FIELD: electrical engineering; relay protective gear. SUBSTANCE: proposed method and device can be used for protecting power transformers and autotransformers using star/star/delta connection of windings with neutral brought out and mounted in power systems upon occurrence of troubles accompanied by various kinds of short circuits. Use is made of only one three-phase differential relay whose saturable transformer primary windings are supplied with resultant currents from secondary windings of current transformers of all phases installed at high-, medium-, and low- voltage sides of three-phase transformer thereby enabling reduction of load on current circuits of protective gear. Provision for disabling arrival of off-operation signal to overcurrent relay make contacts for disconnecting power circuits and also inserting one of phases in parallel opposition to secondary windings of current transformers of other phases in each group of current-transformer secondary winding provides for higher sensitivity of protective gear. EFFECT: enhanced sensitivity; reduced mass and size of protective gear. 7 cl, 2 dwg
