CIRCUIT FOR PROTECTING ELECTRICAL APPARATUSES FROM SHORT CIRCUIT OR OVERLOAD FAULTS

摘要

The invention relates to a circuit for protecting electrical apparatuses from short circuit or overload faults. The circuit includes an inductively coupled signal pick up for a single phase or for each phase. A first zenor diode is adapted to receive a signal voltage from the signal pick up and is in an actuated state only when the current to the apparatus exceeds a first predetermined limit. The first zenor diode is connected to a switching circuit. A second zenor diode is adapted to receive a signal voltage from the inductively coupled signal pick up and is in an actuated state only when the current to the apparatus exceeds a second predetermined limit which is lower than that of said first level. The second zenor diode is connected to the switching circuit through a time delay circuit to provide a delay in the actuation of the switching circuit.