Water leakage detection structure

Abstract

To provide a water leakage detection structure that has a simple structure and can specify the position of water leakage.SOLUTION: A water leakage detection structure 10 is provided inside a closure 1 used for a connection part of cables 3a, 3b. A plurality of electric wires are arranged inside the cable 3a that is a first cable, and a plurality of electric wires are arranged inside the cable 3b that is a second cable. A detection line 17 is connected between a first electric wire 7a of the cable 3a and a second electric wire 7b of the cable 3b, and an alarm line 19 is connected between a third electric wire 9a of the cable 3a and a fourth electric wire 9b of the cable 3b. The detection line 17 has a conducting wire 25 and an insulating layer 27 coating the conducting wire 25 from the whole circumference, and the conducting wire 25 is coated and insulated by the insulating layer 27. At least part of the conducting wire 25 inside the alarm line 19 can be brought into conduction with external water content. A twisted pair 23 is arranged to extend along a bottom face at a lower part inside the closure 1.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a water leakage detection structure for closures, junction boxes, and the like (hereinafter referred to as closures, etc.) used in cable joints. [Background technology]

[0002] Conventionally, closures and the like are used to protect connections of, for example, metal communication cables, etc. Such closures and the like are usually designed to be watertight and to prevent water from entering inside.

[0003] However, water may get into the inside of the closure after installation due to deterioration of the packing, uneven installation work, etc. Therefore, it is necessary to detect the intrusion of water into the inside of the closure.

[0004] As a method for detecting water ingress into such a closure, for example, a pair of metal alarm wires is used, and when water is present between the pair of metal alarm wires inside the closure, the metal alarm wires are detected for conduction or a drop in insulation resistance. If the cable has an exterior, it can also be detected by detecting the conduction or drop in insulation resistance between the exterior and the alarm wire. Note that a metal alarm wire is a core wire at least part of which can conduct with external moisture, and is constructed to be suitable for detecting water ingress, for example by covering the conductor to expose a portion of it, or by wrapping a plastic film around the conductor.

[0005] There is also a method in which water detection wires are arranged at different heights on the side of a closure or the like, and terminals that are conductive to the wires are exposed on the outer surface of the closure or the like, and water ingress inside the closure or the like is detected by electrical conductivity between the terminals (for example, Patent Document 1).

[0006] However, the conventional method of detecting flooding using an alarm line detects flooding in one of some closures at a base station, and therefore it is not easy to identify which closure is flooded at the site.

[0007] In addition, the shape of the closures used varies depending on the manufacturer. For this reason, special methods such as providing terminals on the side of the closures cannot be applied to existing closures. In addition, there is a method in which, when a water leak is detected, an alarm is sent to the outside along with the identification number of the closure via an alarm device, but this requires the installation of alarm devices on all closures, which is costly. Furthermore, there are many problems, such as the alarm device not meeting the environmental temperature resistance requirements, the need for a power supply, and short replacement cycles.

[0008] On the other hand, the Murray method and the TDR (Time Domain Reflectometry) method have been proposed as methods for identifying faults in communication cables. The Murray method can accurately detect, for example, a state in which the insulation resistance of a cable has decreased, but the fault cannot be detected unless a shorted alarm line and a sound line with the same conductor resistance are loop-connected at the opposite terminal to be measured. On the other hand, the TDR method can detect short circuits and breaks, but since it measures changes in the characteristic impedance of the transmission line, it cannot detect a decrease in insulation resistance unless the characteristic impedance is a constant value that the measuring instrument can detect over the entire length.

[0009] In response to this, a new cable has been proposed that has the advantages of both the Murray method and the TDR method by arranging the alarm wire and the detection wire close to each other around the circumference of the cable, making it possible to measure the location of the fault point (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2009-75348 A [Non-patent literature]

[0011] [Non-Patent Document 1] "Development of communication cables to improve the efficiency of fault location identification" Railway and Electrical Technology vol.34 No.2 (February 2023) Published by the Japan Railway Electrical Technology Association Summary of the Invention [Problem to be solved by the invention]

[0012] However, it is not easy to replace all existing cables with the cable described in Non-Patent Document 1. Even if the cable described in Non-Patent Document 1 is used, it is difficult to clearly distinguish between an abnormality in the closure or the like and an abnormality in the cable.

[0013] The present invention has been made in consideration of such problems, and has an object to provide a water leakage detection structure that is simple in structure and capable of identifying the location of water leakage. [Means for solving the problem]

[0014] In order to achieve the above-mentioned object, the present invention provides a water leakage detection structure for a closure or connection box used in a cable connection portion, characterized in that inside the closure or connection box, at least a first cable and a second cable consisting of a plurality of electric wires are connected, a detection wire is connected between the first electric wire of the first cable and the second electric wire of the second cable, and an alarm wire is connected between the third electric wire of the first cable and the fourth electric wire of the second cable, the detection wire has an insulating conductor, at least a part of the alarm wire is capable of conducting with external moisture, and the detection wire and the alarm wire are arranged inside the closure or connection box.

[0015] It is desirable that the detection wire and the alarm wire are twisted in a pair.

[0016] It is preferable that the alarm line has the conductor and an insulating layer covering the conductor, and that a part of the insulating layer is removed to expose the conductor inside.

[0017] It is desirable that the detection wire and the alarm wire are arranged to have a length of 100 mm or more, and further desirable that the detection wire and the alarm wire are arranged to have a length of 800 mm or more.

[0018] It is desirable that the detection wire and the alarm wire are inserted into an insulating protective member.

[0019] It is preferable that the protective member is a spiral tube.

[0020] It is desirable that the detection line and the alarm line are arranged in a serpentine manner.

[0021] The detection wire and the alarm wire may be arranged on an insulating plate-like or sheet-like holding member.

[0022] The detection wire and the alarm wire arranged on the holding member may be covered with an insulating covering member, and at least one of the holding member and the covering member may be water permeable.

[0023] The detection wire and the alarm wire are spirally wound around an insulating plate- or sheet-shaped holding member, and the detection wire and the alarm wire arranged on both sides of the holding member are covered with an insulating covering member to form a module, and both the holding member and the covering member may have holes formed therein that allow water to pass through.

[0024] The module may be positioned in contact with a support bracket.

[0025] The support bracket may be grounded.

[0026] According to the present invention, an insulated detection wire and an alarm wire, at least a portion of which is conductive with external moisture, are connected close to each other within a closure or the like, and are arranged inside the closure or the like. By arranging in this manner, it is possible to detect water leakage within the closure or the like using the same principle as the cable described in Non-Patent Document 1 mentioned above. In this case, there is no need to use a special cable, and the location of the leakage can be identified at the base station, so it is possible to know which closure or the like the leakage occurred in.

[0027] In addition, by twisting the detection line and alarm line together, the distance between the detection line and the alarm line can be more reliably kept approximately constant, resulting in a characteristic impedance that allows for detection of water intrusion; furthermore, by connecting the detection line to the pair of wires within the cable, the characteristic impedance within the transmission path is also constant, making it possible to perform TDR measurements with high accuracy.

[0028] Furthermore, the alarm wire can be easily formed by removing a portion of the insulating layer covering the conductor of the insulated conductor wire to expose the internal conductor.

[0029] In addition, the longer the length of the detection line and alarm line that are submerged in water during a leak, the more accurate the leak detection. For this reason, it is desirable for the detection line and alarm line to be 100 mm or longer, and by making them 800 mm or longer, the accuracy of leak detection can be improved.

[0030] By inserting the detection wire and the alarm wire into an insulating protective member, it is possible to prevent, for example, the alarm wire from coming into contact with metal fittings inside a closure or the like, causing a false detection.

[0031] If such a protective member is a spiral tube, water can be introduced into the inside through the slits, so that the protective member can be prevented from interfering with water leakage detection.

[0032] In this case, by arranging the detection line and the alarm line in a meandering manner, the slits can be opened reliably at the meandering parts, so that water leakage can be detected with high accuracy. For example, if the detection line and the alarm line are rolled up into a ring, as in the conventional case of storing excess cable length, the curvature is smaller than in the case of a meandering arrangement, and the opening of the slits in the spiral tube is smaller. This prevents water from entering the inside of the protective member, which causes a decrease in detection accuracy. In contrast, by arranging the detection line and the alarm line in a meandering manner, water leakage can be detected with high accuracy.

[0033] The detection wire and the alarm wire can also be arranged on an insulating plate-like or sheet-like holding member. This can improve the reproducibility of the arrangement of the detection wire and the alarm wire. For example, if an operator arranges the detection wire and the alarm wire at the bottom of a closure or the like in a zigzag manner, the curvature and size of the zigzag may vary depending on the operator, which may lead to false detection due to contact with other members.

[0034] In this case, the detection wire and the alarm wire arranged on the holding member are covered with an insulating covering member, so that contact with other metal fittings, etc. can be suppressed. In this case, if at least one of the holding member and the covering member is water permeable, the detection accuracy can be maintained.

[0035] Similarly, by spirally winding the detection wire and alarm wire (twisted pair wire) around the holding member, it is possible to easily arrange long twisted pair wires at a high density. Furthermore, by providing holes in the holding member and the covering member, it is possible to ensure that water comes into contact with the detection wire when water enters. In this way, by modularizing, it is possible to easily arrange the detection wire and alarm wire within the closure. Furthermore, by modularizing, it is possible to minimize sensitivity variations due to manufacturing variations.

[0036] In addition, by placing the module in contact with the support metal fitting, the detection wire can be brought closer to the support metal fitting, which increases the change in impedance between the support metal fitting and the detection wire, thereby increasing the sensitivity of the TDR waveform. In addition, by grounding the support metal fitting, TDR measurements can be performed with stable sensitivity. Effect of the Invention

[0037] According to the present invention, it is possible to provide a water leakage detection structure that has a simple structure and is capable of identifying the location of water leakage. [Brief description of the drawings]

[0038] [Figure 1] 1(a) is a plan view of the closure 1, and FIG. 1(b) is a cross-sectional view of the cables 3a and 3b. [Diagram 2] 4A is a diagram showing the inside of the closure 1 with one sleeve 5 removed, and FIG. 4B is a diagram showing the shape of the twisted pair wire 23. FIG. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. 2 is a diagram showing a part of the state in which the twisted pair wire 23 is inserted into the spiral tube 31. [Figure 6] 1A is a diagram showing a state in which the twisted pair wires 23 are arranged on a holding member 35, and FIG. 1B is a diagram showing a state in which a covering member 39 is further arranged in addition to the state shown in FIG. [Figure 7] 1A is a diagram showing a state in which the twisted pair wires 23 are wound in a spiral shape around a holding member 35a, and FIG. 1B is a diagram showing a module 40 in which a covering member 39a is further arranged in addition to the module shown in FIG. [Figure 8] 1(a) and (b) are diagrams showing the arrangement of modules 40 in a closure 1. FIG. [Figure 9] FIG. 1 shows the results of TDR measurements of various samples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] The closure 1 and the like according to an embodiment of the present invention will be described below. Fig. 1(a) is an external plan view showing the closure 1, and Fig. 1(b) is a cross-sectional view of cables 3a and 3b. Fig. 2(a) is a schematic plan view showing a water leakage detection structure 10 inside the closure 1 in an open state with the cover (one sleeve 5) removed. Note that although the following description will be directed to the closure 1, the same applies to other connection boxes that house connections between cables.

[0040] The water leakage detection structure 10 is provided inside a closure 1 used for connecting the cables 3a and 3b. In the illustrated example, two cables are connected to the closure 1, but the number of cables to be connected is not particularly limited.

[0041] A plurality of cables 3a, 3b are connected, and the connection between the cables 3a, 3b is housed inside the closure 1. As shown in FIG. 1(b), a plurality of electric wires are arranged inside the cable 3a, which is a first cable, and a plurality of electric wires are arranged inside the cable 3b, which is a second cable. In the illustrated example, five quad-twisted electric wires are housed in each cable. The cross-sectional shape of the cables 3a, 3b is not limited to the illustrated example, and does not need to be a special structure (for example, a cable in which a detection wire and an alarm wire are arranged close to each other as in Non-Patent Document 1).

[0042] Here, among the multiple electric wires housed in the cable 3a, a specific one is referred to as the first electric wire 7a, another specific one is referred to as the third electric wire 9a, and the remaining electric wires are referred to as the electric wire 11a. Similarly, among the multiple electric wires housed in the cable 3b, a specific one is referred to as the second electric wire 7b, another specific one is referred to as the fourth electric wire 9b, and the remaining electric wires are referred to as the electric wire 11b. The first electric wire 7a, the second electric wire 7b, the third electric wire 9a, and the fourth electric wire 9b are not used for communication purposes, etc., but are used for water leakage detection. On the other hand, the electric wires 11a and 11b are used for their respective purposes such as communication, etc.

[0043] The closure 1 is formed into a generally cylindrical shape by combining upper and lower sleeves 5. A packing or the like (not shown) is provided on the mating surfaces of the sleeves 5 to prevent water or the like from entering through the gaps between the sleeves 5. The sleeve 5 is made of a known sleeve material such as resin or metal.

[0044] As shown in Fig. 2(a), end plates 13 are provided on both ends (in the direction in which the cables 3a, 3b are introduced and led out) of the generally cylindrical closure 1. The end plates 13 are, for example, cylindrical rubber members, and have a hole or a thin-walled portion formed in the center through which the cables 3a, 3b are inserted. The outer periphery of the end plates 13 is in close contact with the mating surface of the sleeve 5. Therefore, the end plates 13 are sealed at the portions in contact with the cables 3a, 3b and the sleeve 5, and the closure 1 is kept watertight.

[0045] Inside the closure 1, the electric wires 11a, 11b are connected at a connection portion 15. In the illustrated example, the electric wires 11a, 11b and the connection portion 15 are arranged in a straight line, but inside the closure 1, the electric wires 11a, 11b are arranged, for example, above the support bracket 21 with an excess length.

[0046] 2(b), the first electric wire 7a is connected to the detection wire 17 at the connection portion 15a, and the second electric wire 7b is connected to the detection wire 17 at the connection portion 15c. The third electric wire 9a is connected to the alarm wire 19 at the connection portion 15b, and the fourth electric wire 9b is connected to the alarm wire 19 at the connection portion 15d. That is, the detection wire 17 is connected between the first electric wire 7a of the cable 3a and the second electric wire 7b of the cable 3b, and the alarm wire 19 is connected between the third electric wire 9a of the cable 3a and the fourth electric wire 9b of the cable 3b.

[0047] The detection wire 17 and the alarm wire 19 are twisted in a pair. Here, the detection wire 17 and the alarm wire 19 twisted in a pair are referred to as a twisted pair 23. As shown in Figures 2(a) and 2(b), the twisted pair 23 is arranged so as to meander in a plan view.

[0048] 3 is a diagram showing a cross section of the twisted pair wire 23. The detection wire 17 has a conductor 25 and an insulating layer 27 that covers the entire conductor 25, and the conductor 25 is insulated with the insulating layer 27. The alarm wire 19 has a conductor 25 and an insulating layer 27 that covers the conductor 25, but a part of the insulating layer 27 is cut away to expose the internal conductor 25. That is, in the alarm wire 19, at least a part of the internal conductor 25 can be conductive to external moisture. Note that, even if a part of the insulating layer 27 is not completely cut as shown in the figure, a slit reaching the conductor 25 may be formed in the insulating layer 27, or a gap may be formed in a film winding.

[0049] 4 is a vertical cross-sectional view of the closure 1. The twisted pair 23 is arranged such that the connection parts 15a, 15b, 15c, and 15d at both ends are disposed at an upper position inside the closure 1, and the twisted pair 23 is disposed along the bottom surface at the lower part inside the closure 1. For example, when water 29 enters the closure 1 due to a water leak, the twisted pair 23 is immersed in the water 29. Meanwhile, by disposing each connection part above the closure 1, it is possible to suppress erroneous detection due to a small amount of moisture, such as condensation, adhering to the connection parts.

[0050] At this time, the insulation resistance of the alarm wire 19 changes due to the influence of water, making it possible to detect an abnormality. In the present invention, the alarm wire 19 and the detection wire 17, which is a good wire (a wire that is always insulated), are twisted together and kept at a constant distance, thereby making it possible to keep the characteristic impedance between the measurement lines low. In this way, by using the alarm wire 19 and the detection wire 17, it becomes possible to perform measurement using the Murray method, and since the characteristic impedance between the measurement lines can be kept low, the TDR method can also be used. Therefore, when there is a water leak, not only can the abnormality be detected, but its location can also be determined.

[0051] In order to improve the accuracy of detecting an abnormality, for example, the TDR waveform must have a clear step in the waveform when water leaks. In this case, the detection accuracy improves as the length of the twisted pair 23 immersed in the water 29 increases. For this reason, the twisted pair 23 is arranged in a serpentine manner as described above. For example, the length of the twisted pair 23 arranged at the bottom of the closure 1 is preferably 100 m or more, and more preferably 800 mm or more.

[0052] As described above, a part of the insulating layer 27 of the alarm wire 19 is cut away. Therefore, there is a risk of contact with, for example, the support metal fitting 21 inside the closure 1. For this reason, it is desirable to insert the twisted pair wire 23 into an insulating protective member. Figure 5 shows an example in which a spiral tube 31 is used as the protective member.

[0053] The spiral tube 31 has slits 33 formed in a helical shape in the longitudinal direction. When the spiral tube 31 is straightened, the slits are closed, although this depends on the type of the spiral tube 31. In this case, water is less likely to infiltrate through the slits 33, which may cause the twisted pair wires 23 to float up in the event of a water leak.

[0054] As described above, the excess length of the electric wire is generally rolled up into a plurality of turns and housed in a closure or the like. However, if the curvature is small, the opening of the slit 33 is not sufficient, which may prevent water from entering the inside, and may deteriorate the detection accuracy. For this reason, in this embodiment, it is preferable to meander the twisted pair wire 23 while it is inserted into the spiral tube 31. By meandering the twisted pair wire 23 (spiral tube 31) in this way, it is possible to repeatedly bend the twisted pair wire 23 with a larger curvature, so that the slit 33 can be opened efficiently to introduce water into the inside of the spiral tube 31. In addition, a spiral tube 31 with the slit 33 spaced apart in advance may be used so that the opening of the slit 33 of the spiral tube 31 is not sufficient to prevent water from entering the inside, and in that case, meandering wiring is not necessary. In this way, the detection accuracy can be improved.

[0055] The meandering arrangement of the twisted pairs 23 may be a cause of variation depending on the worker. For this reason, as shown in Fig. 6(a), the twisted pairs 23 (spiral tube is not shown) may be arranged on a holding member 35. The holding member 35 is an insulating plate-like or sheet-like member. For example, a pin-shaped guide 37 is arranged on the holding member 35 at a predetermined position, and the twisted pairs 23 can be hooked on this guide 37 and meandered, thereby enabling a stable arrangement of the twisted pairs 23 with good reproducibility.

[0056] It should be noted that the pin-shaped guide 37 is not necessarily required, and other structures may be used as long as the meandering shape is known. In the illustrated example, the twisted pair wires 23 are arranged only on one side of the holding member 35, but they may be made to meander across both sides.

[0057] 6(b), the twisted pairs 23 arranged on the holding member 35 may be covered with an insulating covering member 39. In this case, it is desirable that at least one of the holding member 35 or the covering member 39 is water permeable. For example, by using a nonwoven fabric or the like as the covering member 39, it is possible to ensure the insulation of the twisted pairs 23 while allowing water to penetrate. In this case, the spiral tube 31 may be disposed only in the portion exposed from the holding member 35 or the covering member 39.

[0058] Moreover, Fig. 7(a) is a diagram showing another method. The holding member 35a is an insulating plate-like or sheet-like member, and it is desirable that a large number of holes (not shown) are formed on the entire surface. As shown in Fig. 7(a), the twisted pairs 23 are wound in a spiral shape around the outer periphery of the holding member 35a. That is, the twisted pairs 23 are arranged on both sides of the holding member 35a at a predetermined interval so as not to contact each other.

[0059] From this state, as shown in Fig. 7(b), covering members 39a larger in size than the holding member 35a are placed on both sides of the holding member 35a around which the twisted pair wires 23 are wound. That is, the pair of covering members 39a sandwich and cover the holding member 35a and the twisted pair wires 23. The covering member 39a is an insulating plate-like or sheet-like member similar to the holding member 35a, and has a large number of holes (not shown) formed on the entire surface. For example, both the holding member 35a and the covering member 39a can be made of a resin plate.

[0060] The front and back covering members 39a are fixed by, for example, an insulating fixing member.

[0061] 8(a) is a diagram showing an example of the arrangement of the module 40. As described above, electric wires such as communication lines are arranged on the support bracket 21, but in the following figures, illustration of the communication lines etc. is omitted. The support bracket 21 is grounded. For example, if there is an earth wire inserted inside the cable, it may be connected to the earth wire for grounding.

[0062] As shown in Fig. 8(a), the module 40 is placed above the support metal fitting 21. In this case, the communication lines and the like are placed on the module 40. In other words, it is desirable to place the module 40 and the support metal fitting 21 so that they are in contact with each other, and to bring the twisted pair wire 23 and the support metal fitting 21 close to each other. In this way, a large change in impedance occurs between the twisted pair wire 23 and the support metal fitting 21, and the sensitivity of the TDR waveform can be increased. In addition, since the twisted pair wire 23 can be wired close to the support metal fitting 21, variation can also be reduced.

[0063] 8(b), the module 40 may be disposed below the support metal fitting 21. Even in this case, it is preferable to dispose the module 40 and the support metal fitting 21 so that they are in contact with each other, and to bring the twisted pair wire 23 close to the support metal fitting 21. Even in this case, high sensitivity can be obtained by bringing the support metal fitting 21 and the twisted pair wire 23 close to each other.

[0064] In the example shown in Figures 8(a) and 8(b), the module 40 (twisted wire pair 23) is arranged so as to contact the support metal fitting 21, and therefore the module 40 (twisted wire pair 23) is arranged at a position away from the bottom surface of the closure. For this reason, there is a risk that water intrusion cannot be detected when only a small amount of water has entered (when the water level is low). In this case, an additional detection wire may be further added and arranged on the bottom surface of the closure to perform initial detection, and the module 40 may be used to perform accurate detection when the water level has risen to a certain level.

[0065] According to this embodiment, the alarm wire 19, whose insulation resistance changes when water intrudes, and the detection wire 17, which is always a good wire, are arranged inside the closure 1 so that the distance between the two wires is approximately constant, so that the location of the abnormality can be grasped by the Murray method as well as detection by the TDR method. Therefore, by monitoring from a base station, for example, it is possible to grasp the location (which closure, etc.) where the abnormality occurred.

[0066] For example, the cable described in Non-Patent Document 1 states that its position can be determined with an error of about 100 m. However, since the connection points (closures, etc.) between cables are often placed at intervals of 100 m or more, it is possible to easily identify closures that have abnormalities.

[0067] Furthermore, instead of using a special cable as in Non-Patent Document 1, an alarm wire 19 and a detection wire 17 are placed inside the closure 1 between the connections between the electric wires, so that it can be easily applied to existing cables.

[0068] Furthermore, by inserting the twisted pair wire 23 into the spiral tube 31 in the closure 1, it is possible to prevent the alarm wire 19 from coming into contact with metal fittings inside the closure 1 and causing a short circuit. At this time, by arranging the twisted pair wire 23 in a serpentine manner, the slits 33 in the spiral tube 31 can be opened to allow water to enter. A spiral tube 31 with a large gap between the slits 33 may be used, and water can be allowed to enter even without serpentine wiring.

[0069] Furthermore, by fixing the twisted pairs 23 to the holding member 35, variation due to the worker is suppressed, and the twisted pairs 23 can be arranged inside the closure 1 under approximately constant conditions. For example, when trying to arrange the twisted pairs 23 in a serpentine manner, it is difficult to make the serpentine shape constant, but by using the holding member 35, the twisted pairs 23 can be arranged in a desired shape, for example, by the guide 37. Furthermore, since the twisted pairs 23 can be fixed to the holding member 35 in advance, work on site can be facilitated.

[0070] Furthermore, by spirally winding the twisted pairs 23 around the holding member 35a to form the module 40, it is possible to easily arrange a longer twisted pairs 23. In this case, insulation of the twisted pairs 23 from the outside can be ensured by covering the twisted pairs 23 with an insulating covering member 39a. Furthermore, since holes are formed over substantially the entire surfaces of the holding member 35a and the covering member 39a, water can be efficiently brought into contact with the twisted pairs 23.

[0071] Moreover, modularizing the twisted pair 23 makes it easier to place it in the closure. Also, by placing the module 40 in contact with the support metal fitting 21, the twisted pair 23 can be brought closer to the support metal fitting 21, and the impedance change between the support metal fittings 21 can be increased, thereby increasing the sensitivity of the TDR waveform.

[0072] In the above-described embodiment, one twisted pair 23 (one pair of alarm wire 19 and detection wire 17) is used, but two twisted pairs 23 may be used. Also, the first electric wire 7a and the third electric wire 9a connected to the alarm wire 19 and the detection wire 17 are arranged inside the same cable 3a, but electric wires of separate cables may be used. Similarly, the second electric wire 7b and the fourth electric wire 9b connected to the alarm wire 19 and the detection wire 17 are arranged inside the same cable 3b, but electric wires of separate cables may be used. When electric wires of separate cables are used, at least position detection by the Murray method is possible.

[0073] Even in this case, the multiple cables connected from one side (the cables on the left side of closure 1 in FIG. 1(a)) are all referred to as first cables, and the multiple cables connected from the other side (the cables on the right side of closure 1 in FIG. 1(a)) are all referred to as second cables. In other words, in this invention, a "first cable" does not refer to one specific cable, but is a general term for one or more cables connected from one side of closure 1, and a "second cable" does not refer to one specific cable, but is a general term for one or more cables connected from the other side of closure 1. EXAMPLES

[0074] TDR measurements were performed by placing a twisted pair of a specified length 3000 m from one end of the 7500 m cable. The twisted pairs were 0.8 m long, 6 m long, and a module (corresponding to module 40 in Figure 7(b)) made of a 6 m twisted pair. No spiral tube was used, but the twisted pairs were placed so that they would not come into contact with each other.

[0075] In modularizing the device, the holding member and covering were both made of plastic, and a plate material with holes on all sides to allow water to pass through in the event of flooding was used. Approximately 6 m of twisted pair wire was wound around a holding member 450 mm long, 100 mm wide, and 10 mm thick, which was then covered with a covering member, and the holding member and covering member were fixed together with an insulating member.

[0076] TDR measurements were performed on each of the above samples, one placed on a grounded support metal fitting, and the other placed at a different location from the support metal fitting. The module was placed so that it was in contact with the support metal fitting, but the 0.8m and 6m samples were not in direct contact with the support metal fitting. The results are shown in Figure 9.

[0077] The vertical axis of each graph is the strength of the reflected wave (reflection coefficient) according to the change in impedance, and the horizontal axis corresponds to the distance. The change in the curve (the concave part indicated by the arrow in the graph) is the part detected by the TDR (i.e., approximately 3000 m). The larger the shape of this change, the higher the sensitivity.

[0078] Compared to the 0.8m sample, the 6m sample (including the 6m module) was able to measure with higher sensitivity. This is thought to be because the length in contact with water is longer. Also, the sensitivity was better when the sample was placed closer to the support bracket than when the sample was placed away from the support bracket. This is thought to be because there was a large change in impedance between the twisted pair and the support bracket.

[0079] In addition, when comparing 6m twisted pair wires, the sensitivity was slightly better when modularized compared to when not modularized. This is thought to be because modularization allowed the twisted pair wires to be positioned more stably and closely spaced from the support brackets.

[0080] Although the embodiment of the present invention has been described above with reference to the attached drawings, the technical scope of the present invention is not limited to the above-described embodiment. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention. [Explanation of symbols]

[0081] 1. Closure 3a, 3b………Cable 5. Sleeve 7a……1st electric wire 7b……Second electric wire 9a……3rd electric wire 9b……4th electric wire 10...Leak detection structure 11a, 11b……Electric wire 13……End plate 15, 15a, 15b, 15c, 15d... Connection parts 17....Detection line 19....Alarm line 21...Support bracket 23...Twisted pair wire 25……Conducting wire 27....Insulating layer 29……Water 31...Spiral tube 33………Slit 35, 35a...Holding member 37………Guide 39, 39a... Covering member 40………Module

Claims

1. A water leakage detection structure for a closure or a joint box used in a cable joint, comprising: At least a first cable and a second cable, each of which is made up of a plurality of electric wires, are connected inside the closure or the connection box; a detection line is connected between the first electric wire of the first cable and the second electric wire of the second cable, and an alarm line is connected between the third electric wire of the first cable and the fourth electric wire of the second cable; The detection wire has an insulating coating on a conductor, and the alarm wire has at least a part of the conductor that is conductive to external moisture; A water leakage detection structure, characterized in that the detection line and the alarm line are arranged inside the closure or junction box.

2. 2. The water leakage detection structure according to claim 1, wherein the detection wire and the alarm wire are twisted in a pair.

3. 2. The water leakage detection structure according to claim 1, wherein the alarm line comprises the conductor and an insulating layer covering the conductor, and a part of the insulating layer is removed to expose the conductor inside.

4. 2. The water leakage detection structure according to claim 1, wherein the detection wire and the alarm wire are disposed to have a length of 100 mm or more.

5. 2. The water leakage detection structure according to claim 1, wherein the detection line and the alarm line are disposed to have a length of 800 mm or more.

6. 2. The water leakage detection structure according to claim 1, wherein the detection wire and the alarm wire are inserted into an insulating protective member.

7. 7. The water leakage detection structure according to claim 6, wherein the protective member is a spiral tube.

8. 8. The water leakage detection structure according to claim 7, wherein the detection line and the alarm line are arranged in a serpentine manner.

9. 2. The water leakage detection structure according to claim 1, wherein the detection wire and the alarm wire are arranged on an insulating plate-like or sheet-like holding member.

10. The water leakage detection structure according to claim 9, characterized in that the detection wire and the alarm wire arranged on the retaining member are covered with an insulating covering member, and at least one of the retaining member or the covering member is water permeable.

11. the detection wire and the alarm wire are wound in a spiral shape around an insulating plate-like or sheet-like holding member, and the detection wire and the alarm wire arranged on both sides of the holding member are covered with an insulating covering member to form a module; 2. The water leakage detection structure according to claim 1, wherein the holding member and the covering member are both formed with holes through which water can pass.

12. The water leakage detection structure according to claim 11, wherein the module is arranged to contact a support bracket.

13. 13. The water leakage detection structure according to claim 12, wherein the support metal fitting is grounded.

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