A　practical　faulty-line-selection　method　based　on　transient　fault　information　is　provided,　based　on　which　the　faulty　line　selector　YH　B811　is　developed.　Its　algorithm　integrates　two　comparing　criteria:　the　amplitude　of　transient　zero　sequence　current　within　the　feature　band　and　that　of　lower-frequency　active　components.　The　former　captures　the　feature　band　adaptively　according　to　the　system　operating　modes　and　fault　conditions;　the　latter　is　applied　when　the　fault　initial　angle　is　small,　the　transient　resistance　is　very　larger　and　the　transient　component　is　very　small.　It　is　suitable　for　different　single-phase　grounding　faults　of　non-neutrally　earthed　or　non-directly　earthed　systems.　The　hardware　of　device　is　based　on　the　accurate　and　fast　working　platform　of　FPGA　and　MCF5272.　This　project　is　supported　by　the　National　High　Technology　Research　and　Development　of　China　(863　Program)　(2006AA05Z247).