Protection device for an electric motor with thermal fault signalling before activation

摘要

The protector has a motor feed current measurer with switch and primary components for producing contact opening signal in case of overload. Secondary components produce, in the event that the overload persists for a predetermined period after the contact opening signal, a release signal (D1) for opening the switch (2). The secondary components have a facility for determining a first entity (leff<2>) representative of the square of the measured current, primary processing equipment (14) connected to the facility for determining a secondary entity (&thetas; 2) representing the thermal state of the motor and primary comparison components (10) which compare the second entity with a release threshold (SLR) which is predetermined. This enables a predetermined function of time/current protection to be effected.