Abstract: A seal construction of a polymer insulator has a core member, an outer cover member including a sheath portion and sheds, which is arranged on an outer surface of the core member, and a securing metal fitting is arranged on each end of the core member. A tip portion of the sheath portion is arranged between the securing metal-fitting and the core member, and a sealant is arranged between an inner surface of the securing metal fitting and an outer surface of the tip portion of the sheath portion. The seal construction mentioned above includes a small rib projecting radially outward from the sheath portion of the outer cover member. The small rib has a side surface connected to an open end portion of the securing metal fitting via the sealant, and the sealant does not protrude from a portion between the side surface of the small rib and the open end portion of the securing metal fitting.

Abstract: A seal construction of a polymer insulator has a core member, an outer cover member including a sheath portion and sheds, which is arranged on an outer surface of the core member, and securing metal fittings arranged on both ends of the core member, wherein a tip portion of the sheathe portion is arranged between the securing metal fitting and the core member and a sealant is arranged between an inner surface of the securing metal fitting and an outer surface of the tip portion of the sheath portion. The seal construction mentioned above has constructions: a small rib projected from the sheath portion of the outer cover member is arranged; a side surface of the small rib is connected to the open end portion of the securing metal fitting via the sealant; and the sealant is not protruded from a portion between the side surface of the small rib and the open end portion of the securing metal fitting.

Abstract: The invention is directed to a method and a mold for forming a zinc collar on an insulator metal cap. The zinc collar forming mold is composed of a setting section for setting the metal cap in position on the mold and an upwardly opening cavity defined around the periphery of the setting section. For molding a zinc collar, the metal cap is immersed in a molten zinc, and the metal cap is set upright on the setting section of the mold with the lower half thereof being still in the molten state. Subsequenctly, a molten zinc is poured from the upper opening of the mold, and upon solidification of the molten zinc, a zinc collar can be formed around the external circumference of the metal cap.

Abstract: Disclosed is a method and a mold for forming a zinc collar on an insulator metal cap. The zinc collar forming mold comprises a setting section for setting the metal cap in position on the mold and an upwardly opening cavity defined around the periphery of the setting section. For molding a zinc collar, the metal cap is immersed in a molten zinc, and the metal cap is set upright on the setting section of the mold with the lower half thereof being still in the molten state. Subsequently, a molten zinc is poured from the upper opening of the mold, and upon solidification of the molten zinc, a zinc collar can be formed around the external circumference of the metal cap.

Abstract: An arrestor unit is disposed between the line and earth sides of transmission lines and in parallel with an insulator by way of aerial discharge gap. Arrestor units accommodated in the arrestor unit is activated by reference voltage larger than a nominal line to ground voltage of the lines and less than the overvoltage of sound phase due to single phase ground fault.