The　hybrid　high-voltage　direct　current　(HVDC)　system,　in　which　the　rectifier　is　made　up　of　the　line　commutated　converter　(LCC)　and　the　inverter　is　composed　of　the　modular　multilevel　converter　(MMC),　has　quite　different　fault　characteristics　from　the　symmetrical　LCC-HVDC　and　MMC-HVDC　systems.　Therefore,　it　is　necessary　to　analyse　the　applicability　of　the　existing　line　protection　principles　to　the　hybrid　HVDC　system.　First,　the　fault　characteristics　of　the　travelling　wave　on　both　ends　of　the　hybrid　HVDC　line　are　obtained　by　analysing　the　boundary　characteristics.　The　applicable　conditions　of　travelling　wave　protection　to　the　hybrid　HVDC　line　are　given　based　on　the　criteria　of　travelling　wave　protection　and　the　fault　characteristics.　Second,　an　electromagnetic　transient　simulation　model　of　the　hybrid　HVDC　system　is　established　in　Power　System　Computer-Aided　Design/Electromagnetic　Transients　including　DC　(PSCAD/EMTDC)　in　order　to　verify　the　theoretical　analysis　results.　A　large　amount　of　simulation　results　show　that　the　travelling　wave　protection　has　good　applicability　in　the　hybrid　HVDC　system,　but　it　has　poor　sensitivity　for　high-resistance　grounding　faults;　an　appropriate　sampling　rate　should　be　chosen　according　to　the　parameters　of　the　boundary　element　for　a　better　performance　of　the　protection.　©　2019　Institution　of　Engineering　and　Technology.All　right　reserved.