Abstract: Alumina cement mortar is used as a source material for a kneaded cement cured body for joining hardware onto an insulator body, whereby the insulator can maintain high initial and long term mechanical strength and high electrical strength over a long period of time, and the curing time for forming the cured body is shortened to reduce the cost of producing the insulator. The alumina cement mortar is formed by kneading a mixture of alumina cement particles having a specific surface area of at least 3500 cm2/g, a polymer-steric-hindrance type water reducing agent, an aggregate, and water, or an alumina cement mortar is obtained by kneading a mixture of alumina cement particles having an amorphous phase on an outer peripheral surface of particles and having a specific surface area of at least 3500 cm2/g, a water reducing agent, an aggregate, and water.

Abstract: Use of alumina cement mortar is enabled as a source material of a cement kneaded product cured body for joining hardwares onto an insulator body, whereby an insulator can maintain a high mechanical strength (initial strength, long-term strength) and a high electrical strength for a long period of time, and the curing time in forming the cured body is shortened to reduce the cost of producing the insulator. As a source material of a cement kneaded product cured body 14 for joining hardwares (12, 13), one makes use of an alumina cement mortar obtained by kneading an alumina cement having a specific surface area of at least 3500 cm2/g, a polymer-steric-hindrance type water reducing agent, an aggregate, and water, or an alumina cement mortar obtained by kneading an alumina cement having an amorphous phase on an outer peripheral surface of particles and having a specific surface area of at least 3500 cm2/g, a water reducing agent, an aggregate, and water.

Abstract: An optical fiber composite insulator which includes an insulator body having a through-hole formed in its axis portion and at least one optical fiber extending through the through-hole and sealed in the through-hole by an inorganic vitreous sealing material at both end portions of the through-hole. The sealing material has substantially the same thermal expansion coefficient as that of the insulator body, has high resistances against breakage in the power frequency voltage test and in the lightning impulse voltage test, against crack formation in the cooling and heating test, heat proof test and heat cycle test, and against the light-transmission loss.

Abstract: High strength alumina porcelains for use in insulators are disclosed herein, in which the maximum particle diameter of quartz grians remaining in the porcelains is not more than 40 .mu.m. A process for producing such high strength alumina porcelains for use in insulators comprises the steps of mixing the alumina of a controlled grain size which is decomposed in a single crystalline state and in which the 50% average particle diameter is in a range from 4 to 14 .mu.m, raw materials ground finely which are selected from the group consisting essentially of feldspar, silica sand, and china stone, and clay together, forming the thus obtained mixture, and drying and firing the formed body.

Abstract: An optical fiber composite insulator which including an insulator body having a through-hole formed in its axis portion and at least one optical fiber extending through the through-hole and sealed in the through-hole by an inorganic vitreous sealing material at both end portions of the through-hole. The sealing material has substantially the same thermal expansion coefficient as that of the insulator body, has high resistances against breakage in the power frequency voltage test and in the lightning impulse voltage test, against crack formation in the cooling and heating test, heat proof test and heat cycle test, and against the light-transmission loss.

Abstract: Optical fiber-containing insulators each comprises an insulator body having a through hole provided in its central portion and extending along an axial direction thereof, an optical fiber core wire passing through the through hole, an insulating material filled between an inner peripheral surface of the through hole and the optical fiber core wire, and arrangements for preventing the filled insulating material from axially protruding out of the insulator body even at high temperature or spacers for holding the optical fiber core wire at the central portion of the through hole of the insulator body.