractive coefficients

Abstract Three-terminal hybrid DC transmission technology has the advantages of long-distance and large capacity, and there is no phase change failure and other problems, which is an effective means of sending out new energy bases. Correspondingly, the reliability of the existing single-ended traveling wave protection is further degraded by the unknown fault characteristics introduced by the greater variety and combination of converters and add-ons in the three-terminal hybrid DC transmission system. Therefore, a single-ended protection scheme based on the refractive coefficient is proposed. First, an expression for the refraction coefficient of a three-terminal hybrid DC system is derived. Subsequently, the variability of the refraction coefficients for different faults is analyzed. Finally, a single-ended protection scheme using the fault characteristics of the refraction coefficients is proposed and validated by simulation. The program has the advantages of theoretical clarity, reliability, and the ability to recognize near-end faults.