ASB-412 digital transformer backup protection and monitoring device applicable to 110KV voltage level substation the three volumes transformer do the high-pressure side of the back-up protection. Main functions: a) three-the composite voltage start direction overcurrent protection functions; b) two-stage zero sequence voltage lockout zero sequence directional overcurrent protection; c) two-time limit of zero sequence current lockout zero sequence overvoltage protection; d) two time limits The gap current protection; e) two-stage overload protection function; f) PT disconnection and insulation monitoring function; g) the control circuit break; h) non-power protection features; i) event logging, fault recording.