Gas leakage site detection method and restoration method

Abstract

Helium gas is supplied to each metal cable 200 routed along a plurality of routes from a communication building 300. After the helium gas is supplied, sound is produced by air column vibration in one or more manholes in which the metal cables 200 are installed. Gas leakage sites are identified, in the order of increasing distance from the communication building 300, on the basis of a change in sound from a steady state. The detected gas leakage sites are shown on a facility map, and a gas leakage site to be restored is determined.

Description

Gas leak detection and recovery methods

[0001] The present disclosure relates to a gas leak location detection method and a recovery method.

[0002] Cables are laid above and below ground to provide communication services such as telephone and internet. There are two types of cables: metal cables, which use copper wires, and optical cables, which use optical fibers. If water gets inside a metal cable, the copper wires corrode, adversely affecting communication. Metal cables laid in manholes and conduits, which are underground facilities, are prone to water getting inside the cable because water tends to accumulate in these facilities. Dry air is continuously sent from the communication building into the metal cable, and the gas pressure prevents water from getting inside the cable.

[0003] Gas leaks increase the risk of flooding, so immediate repairs are necessary. Gas can leak from the part of the closure that covers the cable connection point installed in the manhole where it grips the cable or from the joint of the closure. Gas can also leak when the outer sheath of the cable inside the conduit is damaged.

[0004] A pressure transmitter is placed inside the closure to monitor the gas pressure inside the metal cable and detect gas leaks. Because pressure transmitters are not installed in all closures, pressure measurements at at least four points are used to analyze the pressure distribution and estimate the gas leak point (Non-Patent Document 1).

[0005] "Technical Lecture: Underground Metal Cable Gas Leak Detection Technology," Raisers, Telecommunications Association, July 10, 2017, Vol. 65, No. 4, pp. 19-21. Hiroshi Watanabe and seven others, "Remote Optical Path Switching Nodes Operating in Multistage Loop-Type Optical Access Networks," 2021 IEICE Communications Society Conference, BK-2-3, 2021.

[0006] Conventional methods sometimes fail to pinpoint the exact location of a gas leak. In such cases, the dry air sent into the metal cable is switched to helium gas, and workers then go to the manhole suspected to be the leak point and nearby manholes, where they use a helium gas detection device to measure the presence or absence of helium gas, thereby pinpointing the leak point. However, this sometimes requires entering multiple manholes, which poses an issue of inefficient maintenance.

[0007] Furthermore, when multiple affected areas are affected by a large-scale disaster, there is a problem in that metal cable restoration work cannot be carried out efficiently.

[0008] The present disclosure has been made in view of the above, and aims to more accurately identify gas leakage points in metal cables.

[0009] A gas leak detection method according to one aspect of the present disclosure supplies helium gas from a work base to each of multiple routes of metal cables, and after the helium gas is supplied, generates sound by vibrating an air column in at least one manhole in which the metal cables are laid, and identifies gas leak locations in order of proximity to the work base based on changes in the sound from steady state.

[0010] A restoration method according to one aspect of the present disclosure displays gas leak locations detected by the gas leak location detection method on an equipment map, and determines gas leak locations to be restored.

[0011] According to the present disclosure, gas leakage points in metal cables can be identified more accurately.

[0012] FIG. 1 is a diagram showing an example of the configuration of a detection device. FIG. 2 is a diagram showing an example of the configuration of a gas leak point detection system. FIG. 3 is a flowchart showing an example of a process for detecting a gas leak point. FIG. 4 is a flowchart showing an example of a process for detecting a gas leak point. FIG. 5 is a diagram showing an example of the laying of an optical cable and a metal cable. FIG. 6 is a diagram showing an example of a state in which a failure has occurred in a metal cable. FIG. 7 is a diagram showing an example of a state in which a failure has occurred in a metal cable. FIG. 8 is a diagram showing an example of a state in which multiple damaged locations have occurred. FIG. 9 is a diagram showing an example of repeated identification and restoration of damaged locations. FIG. 10 is a flowchart showing an example of a restoration method. FIG. 11 is a diagram showing an example of an equipment map showing damaged locations. FIG. 12A is a diagram showing an example of information stored in a database. FIG. 12B is a diagram showing an example of information stored in the database. FIG. 12C is a diagram showing an example of information stored in the database. FIG. 12D is a diagram showing an example of information stored in the database.

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0014] An example of the configuration of a detection device 10 for detecting gas leaks in a metal cable will be described with reference to Fig. 1. The detection device 10 shown in the figure includes a remote control function 11, a sound generating unit 12, and a sensor 13.

[0015] The remote control function 11 includes a photoelectric conversion element 111, a power storage unit 112, and a control unit 113. The photoelectric conversion element 111 is connected to the optical cable 100 for power supply light, inputs the power supply light, and converts the power supply light into electrical energy. The power storage unit 112 is, for example, a capacitor, and stores the electrical energy photoelectrically converted by the photoelectric conversion element 111. The control unit 113 operates using the electrical energy stored in the power storage unit 112.

[0016] The optical power supply is transmitted from an in-house node in a communications building via an optical cable 100. The in-house node remotely controls a remote control function 11 by superimposing a control signal on the optical power supply. The remote control function 11 receives the control signal superimposed on the optical power supply, generates sound in a sound generator 12 in accordance with the control signal, and collects the sound generated by the sound generator 12 with a sensor 13. The remote control function 11 can reflect a portion of the optical power supply, superimpose data on the reflected optical signal, and transmit the data to the in-house node.

[0017] The sound generating unit 12 is a mechanism that generates sound by vibrating an air column. The sound generating unit 12 pushes out air that has accumulated inside the hollow body. The pushed-out air vibrates as it is discharged from the hole in the body, generating sound. When the area around the detection device 10 is filled with helium gas, the sound generated by the sound generating unit 12 will be higher-pitched than in the air.

[0018] The sensor 13 collects the sound generated by the sound generator 12. The sensor 13 compares the generated sound with the steady-state sound in the air, and if the sound becomes louder, it can determine that helium gas is leaking. The detection device 10 may analyze the sound data obtained by collecting the sound and determine whether or not helium gas is leaking, or may transmit the sound data to an in-station node.

[0019] The remote optical path switching node described in Non-Patent Document 2 may be equipped with a sound generator 12 and a sensor 13 and used as the detection device 10. The remote optical path switching node is placed at the connection point (for example, inside a manhole) of loops in a multistage loop configuration, and is a device that switches the core fibers between the loops. The remote optical path switching node has an optical cross-connect function, a port monitoring function, and a remote control function.

[0020] An example of the configuration of the gas leak location detection system of this embodiment will be described with reference to Fig. 2. In the gas leak location detection system of this embodiment, the above-mentioned detection device 10 is installed in a manhole in addition to an existing remote gas monitoring system.

[0021] First, an existing remote gas monitoring system will be described. Metal cable 200 is laid in underground pipe 210 and manhole 220. The connection points of metal cable 200 are protected by closure 230. Dry air is supplied to the inside of metal cable 200 from dry air supply device 310 installed in communication building 300. A pressure transmitter is installed in closure 230 to remotely measure gas pressure and obtain a pressure distribution map of gas pressure inside metal cable 200. When a gas leak is detected, the gas leak point can be estimated by analyzing the pressure distribution map.

[0022] The detection device 10 is installed in the upper part of each manhole 220. An optical fiber cable 100 for power supply is connected to the detection device 10. The optical fiber cable 100 is connected to an in-station node 110 and laid in the conduit 210 and the manhole 220. The detection devices 10 are connected in series to the optical fiber cable 100. A plurality of optical fibers 100 may be installed and the detection devices 10 may be connected in parallel.

[0023] The in-station node 110 is installed in the communication building 300. The in-station node 110 supplies optical power, transmits control signals, and receives data from the detection devices 10. Optical power is supplied to the detection devices 10 in a time-division manner. For example, each detection device 10 is equipped with an optical channel selector, and switches between supplying power to itself or to a subsequent detection device 10 according to a control signal from the in-station node 110.

[0024] When a drop in gas pressure is detected by the existing remote gas monitoring system, the gas being supplied to the metal cable 200 is switched from dry air to helium gas. The helium gas is sent to the metal cable 200 from a helium gas supply device 320 in the communications building 300.

[0025] In a manhole 220 from which gas is leaking, helium gas accumulates in the upper part of the manhole 220. The terminal 120 controls the in-station node 110 to cause each of the detection devices 10 to execute a process for detecting a gas leak. The detection devices 10 generate sound and collect the generated sound. The manhole from which the gas leak has occurred is identified based on a change in the sound compared to normal times. The terminal 120 may receive a notification that a gas leak has been detected by the detection devices 10, or may receive sound data from each of the detection devices 10 and analyze the sound data to identify the gas leak point.

[0026] An example of the flow of processing in the gas leak location detection method will be described with reference to the flowchart in Fig. 3. The processing shown in Fig. 3 is processing that is performed after a gas leak is detected by an existing remote gas monitoring system.

[0027] In step S11, the operator switches the gas being sent from the communications building 300 to the metal cable 200 from dry air to helium gas. Helium gas leaks from the gas leak point, manhole 220. Because helium gas is lighter than air, it accumulates in the upper part of the manhole 220.

[0028] Some time after the helium gas is sent out, in step S12, the operator instructs the detection device 10 to generate and collect sound. Specifically, the operator controls the in-station node 110 using the terminal 120 to transmit a control signal to each of the multiple detection devices 10 along the route of the metal cable 200 where a gas leak has been detected, to generate and collect sound. The control signal may be transmitted only to the detection devices 10 installed in one or more manholes 220 close to the gas leak point estimated by the conventional method, or to all detection devices 10 along the route of the metal cable 200. The in-station node 110 superimposes the control signal on the power feed light and transmits the control signal to the detection device 10. For example, the power feed light on which the control signal is superimposed is transmitted to each detection device 10 in a time-division manner.

[0029] When the detection device 10 receives the control signal, the sound generation unit 12 generates a sound, and the sound generated by the sound generation unit 12 is collected by the sensor 13. The sound data obtained by the sensor 13 is stored in a memory provided in the detection device 10.

[0030] Each detection device 10 analyzes the sound data in step S13 and compares the sound data with steady-state sound data in step S14 to determine whether the pitch of the sound has changed. When the sound generation unit 12 generates sound in helium gas, the sound becomes higher-pitched than sound generated in air due to the air column vibration effect. The detection device 10 compares the waveform of the collected sound with the waveform of sound generated in air at steady state to determine whether the waveforms differ. The detection device 10 collects sound in air at steady state in advance and stores the sound data in air at steady state in memory. The detection device 10 may determine the frequency of the collected sound and compare it with the frequency of sound in air at steady state to determine whether the pitch of the sound has changed.

[0031] In step S15, the detection device 10, which has determined that the pitch of the sound has changed, notifies the in-station node 110 that gas is leaking. The detection device 10 reflects a portion of the optical power supply and superimposes a signal notifying of the gas leak on the reflected optical signal. The in-station node 110 can identify the gas leak point by receiving the signal from the detection device 10.

[0032] If the gas leak point is found inside the pipeline 210, a gas leak search using helium gas is carried out using the method described in Non-Patent Document 1.

[0033] Another example of the process flow of the gas leak location detection method will be described with reference to the flowchart of Fig. 4. This process differs from the process of Fig. 3 in that sound data is analyzed by the terminal 120. The process shown in Fig. 4 is performed after a gas leak is detected by an existing remote gas monitoring system.

[0034] In steps S21 and S22, the operator switches the gas being sent from the communications building 300 to the metal cable 200 from dry air to helium gas, and instructs the detection device 10 to generate and collect sound. Steps S21 and S22 are similar to the processes in steps S11 and S12 in FIG. 3 .

[0035] Each of the detection devices 10 records the collected sound in step S23, and transmits the recorded sound data to the in-station node 110 in step S24. The terminal 120 accumulates the sound data received by the in-station node 110 from each of the detection devices 10. For example, when the in-station node 110 supplies power feed light to each of the detection devices 10 in a time-sharing manner, the terminal 120 supplies power feed light with a control signal superimposed to each detection device 10, and after receiving sound data from that detection device 10, switches the supply destination of the power feed light to the next detection device 10.

[0036] In step S25, the terminal 120 analyzes the sound data received from each of the detection devices 10 to identify the gas leak point. For example, the terminal 120 compares the waveform of the received sound data with the waveform of sound generated in the air under steady state conditions to determine whether the waveforms differ. The terminal 120 may compare the waveforms of the sound data received from each of the detection devices 10 and determine the source of sound data showing a high-pitched waveform as the gas leak point.

[0037] As described above, the gas leakage location detection method of this embodiment supplies helium gas to the metal cable 200, generates sound by vibrating an air column in at least one manhole 220 in which the metal cable 200 is laid, and identifies the gas leakage location based on a change in the sound from a steady state. This makes it possible to more accurately identify the gas leakage location in the metal cable.

[0038] In the gas leak location detection method of this embodiment, a detection device 10 equipped with a sound generator 12 that generates sound by air column vibration and a sensor 13 that collects the sound is installed in the upper part of a manhole 220. The detection device 10 generates sound by air column vibration, collects the generated sound, compares the collected sound with steady-state sound, and determines that gas is leaking in a manhole where the sound becomes louder. The detection device 10 operates using electrical energy obtained by photoelectric conversion of power supply light transmitted via an optical cable 100, and is controlled by a control signal superimposed on the power supply light. This allows the location of a gas leak to be identified by remote control without having to dispatch a worker to the site.

[0039] [Example of Use of Gas Leak Detection Method] Next, an example of an efficient method for restoring a damaged portion of underground equipment using the method for detecting gas leaks from a metal cable will be described.

[0040] 5, a metal cable 200 is laid in an underground conduit 210, and a connection point of the metal cable 200 is protected by a closure 230 in a manhole 220. Dry air is supplied to the inside of the metal cable 200.

[0041] The detection device 10 is installed in the upper part of the manhole 220. The optical cable 100 is laid in the underground conduit 210 and connected to the detection device 10.

[0042] When a drop in gas pressure in the metal cable 200 is detected, helium gas is supplied to the metal cable 200 and the detection device 10 detects the gas leaked into the manhole 220.

[0043] The optical cable 100 has a small outer diameter, so there is ample space within the conduit 210. The metal cable 200 has a large outer diameter, so that its size is close to the inner diameter of the conduit 210, so there is no ample space within the conduit 210.

[0044] If the central portion of the conduit 210 is crushed by an external force such as an earthquake, the metal cable 200 will be pulled together with the conduit 210, and as shown in Fig. 6, the metal cable 200 may come off the closure 230, causing gas leakage within the metal cable 200. On the other hand, since there is ample space within the conduit 210, the optical cable 100 will not be pulled together with the conduit 210, and the optical cable 100 will rarely come off the detection device 10.

[0045] 7, an external force such as an earthquake may cause shear fracture at the joint surface between the conduit 210 and the manhole 220, causing the conduit 210 to shift. In this case, the metal cable 200 is easily damaged because its outer diameter is close to the inner diameter of the conduit 210. On the other hand, the optical cable 100 is less likely to be damaged because there is ample space within the conduit 210.

[0046] In either case, the optical cable 100 is less likely to become detached from the detection device 10 than the metal cable 200. Therefore, even if the underground facility is damaged and gas leaks from the metal cable 200, if the detection device 10 can be remotely controlled via the optical cable 100, the gas leak detection method of the present disclosure can be used to pinpoint the damaged manhole 220.

[0047] [Restoring Underground Facilities During Earthquakes] In a disaster such as an earthquake, it is conceivable that underground facilities (manholes, etc.) in multiple locations will be damaged, as shown in Fig. 8. Fig. 8 shows the underground route extending from the communications building 300 and the locations of the manholes (circles in the figure). In the example of Fig. 8, many manholes above the communications building 300 on the figure have been damaged, resulting in nine damaged locations a to i.

[0048] Immediately after an earthquake occurs, the locations and number of affected areas are unknown, so it is necessary to sequentially identify the affected areas of underground facilities for each underground route. By using the gas leak detection method disclosed herein, it is possible to identify only one affected area for each underground route that is closest to the communications building 300. It is assumed that optical cables 100 are laid in each underground route and detection devices 10 are installed in manholes.

[0049] When a gas leak is detected during a disaster, a maintenance person sends helium gas from the communications building 300 into the metal cable 200. After supplying helium gas into the metal cable 200, the maintenance person remotely controls the detection device 10 installed in a manhole through the optical cable 100 laid in an underground route, generates sound by vibrating the air column, and identifies the location of the gas leak based on the change in sound from normal conditions. This makes it possible to identify the affected area closest to the communications building 300. After identifying the location of the gas leak, the maintenance person restores the affected area.

[0050] By repeating the process of identifying and restoring the damaged areas, it is possible to identify and restore the damaged areas in order of proximity to the communications building 300, as shown in Figure 9. By repeating the process of identifying and restoring the damaged areas until it is confirmed that there is no longer any helium gas leakage, it is possible to restore all damaged areas on the same underground route.

[0051] An example of the recovery method of this embodiment will be described with reference to the flowchart of FIG.

[0052] When a gas leak is detected due to an earthquake, in step S1, a maintenance person sends out helium gas to underground routes in all directions.

[0053] In the example of Figure 8, four underground routes are connected to the communications building 300, and helium gas is sent to each of the metal cables of the four underground routes. At the branching points of the underground routes, the metal cables are sealed with closures and branch off, so helium gas is also supplied to the branching underground routes. In the example of Figure 8, underground route 1-1 and underground route 1-2 branch off from underground route 1. Note that separate metal cables may be laid for each underground route, even in the same direction. For example, three metal cables may be laid from the communications building 300 to form underground route 1, underground route 1-1, and underground route 1-2. Helium gas is supplied to each of the three metal cables.

[0054] After the helium gas is sent out, in step S2, the maintenance person remotely controls the detection device 10 to identify the gas leak location (disaster location). Because helium gas leaks from the metal cable 200 at the disaster location, it is difficult for the helium gas to reach manholes farther from the disaster location. Therefore, the disaster location closest to the communications building 300 can be identified for each underground route. In the example of FIG. 8 , first, the three disaster locations a, h, and i closest to the communications building 300 can be identified for each underground route. Note that if gas leaks from the metal cable 200 inside the conduit 210, the helium gas travels through the conduit 210 to two manholes connected to the conduit 210, and the gas leak may be detected by the detection devices 10 in the two manholes.

[0055] In step S3, the maintenance person checks whether or not there is any damaged area. If there is no damaged area, the restoration is complete.

[0056] In step S4, the maintenance person issues an instruction to dispatch a restoration team at the same time to all of the affected locations identified in step S2. In conventional restoration methods, a restoration team is dispatched each time a customer reports a service outage or a gas pressure drop alarm is received from the gas leak detection system. In the example of FIG. 8, nine separate dispatch instructions were required for the nine affected locations a to i. In this embodiment, restoration team dispatches are issued at the same time in order of proximity to the communications building 300, thereby enabling efficient management of the restoration team dispatch plan.

[0057] Once the recovery work is completed, the procedure from step S1 is repeated again.

[0058] [Visualization of Damaged Areas] Figure 11 shows an example of damaged areas displayed on an underground facility map. By managing damaged areas in a database and displaying them on an underground facility map, it becomes possible to visually grasp the damage situation and efficiently manage the dispatch plan for recovery work teams.

[0059] The damage status is managed in an underground facility damage recovery management database. Examples of data stored in the database are shown in Figures 12A to 12D. When a gas leak is detected by the detection device 10, the terminal 120 (or another device) in the communications building 300 records the gas leak in the record for the corresponding manhole and indicates the damaged area on an underground facility map based on the record in the database.

[0060] The maintenance person manages the dispatch plan for the restoration work team while viewing the underground facility map displayed on the terminal 120. For example, the maintenance person selects multiple disaster-stricken areas on the map that are about the same distance from the communications building 300, and dispatches the restoration work team to the selected disaster-stricken areas at the same time. Alternatively, the maintenance person may select one restoration target from each route, and dispatch the restoration work team to the selected disaster-stricken areas at the same time. In FIG. 11 , the first group restores the damaged area indicated by reference numeral 410, the second group restores the damaged area indicated by reference numeral 420, the third group restores the damaged area indicated by reference numeral 430, and the fourth group restores the damaged area indicated by reference numeral 440. The terminal 120 may select the damaged areas to be restored at the same time based on the distance from the communications building 300 and the route.

[0061] In addition to communication cables, underground facilities also contain water pipes, gas pipes, etc., which are widely distributed across the surface. Water pipes and gas pipes can also be damaged by earthquakes and other disasters, but due to their characteristics, even if damage can be detected, it is difficult to identify the damaged area. For example, water pipes will leak when damaged. If the leak is large-scale, it can be detected remotely by checking the water pressure. If the water pressure does not decrease significantly, it is difficult to detect remotely.

[0062] Typically, communication cable conduits, water pipes, and gas pipes run parallel to one another along the same route. If the locations of damaged underground facilities for communication cables are identified, it can be assumed that water pipes and gas pipes may also be damaged, since the ground strength in the same area is similar.

[0063] Furthermore, it is difficult to remotely determine whether large structures have been damaged by earthquakes, etc. It is possible that large structures near damaged underground facilities for communication cables may also have been damaged.

[0064] By actively providing disaster information visualized by area to waterworks bureaus, gas companies, large structure management companies, local governments, etc., it will be possible to extend the lifespan of infrastructure facilities and large structures that support society and to facilitate quicker recovery in the event of a disaster.

[0065] As described above, helium gas is supplied from the communications building 300 to each of the metal cables 200 on multiple routes, and after the helium gas is supplied, sound is generated by air column vibration in at least one or more manholes in which the metal cables 200 are laid, and based on the change in sound from a steady state, gas leak locations are identified in order of proximity to the communications building 300. This makes it possible to identify multiple gas leak locations with high accuracy.

[0066] According to this embodiment, the detected gas leak locations are displayed on an equipment map, and the gas leak locations to be restored are determined, which makes it possible to visually grasp the damage situation and also to efficiently manage the dispatch plan for restoration work teams.

[0067] REFERENCE SIGNS LIST 10 Detector 11 Remote control function 111 Photoelectric conversion element 112 Power storage unit 113 Control unit 12 Sound generation unit 13 Sensor 110 In-station node 120 Terminal 100 Optical cable 200 Metal cable 210 Pipe 220 Manhole 230 Closure 300 Communication building 310 Dry air supply device 320 Helium gas supply device

Claims

1. A gas leak detection method comprising the steps of: supplying helium gas from a work base to each of a plurality of metal cables along a plurality of routes; generating sound by air column vibration in at least one manhole in which the metal cables are laid after the helium gas is supplied; and identifying gas leak locations in order of proximity to the work base based on changes in the sound from steady state.

2. A restoration method comprising: displaying the gas leakage locations detected by the gas leakage location detection method according to claim 1 on an equipment map; and determining the gas leakage locations to be restored.

3. A restoration method according to claim 2, comprising dispatching restoration work teams to a plurality of gas leakage locations at the same time.

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