Determination of the proportion of differential current made up of faulty current

摘要

The method involves detecting differential current as current sum over lines (L, N) that supply current of an alternating current (AC) generator. An electric signal (27) is generated, and is subtracted from the differential current, where the signal depends on voltages present at the generator with respect to earth potential (PE). The signal is multiplied with scaling factor before subtraction. The factor is repeatedly updated such that effective value of the differential current reaches minimum at actual value of the factor after subtraction of a scaled electric signal (28). An independent claim is also included for a device for determining a fault current component of a differential current.