PURPOSE: To break feeders with the possibility of ground faults with reducing the frequency of unnecessary breaking of normal feeders in the process of sequential braking of feeders by breaking feeders with possible ground faults sequentially from a feeder having high possibility of ground fault and a large zero-phase current to a feeder with low possibility of ground fault.

CONSTITUTION: When a ground overvoltage relay element 64BL detects voltage Vo, an Io sequential detecting element 9 measures values of currents Io flowing from outputs thereof to feeders F1-F8 and determines a sequence of the magnitudes of measured values of currents Io. A selective breaking element 10 sets up a breaking sequence of feeders in accordance with a sequence of measured values of currents Io and breaks feeders in accordance with a determined sequence of current values. When voltage Vo is eliminated by breaking the feeder with the first breaking sequence, the ground overvoltage relay element 64BL is recovered. In case breaking the first sequence feeder does not cause voltage Vo to disappear, the selective breaking element 10 breaks each feeder sequentially until voltage Vo disappears.