Protection apparatus for electric power transmission systems

摘要

In a protection apparatus for a feeder (H) of an electric power transmission system compensation for mutual coupling between the feeder and another feeder (G) is controlled in dependence on the ratio of the zero sequence currents (IM, IN) in the two feeders. The mutual coupling compensation signal (IMZM') is arranged to be proportional to the zero sequence current (IM) in the other feeder when the ratio of the zero sequence currents is below a predetermined value, and to be limited to a value proportional to the protected feeder zero sequence current (IN) when said ratio is above the predetermined value. The arrangement reduces the possibility of maloperation of the feeder protection due to faults on the other feeder.