| 摘要 |
PROBLEM TO BE SOLVED: To shorten the time from impression of a surge to arc discharging, lower a discharge start voltage, and to suppress deterioration of a conductive film and of micro gaps at the time of discharge, by forming, on a surface of an insulator, separate and independent conductive films having continuous triangular or sawtooth shapes and lying in rows on a plurality of parallel straight lines separated by micro gaps and running vertical to the surge impressing direction. SOLUTION: A cylindrical insulator element is made by depositing a conductive film 2 on the entire surface of an insulator 1 made by extrusion molding mullite powder into a cylindrical shape and baking it, and the conductive films 2 of triangular or sawtooth shapes having a width of 50 to 100μm are formed by a laser beam at 100μm intervals in parallel relation to the circumferential direction. Because the fine conductive films 2 of triangular or sawtooth shapes are thus formed continuously in rows on straight lines separated by the micro gaps 3 and the conductive films 2 are used as discharge electrodes, electric charge concentrates on the edge parts of the conductive films 2, generation of surface discharge causing trigger discharge is facilitated, and discharge start voltage is lowered.
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