FIELD: electric technique, relay protection of electric system elements. SUBSTANCE: device has intermediate current transformers equalizing currents of ports; protection current transformers operable with an error which can cause intolerable unbalance at external short-circuiting in comparison with an operate setting; auxiliary relay for locking differential protection operation. The device provides an enhanced sensitivity to inner damage currents due to locking at external short-circuiting heavy currents with the aid of the locking relay. The device can be used at any number of current transformers with different transformation rations. EFFECT: enhanced sensitivity, widened application range. 4 dwg
