PURPOSE:To alleviate electric field, form a compact tank and form a tap changeover switch just suitable for SF6 gas transformer by changing the shape of electrostatic shield to be attached to the external circumference of insulation cylinder. CONSTITUTION:The radius N of electrostatic shield 10 attached to the external circumference of insulation cylinder 5 is a little shorter than the radius M of electrostatic shield 1 attached to the internal circumference of insulation cylinder 5 (NM), shape of section at the end part forms almost quadrant obtained by dividing the circular section into four sections and the curvature R of arc of side surface opposed to the tank 4 is set large. In case two electrostatic shields 1, 10 in different shapes are provided in parallel in both sides of insulation cylinder 5, a large arc can be delineated as a whole due to the difference of radius D (D=M-N) of radii and difference in curvatures R, r. In other words, the interval of equal voltage lines of lead wire connecting bolt 3B and the end of electrostatic shields 10, 1 is almost equal and is harmonized. Particularly, interval of equal voltage lines of electrostatic shield 10 at the external circumference of insulation cylinder 5 is expanded and concentration of electric field to the end (b) can be alleviated distinctively.
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