FIELD: electrical engineering. SUBSTANCE: current circuits of protective gear incorporate summing current transformers accurate to 10% whose primary windings are connected in series with threshold element (relay) and secondary windings, in parallel with threshold element (relay), that is, they use summing circuit arrangement. Current circuits of differential protective gear may optionally incorporate autotransformers in which case part of current autotransformer windings in front of autotransformer lead are series- connected to threshold element (relay) and other part after autotransformer lead is parallel-connected to threshold element (relay), that is, they use summing circuit arrangement. EFFECT: improved sensitivity due to reduced number of working points on magnetizing curves of current transformers forming differential circuit; reduced unbalance current. 2 cl, 3 dwg
