ELECTRIC MOTOR PROTECTIVE DEVICE Russian patent published in 2002 - IPC

FIELD: electrical engineering for various industries; motor deenergizing under abnormal conditions. SUBSTANCE: device has current transformers 1,2,3, rectifier 4, overload monitoring unit 5, time-current characteristic shaping unit incorporating motor heat simulator 6, comparator 7, and final relay 8. Upon the occurrence of overload rectifier 4 passes current exceeding rated value. Current value is recorded by means of shunt resistor, Voltage is built up across output of simulator 6, its magnitude being proportional to heat energy of motor. When this voltage exceeds certain value set by reference voltage, electronic switch of comparator 7 closes and energizes final relay 8 which disconnects motor from supply mains; unit 5 has two series-connected circuits set up of shunt resistors 12, 13 and voltage regulator diodes 11, 14 which function to regulate output voltages of rectifier 14 and to enable using these voltages for feeding operational amplifier and comparator. EFFECT: enhanced reliability of device without complicating its mechanical design. 3 cl, 3 dwg