Earth leakage detector, earth leakage alarm and earth leakage breaker using the same

摘要

PROBLEM TO BE SOLVED: To solve the problem of a conventional leakage detector used for a grounding system cable way, such as a three-phase cable way of which one phase is groundeds being expensive and has low measurement accuracy, because the detection of phase which is difficult in obtaining precision and complicated calculations which include trigonometric functions being required. SOLUTION: A zero-phase current i0 measured by a zero-phase current sensor 14 for measuring the zero-phase current i0 of the grounding system cable way, and a phase determination signal id, having a prescribed phase corresponding to the ground phase of the cable way, is added and subtracted vectorially, to form vectors ix and iy. Thus, a resistance ground current igr is obtained from igr=k.x2-y2/4d, where k=1 in the case of a single-phase three-wire circuit, or k=2/3 for a three-phase three-wire circuit, based on effective values x, y, d of the vectors ix, iy, and id.