Electric motor protective device preventing in case of stalling - uses vibration detector to initiate removal of supply if motor vibration frequency is incorrect after start-up delay

摘要

The protective device opens the supply circuit to the motor if the rotor stalls due to seizure of the load mechanism or for any other reason. A circuit breaker (2) is activated by a detector circuit which compares the motor vibration frequency with the frequency at the normal running speed. A delay circuit (5) prevents operation of the detector during motor starting. The vibration detector (1) output passes to a high-pass or pass-band filter (9), the output of which is coupled to a threshold detector (11). If after the start-up delay the vibration frequency falls below the set frequency the trip contact is closed, initiating opening of the supply to the motor.; motor.