The　fast　DC　line　protection　technology　is　one　of　the　main　challenges　to　high-voltage　direct　current　(HVDC)　grids.　Based　on　the　Zhangbei　HVDC　grid　project,　this　paper　proposes　a　non-unit　overhead　transmission　line　protection　scheme　for　bipolar　voltage-source　converter-based　HVDC　grids　equipped　with　DC　circuit　breakers.　The　voltage　gradient　is　used　to　detect　faults　rapidly　and　start　the　protection　algorithm,　and　the　voltage　derivative　criterion　is　adopted　to　discriminate　the　internal　faults　from　the　external　ones.　Two　kinds　of　faulty　pole　identification　methods　are　proposed　based　on　the　propagation　characteristics　between　the　line-　and　zero-mode　voltages,　ensuring　the　selectivity　of　the　protection.　The　Zhangbei　HVDC　grid　model　is　built　in　power　systems　computer-aided　design/electromagnetic　transients　including　DC　and　the　performance　of　the　proposed　protection　scheme　is　verified　by　simulation　results　of　various　fault　conditions.　©　2019　Institution　of　Engineering　and　Technology.All　right　reserved.