The　hybrid　high-voltage　direct　current　(HVDC)　transmission　system　comprising　a　line-commutated　converter　(LCC)　on　the　rectifier　side　and　a　voltage　source　converter　(VSC)　on　the　inverter　side　combines　the　advantages　of　both　LCC　and　VSC.　It　has　broad　prospects　in　many　application　fields.　However,　at　the　VSC-based　inverter　side　of　the　hybrid　system,　there　is　no　dc　filters,　and　the　inductance　of　the　smoothing　reactor　is　much　smaller　than　that　of　the　LCC　station.　Therefore,　it　is　hard　to　distinguish　line　internal　and　external　faults　at　the　VSC　side　for　the　conventional　protections　based　on　the　attenuation　characteristic　of　the　line　boundary.　In　order　to　solve　this　problem,　this　study　proposes　a　non-unit　protection　for　hybrid　HVDC　transmission　lines.　The　protection　judges　the　fault　section　based　on　the　differences　of　the　backward　travelling　waveforms　under　internal　and　external　fault　conditions.　Simulation　results　show　that　the　proposed　protection　is　able　to　distinguish　internal　faults　from　external　ones,　identify　the　faulty　pole　exactly,　and　has　enough　sensitivity　under　large　resistance　faults.　©　2019　Institution　of　Engineering　and　Technology.All　right　reserved.