Importance

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Abstract

A fuse for an alternating current power circuit in the medium voltage (3.3 kV to 38 kV) range. The fuse comprises a sealed chamber and a first electrode (41) is mounted within the chamber, the first electrode having a substantially circular periphery (42) and being electrically connected to a first terminal (3) to which a first conductor may be connected. A second electrode (35) is arranged with a conductive surface internally of the chamber, the conductive surface being spaced from the first electrode. A coil (10) is connected in an electrical path between the second electrode (35) and a second terminal (18) to which a second conductor may be connected. An additional electrical contact (44) is mounted within the chamber and in direct electrical connection with the second terminal, and a fusible element (43) directly electrically connects the first electrode (41) and the additional electrical contact (44). An electronegative halogenated medium fills free space within the chamber. The normal current path between the first and second terminals and through the fuse is by way of the first electrode (41), the fusible element (43) and the additional electrical contact (44). The arrangement is such that when the fusible element (43) breaks, the resulting fault current forms an arc between the first electrode (41) and the additional contact (44), one root of the arc subsequently commutates from the additional contact (44) to the second electrode (35), the fault current flows through the coil (10) and induces a magnetic field, the magnetic field causes the arc to rotate around the first electrode in the electronegative medium, and the arc is thereby extinguished, so interrupting the fault current.

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