FIELD: electrical engineering. SUBSTANCE: electrical apparatus for differential protection has tripping mechanism incorporating transformer for detection of differential current, tripping relay of breaking mechanism of switch and circuit testing functioning of tripping mechanism. Relay includes immobile yoke carrying coil and armature that moves relative to yoke. When apparatus functions normally armature is pressed against immobile yoke and with emergence of some differential current armature sets breaking mechanism in action. Testing circuit incorporates aid to form vibration of armature without release of mechanism to check capability of armature to separate from immobile yoke. Preferable version of realization of electrical apparatus ensures vibration by way of application of some pulse voltage to terminals of relay coil. EFFECT: increased functional reliability of electrical apparatus. 10 cl, 3 dwg
