DEVICE FOR PROTECTION OF THREE-PHASE ELECTRIC DEVICE Russian patent published in 1995 - IPC

FIELD: electric engineering. SUBSTANCE: device has contactor, first three-phase single-pulse rectifier 4, controlled semiconductor gate 3, "Stop" button terminal 5, "Start" button terminal 6. Second three-phase single-pulse rectifier 9, current sensors 10, comparator 16, which has positive feedback and which ratio of upper and lower operating thresholds are independent from input voltage, integrator 25, Schmidt-flip-flop 26 and amplifier 27 are introduced to accomplish the goal of invention. Lack of symmetry in phase currents as well as fact that they are over upper limit are tested by ratio of maximal voltage level at output of three-phase rectifier to constant constituent of said voltage. EFFECT: increased reliability, increased quality of testing. 4 dwg