Optical fiber-containing insulators

Abstract: An optical fiber-containing insulator comprises an insulator body (1) having a through hole (2) provided in its central portion and extending along an axial direction thereof, an optical fiber core wire (3) passing through the through hole, and an insulating material (4) filled between an inner peripheral surface of the through hole and the optical fiber core wire. To avoid tension on the optical fiber, means e.g. a taper (2a) are provided for preventing the filled insulating material from axially protruding out of the insulator body even at high temperatures. To prevent the fiber (3) touching the body (1), there are means for holding the optical fiber core wire at the central portion of the through hole of the insulator body.

Description: The present invention relates to optical fiber-containing insulators in which an optical fiber is buried to transmit signals from a power transmission line to a ground contact side. As disclosed in Japanese patent application Laid-open No. 60-158,402, there have formerly been known optical fiber-containing insulators in which a through hole of a small diameter is formed in an axial portion of an insulator body and an optical fiber is passed through the through hole, while an insulating material such as an epoxy resin is filled between the inner peripheral surface of the through hole and the optical fiber. The insulating material filled has important roles in preventing a leakage current from flowing along the optical fiber and preventing decrease in a surface leakage-insulating distance of the insulator. When the insulator is subjected to high temperatures, the insulating material such as epoxy resin is greatly forced out from the insulator body in an axial direction thereof due to great difference in coefficient of thermal expansion between the porcelain and the insulating material so that a tension acts upon the optical fiber and that adhesion between the insulating material and the insulator body is lost. Consequently, it is feared that penetrating voltage resistance of the insulator is greatly lowered. Further, since the through hole is long and small in diameter, it is difficult to accurately hold the optical fiber in the center of the through hole so that there is the possibility that the optical fiber partially touches the inner peripheral wall of the through hole. Since no insulating material is present between the optical fiber and the inner peripheral wall of the through hole there, adhesion is lost at that portion so that water or moisture is likely to enter to lower electric insulation performance. The present invention has been accomplished to solve the above-mentioned problems. FR-A-2204812 discloses inter alia a bundle of optical fibers which passes through a chain of glass washers, in which the parts of the optical fibers which pass through them are moulded with the aid for example of a drop of glass melting at a lower temperature than the fibers. Between the washers, the fibers remain free and maintain their flexibility. The moulding of the fibers may also take place by epoxy resin. The washers may be retained in an appropriate support inside an insulator, for example. No insulator is shown. The aim of the document is particularly to remedy disadvantages arising in an arrangement of optical fibers in an oil-filled sheath. The present invention is set out in claim 1. The present invention makes it possible to obtain optical fiber-containing insulators which can completely prevent reduction in insulation due to contact between the optical fiber and the inner peripheral wall of the through hole. Optional features, and advantages of the invention will be appreciated upon reading of the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes of the same could be made by the skilled person in the art to which the invention pertains. For a better understanding of the invention, reference is made to the attached drawings, wherein: Fig. 1 is an axial cross sectional view of an embodiment of the optical fiber-containing insulator according to the present invention; and Fig. 2 is a perspective view of a spacer shown in Fig. 1. An embodiment according to the present invention will be explained with reference to Figs. 1 and 2. This embodiment is characterized in that a spacer is provided inside a through hole of an insulator between the inner peripheral wall of the through hole and an optical fiber and that the optical fiber is passed through a central hole of the spacer. First turning to Fig. 1, reference numerals 1 and 2 denote an insulator body made of a porcelain and a through hole formed in the central portion of the insulator body 1. Optical fibers 3 pass through the through hole 2. The optical fibers 3 are fixed to the insulating body with an insulating material 4 such as an epoxy resin filled in the tapered through hole 2. An appropriate number of spacers 9 are inserted inside the through hole 2 so that optical fibers 3 are held in the central portion of a through hole 2 by these spacers 9. That is, the optical fibers 3 are held in the central portion of the through hole 2 in the state that the optical fibers are passed through respective central holes 10 formed in the spacer 9. This is seen in Fig. 2 in an enlarged scale. The spacer 9 is provided with the central holes 10 through which the optical fibers 3 are passed and with penetrating holes 11 provided around the central holes 10 to allow the sealing material to enter therein. In this embodiment, two central holes are formed, through which two optical fibers 9 are passed. However, as a matter of course, if one optical fiber 3 is to be held by the insulator body, a single central hole 10 has only to be formed in a spacer 9. The spacer 9 is fixed with the sealing material 4 as shown in Fig. 1. In order to effect complete joining between the spacer and the sealing material, the spacer 9 is made of substantially the same material as that of the sealing material 4. The configuration of the spacer 9 is not necessarily limited to a planar shape shown. The spacer 9 may be designed in any shape so long as the spacer can hold the optical fiber 3 in the central portion of the through hole 2. It is preferable to set a pitch between the spacers 9, 9 in a range from about 50 to about 300 mm. This is because if it is less than 50 mm, the number of steps for producing the insulator increases, while if it exceeds 300 mm, the optical fiber 3 may slacken so that the optical fiber is difficult to assuredly be supported in the center of the through hole of the insulator body. The above-constituted insulator is produced by preliminarily passing the optical fibers 3 through the central holes 10 of the spacers 9, inserting the spacers 9 and the optical fibers 3 into the through hole 2 of the insulator body 1, pouring a liquid sealing material 4 inside the through hole 2 from an end face of the insulator body 1, and curing the sealing material 4 inside the through hole 2. Since the optical fibers 3 are accurately held in the central portion of the through hole 2 by the spacers 9 before the sealing material 4 is poured thereinto, the sealing material 4 is uniformly filled all around the optical fibers 3. Therefore, the optical fibers 3 are completely fixed inside the through hole 2 of the insulator body 1 with the sealing material 4 without leaving any dead space. Thus, when the optical fiber-containing insulator according to the present invention is used to transmit optical signals taken out from a high voltage power transmission electric line to a ground contact side, insulation characteristic of the insulator will not be degraded due to invasion of water, moisture, etc. and troubles such as insulation breakage will not occur. As is evident from the aforegoing explanation, according to this embodiment, the optical fiber or fibers can accurately be held in the central portion of the through hole of the insulator body by a simple construction so that degradation of the insulation due to eccentrical deviation of the optical fiber or fibers can assuredly be prevented. Thus, the optical fiber-containing insulator of this type has great practical value.

Claims: An optical fiber-containing insulator comprising an insulator body (1) having a through hole (2) axially extending at a central portion thereof, and insulating material (4) filled in the through hole, there being at least one optical fiber (3) passing through the through hole, characterized by a spacer (9) for holding the optical fiber or fibers (3) at the central portion of the through hole, while allowing the insulating material to enter the through hole so that the insulating material is filled between the inner peripheral surface of the through hole and the surface of the or each of the optical fibers, said spacer (9) being made of substantially the same material as the insulating material (4) and having a central hole or holes (10) for the optical fibers (3) and said spacer having holes (11) through it not blocked by the optical fiber or fibers (3). An optical fiber-containing insulator having a plurality of said spacers (9) spaced apart along said through hole (2).

Inventors: HARADA HIROSHI, KAWAGUCHI TOSHIYUKI, NAKAJIMA ISAO, NAKANISHI KAZUMI, OGURI NORIYASU, SHINODA KATSURO, HARADA, HIROSHI, KAWAGUCHI, TOSHIYUKI, NAKAJIMA, ISAO, NAKANISHI, KAZUMI, OGURI, NORIYASU, SHINODA, KATSURO
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1988
Main classification: H01B17
IPC codes: H01B17, G02B6