ELECTRIC MOTOR PROTECTIVE DEVICE Russian patent published in 2002 - IPC

FIELD: electrical engineering. SUBSTANCE: device has current sensor 3 for connecting electric circuit to supply mains, squarer 5, electric-circuit heat simulator 6, comparator 7, and final relay 8. Upon occurrence of overload in electric circuit signal exceeding rated value is built up across output of sensor 3. Signal proportional to root-mean-square current in windings of motor 1 is set up across output of squarer 5; voltage proportional in magnitude to motor heat energy is built up across output of simulator 6. When this voltage exceeds certain value set by reference voltage, electronic switch of comparator 7 closes and connects coil of final relay 8 to power supply; in the process electric circuit is disconnected from supply mains. Squarer 5 is built around operational amplifier whose feedback circuit incorporates field-effect transistor 9 characterized in quadrature dependence at initial section of its current-voltage characteristic. EFFECT: enhanced precision of device operation. 1 cl, 1 dwg