Title of Invention	AN APPARATUS FOR ANCHORING SELF-SUPPORT OPTICAL CABLE
Abstract	An apparatus for anchoring a self-support optical cable suspended under a power utility transmission line substantially parallel with said power utility transmission line to an overhead tower comprising a sea-air-resistant insulator with its axial line in a substantially vertical direction.

Full Text

The present invention relates to an apparatus for anchoring a self-support optical cable suspended below a power utility transmission line substantially parallel with that power utility transmission line. As shown in Fig. 1, power utility transmission lines 1 are suspended between overhead towers 2. Sometimes, a self-support optical cable 3 is suspended below the power utility transmission lines 1 substantially parallel with those power utility transmission lines 1. The self-support optical cable 3 is anchored to the overhead towers 2 through metal clamps 4. A self-support optical cable suspended below a power utility transmission line substantially in parallel with the power utility transmission line in the above way is placed in a strong electromagnetic field. A self-support optical cable situated in such a strong electromagnetic field ends up becoming carbonized on its surface, resulting in the problem of "tracking". That is, when the surface of a self-support optical cable situated in a strong electromagnetic field becomes electroconductive due to deposition of long years of atmospheric pollutants or rain, mist, etc. including in particular salt, an electrostatic bond is formed between the power utility transmission line and the self-support optical cable causing a ground current to flow to the surface of the self-support optical cable. If the heat generated by this current dries the surface of the self-support optical cable, the current path is broken and a dry band arc is caused at this portion. Due to the high heat generated by this arc, the surface of the self-support optical cable ends up being carbonized and tracking occurs. This carbonization of a self-support optical cable causes a reduction in the insulating properties of the self-support optical cable and, in some cases, results in the problem of the self-support optical cable burning. As methods of preventing such tracking, consideration has been given to the method of using a material superior in its anti-tracking property as the insulating material of the self-support optical cable, the method of interposing strain insulators between the metal clamps holding the self-support optical cable and the overhead towers to break the path of current flowing to the surface of the self-support optical cable, etc. The method of using a material superior in anti-tracking as the insulating material of the self-support optical cable, however, suffers from the problems of a high cost of the material superior in anti-tracking and the fact that tracking cannot be fully prevented even with a material superior in anti-tracking. Further, the method of interposing strain insulators between the metal clamps holding the self-support optical cable and the overhead towers to break the path of current flowing to the surface of the self-support optical cable can be expected to be effective in breaking the current at all times, but there is the problem that when the strain insulators become fouled or wet, current flows to the surface of the insulators and therefore it becomes impossible to sufficiently block the ground current flowing to the surface of the self-support optical cable. The reason is believed to be that since a strain insulator is disposed substantially horizontally, the overall surface of the strain insulator becomes fouled and easily wet, so a ground current ends up flowing to the surface of the insulator. SUMMARY OF THE INVENTION The present invention was made in consideration of this situation and has as its object to provide a method of anchoring a self-support optical cable which makes a strain insulator resistant to fouling and thereby makes it difficult for ground current to flow to the surface of the insulator. To achieve the above object, the method of anchoring a self-support optical cable according to the present invention is comprised of anchoring a self-support optical cable suspended under a power utility transmission line substantially parallel with the power utility transmission line to an overhead tower using sea-air-resistant insulators and disposing the sea-air-resistant insulators so that they stand with their axial lines in a substantially vertical direction. Preferably, a deep pleat type sea-air-resistant insulator is used as the sea-air-resistant insulator, and the sea-air-resistant insulator is comprised of a holding rod and an insulator body disposed so as to surround the periphery of the holding rod and formed with deep pleats opening toward the bottom. More preferably, two locations of the self-support optical cable in the longitudinal direction are gripped by a pair o£ clamps, these clamps are connected by a link, two locations of the link in the longitudinal direction are held so that the axial line of the sea-air-resistant insulator becomes substantially the vertical direction in each of the pair of sea-air-resistant insulators, and the top end of each of the sea-air-resistant insulators hangs down from the overhead tower. By anchoring the self-support optical cable to an overhead tower using sea-air-resistant insulators and disposing the sea-air-resistant insulators in a substantially vertical direction, it becomes possible to prevent the overall surfaces of the sea-air-resistant insulators from being fouled etc. That is, since a sea-air-resistant insulator is formed with deep pleats, as is well known and, further, the sea-air-resistant insulators are disposed in a substantially vertical direction, the overall surfaces of the sea-air-resistant insulators are not fouled. Even if fouled, the pollutants easily fall off in the vertical direction. Therefore, there is little reduction of the insulation resistance of the sea-air-resistant insulators, there is no flow of ground current to the surface of the sea-air-resistant insulators, and, in the end, it is possible to prevent a flow of current to the surface of the self-support optical cable, so it is possible to efficiently prevent tracking. Note that when sea-air-resistant insulators are used to anchor the self-support optical cable disposed in substantially the horizontal direction, the inside of the deep pleats of the sea-air-resistant insulators become easily fouled and pollutants easily accumulate, so the insulation resistance falls and current easily flows to the sur&ce of tlie self-support optical cable. Accordingly the present invention provides an apparatus for anchoring a self-support optical cable suspended under a power utility transmission line substantially parallel with said power utility transmission line to an overhead tower comprising a sea-air-resistant insulator with its axial line in a substantially vertical direction. These and other objects and features of the present invention will become more apparent from the following description of the preferred embodiments made with reference to the attached drawings, wherein: Fig. 1 is a view explaining the state of suspension of a self-support optical cable; Fig. 2 is a schematic view of key portions showing a method of anchoring a self-support optical cable according to one embodiment of the present invention; Fig. 3 is a semi-cross-sectional view of a sea-air-resistant insulator used in Fig. 2; Fig. 4 is a lateral cross-sectional view of an example of the self-support optical cable shown in Fig. 2; Fig. 5 is a schematic view of key portions showing a method of anchoring a self-support optical cable according to another embodiment of the present invention; Fig. 6 is a schematic view of key portions showing a method of anchoring a self-support optical cable according to still another embodiment of the present invention; and Fig. 7 is a table showing the effects of sea-air-resistant insulators. DESCRIPTION OF THE PREFERRED EMBODIMENTS Below, an explanation will be made of embodiments of the present invention with reference to the drawings. The embodiment shown in Fig. 2 shows the case of application of the present invention to a strain tower. As shown in Fig. 2, metal clamps 4, 4 comprised of aluminium alloy for example are attached to the anchored portions of the self-support optical cable 3 (two locations in the longitudinal direction). The distance L between the anchored portions of the self-support optical cable 3 is not particularly limited, but is for example 200 to 600m. The self-support optical cable 3 is not particularly limited, but for example use is made of one of the cross-sectional structure shown by Fig. 4. The self-support optical cable 3 has four buffer tubes 22 with a number of optical fibers 20 disposed inside them. The circumferences of the buffer tubes 22 are covered by an inner polymer sheath 24. An aramid yarn reinforcing member for example is wound around the outer circumference of the inner polymer sheatli 24. The circumference of this in turn is covered by a cable sheath 28. As shown in Fig. 2, the metal clamps 4, 4 holding the self-support optical ceQ}le are anchored to the overhead tower 2 through connecting fittings 5, 5, sea-air-resistant insulators 6, 6, and a T-member 7. The overall construction of the overhead tower 2 is similar to that shown in Fig. 1. Reference numeral 8 shown in Fig. 2 is a link connecting the front ends of the sea-air-resistant insulators 6, 6. This is used for ensuring the sea-air-resistant insulators 6, 6 are disposed with their axial lines lie in the substantially vertical direction. The sea-air-resistant insulators 6, 6 hold two locations of the link 8 in the longitudinal direction and are disposed so the axial lines of the insulators run in the substantially vertical direction to form an inverted V-configuration. In this embodiment, the sea-air-resistant insulator 6, as shown in Fig. 3, is a deep pleat type sea-air-resistant insulator 6 comprised of a holding rod 10 with a lower end for attachment to the link 8 shown in Fig. 2 and an insulator body 12 formed with deep pleats opening downward. The holding rod 10 is for example comprised of forgeable cast iron, while the insulator body 12 is comprised of porcelain. The insulator body 12 and the top of the holding rod 10 are joined by a filler 16. A mounting fitting 14 is attached to the top of the insulator body 12 through the filler 16. The filler 16 is not particularly limited, but for example use may be made of cement. The mounting fitting 14 is comprised of a similar material as the holding rod 10 and is attached to the T-member 7 shown in Fig. 2. According to this method of anchoring, the axial lines of the insulators 6, 6 become substantially vertical in direction, so the insides of the deep pleats of the sea-air-resistant insulators become resistant to fouling, so there is little reduction of the insulating property and ground current will not travel over the surface of the sea-air-resistant insulators and flow to the overhead tower. Accordingly, since it is possible to prevent the flow of current to the surface of the self-support optical cable, it becomes possible to effectively prevent tracking. Figure 5 is a front view of another embodiment of a method of anchoring a self-support optical cable according to the present invention. The point of difference of this embodiment from the above embodiment is that the sea-air-resistant insulators 6, 6 are hung from two locations of the overhead tower 2 and are disposed so that the axial lines of the insulators form a V-configuration. To make them disposed in this way, the top ends of the insulators 6, 6 are attached to the overhead tower 2 through mounting fittings 7a, 7a. Note that in Fig. 5, portions the same as in Fig. 2 are given the same reference numerals and are not explained further. Even if disposing the sea-air-resistant insulators 6, 6 in a V-configuration hung from two locations of the overhead tower 2, the overall surfaces of the sea-air-resistant insulators are not fouled, so ground current will not be transmitted to the surfaces of the sea-air-resistant insulators and flow to the overhead tower, it becomes possible to prevent current from flowing to the surface of the self-support optical cable, and thereby it becomes possible to effectively prevent tracking. Figure 6 shows still another embodiment of the present invention. The embodiment shown in Fig. 6 has a single insulator 6 hung down from the overhead tower 2 through a mounting fitting 7b and has a link 8 held at the bottom end of the insulator 6. Otherwise, the self-support optical cable 3 is anchored in the same way as the above embodiments. In this embodiment as well, a similar action is exhibited as with the above embodiments, but the above two embodiments are superior from the viewpoint of the stability of the anchored portions. Note that in the above embodiments, the explanation was made of the case of application of the present invention to a strain tower, but the present invention may also be applied in the same way to a dead-end tower. Further, the angle of disposition of the sea-air-resistant insulator with respect to the substantially vertical direction is not particularly limited. It may be an angle which prevents rain etc. from entering the inside of the deep pleats of the sea-air-resistant insulator. Specifically, if the angle between the axial line of the insulator 6 and the vertical direction is within about ±45°, the insulator is substantially vertical in direction and the initial object of the present invention can be achieved. As explained above, the method of anchoring a self-support optical cable according to the present invention comprises anchoring the self-support optical cable to an overhead tower using sea-air-reslstant insulators and disposing the sea-air-resistant insulators in a substantially vertical direction. Accordingly, it is possible to prevent the overall surfaces of the sea-air-resistant insulators from being fouled. No current flows to the surfaces of the sea-air-resistant insulators and, in the end, it is possible to prevent current flowing to the surface of the self-support optical cable, so it is possible to effectively prevent tracking. Next, the present invention will be explained based on more specific examples, but the present invention is not limited to these examples in any way. Example 1 As shown in Fig. 7, use was made of a sea-air-resistant insulator of an outer diameter of 375 mm made by KAWASO TEXCEL Co. Ltd.. It was disposed with its eucial line in the vertical direction and was sprayed in a test spraying chamber by a fouling solution (aqueous solution of 3 wt% table salt and 4 wt% polishing powder) from below to above at an angle of 45 degrees at a rate of 1 mm/cm^ per minute. A used line voltage of 6600V (4000V with ground) was applied for 3 minutes, the leakage current was measured, then the insulation resistance was measured. The results are shown in Fig. 7. AS Shown in Fig. 7, it was confirmed that there is little reduction in the insulation resistance when using a sea-air-resistant insulator. Comparative Example 1 The same procedure was followed as in Example 1 except that use was made of an ordinary insulator made by KAWASO TEXCEL Co. Ltd. of the construction shown in Fig. 7 and having an outer diameter of 235 mm so as to investigate the reduction of the insulation resistance. As shown in Fig. 1, the superiority of the sea-air-resistant insulator of Example 1 was confirmed. Comparative Example 2 The same procedure was followed as in Example 1 except that use was made of an ordinary insulator made by KAWASO TEXCEL Co. Ltd. of the construction shown in Fig. 7 and having an outer diameter of 135 mm so as to investigate the reduction of the insulation resistance. As shown in Fig. 7, the superiority of the sea-air-resistant insulator of Example 1 was confirmed. Experiment The insulation resistance after the elapse of 1.0 hours was compared in two cases: the case of disposing the sea-air-resistant insulator used in Example 1 in the horizontal direction and spraying a fouling solution from the horizontal direction and the case of disposing the sea-air-resistant instilator in the vertical direction and spraying a fouling solution from the horizontal direction. The insulation resistance after 1.0 hours when the sea-air-resistant insulator was disposed in the vertical direction was 900MQ, while the insulation resistance after 1.0 hours when the sea-air-resistant insulator was disposed in the horizontal direction was 35MΩ. It was confirmed that there was considerably less of a reduction of the insulation resistance when it was disposed vertically. That is, the superiority of the present invention was confirmed. WE CLAIM: 1. An apparatus for anchoring a self-support optical cable suspended under a power utility transmission line substantially parallel with said power utility transmission line to an overhead tower comprising a sea-air-resistant insulator with its axial line in a substantially vertical direction. 2. The apparatus as claimed in claim 1 wherein the sea-air-resistant insulator is a deep pleat type comprising of a holding rod and an insulator body disposed so as to surround the periphery of the holding rod and formed with deep pleats opening toward the bottom. 3. The apparatus as claimed in claim 1 or 2, wherein a pair of clamps are provided at two locations to grip said self support optical cable in the longitudinal direction. 4. The apparatus as claimed in claim 3 wherein the clamps are connected by a link, two locations of the link in the longitudinal direction are held for the axial line of the sea-air-resistant insulator to become the substantially vertical direction in each of a pair of sea-air-resistant insulators, and to hold the top end of each of said sea-air-resistant insulators from the overhead tower. 5. An apparatus for anchoring a self-support optical cable substantially as herein described with reference to the accompanying drawings.

Documents:

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1325-mas-1995 description(complete).pdf

1325-mas-1995 drawings.pdf

1325-mas-1995 form-1.pdf

1325-mas-1995 form-26.pdf

1325-mas-1995 form-4.pdf

1325-mas-1995 petition.pdf