MOTORSCHUTZRELAIS

摘要

Electric motors and especially their winding can be damaged or destroyed if the operating current rises above the permissible maximum current or during a relatively long operating time at more than the rated current. The described motor protection circuit for this purpose contains an overcurrent monitoring device (22) for the operating current, an electronic motor model (21) whose output signal is a measure of the motor operating temperature, and an electronic circuit (19) which monitors the starting current and/or the starting time and the rated current. Each of these three devices is connected via a gate circuit (27) to a threshold value trip device (28) which opens the switch (12) for the motor current as soon as one of the monitored variables exceeds the predetermined value. <IMAGE>