OVER TEMPERATURE AND MOISTURE PROTECTIVE DEVICE FOR ELECTRIC MOTOR Russian patent published in 1995 - IPC

FIELD: electrical engineering. SUBSTANCE: electric motor is protected against excessive temperature rise using thermal analog as basis by its disconnection from supply mains at critical temperature or rate of temperature rise in windings. Moisture protection is effected by creating temperature rise on windings above ambient during servicing intervals and automatic maintenance of this temperature rise by passing current through windings. Device has thermal analog unit 3, first adjusting resistor 4, second adjusting resistor 5. For protection against excessive temperature rise, signals indicating winding temperature and rate of its rise actuate first threshold element 7 and second threshold element 8 which switch off the motor. Moisture protection is effected by winding temperature signal coming to input of differential amplifier 16 incorporating ambient temperature meter 18 which is coupled via comparison unit 15 having winding temperature rise setter 17 with phase control unit 14 that controls winding heating temperature of motor 13. EFFECT: improved reliability due to more accurate simulation of motor thermal state, which improves operating reliability of motor. 4 dwg