To reduce the quantity of magnetic shield disposition for the core of a zero-phase sequence current transformer having circular form or non-circular form and restrict the number of components as a whole.
An earth leakage breaker comprises: a zero-phase sequence current transformer including a core made of a ring-shaped magnetic material which lets a plurality of primary conductors forming an AC electric path pass through the inside thereof and a toroidal-shaped coil wound around the core; a leakage current determination section which, according to the output voltage detected by the zero-phase sequence current transformer, determines whether leakage current is flowing in the AC electric path; a balanced current determination section which, based on waveform information on the output voltage detected by the zero-phase sequence current transformer, determines whether conducting current in the AC electric path is balanced current; a leakage determination section which, according to the respective determination results from the leakage current determination and the balanced current determination sections, determines whether leakage has occurred in the AC electric path; and an opening/closing control section which, according to the determination result from the leakage determination section, opens or closes an electric path contact provided in the AC electric path.
YAMAZOE KOICHI
MIYAMURA YUSUKE
SHINOHARA HIROKI
Toshimitsu Ichikawa
Kimihide Hashimoto
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