Method and apparatus for determining a fault current proportion of a differential current

摘要

In the determination of a fault current component (i_F) on a differential current (i_diff(t)), the on an inverter (1) is measured, for the determination of a changing fault current component on the differential current (i_diff(t)) a to an ac output of the inverter (1) which is applied to the ac voltage (u_Ac(t)) and detected as a function of the detected alternating voltage (u_Ac(t)) a periodic reference function (y (t)) generates alternating sign. The differential current (i_diff(t)), with the periodic reference function (y (t)), and the product of the differential current (i_diff(t)) and the reference function (y (t)), by way of a whole number of periods (t) of the reference function (y (t)) are averaged. In this case, the reference function (y (t)) at least for one operating state of the inverter (1) with a predetermined phase offset to the detected alternating voltage (u_Ac(t)) and / or with a frequency is generated, which is an integral multiple of the frequency of the detected alternating voltage (u_Ac(t)) is.