Differential protection device

摘要

The device includes an adjustable load on the detection circuit, enabling adjustment of threshold operating value. The differential protection device comprises a torus (1) for measuring the differential currents in the main conductors (2). It includes a first secondary winding (6) connected to a processing circuit, and a second secondary winding (8) connected to a signaling circuit. There is also a supplementary winding (10) in which a test current (It) can flow. The processing circuit (7) includes a threshold control device (12) which modifies the load of the first secondary winding (6) in order to change the calibrated operating value. When the load on the first secondary winding is very much less than the load on the second secondary winding, signaling is dependent on the selected calibration. The protection device includes a test circuit which selects a low calibration when the test current flows.