Optical fiber-containing insulators and process for producing same

Abstract: An optical fiber-containing insulator including an insulator body (1) having a through hole and an optical fiber inserted into the through hole (2) in which an insulation gas or an organic material (6) is filled in a middle portion (2-1) of the through hole is disclosed, which comprises wide-mouthed portions (2-2) arranged in both end portions of the through hole, cylindrical members (4) inserted into the wide-­ mouthed portions and heat-resistive adhesive agent member (7) arranged between the insulation gas or organic insulation material and the cylindrical member. The space between the cylindrical member and inner wall of the hole and the space between the cylindrical member and the optical fiber is sealed with an inorganic material (5). A process for producing such an optical fiber-­ containing insulator is also disclosed.

Description: The present invention relates to optical fiber-containing insulators which can endure environmental stresses, for example, due to temperature variations of the environments to be used and which can maintain airtight properties for a long time, and to a process for their production. In power substations, power-transmission lines and power-distribution lines, it is desired to provide a system for quickly detecting faults in electric power systems and for immediately repairing these faults. Usually, there has been known an apparatus for detecting unusual currents or unusual voltages which utilizes an optical sensor having characteristics such as Faraday effects and Pockels effects. Moreover, in order to insulate the transmission current or the transmission voltage between a fault locator and the optical sensor arranged to a conductor of the normally power supplying side, use is made of an insulator. Therefore, it is necessary to use an optical fiber-containing insulator which transmits only optical signals while maintaining the electric insulating properties. In the optical fiber-containing insulator used for this purpose, it is necessary to maintain the mechanical strength and the electric insulation property for a long time, in addition to the transmission properties of the optical signals. In the optical fiber-containing insulators, as to sealing materials for maintaining air-tight properties between the optical fiber and the porcelain, use is made of an organic material or an inorganic material such as glass, and both of them have especial merits and demerits respectively. In the case that use is made of an organic material such as silicone rubber as the sealing material, it is possible to seal airtightly a space between the optical fiber and the porcelain and to perform a sealing operation easily at low temperatures, and thus there is a merit such that the manufacturing of the optical fiber-containing insulator can be performed easily on a large scale. Contrary to this, in the case that use is made of an inorganic material such as glass as the sealing material, the inorganic material has basically excellent weatherproof and chemical corrosionproof properties in comparison with the organic material and thus if material characteristics such as thermal expansion coefficients of the inorganic material meet with those of the surrounding material, it is possible to achieve an excellent long reliability of the air-tight and insulation properties. In the optical fiber-containing insulator in which an organic material is used as the sealing material, since thermal expansion coefficients between the organic material and the porcelain are largely different from each other in a general case, there is a drawback that there occurs deterioration of the organic material used as the sealing material due to temperature variation generated in the environmental temperatures and breakage of the optical fiber due to the deterioration of the organic material. Moreover, since the organic material is deteriorated due to tracking generated therein in the long term, it is preferred that, as to the sealing material for maintaining the air-tight and insulation properties, use is made of an inorganic material such as glass having substantially the same thermal expansion coefficient as that of porcelain. Contrary to this, in the optical fiber-containing insulator using glass mentioned above, since a large furnace must be used so as to melt the glass by heating the whole long porcelain, there is a drawback such that equipment cost increases and the cost of power consumings also increases. Further, as to the optical fiber used in the optical fiber-containing insulator, it is necessary to use optical fiber made of quartz glass in view of the heat resistive properties. The mechanical strength of the optical fiber is maintained by covering an organic material as a covering layer, such as silicone resin, urethane resin and epoxy resin, on an outer surface of threads just after spinning the threads out of the mother material made of quartz glass. Since the mechanical strength of the optical fiber is extremely low if there is no covering layer, the covering layer must be arranged on the outer surface of the optical fiber so as to handle it. However, such an organic covering layer does not basically endure a heat treatment performed above 300°C. Therefore, if the organic covering layer is once deteriorated by the heat treatment etc., the optical fiber becomes very brittle and thus it is broken under much lower stress than that before the heat treatment. For example, in the case that a diameter of the optical fiber is 125 µm, the breaking load of the optical fiber is 6 kg before the heat treatment and is 0.5 kg after the heat treatment. Accordingly, in the case that the whole insulator is heated so as to melt the glass materials for the sealing, the strength of the part of the optical insulator projected from the porcelain becomes low and then the optical fiber is broken in the next step. Therefore, after sealing the optical fibers in the porcelain, the opposed end surfaces of the insulator containing the optical fibers are mirror-polished, and then it is necessary to connect optically the other optical fibers to the bared optical fibers in the insulator by using ferrules. In this case, there occurs a drawback such that the manufacturing steps become complicated and thus the manufacturing cost increases. JP-A-60-158402 discloses an optical fiber composite insulator in which the optical fiber is sealed with an epoxy resin. It is desirable to eliminate the drawbacks mentioned above and to provide optical fiber-containing insulators and a process for their production, in which reliable optical fiber-containing insulators can be produced in an easy manner. The present invention therefore provides an optical fiber-containing electrical insulator as set out in claim 1. It also provides a process for producing an optical fiber-containing electrical insulator as set out in claim 3. Suitably, use is made of a glass material having a thermal expansion coefficient close to that of the porcelain as a sealing material, during use of the optical fiber-containing insulator, sealed portions become resistive with respect to a heat stress generated due to variation of environmental temperature and show good airtight properties for a long time. Further, since use is made of an inorganic material, it is possible to obtain a sealing portion having good weatherproof properties. Moreover, since an insulation gas such as SF₆ etc. or an organic insulation material such as silicone oil, mineral oil, silicone grease, urethane rubber, silicone rubber etc. is filled in the inner through hole portion of the insulator except for both end portions which are sealed by the glass material, the withstanding voltage of the inner through-hole portion of the insulator can be made larger than that of the surface of the insulator, and thus it is possible to eliminate flashover in the inner through hole portion of the insulator. Further, since an insulation material such as silicone oil, mineral oil, silicone grease, urethane rubber, silicone rubber etc. which can seal or adhere airtightly a space between the optical fibers and the porcelain, predetermined airtight properties can be maintained even if the airtight sealing is broken by mechanical damage of the sealing portion etc. and thus an optical fiber-containing insulator having higher airtight reliability can be obtained. Furthermore, since the organic insulation material is filled in the inner through-hole portion, no void portions are existent in the inner through-hole portion, or since the insulation gas, such as SF₆ etc. is arranged in the inner hole portion, the withstanding voltage of the inner through-hole portion of the insulator can be increased. Therefore, no corona is generated in the inner through-hole portion and thus it is possible to eliminate a little tracking of the covering layer of the optical fiber generated in an always voltage applied state. Moreover, the optical fiber-containing insulator has a construction such that both end portions of the inner through-hole portion are constructed by wide-mouthed portions having preferably a tapered shape, and a conductive cylindrical member having an outer surface whose shape corresponds to an inner surface of the wide-mouthed portion is inserted into the inner through-hole portion. Therefore, the space between the outer surface of the cylindrical member and the insulator, and the space between the inner surface of the cylindrical member and the optical fiber can be easily sealed by the glass material, by heating inorganic glass arranged on the inner and outer portions of the conductive cylindrical member, by means of a high-frequency induction heating, and thus it is possible to easily produce the end sealed portions. Moreover, since an inorganic adhesive agent suitably consisting mainly of silica and alumina, or an heat-resistive organic adhesive agent, such as polyimide resin or fluorosilicone resin, is arranged between the insulation gas or the organic insulation material and the cylindrical member, it is possible to reduce the heat conduction to the insulation gas, such as SF₆ etc. or the organic insulation material, which suffers damage easily in case that the insulator is heated for the sealing treatment of the end portions. In the case that the optical fiber-containing insulator has the construction mentioned above, and the organic insulation material such as silicone rubber, urethane rubber etc. is filled in the inner through hole portion, it is preferred to use an optical fiber, such that an outer surface of the glass fiber consisting mainly of quartz is covered with an organic material, which is airtightly connected with the optical fiber, so as to maintain the mechanical strength thereof and with respect to the outer surface of the covered layer is performed a primer treatment, using a silane coupling agent, so as to maintain good connections between the rubber and the optical fiber. Moreover, as to the rubber mentioned above, it is preferred to use a material having a predetermined tensile strength and elongation at break point since it is better for shrinkage and expansion generated by variation of environmental temperature. Further, as to the glass for the sealing material, it is preferred to use glass having a lower thermal expansion coefficient than that of the porcelain, so as to reduce the residual stress on the sealing operation and to maintain the mechanical strength of the glass sealing portion with respect to thermal stress generated due to variation of the environmental temperature, and to use glass which can perform the sealing operation at a low temperature. Furthermore, since the glass is volume-shrinked in the molten state, it is preferred to use a glass formed body which is formed in a fitting shape into the conductive cylindrical member and has holes through which the optical fibers are passed, and then is calcined, so as to seal the predetermined length between the inner surface of the conductive cylindrical member and the optical fibers effectively. As to the sealing operation of the glass portion, it is necessary to use high-frequency induction heating which can melt the glass by a partial heating, so as to make the end sealing construction by one heating operation. Moreover, as to a material for the conductive cylindrical member which is to be heated by the high-frequency induction heating mentioned above, it is preferred to use a material having a lower thermal expansion coefficient than that of the porcelain, as is the same as the glass material, such as conductive ceramics such as zirconium diboride, and metal materials such as Kovar consisting mainly of iron and nickel-based alloys. As to the metal materials, it is preferred to use the metal materials on which surface treatments such as an oxidizing process are previously performed, so as to improve the wettability with respect to the glass and to eliminate deterioration of the glass on the heating for the sealing operation. Examples of the invention are now discussed with reference to the drawings, wherein:- Fig. 1 is a schematic view showing one end structure of an optical fiber-containing insulator according to the invention; and Figs. 2a to 2e are schematic views illustrating respective steps of a producing process of the optical fiber-containing insulator shown in Fig. 1. Fig. 1 is a schematic view showing one end structure of an optical fiber-containing insulator according to the invention. In the embodiment shown in Fig. 1, at least one optical fiber 3 in which a part of a covering layer corresponding to a glass sealing portion is removed and a middle portion 2-1 of a through hole 2 arranged in a middle axis of an insulator 1 are sealed with each other by using a silicone rubber 6 which is one example of organic insulation materials. Moreover, the optical fiber 3 arranged between the middle portion 2-1 of the through hole 2 and a wide-mouthed portion 2-2, having preferably a tapered shape, of the through hole 2 is sealed by using inorganic or organic adhesive agents 7 having heat-resistive properties. Further, a space between the optical fiber 3 and a cylindrical member 4 having an optical fiber insertion hole at its bottom portion and made of conductive ceramics or metal materials etc. and a space between the cylindrical member 4 and the wide-mouthed portion 2-2 of the through hole 2 are airtightly sealed by a glass 5. Furthermore, a part of the optical fiber 3 projected outwardly from the wide-mouthed portion 2-2 is covered with a silicone rubber 6 so as to protect the projected part of the optical fiber 3. Hereinafter, a producing process of the optical fiber-containing insulator mentioned above will be explained. Figs. 2a to 2e are schematic views showing respective steps of the producing process of the optical fiber-containing insulator shown in Fig. 1, in which silicone rubber is especially used as a sealing material among an insulation gas and organic insulation materials. Fig. 2a is a schematic view showing one embodiment of an optical fiber used for a sealing. In Fig. 2a, as to the optical fiber 3, use is made of a fiber made of quartz glass having a core diameter of 80 µm and a clad diameter of 125 µm. In order to maintain airtight properties of the optical fiber 3 itself, a covering portion 3-2 made of UV cured polyurethane acrylate resin is adhered airtightly on an outer surface of a core portion 3-1 made of quartz glass. The reason for using acrylic resin of polyurethane system as the covering portion 3-2 of the optical fiber 3 is that it has good properties against a temperature variation after adhering with a silicone rubber filled in the middle portion of the through hole 2 of the insulator 1. Moreover, a silane coupling agent 3-3 is applied on an outer surface of the covering portion 3-2 of the optical fiber 3 so as to improve airtight connection properties between the silicone rubber and the covering portion 3-2. Further, in order to perform a complete airtight sealing between a sealing glass and the optical fiber 3 and in order not to foam the sealing glass by firing the organic covering portion 3-2 of the optical fiber 3 due to a high temperature on a melting of the sealing glass, a part of 35 mm long of the covering portion 3-2 corresponding to a sealing portion between the optical fiber 3 and the sealing glass is immersed in ethanol for 30 minutes, and then is removed mechanically by means of a jacket stripper so as to make a remove portion 3-4 of the covering portion 3-2. Fig. 2b is a schematic view showing a step for sealing the optical fiber into the center axis portion of an inner hole portion by using a silicone rubber as an adhesive agent. The insulator 1 having 826 mm long has a body portion having a diameter of 80 mm and the through hole 2 having a diameter of 10 mm at its center axis. Moreover, wide-mouthed portions 2-2, 2-3 having 50 mm long in its center axis direction of the insulator 1 and having a taper angle of 5° are arranged in its both end portions of the through hole 2. One optical fiber 3, to which the above preprocess is performed, is set into the through hole 2 formed at its center axis of the insulator 1. After that, the silicone rubber 6 to which a vacuum defoaming treatment is performed for 30 minutes under a vacuum pressure beneath 1 Torr (100 Pa). is filled in the middle portion 2-1 of the through hole 2 along 660 mm long. The filling operation is performed so as not to damage the optical fiber 3 by using a support member 8 having an insertion hole of the optical fiber 3 and a hole for filling the silicone rubber 6 and on an outer surface of which is applied a fluoroplastics layer so as not to adhere with the silicone rubber 6. In this case, it is preferred to perform a vacuum aspiration from the wide-mouthed portion 2-3 opposed to the wide-mouthed portion 2-2 from which the silicone rubber 6 is pressure-inserted, since the silicone rubber 6 is not foamed on the filling operation. After the silicone rubber 6 is filled along 660 mm at its middle portion, the silicone rubber is cured at 80°C for 4 hours. Moreover, as to the silicone rubber 6, it is preferred to use a silicone rubber of addition reaction type having a good curing property when it is filled into a long narrow inner through hole. Further, it is preferred to use a silicone rubber having a large tensile strength and a large elongation on the break-down point since it is good against deteriorations. Fig. 2C is a schematic view showing a step for filling the heat-resistive adhesion agent proceeding from the silicone rubber filling step. After filling the silicone rubber 6, the heat-resistive adhesive agents 7 are filled from end portions 6-1 and 6-2 of the silicone rubber 6 to the end portions of the wide-mouthed portions 2-2 and 2-3 of the insulator 1. The filling operation of the heat-resistive adhesive agent 7 is performed by using the same support member as that of the filling operation of the silicone rubber 6. Moreover, use is made of the heat-resistive adhesive agent 7 having a paste state and to which the vacuum defoaming treatment is previously performed. As to the heat-resistive adhesive agent 7, use is made of an inorganic material consisting mainly of silica and alumina and having a heat proof temperature of 1600°C or a heat-resistive organic material consisting mainly of polyimide resin and having a heat proof temperature of 500°C. The hardening operation of the adhesive agent 7 is performed by heating it for 2 hours at 100°C after a pre-hardening operation for 12 hours at room temperatures and then for 4 hours at 80°C in case of the inorganic adhesive agent or by heating it for 2 hours at 180°C after a pre-curing operation for 30 minutes at 100°C and then for 30 minutes at 120°C in case of the heat-resistive organic adhesive agent. Fig. 2d is a schematic view showing a step for a glass sealing of the end portions proceeding from the heat-resistive adhesive agent filling step. At first, the cylindrical member 4 made of Kovar, comprising an outer portion having the same taper angle of 5° as that of the inner portion of the wide-mouthed portions 2-2 and 2-3 of the insulator 1, a bottom portion having an insertion hole for the optical fiber 3 and to which the glass 5 is previously applied, is formed. A washing for degrease is performed and then a surface washing is performed, by using an acid such as FeCl₃ solution with respect to the thus formed cylindrical member 4. Further, an oxidizing treatment is performed for improving the wettability with the glass 5 and for making the adhesion reaction on the glass melting complete. The oxidizing treatment is performed for 20 hours at 800°C under the atmosphere. The glass 5 is sprayed to about 1 mm thick on the outer portion of the cylindrical member 4 made of Kovar. After that, the thus sprayed cylindrical member 4 is dried for 30 minutes at 80°C and is calcined for 1 hours at 320°C by using an electric furnace. Then, the cylindrical member 4 on which the glass 5 is adhered by the calcining operation is set in the wide-mouthed portion 2-3 of the through hole 2 of the insulator. Moreover, as to the glass 5, use is made of lead borate glass having a low thermal expansion coefficient and a low melting point. Further, a glass calcined member 5-1 having a length of 35 mm, an outer diameter substantially equal to an inner diameter of the cylindrical member 4 and a through hole for the optical fiber 3 is set in the cylindrical member 4. The glass calcined member 5-1 is formed by mixing a little amount of an organic binder such as methylcellulose and a water with the lead borate glass, pressing the mixed glass,processing an outer surface of the pressed body and a through hole for the optical fiber, heating the processed body for 1 hour at 320°C after increasing a temperature by a heating rate of 50°C/Hr. Then, a coil 10 having seven turns and made of copper is arranged around the outer surface of the insulator 1 and a high-frequency voltage is applied to the coil 10 from a generator of the high-frequency induction voltage. By applying the high-frequency voltage to the coil 10, a high-frequency induction current is generated in the Kovar cylindrical member 4 and thus the cylindrical member 4 is self-heated. In this case, a condition of applied high-frequency voltage and current is set in the manner such that a temperature of the cylindrical member 4 becomes 500°C. As a result, a temperature of the cylindrical member 4 becomes 500°C for about 20 minutes after a start of the high-frequency voltage applying. Then, the cylindrical member 4 is maintained for about 10 minutes at 500°c under the condition such that a load of 20 kg is applied on an upper surface of the cylindrical member 4 so as to seal airtightly a space between an outer surface of the cylindrical member 4 and the wide-mouthed portion 2-3 by a melted glass 5 and also to melt the glass calcined member 5-1 arranged in the cylindrical member 4. After that, an air cooling is performed. Fig. 2e is a schematic view showing a step of protecting the optical fiber at the end portions of the insulator proceeding to the glass sealing step. In order to protect the covering portion 3-2 of the optical fiber 3 projected from the glass sealing portion in the wide-mouthed portion 2-3 of the insulator 1, a vacuum defoamed silicone rubber 6 is filled around the projected optical fiber 3 in the wide-mouthed portion 2-3 and is cured by heating it for 1 hour at 80°C. In a series of processing steps mentioned above, at first the sealing step and the protecting step of the covering portion are effected with respect to one end portion of the insulator, and then after the insulator 1 is turned over the same steps are effected with respect to the other end portion of the insulator. In this case, in the case that use is made of the insulation gas such as SF₆ or the insulation material such as the insulation grease or oil as the center filling member in the insulator, the sealing step of the end portion and the protecting step of the covering portion are performed in the same manner as those of the steps mentioned above. However, in this case, after the sealing step and the protecting step are performed with respect to one end portion of the insulator, the optical fiber-containing insulator is produced by turning over the insulator, filling the insulation gas or material and performing the sealing step and the protecting step with respect to the other end portion. After that, a flange metal member is adhered to an outer end portion of the insulator by using a cement in the same manner as that of the known insulator, and finally the optical fiber-containing insulator is obtained. Hereinafter, an actual embodiment in case that use is made of the silicone rubber as the filling material will be explained. Embodiment Optical fiber-containing insulators were produced in the producing steps shown in Figs. 2a to 2e by using two kinds of the insulators 1 and two kinds of the sealing glasses 5 both having properties shown in Table 1, the optical fiber 3 made of the covering portion 3-2 and the silicone rubber 6 both having properties shown in Table 2, the cylindrical members 4 made of the materials shown in Table 3 and the heat-resistive adhesive agents having properties shown in Fig. 4. With respect to the optical fiber-containing insulators mentioned above, a few of various test items shown in Table 5 were performed according to test conditions shown in Table 5. Moreover, as comparison examples, optical fiber-containing insulators having a conventional structure such that the silicone rubber 6 was filled in all the through hole 2 of the insulator 1 or having a conventional structure such that the sealing was performed only by the glass 5 in the wide-mouthed portions 2-2, 2-3 of the through hole 2. Material combinations to be tested are shown in Table 6. Insulator A Insulator B Glass A Glass B Thermal expansion coefficient (×10⁻⁷/°C) 74 56 42 58 Melting temperature (°C) - - 420 450 Main composition SiO₂, Al₂O₃ SiO₂, Al₂O₃ PbO, TiO₂ B₂O₃ PbO, SiO₂ B₂O₃, Li₂O Covering portion of the optical fiber Silicone rubber Tensile strength (kg/cm²) 400 50 Elongation at breaking (%) 45 500 Hardness (Shore D) 55 (JIS) 30 Material UV cured polyurethane acrylate resin Silicone rubber of addition reaction type Kovar 42Ni Alloy ZrB₂ (A) ZrB₂ (B) Thermal expansion coefficient (×10⁻⁷/°C) 47 66 55 63 Specific resistance at R.T. (µΩ·cm) 100 100 500 10 Tensile breaking strength (kg/cm²) 5600 4000 8300 5500 Material 29%Ni, 17%Co, remainder Fe 42%Ni remainder Fe Zr, B Zr, B Inorganic adhesion agent 1 Inorganic adhesion agent 2 Heat-resistive organic adhesive agent 3 Heat-resistive temperature (°C) 1600 1200 500 Adhesion strength (kg/cm²) 15 50 200 Thermal expansion coefficient (×10⁻⁷/°C) 60 40 770 Main composition SiO₂, Al₂O₃ SiO₂, Al₂O₃ Polyimide of addition reaction type Test items Test conditions Thermal shock test Temperature difference : 90°C (warm water 90°C cold water 0°C) Immersed time : 30 minutes Number of immersed time : 5 cycles Heat proof test Heating temperature : 60∼160°C (20°C interval) Constant temperature time : 3 hrs. Heating rate : 100°C/Hr Heat cycle test Temperature difference : 110°C (warm 90°C, cold -20°C) Constant temperature time : 3 hrs. Number of cycle : 3000 cycles Long-term voltage applying test Applied voltage : 46.5 kV(AC) (voltage applied in open-air) Sample No. Material Remarks Insulator Cylindrical member Glass Silicone rubber Heat-resistive inorganic adhesive agent 1 A Kovar A filled 1 Present invention 2 A ZrB₂(B) A filled 2 3 B 42Ni alloy B filled 1 4 B Kovar A filled 1 5 B Kovar A filled 3 6 B ZrB₂(A) B filled 2 7 A 42Ni alloy B none none Comparison 8 B Kovar A none none 9 A none none filled none 10 B none none filled none The various test items shown in Table 5 were performed for examining long-term properties of the sealing portion of the optical fiber-containing insulator. As to the thermal shock test, a fluorescent penetrant examination was performed with respect to the insulators of the sample Nos. 1 to 8 having the glass sealing construction so as to detect whether or not cracks were generated. Moreover, in the conventional insulators of the sample Nos. 9 and 10 having the silicone rubber sealing construction, whether or not the silicone rubber was projected from the seal end portion and whether or not cracks in the silicone rubber were generated were detected. In the heat proof test, whether or not a light transmission loss before and after the heat proof test was existent, whether or not cracks in the sealing portion or in the insulator were generated and whether or not the silicone rubber was projected were detected. Moreover, in the heat cycle test, a deterioration state of the sealing portion due to a long-term temperature stress was detected. In the insulators of the sample Nos. 1∼8 having the glass sealing construction, whether or not cracks were generated was detected, and in the insulators of the sample Nos. 9 and 10 having the silicone rubber sealing construction, whether or not cracks were generated in the silicone rubber was detected. As to the long-term voltage applying test, whether or not a tracking was generated in the optical fiber-containing insulator after the long-term voltage applying operation was detected by cutting the insulator to pieces. Test results were shown in Table 7. Marks shown in Table 7 mean as follows. For the thermal shock test, the heat proof test and the heat cycle test, use was made of ten optical fiber-containing insulators for respective one of samples. Moreover, for the heat proof test and the heat cycle test, the same sample was used repeatedly at respective test levels. In the test items mentioned above, a mark O ○ shows that all the ten samples have no cracks, a mark ▵ shows that only one sample has cracks and the other nine samples have no cracks and a mark X shows that more than two samples have cracks and the other samples have no cracks. Moreover, as to the long-term voltage applying test, use was made of five optical fiber-containing insulators at respective test levels. In this case, a mark O ○ shows that all the five samples have no trackings therein, a mark ▵ shows that one sample has trackings therein and the other four samples have no trackings therein and a mark X shows that more than two samples have trackings therein and the other samples have no trackings therein. As a result, in the thermal shock test, it is confirmed that all the samples have no cracks. It is suggested that thermal expansion coefficients of the materials to be tested are suitably selected. Moreover, in the heat proof test, it is confirmed that all the sample Nos. 1 to 8 having the glass sealing construction show no faults till a temperature of 160°C and therefore have good properties. Contrary to this, it is confirmed that the sample Nos. 9 and 10 having the silicone rubber sealing constructions generate a projection of the silicone rubber at a temperature more than 120°C. It is suggested that, since the thermal expansion coefficient of the silicone rubber is about 30 times larger than that of the porcelain, the silicone rubber is expanded largely in a high temperature and thus the projection of the silicone rubber is generated due to a high stress concentration larger than a proper tensile strength of the silicone rubber. In the insulator used in substations etc., a temperature of the insulator becomes more than 80°C due to a heat absorption in summer, and thus the optical fiber-containing insulator comprising the silicone rubber sealing construction having a low heat-resistive temperature is assumed to be wrong on the long-term properties. In the heat cycle test, the sample Nos. 1 to 8 having the glass sealing construction show no faults up to 3000 cycles and thus has good properties. Contrary to this, the sample Nos. 9 and 10 having the silicone rubber sealing construction generate cracks in the silicone rubber over 2000 cycles. Moreover, in a part of the samples, an exfoliation is detected between the silicone rubber and the covering portion of the optical fiber and between the silicone rubber and the inner through hole of the insulator boundary of the silicone rubber. From the result of a cutting examination after performing the heat cycle test of 3000 cycles with respect to the sample Nos. 1 to 6 having the glass sealing construction in which the silicone rubber is filled, the cracks in the silicone rubber or the exfoliation between the silicone rubber and the covering portion of the optical fiber are not detected at all, and thus it is assumed that deteriorations of the exfoliation are dependent upon a water component. That is to say, in the sample Nos. 9 and 10, since the heat cycle test is performed under a condition such that the insulator is exposed directly by the water component, it is assumed that the deteriorations proceeds due to an existence of the water component. As a result of the long-term voltage applying test, the sample Nos. 1 to 6 having the glass sealing construction in which the silicone rubber is filled show no trace of the trackings even after performing the long-term voltage applying test of 500 days. Contrary to this, the sample Nos. 7 and 8 having the glass sealing construction in which a vacant portion is arranged generate the partial trackings in the covering portion of the optical fiber even after performing the long-term voltage applying test of 300 days. Moreover, in the sample Nos. 9 and 10 having the silicone rubber sealing construction, it is confirmed that the trackings extend gradually from the sealing end portion to the inner portion. In the sample Nos. 7 and 8, it is assumed that the trackings generate gradually from near the end portion due to the water component and a stain etc. remained in the inner vacant portion on the sealing operation. As can be seen from the test results mentioned above, the glass sealing construction is better than the silicone rubber sealing construction on the long-term properties, but, in case that the inner vacant portion remains, there is a fear of the tracking generation under the long-term voltage application. Therefore, the optical fiber-containing insulator according to the invention having the glass sealing construction at its both end portions of the through hole, in which the silicone rubber is filled in the middle portion of the through hole and the heat-resistive inorganic adhesive agent between the silicone rubber and the cylindrical member is filled in the through hole, is effective for improving a merit of the glass sealing construction. It should be noted that the optical fiber-containing insulator in which urethane rubber, silicone oil, silicone grease or SF₆ gas is filled in the through hole in spite of the silicone rubber mentioned above can also obtain the substantially same properties. As can be seen from the above, according to the optical fiber-containing insulator and the producing process thereof mentioned above, since the optical fiber-containing insulator has the merits of inorganic sealing construction and the organic sealing construction at its both end portions can be performed at one induction heating operating, it is possible to obtain a reliable optical fiber-containing insulator in an easy producing process.

Claims: An optical fiber-containing electrical insulator including an elongate insulator body (1) having a through-hole (2) provided along the center axis thereof, and an optical fiber (3) extending along said through-hole (2), in which an insulation gas or an organic insulation material (6) fills a middle portion (2-1) of said through-hole (2), characterised by comprising: in said insulator body (1), wide-mouthed portions (2-2) arranged at both end portions of said through-hole (2); conductive hollow cylindrical members (4) inserted into said wide-mouthed portions (2-2), and having outer surfaces corresponding to the inner surfaces of said wide-mouthed portions (2-2), the spaces between the optical fiber (3) and said cylindrical members (4), and the spaces between the outer surfaces of said cylindrical members (4) and the inner surfaces of said wide-mouthed portions (2-2), being sealed by an inorganic material (5); and heat-resistive adhesive material (7) disposed in said through-hole (2) between said insulation gas or organic insulation material (6) and said cylindrical members (4). An optical fiber-containing insulator according to claim 1, wherein said wide-mouthed portions (2-2) have a tapered shape. A process for producing an optical fiber-containing electrical insulator according to claim 1 comprising the steps of (a) inserting an optical fiber (3) along a through-hole (2), provided along the center axis of an elongate insulator body (1), in which both end portions of said through-hole (2) have wide-mouthed portions (2-2), (b) filling an insulation gas or organic insulation material (6) into a middle portion of said through-hole (2), characterised by the further steps of; (c) arranging heat-resistive adhesive material (7) in said through-hole (2) between the middle portion consisting of said insulation gas or organic insulation material (6) and said wide-mouthed portions (2-2), (d) inserting conductive hollow cylindrical members (4), having outer surfaces corresponding to the inner surfaces of said wide-mouthed portions (2-2), into said wide-mouthed portions (2-2), said outer surfaces being coated with an inorganic glass (5), (e) inserting inorganic glass members (5-1) into said conductive cylindrical members (4) around the optical fiber (3), and (f) melting said inorganic glass (5) arranged between the inner surfaces of said wide-mouthed portions (2-2) and the outer surfaces of said cylindrical members (4) and said inorganic glass members (5-1) arranged in said cylindrical member (4), through which the optical fiber (3) is arranged, by heating said conductive cylindrical members (4) by means of a high-frequency induction heating method so as to form end sealing constructions.

Inventors: MIMA TOSHIYUKI, MORI KOICHI, SEIKE SHOJI, MIMA, TOSHIYUKI, MORI, KOICHI, SEIKE, SHOJI
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1989
Main classification: G02B6
IPC codes: G02B6