METHOD AND APPARATUS FOR USE IN EARTH-FAULT PROTECTION

摘要

A method and an apparatus for use in an earth-fault protection in a three-phase electric network, the apparatus configured to detect a phase-to-earth fault (60) in the three-phase electric network (50), to determine for each of the three phases (A, B, C) of the three-phase electric network a phase current during the detected phase-to-earth fault or a change in the phase current due to the detected phase-to-earth fault, to determine an estimate of an earth-fault current on the basis of the determined phase currents or on the basis of the determined changes in the phase currents, to determine, if the estimate of the earth-fault current represents an actual earth-fault current or an apparent earth-fault current, and to determine, in response to determining that the estimate of the earth-fault current represents the actual earth-fault current, that the estimate of the earth-fault current is valid.