Event detection system, measuring instrument, and event detection method

Abstract

To provide an even detection system, a measuring instrument, and an even detection method with which it is possible to quickly detect the occurrence of an event by a simple composition.SOLUTION: An event detection system comprises: an optical fiber provided to a measurement object; and a measuring instrument for entering an optical pulse to the optical fiber from one end and receiving rear Rayleigh scattering light occurring to the optical fiber that is emitted from the one end of the optical fiber so as to measure a change in phase or intensity of the Rayleigh scattering light occurring at each longitudinal point of the optical fiber, calculating a chronological or a distance change in phase or intensity or in both phase and intensity of the Rayleigh scattering light, and determining the occurrence position or occurrence time of an event occurring to the measurement object that accompanies a temperature change, on the basis of the calculated change.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an event detection system, a measuring instrument, and an event detection method. [Background technology]

[0002] OPGW (Optical Ground Wire) is a type of overhead ground wire that is stretched between the tops of power transmission towers and also serves as a lightning protection. OPGW consists of an aluminum tube with an optical fiber inside, and an aluminum-coated copper wire twisted in a spiral around the outside. If a lightning strike to an OPGW causes damage to surrounding equipment, repairs will be necessary, so identifying the lightning strike point is an issue, and various lightning strike location methods have been proposed.

[0003] Known optical sensing methods using optical fiber in an OPGW utilize the polarization fluctuation of propagating light (Patent Documents 1, 2, and 3). When lightning strikes, part of the extremely large lightning current flows like a coil that wraps around the central optical fiber, generating a magnetic field inside the OPGW due to the Faraday effect, and the light traveling through the OPGW experiences large polarization fluctuations due to the influence of this magnetic field.

[0004] Therefore, by installing a laser light source on one side of the OPGW of the power transmission line to be monitored for lightning, shining laser light into the OPGW from one side, and analyzing the polarization fluctuation of the light that returns from the other side using a polarization fluctuation analysis unit, it is possible to locate the location of the lightning strike.

[0005] This method of detecting polarization fluctuations caused by lightning strikes on light propagating through an optical fiber requires the use of two optical fibers, and a configuration is required in which the two optical fibers are connected at the end.

[0006] Furthermore, a method for detecting temperature rises when lightning strikes an OPGW has been disclosed as a lightning location method using the optical fiber of an OPWG (Patent Document 4). In this method, a Raman OTDR (ROTDR), a type of OTDR (Optical Time Domain Reflectometry), is used to measure changes in temperature distribution along the optical fiber.

[0007] ROTDR, also known as DTS (Distributed Temperature Sensor), is the most commonly used measurement method for temperature measurement using optical fiber. ROTDR uses pulsed light propagating through the optical fiber core to exchange energy with the lattice vibrations of the quartz molecules that make up the optical fiber, and observes the wavelength-shifted backscattered Raman light. In particular, the intensity of the anti-Stokes light, which shifts to higher frequencies, varies greatly depending on the temperature at the scattering location. Therefore, by measuring the intensity of the Raman scattered light, it is possible to measure the temperature distribution at each position along the optical fiber.

[0008] Because the intensity of Raman scattered light is very weak, it is necessary to improve the SNR by averaging the scattered light from the optical pulse multiple times. The time interval for injecting the optical pulse must be set so that the next pulse is sent out after waiting for the Raman scattered light generated at the end of the optical fiber to return to the device. Therefore, as the length of the optical fiber increases, the repetition period of the pulse light becomes longer, and the measurement averaging time also becomes longer, which can take from several tens of seconds to several minutes.

[0009] Another method for measuring changes in temperature distribution in the longitudinal direction of an optical fiber is BOTDR (Brillouin OTDR) (Non-Patent Document 1). BOTDR is a method for detecting Brillouin scattered light that travels in the opposite direction (backward) to the direction of propagation of pulsed light propagating through the optical fiber core. The amount of frequency shift of Brillouin scattered light relative to incident pulsed light changes in proportion to the strain and temperature of the optical fiber. Therefore, by measuring the amount of frequency shift of the backscattered Brillouin scattered light, it is possible to calculate the distribution of strain or temperature in the longitudinal direction of the optical fiber.

[0010] With Brillouin scattering, the frequency shift changes depending on both the strain and temperature of the optical fiber, making it difficult to determine whether the change in the shift is due to strain or temperature. Also, like Raman scattering, the intensity of Brillouin scattered light is low, so it is necessary to average the scattered light from the optical pulse multiple times to improve the SNR. As a result, a single measurement can take anywhere from several tens of seconds to several tens of minutes. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 2818674 [Patent Document 2] Patent No. 4302273 [Patent Document 3] Patent No. 4786036 [Patent Document 4] Japanese Patent Application Publication No. Hei 2-159925 [Non-patent literature]

[0012] [Non-Patent Document 1] H. Ohno, H. Naruse, M. Kihara, and A. Shimada, “Industrial Applications of the BOTDR Optical Fiber Strain Sensor” Optical Fiber Technology 7, 45-64 2001. [Non-patent document 2] Yonas Muanenda, “Recent Advances in Distributed Acoustic Sensing Based on Phase-Sensitive Optical Time Domain Reflectometry” Journal of Sensors Volume 2018, Article ID 3897873, 16 pages [Non-patent document 3] Hanshin Expressway Public Corporation Technical Report No. 21 2003 Summary of the Invention [Problem to be solved by the invention]

[0013] Systems using ROTDR or BOTDR are configured using only a single optical fiber, without requiring an optical fiber connection configuration at the end of the OPGW. However, there is an issue that measuring the temperature distribution in the longitudinal direction of the optical fiber requires a long measurement time, making it impossible to capture temperature changes in a short period of time.

[0014] Although the temperature rise of the OPGW due to a lightning strike is large, the duration of current flow during a lightning strike is only a moment (on the order of tens of microseconds), and the heat is dispersed by the metal-coated copper wire that makes up the OPGW. Therefore, in order to accurately locate the lightning strike location by measuring the temperature rise, it is necessary to observe temperature changes at a higher speed.

[0015] From the above perspective, there is a need for a method to detect the location of a lightning strike on an OPGW more accurately with a simple configuration using only a single optical fiber, without requiring an optical fiber connection configuration at the end of the OPGW, and to detect the change in temperature rise over time at the lightning strike location more quickly.

[0016] Detecting the location and time of occurrence of such an event accompanied by a temperature change in a localized part of an optical fiber is a challenge not only for lightning location in OPGW but also in various facilities and equipment where optical fiber is installed.

[0017] The present invention has been made in view of the above, and an object of the present invention is to provide an event detection system, a measuring instrument, and an event detection method that can detect the occurrence of an event at high speed with a simple configuration. [Means for solving the problem]

[0018] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention is an event detection system comprising an optical fiber installed in an object to be measured, and a measuring instrument that measures changes in the phase or intensity of the Rayleigh scattered light generated at each point along the length of the optical fiber by inputting an optical pulse into one end of the optical fiber and receiving backward Rayleigh scattered light generated in the optical fiber and output from the one end of the optical fiber, calculates changes in the phase or intensity or both the phase and intensity of the Rayleigh scattered light over time or distance, and determines the location or time of occurrence of an event involving a temperature change occurring in the object to be measured based on the calculated changes.

[0019] The determination may be made by comparing the change in the phase or intensity, or both the phase and intensity, of the Rayleigh scattered light in the longitudinal direction of the optical fiber at each arbitrarily determined elapsed time with a predetermined threshold value.

[0020] The determination may be a determination of the occurrence of an event by comparing the temporal change in the phase or intensity, or both the phase and intensity, of the Rayleigh scattered light within an arbitrarily defined longitudinal section of the optical fiber with a predetermined threshold value.

[0021] The determination may be made by dividing the optical fiber into multiple regions defined by an arbitrarily determined elapsed time and longitudinal distance, and comparing the distribution of the phase or intensity, or both the phase and intensity, of the Rayleigh scattered light within the multiple regions to determine whether an event has occurred.

[0022] The optical fiber may be divided into a plurality of regions determined by an arbitrarily determined elapsed time and longitudinal distance, and the distribution state of the phase or intensity or both the phase and intensity of the Rayleigh scattered light within the plurality of regions may be compared. As a characteristic of the distribution state within each region, the phase or intensity of a distance section that is close to but far from the position where the event is estimated to have occurred may be compared to determine whether or not the event is the subject of judgment.

[0023] The event occurring in the object to be measured accompanied by a temperature change may be one in which the temperature change has a rate of change of 1° C. / second or more over time.

[0024] The object to be measured may be an overhead ground wire or a power transmission line in which the optical fiber is housed, and the measuring instrument may perform the determination by locating the position and time of a lightning strike occurring on the overhead ground wire or the power transmission line.

[0025] The measuring instrument may determine whether or not a lightning strike has occurred, and may also determine surrounding environmental conditions or occurring events other than a lightning strike that may occur on the overhead ground wire or power transmission line.

[0026] The measuring device may determine the location and time of occurrence of a heat generation phenomenon or a combustion phenomenon in the measurement object as the determination.

[0027] The object to be measured may be a power cable containing the optical fiber, and the measuring instrument may determine the location and time of occurrence of a fault in the power cable as the judgment.

[0028] One aspect of the present invention is a measuring instrument that includes a measurement unit that measures changes in the phase or intensity of Rayleigh scattered light generated at each point along the length of an optical fiber by inputting a light pulse into one end of an optical fiber installed in an object to be measured and receiving backward Rayleigh scattered light generated in the optical fiber that is output from the one end of the optical fiber, and a determination unit that calculates changes in the phase or intensity, or both the phase and intensity, of the Rayleigh scattered light over time or distance, and determines the location or time of occurrence of an event that occurs in the object to be measured and involves a temperature change based on the calculated changes.

[0029] One aspect of the present invention is an event detection method that includes: injecting a light pulse into one end of an optical fiber installed in an object to be measured; receiving backward Rayleigh scattered light generated in the optical fiber and outputting it from the one end of the optical fiber; measuring changes in the phase or intensity of the Rayleigh scattered light generated at each point along the length of the optical fiber; calculating changes in the phase or intensity, or both the phase and intensity, of the Rayleigh scattered light over time or distance; and determining the location or time of an event occurring in the object to be measured that involves a temperature change, based on the calculated changes. [Effects of the Invention]

[0030] According to the present invention, the occurrence of an event can be detected at high speed with a simple configuration. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a configuration diagram showing a lightning location system according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view illustrating the configuration of the OPGW. [Figure 3] FIG. 3 is a diagram illustrating an example of the configuration of the measuring device. [Figure 4] FIG. 4 is a flow diagram of the lightning location method performed by the measuring device. [Figure 5] FIG. 5 is a diagram showing the phase value distribution of Rayleigh scattered light in the longitudinal direction of the optical fiber, calculated by the calculation unit. [Figure 6] FIG. 6 is a diagram showing the change over time of the phase value at a certain point in the distance direction in FIG. [Figure 7] FIG. 7 is a diagram showing the phase value distribution of Rayleigh scattered light in the longitudinal direction of the optical fiber, calculated by the calculation unit. [Figure 8] FIG. 8 is a diagram showing the positional change of the Rayleigh scattering characteristic value at the time of occurrence of the event in FIG. [Figure 9] FIG. 9 is a diagram showing the phase value distribution of Rayleigh scattered light in the longitudinal direction of the optical fiber, calculated by the calculation unit. [Figure 10]FIG. 10 is a diagram showing the phase value distribution of Rayleigh scattered light in the longitudinal direction of the optical fiber, calculated by the calculation unit. [Figure 11] FIG. 11 is a diagram showing the phase value distribution of Rayleigh scattered light in the longitudinal direction of the optical fiber, calculated by the calculation unit. [Figure 12] FIG. 12 is a diagram showing the phase value distribution of Rayleigh scattered light in the longitudinal direction of the optical fiber, calculated by the calculation unit. [Figure 13] FIG. 13 is a diagram showing the change over time in the phase value of Rayleigh scattered light at the event occurrence position when the event to be detected occurs, calculated by the calculation unit. [Figure 14] FIG. 14 is a configuration diagram of a fire detection system according to the second embodiment. [Figure 15] FIG. 15 is an exemplary schematic cross-sectional view of an optical fiber cable used in the second embodiment. [Figure 16] FIG. 16 is an exemplary schematic cross-sectional view of an optical fiber cable used in the second embodiment. [Figure 17] FIG. 17 is an exemplary schematic cross-sectional view of an optical fiber cable used in the second embodiment. [Figure 18] FIG. 18 is an exemplary schematic cross-sectional view of an optical fiber cable used in the second embodiment. [Figure 19] FIG. 19 is a configuration diagram of a power cable fault detection system according to the third embodiment. [Figure 20] FIG. 20 is an exemplary schematic cross-sectional view of a power cable used in the third embodiment. [Figure 21] FIG. 21 is a flowchart showing an example of a processing procedure in the measuring device. DETAILED DESCRIPTION OF THE INVENTION

[0032] Exemplary embodiments and modifications of the present invention are disclosed below. The configurations of the embodiments and modifications shown below, as well as the actions and results (effects) brought about by these configurations, are merely examples. The present invention can also be realized by configurations other than those disclosed in the following embodiments and modifications. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derivative effects) obtained by the configurations.

[0033] The following embodiments have similar components, and in the following description, the same reference numerals will be used to designate the similar components, and redundant explanations may be omitted.

[0034] [First embodiment] 1 is a configuration diagram showing a lightning location system according to a first embodiment. The lightning location system 1 according to this embodiment is an example of an event detection system, and includes an OPGW 10, a steel tower 20, and a measuring instrument 30. The OPGW 10 is an example of an object to be measured.

[0035] 2 is a cross-sectional view illustrating the configuration of the OPGW 10. The OPGW 10 includes a plurality of aluminum-coated copper wires 11, an aluminum tube 12, and an optical fiber 13. The OPGW 10 houses the optical fiber 13 inside the aluminum tube 12. The aluminum-coated copper wires 11 are twisted around the aluminum tube 12. The optical fiber 13 is an example of an optical fiber provided in the object to be measured.

[0036] The optical fiber 13 is preferably a single-mode optical fiber, but a multimode optical fiber can also be used. In the case of a single-mode optical fiber, it may be a single-mode optical fiber conforming to, for example, G.652, G.653, G.654, G.655, G.656, or G.657 specified by the International Telecommunication Union.

[0037] In addition, the optical fiber 13 in the embodiment for detecting Rayleigh scattered light can be an optical fiber having a core in which a fiber Bragg grating (hereinafter referred to as FBG) whose refractive index changes periodically in the longitudinal direction is continuously formed over the entire length.

[0038] The measuring instrument 30 transmits an optical pulse, which is incident on one end of the optical fiber 13 in the OPGW 10. The transmitted optical pulse propagates through the optical fiber 13. Backward Rayleigh scattering occurs in the optical fiber 13, and the scattered light travels in the opposite direction to the traveling direction of the optical pulse. This backward Rayleigh scattered light is emitted from the one end of the optical fiber 13 and reaches the measuring instrument 30. The measuring instrument 30 receives the backward Rayleigh scattered light. By calculating the characteristics of the Rayleigh backscattered light that arrives in time series, the measuring instrument 30 can investigate the generation state of Rayleigh scattered light at each point along the optical fiber.

[0039] By receiving the backward Rayleigh scattered light, the measuring instrument 30 measures changes in the phase or intensity of the Rayleigh scattered light generated at each point in the longitudinal direction of the optical fiber 13. Then, the measuring instrument 30 calculates changes in the phase or intensity, or both the phase and intensity, of the Rayleigh scattered light over time or distance. Furthermore, based on the calculated changes, it is possible to determine the location or time of an event (lightning strike) that occurs in the OPGW 10 and involves a temperature change.

[0040] Since the measuring instrument 30 needs to measure the Rayleigh scattered light characteristics corresponding to the relatively rapid temperature changes that occur with time during a lightning strike, it is necessary to measure the time change in the distribution of Rayleigh scattered light characteristics in the longitudinal direction of the optical fiber 13. A distributed acoustic sensor (DAS) can be used as a device for such purposes (Non-Patent Document 2). By using a DAS, it is possible to determine the change in the intensity or phase of the Rayleigh scattered light in the longitudinal direction of the optical fiber 13.

[0041] 3 shows an example configuration of measuring device 30. Measuring device 30 has a measuring unit 31, a calculating unit 32, a memory unit 33, an information saving unit 34, and a determining unit 35. Calculating unit 32, memory unit 33, information saving unit 34, and determining unit 35 can be configured by a computer equipped with, for example, a CPU, RAM, ROM, etc., and its peripheral devices.

[0042] The measurement unit 31 has a light source 311, optical couplers 312 and 315, an optical modulator 313, an optical circulator 314, a photodetector 316, an AD converter 317, and a pulse generator 318. The light source 311, the optical couplers 312 and 315, the optical modulator 313, the optical circulator 314, and the photodetector 316 are connected by optical fibers. The photodetector 316 and the AD converter 317 are connected by an electrical signal line. Note that the configuration of the measurement unit is an example, and various configurations can be used. The optical circulator 314 is connected to the optical fiber 13 housed in the OPGW 10.

[0043] Next, the operation of the measuring device 30 and the event detection method (lightning stroke location method) will be described with reference to the flow charts of FIGS.

[0044] (Measurement part 31) Continuous light output from light source 311 is branched into two by optical coupler 312, and one of the lights is input to optical modulator 313. Optical modulator 313 receives an electrical pulse signal generated by pulse generator 318, and modulates the input light with a time change synchronized with the electrical pulse to generate an optical pulse. The generated optical pulse is input to optical circulator 314 via an optical fiber, and the optical pulse is sent from optical circulator 314 to optical fiber 13 in OPGW 10 and input thereto (step S101 in FIG. 4).

[0045] The optical pulse incident on the optical fiber 13 in the OPGW 10 propagates through the optical fiber 13, generating backward Rayleigh scattered light at each point along the length of the optical fiber 13. The measurement unit 31 receives the generated backward Rayleigh scattered light (step S102 in FIG. 4). Specifically, the generated backward Rayleigh scattered light passes through the optical circulator 314 and is multiplexed by the optical coupler 315 with the other light generated from the light source 311 and branched by the optical coupler 312. The light multiplexed by the optical coupler 315 enters the photodetector 316, where it is converted into an analog electrical signal and input to the AD converter 317. The AD converter 317 converts the input analog electrical signal into a digital electrical signal and sends it to the calculation unit 32.

[0046] (Calculation part 32) The digital electrical signal obtained by the measuring unit 31 is sent to the calculating unit 32. The calculating unit 32 calculates a Rayleigh scattered light characteristic value based on the information contained in the digital electrical signal. Here, the Rayleigh scattered light characteristic value is a feature quantity that characterizes the state of Rayleigh scattered light generated at each point in the optical fiber 13, such as the intensity of Rayleigh scattered light or the amount of phase change of the Rayleigh scattered light. These values ​​change due to the propagation of vibration or sound through the optical fiber 13, deformation of the optical fiber 13 itself, temperature changes, etc. The calculating unit 32 calculates the Rayleigh scattered light characteristic value that changes in the longitudinal direction of the optical fiber 13. The result calculated by the calculating unit 32 is a data string in which a plurality of Rayleigh scattered light characteristic values ​​that have been discretized for each distance in the longitudinal direction of the optical fiber 13 corresponding to each optical pulse sent to the optical fiber 13 by the measuring unit 31 are repeatedly linked together.

[0047] (Storage unit 33) The calculation unit 32 converts the data string resulting from the calculation into two-dimensional data at any time interval, with the interval being the longitudinal distance of the optical fiber 13 and the repetition time of the optical pulse, and stores the data in the storage unit 33 (step S104 in FIG. 4). The storage unit 33 may be a computer-readable recording medium.

[0048] (Information storage unit 34, determination unit 35) The information storage unit 34 stores reference data for comparison with the calculated Rayleigh scattered light characteristic value. The determination unit 35 reads out the Rayleigh scattered light characteristic value data in the longitudinal direction of the optical fiber 13 at an arbitrary time that was temporarily stored in the memory unit 33 and the reference data held by the information storage unit 34 (step S105 in FIG. 4), and first determines whether or not a lightning strike has occurred (step S106 in FIG. 4). If it is determined that a lightning strike has occurred (step S106, Yes), it calculates the location of the strike (lightning strike site), specifically the distance from the measuring instrument 30, and the time of the strike (step S107). If necessary, it also estimates the distance range of the optical fiber affected by the lightning strike from the Rayleigh scattered light characteristic value. If it is determined that a lightning strike has not occurred (step S106, No), it ends the flow.

[0049] (Determining the time of lightning strike) FIG. 5 shows the phase value distribution (an example of two-dimensional data) of the Rayleigh scattered light in the longitudinal direction of the optical fiber 13 for two minutes, calculated by the calculation unit 32.

[0050] In Fig. 5, the horizontal axis represents time and the vertical axis represents distance. The origin (zero point) of the distance on the vertical axis is the position where measuring device 30 is installed. The white parts are areas with large phase values. The same applies to Figs. 7, 9 to 12 below.

[0051] Figure 6 shows the time change of the phase value at a certain point in the distance direction (the point indicated by the arrow along the time axis in Figure 5) in Figure 5. The phase value is an example of the Rayleigh scattered light characteristic.

[0052] In Figure 6, the dashed line along the time axis indicates the threshold value for determining a phase change due to a lightning strike. It can be seen that the phase change exceeds the threshold value at approximately 30 seconds on the time axis. Therefore, it can be determined that a lightning strike occurred at the point where the threshold value is exceeded, at the position indicated by the arrow along the time axis in Figure 5. This is an example of a determination made by the measuring instrument 30 by comparing changes in the phase or intensity, or both the phase and intensity, of the Rayleigh scattered light in the longitudinal direction of the optical fiber 13 with a predetermined threshold value at every arbitrarily determined elapsed time. The time of approximately 30 seconds on the time axis is an example of an arbitrarily determined elapsed time. The threshold value is an example of reference data stored in the information storage unit 34.

[0053] The time change in the phase of the Rayleigh scattered light when a lightning strike occurs, as shown in Figure 6, shows a distinctive feature. That is, as the temperature of the OPGW 10 rises due to Joule heat from the discharge caused by the lightning strike, the phase value rises sharply, and then after a certain time interval (approximately 10 seconds in the case of Figure 6), the phase value drops. This is thought to be because a phase change was detected due to the elongation of the optical fiber 13 when the temperature rose, but then the heat was transmitted through the aluminum-coated copper wire 11 that makes up the OPGW 10 and diffused, and the elongation of the optical fiber 13 stopped, causing the phase change to decrease.

[0054] In other words, in the case of a lightning strike on an OPGW, the time change in the Rayleigh scattered light immediately after the strike is a characteristic waveform with a sudden rise and a fall after a certain time interval. Therefore, by observing the time waveform of the phase of the Rayleigh scattered light, it is possible to determine whether or not a lightning strike has occurred.

[0055] (Determining the location of a lightning strike) FIG. 7 shows a phase value distribution (an example of two-dimensional data) of Rayleigh scattered light in the longitudinal direction of the optical fiber 13 for two minutes, different from that in FIG. 5, calculated by the calculation unit 32.

[0056] FIG. 8 shows the change in phase value with respect to distance at a certain time in the time direction in FIG. 7 (time indicated by an arrow along the distance axis shown in FIG. 7).

[0057] In Figure 8, the dashed line along the distance axis indicates the threshold value for determining a phase change due to a lightning strike. It can be seen that the phase change exceeds the threshold value at a position of approximately 49,600 m on the distance axis. Therefore, it can be determined that a lightning strike occurred at the position exceeding the threshold value at the time indicated by the arrow along the distance axis in Figure 7. This is an example of an event occurrence determination in the measuring instrument 30 by comparing the temporal change in the phase or intensity, or both the phase and intensity, of Rayleigh scattered light within an arbitrarily determined longitudinal section of the optical fiber 13 with a predetermined threshold value. The position of approximately 49,600 m on the distance axis is an example of a position included in the arbitrarily determined longitudinal section of the optical fiber 13. The threshold value is an example of reference data stored in the information storage unit 34.

[0058] The change in the phase of the Rayleigh scattered light with distance when a lightning strike occurs, as shown in Figure 8, shows a distinctive feature. The waveform is slightly different before and after 49,600 m, which is the location of the lightning strike. It can be seen that the average level of the phase value is slightly higher after 49,600 m than before the lightning strike. This is thought to be because the sudden change in optical fiber 13 at the lightning strike location causes a change in the phase of the optical pulse propagating through that point and the Rayleigh backscattered light generated in the section after the lightning strike.

[0059] In other words, in the case of a lightning strike on OPGW10, the waveform of the change in the phase of Rayleigh scattered light with respect to distance (distance waveform) before and after the strike position is a characteristic waveform with different change patterns before and after the strike position. Therefore, by observing the distance waveform of the phase of Rayleigh scattered light, it is possible to determine whether or not a lightning strike has occurred.

[0060] (Determining the location and time of lightning strikes) FIG. 9 shows a phase value distribution (an example of two-dimensional data) of Rayleigh scattered light in the longitudinal direction of the optical fiber 13 for two minutes calculated by the calculation unit 32, different from those in FIGS.

[0061] 9, the divided regions (regions 1 to 8) defined by an arbitrarily determined elapsed time and longitudinal distance of the optical fiber 13 are indicated by dashed frames. The determination unit 35 can determine whether or not a target event has occurred by comparing the distribution of phase values ​​within each region. That is, this is an example of determining the occurrence of an event by dividing the optical fiber 13 into multiple regions defined by an arbitrarily determined elapsed time and longitudinal distance, and comparing the distribution states of the phase or intensity, or both the phase and intensity, of the Rayleigh scattered light within these multiple regions.

[0062] In Figure 9, it can be seen that the phase change is larger in region 3 compared to regions 1 and 2, and it can be determined that a lightning strike event occurred at a time and location within this region. Region comparison can be performed by extracting and comparing feature amounts or by using a trained model.

[0063] FIG. 10 shows a phase value distribution (an example of two-dimensional data) of Rayleigh scattered light in the longitudinal direction of the optical fiber 13 for the same two minutes as in FIG. 9, calculated by the calculation unit 32.

[0064] In Fig. 10, the divided regions (regions 1 to 5) determined by an arbitrarily determined elapsed time and a longitudinal distance of the optical fiber 13 are indicated by dashed frames. The occurrence of a target event can be determined by comparing the distribution of phase values ​​within each region. Fig. 10 shows an example of a different division of regions from Fig. 9.

[0065] In Figure 10, we can see that the changes in the phase distribution state are different when comparing areas 1 and 2 with areas 3 and 5. Therefore, we can determine that the location where the target event is occurring is the boundary between areas 2 and 3.

[0066] Fig. 11 shows the phase value distribution (an example of two-dimensional data) of the Rayleigh scattered light in the longitudinal direction of the optical fiber 13 for two minutes at the time of the lightning strike, calculated by the calculation unit 32. In Fig. 11, an area defined by a certain elapsed time and a distance in the longitudinal direction of the optical fiber is indicated by a dashed frame. Here, the dashed frame is drawn so that it includes the position and time at which the event occurred.

[0067] Figure 12 shows the phase value distribution of Rayleigh scattered light in the longitudinal direction of optical fiber 13 for two minutes when an event other than a lightning strike occurred, as calculated by calculation unit 32. In Figure 12, an area defined by a certain elapsed time and a distance in the longitudinal direction of the optical fiber is indicated by a dashed frame. Here, the dashed frame is drawn so that it includes the location where the event occurred.

[0068] Comparing the distribution of phase values ​​within the frames defined by the dashed lines in Figures 11 and 12, it can be seen that the phase values ​​increase in the direction away from the event occurrence position in Figure 11. On the other hand, in Figure 12, although the phase values ​​increase at the event occurrence position, there is no change in the direction away from the event occurrence position, as seen in Figure 11.

[0069] When a lightning strike occurs, Joule heat caused by the discharge causes a sudden temperature rise. The light pulse from the measuring device 30 propagates through the optical fiber 13, where the temperature has risen sharply in parts, and the backscattered Rayleigh light generated from optical fiber farther from the location where the event occurred also propagates through the heated optical fiber part and proceeds to the measuring device 30.

[0070] A phase change occurs when the optical pulse and Rayleigh scattered light propagate through a part of the optical fiber 13 where the temperature has risen, and this causes a phase change to appear in a distant part of the optical fiber 13 where no temperature change should have occurred. This phenomenon occurs when a phenomenon occurs in which the phase changes suddenly, and a lightning strike is one example of this.

[0071] Therefore, by comparing Figures 11 and 12, as a characteristic of the distribution state within each region, by comparing the phase or intensity of the distance section that is far from the position where the event is estimated to have occurred as viewed from the measuring instrument 30, it is possible to determine whether the event is the subject of judgment (here, a lightning strike).

[0072] Fig. 13 shows the change over time in the phase value of the Rayleigh scattered light at the event occurrence position when the event to be detected occurs, calculated by the calculation unit 32. In Fig. 13, the arrow indicates the time when the event occurs.

[0073] In the method for detecting the phase or intensity of Rayleigh scattered light, the difference between two local points on the optical fiber 13 is found. Therefore, if the rate of temperature change over time is small, the detected difference becomes small, making it difficult to detect the temperature change. From the results of comparing the phase change of Rayleigh scattered light and the temperature change when an event such as that shown in Figure 13 occurs, it was found that the most optimal detection condition is 1°C / sec or more. Therefore, it is preferable that an event that occurs in the object to be measured and involves a temperature change is an event in which the temperature change has a rate of change over time of 1°C / sec or more.

[0074] (Detection of events other than lightning strikes) In the lightning location system 1 shown in FIG. 1, in addition to lightning location, it is also possible to detect the environmental conditions around the OPGW 10 and events occurring in the OPGW 10.

[0075] The OPGW 10 is equipped with a lightning protection function and is stretched atop a steel tower 20, which is a power transmission line. As a result, the OPGW 10 vibrates due to wind force. The vibration of the optical fiber 13 housed in the OPGW 10 changes the phase or intensity of the Rayleigh backscattered light measured by the measuring instrument 30 shown in Figure 3. However, as mentioned above, the changes in the phase or intensity of the Rayleigh backscattered light caused by a lightning strike have characteristics that differ from other phenomena, and therefore can be distinguished from changes due to wind volume, etc.

[0076] Therefore, the lightning location system 1 can detect lightning strikes and also observe wind conditions by measuring changes in the phase or intensity of Rayleigh scattered light.

[0077] In the lightning location system 1, the OPGW 10 may be replaced with a power transmission line containing an optical fiber.

[0078] [Second embodiment] 14 is a configuration diagram showing a fire detection system according to a second embodiment. The fire detection system 2 of this embodiment includes a measuring instrument 30 and an optical fiber cable 22 installed in a tunnel 21. The fire detection system 2 is an example of an event detection system. The tunnel 21 is an example of an object to be measured.

[0079] The optical fiber cable 22 installed in the tunnel 21 only needs to include one or more optical fibers, and various types of cables can be used.

[0080] Fig. 15 is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber cable 22a as an example of the optical fiber cable 22 used in the second embodiment. As shown in Fig. 15, the optical fiber cable 22a has a tension member 222 extending in the longitudinal direction at the center of the cross section, four optical fibers 221 arranged to surround the periphery of the tension member 222 and extending in the longitudinal direction, and a coating layer 223 surrounding the outer periphery.

[0081] Fig. 16 is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber cable 22b as an example of the optical fiber cable 22 used in the second embodiment. As shown in Fig. 16, the optical fiber cable 22b has a plurality of optical fibers 224 extending in the longitudinal direction at the center of the cross section, a coating layer 226 surrounding the outer periphery, and a tension member 225 extending in the longitudinal direction within the coating layer 226.

[0082] Fig. 17 is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber cable 22c as an example of the optical fiber cable 22 used in the second embodiment. As shown in Fig. 17, the optical fiber cable 22c includes a plurality of optical fiber ribbons 227, a tension member 228, outer coating layers 229a and 229b, and a slot member 230. The slot member 230 extends in the longitudinal direction of the optical fiber cable 22c.

[0083] The slotted material 230 has a plurality of grooves 231 formed at equal intervals around its outer periphery. Each groove 231 extends around the axis with an S twist (left twist), a Z twist (right twist), or an SZ twist, which is a combination of these and reverses the twist direction at regular intervals in the longitudinal direction. In other words, multiple twists are formed in the plurality of grooves 231. The slotted material 230 can be made of, for example, a synthetic resin material.

[0084] 18 is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber cable 22d as an example of the optical fiber cable 22 used in the second embodiment. As shown in FIG. 18, the optical fiber cable 22d has two optical fibers 232, a plurality of tension members 233, an inner coating layer 234, an outer coating layer 235, three power wires 236, and a ground wire 237.

[0085] When a fire breaks out in tunnel 21, the temperature of the optical fiber in optical fiber cable 22 near the fire site rises. This causes changes in the characteristics (phase, intensity) of the Rayleigh scattered light observed by measuring instrument 30. It is estimated that the temperature rise in a tunnel due to a fire can range from several tens of degrees Celsius to several hundred degrees Celsius above the steady-state outside air temperature (Non-Patent Document 3). This is an example of a heat generation or ignition phenomenon, and is an example of an event that occurs in tunnel 21 and involves a temperature change.

[0086] This causes a large temperature change, similar to the temperature rise that occurs when a lightning strike occurs in an OPGW, which in turn causes a large change in the characteristics of the Rayleigh scattered light from the optical fiber.

[0087] The process flow of fire detection by the measuring device 30 in this embodiment is similar to the flow of the lightning location process in the first embodiment (FIG. 4), so a detailed description will be omitted.

[0088] In a system for fire detection such as that of the second embodiment, the most important thing is to detect the occurrence of a fire as quickly as possible and to identify the location of the fire as accurately as possible. To achieve this, the fire detection system 2 according to the second embodiment can instantly grasp the signs of a fire by capturing the characteristics of Rayleigh scattered light from an optical fiber, and has characteristics that surpass the performance of conventional fire detection systems.

[0089] While Figure 14 shows an example of fire detection for a tunnel, embodiments of the fire detection system include those that can be installed in a variety of facilities and equipment, such as oil and gas plants, power plants, airports, pipelines, etc.

[0090] [Third embodiment] 19 is a configuration diagram showing a power cable fault detection system of the third embodiment. The fault detection system 3 of this embodiment includes a measuring instrument 30 and a power cable 40 installed in an underground manhole 43 and a pipeline 42. The power cable 40 contains an optical fiber 402. The optical fiber 402 is connected to the measuring instrument 30. The fault detection system 3 is an example of an event detection system. The power cable 40 is an example of an object to be measured.

[0091] Fig. 20 is a cross-sectional view perpendicular to the longitudinal direction of a power cable 40 used in the third embodiment. As shown in Fig. 20, the power cable 40 has three power lines 401, an optical fiber 402, an inner coating layer 403 surrounding the power lines 401 and the optical fiber 402, and an outer coating layer 404 surrounding the outer periphery.

[0092] In the power cable 40, breakdown may occur due to the application of an impulse voltage caused by a lightning strike, deterioration of the insulation of the power cable 40, or external damage to the power cable 40. This may result in a ground fault accident in which a large current flows from the part where breakdown occurred to the grounding system, causing damage to the power cable 40.

[0093] Furthermore, if the power cable 40 has insulation weaknesses such as voids, scratches, or areas where electric fields are concentrated in the insulator, partial discharges may occur inside the voids while the power cable 40 is in operation, causing insulation deterioration of the equipment in the power cable 40 and ultimately problems such as insulation breakdown.

[0094] When a fault such as a ground fault or partial discharge occurs, a large current flows from the conductor to the insulator or grounding system, causing heat to be generated around the cable, which in turn heats up the optical fiber 402 embedded in the power cable 40.

[0095] The process flow for detecting faults such as ground faults and partial discharges in the measuring instrument 30 in this embodiment is similar to the flow of the lightning location process in the first embodiment (FIG. 4), so a detailed description will be omitted.

[0096] The fault detection system 3 for the power cable 40 according to the third embodiment can detect the occurrence of a fault earlier and identify the location of the fault more accurately.

[0097] 19 shows an example of fault detection for a power cable installed underground, but embodiments of the fault detection system include embodiments that can be introduced to power cables laid in various forms, such as submarine power cables for power transmission, overhead power cables, etc.

[0098] In the event detection systems shown in the first, second and third embodiments, an example of the processing procedure in the measuring device 30 will be shown below.

[0099] [Processing Procedure] FIG. 21 is a flowchart showing an example of a processing procedure in the measuring device 30, which includes machine learning.

[0100] First, the calculation unit 32 performs calculations based on the data measured by the measurement unit 31 to obtain physical quantities such as the intensity or phase of Rayleigh scattered light, and stores the obtained quantities in the storage unit 33 (step S201). Next, event discrimination is performed (step S202). In event discrimination, output parameters for input parameters are obtained based on, for example, a trained model stored as a program in the information storage unit 34, and the determination unit 35 discriminates events based on the output parameters. Here, discriminable events include the presence or absence of a lightning strike, its location, and the time of occurrence. This method can be used not only in lightning location systems but also in the fire detection system described in the second embodiment. In step S201, an object that is the subject of an event not classified by a previous trained model, i.e., a new object different from previously classified objects, may be classified. Furthermore, the trained model can be obtained by machine learning (step S203) using training data in which measurement data measured using the lightning location system is associated with a label indicating the corresponding event. Deep learning techniques such as neural networks can be used as machine learning techniques.

[0101] Next, the results of the machine learning are updated or stored in the trained model (step S204). Note that updating is a process of deleting a portion of past data corresponding to new data, and storing is a process of adding new data to past data without deleting it.

[0102] It should be noted that the present invention is not limited to the above-described embodiments. The present invention also includes configurations in which the components of the above-described embodiments are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible. [Explanation of symbols]

[0103] 1. Torpedo targeting system 2...Fire detection system 3...Fault detection system 10...OPGW 11...Aluminum-coated copper wire 12...Aluminum tube 13...Optical fiber 20...Steel tower 21...Tunnel 22...Fiber optic cable 22a...optical fiber cable 22b...optical fiber cable 22c...fiber optic cable 22d...Fiber optic cable 30…Measuring instrument 31...Measuring part 32...Calculation section 33...Storage section 34…Information storage department 35…Judgment section 40...Power cable 42…Pipeline 43...Manhole 221...Optical fiber 222...Tension member 223…Covering layer 224...Optical fiber 225...Tension member 226…Covering layer 227...Optical fiber ribbon 228...Tension member 229a, 229b...Outer coating layer 230...Slot material 231...Groove 232...Optical fiber 233...Tension member 234…Inner coating layer 235...Outer coating layer 236...Power lines 237...Earth wire 311...Light source 312...Optical coupler 313...Optical modulator 314...Optical circulator 315...Optical coupler 316...Photodetector 317...AD converter 318...Pulse generator 401...Power lines 402...Optical fiber 403…Inner coating layer 404...Outer coating layer

Claims

1. an optical fiber provided in the object to be measured; a measuring instrument that inputs an optical pulse into one end of the optical fiber, receives backward Rayleigh scattered light emitted from the one end of the optical fiber, measures changes in the phase or intensity of the Rayleigh scattered light generated at each point in the longitudinal direction of the optical fiber, calculates changes in the phase or intensity or both the phase and intensity of the Rayleigh scattered light over time or distance, and determines the location or time of occurrence of an event that occurs in the object to be measured and is accompanied by a temperature change, based on the calculated changes; Equipped with the object to be measured is an overhead ground wire or a power transmission line in which the optical fiber is housed, The event accompanied by a temperature change occurring in the measurement object has a temperature change rate of 1°C / sec or more with respect to time, The event detection system, wherein the measuring instrument determines the position and time of a lightning strike occurring on the overhead ground wire or power transmission line as the determination.

2. The determination is made by comparing a change in the phase or intensity or both the phase and intensity of the Rayleigh scattered light in the longitudinal direction of the optical fiber with a predetermined threshold value for each arbitrarily determined elapsed time. The event detection system of claim 1 .

3. The determination is made by comparing the temporal change in the phase or intensity or both the phase and intensity of the Rayleigh scattered light within an arbitrarily determined section in the longitudinal direction of the optical fiber with a predetermined threshold value. The event detection system of claim 1 .

4. The determination is made by dividing the optical fiber into a plurality of regions defined by an arbitrarily determined elapsed time and a longitudinal distance of the optical fiber, and comparing the distribution states of the phase or intensity, or both the phase and intensity, of the Rayleigh scattered light within the plurality of regions to determine whether an event has occurred. The event detection system of claim 1 .

5. The optical fiber is divided into a plurality of regions determined by an arbitrarily determined elapsed time and a longitudinal distance of the optical fiber, and the distribution states of the phase or intensity or both the phase and intensity of the Rayleigh scattered light within the plurality of regions are compared, As a feature of the distribution state within each region, the phase or intensity of the distance section that is close to the location where the event is estimated to have occurred as viewed from the measuring device is compared to determine whether or not the event is a target for judgment. The event detection system of claim 4 .

6. The measuring device determines whether or not a lightning strike has occurred based on the fact that the time change in the phase of the Rayleigh scattered light is a waveform having a sudden rise and a fall after a certain time interval. The event detection system of claim 1 .

7. The measuring instrument determines whether or not a lightning strike has occurred, and also determines the surrounding environmental conditions and occurrences of events other than a lightning strike that occur on the overhead ground wire or power transmission line. An event detection system according to any one of claims 1 to 6.

8. The measuring device determines the location and time of occurrence of a heat generation phenomenon or a combustion phenomenon in the measurement object as the determination. An event detection system according to any one of claims 1 to 7.

9. a measuring unit that measures a change in the phase or intensity of Rayleigh scattered light generated at each point in the longitudinal direction of the optical fiber by inputting an optical pulse into one end of an optical fiber provided in the object to be measured and receiving backward Rayleigh scattered light generated in the optical fiber and outputted from the one end of the optical fiber; a determination unit that calculates a change in the phase or intensity or both the phase and intensity of the Rayleigh scattered light over time or distance, and determines the occurrence position or occurrence time of an event that occurs in the measurement object and is accompanied by a temperature change, based on the calculated change; Equipped with the object to be measured is an overhead ground wire or a power transmission line in which the optical fiber is housed, The event accompanied by a temperature change occurring in the measurement object has a temperature change rate of 1°C / sec or more with respect to time, The determination unit determines the position and time of a lightning strike occurring on the overhead ground wire or power transmission line as the determination.

10. A light pulse is input from one end of an optical fiber installed in the object to be measured, measuring a change in the phase or intensity of the Rayleigh scattered light generated at each point in the longitudinal direction of the optical fiber by receiving backward Rayleigh scattered light generated in the optical fiber and outputted from the one end of the optical fiber; a change in the phase or intensity or both the phase and intensity of the Rayleigh scattered light over time or over distance is calculated, and a determination is made of the location or time of an occurrence of an event that occurs in the object to be measured and is accompanied by a temperature change based on the calculated change; the object to be measured is an overhead ground wire or a power transmission line in which the optical fiber is housed, The event accompanied by a temperature change occurring in the measurement object has a temperature change rate of 1°C / sec or more with respect to time, The event detection method includes determining the position and time of a lightning strike occurring on the overhead ground wire or power transmission line as the determination.

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