JP2023050426A - Event detection system, measuring instrument, and event detection method - Google Patents

Abstract

The object of the present invention is to provide an event detection system, a measuring instrument, and an event detection method capable of detecting the occurrence of an event at high speed with a simple configuration.
Kind Code: A1 An event detection system includes an optical fiber provided in an object to be measured, and an optical pulse incident on one end of the optical fiber and emitted from the one end of the optical fiber. Receiving the Rayleigh scattered light, measuring changes in the phase or intensity of the Rayleigh scattered light occurring at each point in the longitudinal direction of the optical fiber, and measuring the phase or intensity of the Rayleigh scattered light or both the phase and intensity over time a measuring device that calculates a change in target or distance, and based on the calculated change, determines the position or time of occurrence of an event that accompanies a temperature change that occurs in the object to be measured.
[Selection drawing] Fig. 1

Description

The present invention relates to an event detection system, a meter and an event detection method.

An OPGW (Optical Ground Wire) is a type of overhead ground wire, which is stretched between the tops of transmission line towers and also serves as a lightning protection. The OPGW has a structure in which an aluminum-coated copper wire is helically twisted on the outside of an aluminum tube containing an optical fiber in the center. When a lightning strike to an OPGW causes damage to peripheral equipment, it is necessary to repair the damage, and the identification of the location of the lightning strike is a problem.

As an optical sensing method using an optical fiber in an OPGW, a method using polarization fluctuation of propagating light is known (Patent Documents 1, 2, and 3). At the time of a lightning strike, part of the very large lightning current flows like a coil that wraps around the optical fiber in the center, and a magnetic field is generated inside the OPGW due to the Faraday effect. occur.

Therefore, if a laser light source is provided on one side of the OPGW of the transmission line to be monitored for lightning strikes, the laser light is incident on one side of the OPGW, and the light returned from the other side is analyzed by the polarization variation analysis section, lightning strikes can be performed. It is possible to locate the position.

In this way, the method of detecting the light propagating through the optical fiber by using the polarization variation caused by lightning strikes requires the use of two optical fibers, and a configuration that connects the two optical fibers at the end is required. Become.

In addition, as a lightning strike position locating method using an OPWG optical fiber, a method of detecting a temperature rise when a lightning strike occurs in an OPGW is disclosed (Patent Document 4). In this method, ROTDR (Raman OTDR), which is a kind of OTDR (Optical Time Domain Reflectometry), is used as a method for measuring temperature distribution changes in the longitudinal direction of the optical fiber.

ROTDR is also called DTS (Distributed Temperature Sensor), and is generally the most widely used measurement method for temperature measurement using optical fibers. ROTDR is a method of observing wavelength-shifted backscattered Raman light by performing lattice vibration and energy exchange of quartz molecules constituting the optical fiber with respect to pulsed light propagating through an optical fiber core. In particular, the intensity of the anti-Stokes light, which shifts to the high frequency side, varies greatly depending on the temperature at the position where the scattering occurs. Therefore, by measuring the intensity of the Raman scattered light, it is possible to measure the temperature distribution at each position in the longitudinal direction of the optical fiber. can.

Since the light intensity of Raman scattered light is very weak, it is necessary to average the scattered light from the light pulse many times to improve the SNR. The time interval for incident light pulses must be set so that the next pulse is sent after waiting for the Raman scattered light generated at the end of the optical fiber to return to the device side. Therefore, when the length of the optical fiber becomes longer, the repetition period of the pulsed light becomes longer, and the averaging time for measurement becomes even longer, which may take several tens of seconds to several minutes.

In addition, there is BOTDR (Brillouin OTDR) as a method for measuring temperature distribution changes in the longitudinal direction of an optical fiber (Non-Patent Document 1). BOTDR is a method of detecting Brillouin scattered light traveling in the opposite direction (backward) to the traveling direction of pulsed light propagating through an optical fiber core. The frequency shift amount of the Brillouin scattered light with respect to the incident pulsed light changes in proportion to the strain and temperature of the optical fiber. Therefore, by measuring the frequency shift amount of the backscattered Brillouin scattered light, it is possible to calculate the strain or temperature distribution in the longitudinal direction of the optical fiber.

In Brillouin scattering, the amount of frequency shift changes depending on both the amount of strain and the temperature of the optical fiber, so it is difficult to determine whether the cause of the shift amount change is strain or temperature change. Like Raman scattered light, Brillouin scattered light has a low light intensity, so it is necessary to improve the SNR by averaging the scattered light from the light pulse many times. Therefore, it may take several tens of seconds to ten minutes for one measurement.

Japanese Patent No. 2818674 Japanese Patent No. 4302273 Japanese Patent No. 4786036 JP-A-2-159925

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. 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 Hanshin Expressway Public Corporation Technical Report No. 21 2003

A system using ROTDR or BOTDR does not require an optical fiber connection configuration at the end of the OPGW and uses only one optical fiber. However, there is a problem that the measurement time is long and it is not possible to capture the temperature change in a short time.

A lightning strike causes a large temperature rise in the OPGW, but the energization time of the lightning strike is instantaneous (on the order of several tens of microseconds), and the heat is diffused by the metal-coated copper wires forming the OPGW. Therefore, it is necessary to observe the temperature change at a higher speed in order to accurately locate the lightning strike position by measuring the temperature rise.

From the above point of view, as a method for more accurately detecting the lightning strike position to the OPGW with a simple configuration using only one optical fiber without requiring an optical fiber connection configuration at the end in the OPGW, lightning strike There is a need for a faster method of detecting temperature rise over time at a location.

Detecting the location and time of occurrence of an event involving temperature change in such a localized part of an optical fiber is a problem in various facilities and equipment where optical fibers are arranged, in addition to lightning strike location in OPGW. It has become.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an event detection system, a measuring instrument, and an event detection method capable of detecting the occurrence of an event at high speed with a simple configuration. be.

In order to solve the above-described problems and achieve the object, one aspect of the present invention provides an optical fiber provided in an object to be measured; By receiving the backward Rayleigh scattered light generated in the optical fiber emitted from the optical fiber, a change in the phase or intensity of the Rayleigh scattered light generated at each point in the longitudinal direction of the optical fiber is measured, and the Rayleigh scattered light calculating temporal or distance changes in the phase or intensity or both phase and intensity of the measurement object, and based on the calculated changes, determining the position or time of occurrence of the event accompanied by the temperature change occurring in the measurement object an event detection system comprising:

The determination is performed 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 with a predetermined threshold for each arbitrarily determined elapsed time. It may be done by doing.

The determination is based on temporal changes in phase or intensity or both phase and intensity of the Rayleigh scattered light within an arbitrarily defined longitudinal section of the optical fiber and a predetermined threshold value. It may be a determination of occurrence of an event by comparison.

The determination is divided into a plurality of regions defined by an arbitrarily defined elapsed time and a distance in the longitudinal direction of the optical fiber, and the phase or intensity of the Rayleigh scattered light or the phase and intensity of the Rayleigh scattered light in the plurality of regions. It may be determination of event occurrence by comparing both distribution states.

Divided into a plurality of regions defined by an arbitrarily defined elapsed time and a distance in the longitudinal direction of the optical fiber, and a distribution state of phase or intensity or both phase and intensity of the Rayleigh scattered light within the plurality of regions When comparing , as a feature of the distribution state in each area, by comparing the phase or intensity of the distance section that is far and close to the measuring device from the position where the event is estimated to have occurred. It may be determined whether or not the event is a target event.

The event accompanied by a temperature change occurring in the object to be measured may have a change in temperature of 1° C./second or more with respect to time.

The object to be measured is an overhead ground wire or a transmission line in which the optical fiber is housed, and the measuring device locates the location and time of occurrence of a lightning strike occurring in the overhead ground wire or transmission line as the determination. It may be something that does what you do.

The measuring device may determine whether or not the lightning strike has occurred, and may also determine the surrounding environmental conditions and occurrence events other than the lightning strike occurring in the overhead ground wire or power transmission line.

As the determination, the measuring device may determine the position and time of occurrence of the heat generation phenomenon or the ignition phenomenon in the measurement object.

The object to be measured may be a power cable housing the optical fiber, and the measuring device may determine a location and time of occurrence of a failure occurring in the power cable as the determination.

According to one aspect of the present invention, a light pulse is incident from one end of an optical fiber provided in a measurement object, and the backward Rayleigh scattered light emitted from the one end of the optical fiber and generated in the optical fiber is received. a measurement unit that measures changes in the phase or intensity of the Rayleigh scattered light generated at each point in the longitudinal direction of the optical fiber; a determination unit that calculates a change in temperature, and determines an occurrence position or occurrence time of an event accompanied by a temperature change that occurs in the object to be measured based on the calculated change.

According to one aspect of the present invention, a light pulse is incident from one end of an optical fiber provided in a measurement object, and the backward Rayleigh scattered light emitted from the one end of the optical fiber and generated in the optical fiber is received. changes in the phase or intensity of the Rayleigh scattered light generated at each point in the longitudinal direction of the optical fiber, and changes in the phase or intensity or both the phase and intensity of the Rayleigh scattered light over time or over distance are measured. and determining the occurrence position or occurrence time of an event accompanied by a temperature change occurring in the object to be measured based on the calculated change.

According to the present invention, occurrence of an event can be detected at high speed with a simple configuration.

FIG. 1 is a configuration diagram showing a lightning strike location system of the first embodiment. FIG. 2 is a cross-sectional view for explaining the configuration of the OPGW. FIG. 3 is a diagram showing a configuration example of a measuring device. FIG. 4 is a flow diagram of a lightning strike location method performed by a measuring instrument. 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 calculator. FIG. 6 is a diagram showing a temporal change in phase value at a certain point in the distance direction in FIG. 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 calculator. FIG. 8 is a diagram showing the position change of the Rayleigh scattering characteristic value at the time when the event in FIG. 7 occurs. 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 calculator. 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 calculator. 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 calculator. 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 calculator. FIG. 13 is a diagram showing the time change of the phase value of Rayleigh scattered light at the event occurrence position when the event to be detected occurs, calculated by the calculation unit. FIG. 14 is a configuration diagram of the fire detection system of the second embodiment. FIG. 15 is an exemplary and schematic cross-sectional view of an optical fiber cable used in the second embodiment. FIG. 16 is an exemplary and schematic cross-sectional view of an optical fiber cable used in the second embodiment. FIG. 17 is an exemplary and schematic cross-sectional view of an optical fiber cable used in the second embodiment; FIG. 18 is an exemplary schematic cross-sectional view of an optical fiber cable used in the second embodiment. FIG. 19 is a configuration diagram of a failure detection system for power cables according to the third embodiment. FIG. 20 is an exemplary and schematic cross-sectional view of a power cable used in the third embodiment; FIG. 21 is a flow chart showing an example of a processing procedure in the measuring device.

Exemplary embodiments and variations of the invention are disclosed below. The configurations of the embodiments and modifications shown below, and the actions and results (effects) brought about by the configurations are examples. The present invention can be realized by configurations other than those disclosed in the following embodiments and modifications. Moreover, according to the present invention, at least one of various effects (including derivative effects) obtained by the configuration can be obtained.

The following embodiments have similar components. In the following description, the same reference numerals are given to the same constituent elements, and overlapping explanations may be omitted.

[First embodiment]
FIG. 1 is a configuration diagram showing a lightning strike location system of the first embodiment. A lightning strike location system 1 of this embodiment is an example of an event detection system, and includes an OPGW 10 , a steel tower 20 and a measuring device 30 . OPGW 10 is an example of a measurement object.

FIG. 2 is a cross-sectional view for explaining the configuration of the OPGW 10. As shown in FIG. The OPGW 10 includes a plurality of aluminum-coated copper wires 11 , aluminum tubes 12 and optical fibers 13 . The OPGW 10 accommodates an optical fiber 13 inside an aluminum tube 12 . An aluminum-coated copper wire 11 is twisted around the aluminum tube 12 . The optical fiber 13 is an example of an optical fiber provided on the object to be measured.

Optical fiber 13 is preferably a single mode optical fiber, but multimode optical fiber can also be used. In the case of single-mode optical fibers, for example G.3 as defined by the International Telecommunications Union. 652, G. 653, G. 654, G. 655, G. 656, G. 657 compliant single mode optical fiber.

In the optical fiber 13 in the embodiment for detecting Rayleigh scattered light, 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. An optical fiber with a core can be used.

The measuring device 30 transmits an optical pulse and enters the optical fiber 13 inside the OPGW 10 from one end. 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 direction opposite to the traveling direction of the light pulse. This backward Rayleigh scattered light is emitted from the one end of the optical fiber 13 and reaches the measuring device 30 . Meter 30 receives the back-Rayleigh scattered light. By calculating the characteristics of the Rayleigh backscattered light arriving in time series with the measuring instrument 30, it is possible to examine the generation state of the Rayleigh scattered light at each point in the longitudinal direction of the optical fiber.

By receiving the backward Rayleigh scattered light, the measuring device 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, temporal or distance changes of the phase or intensity of the Rayleigh scattered light or both of the phase and intensity are calculated. Furthermore, based on the calculated change, it is possible to determine the occurrence position or occurrence time of an event (lightning strike) that occurs in the OPGW 10 and accompanies a temperature change.

Since the measuring instrument 30 needs to measure the Rayleigh scattered light characteristic corresponding to the temperature change that changes relatively quickly with time during a lightning strike, the time change of the Rayleigh scattered light characteristic distribution in the longitudinal direction of the optical fiber 13 is measured. becomes necessary. A DAS (Distributed Acoustic Sensor) can be used as a device used for such applications (Non-Patent Document 2). By using DAS, changes in intensity or phase of Rayleigh scattered light in the longitudinal direction of the optical fiber 13 can be obtained.

FIG. 3 shows a configuration example of the measuring device 30. As shown in FIG. The measuring device 30 has a measurement section 31 , a calculation section 32 , a storage section 33 , an information storage section 34 and a determination section 35 . The calculation unit 32, the storage unit 33, the information storage unit 34, and the determination unit 35 can be configured by, for example, a computer including a CPU, a RAM, a ROM, and peripheral devices thereof.

The measuring section 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, optical couplers 312, 315, optical modulator 313, optical circulator 314, and photodetector 316 are connected by optical fibers. An electric signal line connects between the photodetector 316 and the AD converter 317 . 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 .

Next, the operation of the measuring instrument 30 and the event detection method (lightning strike location method) will be described with reference to the flowcharts of FIGS. 3 and 4. FIG.

(Measuring unit 31)
A continuous light output from a light source 311 is split into two by an optical coupler 312 , and one light is input to an optical modulator 313 . The optical modulator 313 receives the electrical pulse signal generated by the pulse generator 318, modulates the input light with a time change synchronized with the electrical pulse, and generates an optical pulse. The generated optical pulse is input to the optical circulator 314 via the optical fiber, and the optical pulse is sent from the optical circulator 314 to the optical fiber 13 in the OPGW 10 and is incident (step S101 in FIG. 4).

A light pulse that has entered the optical fiber 13 in the OPGW 10 propagates through the optical fiber 13 and generates backward Rayleigh scattered light at each point in the longitudinal direction 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 combined with the other light generated from the light source 311 and branched by the optical coupler 312 by the optical coupler 315 . The light multiplexed by the optical coupler 315 is incident on the photodetector 316 , converted into an analog electrical signal, and input to the AD converter 317 . The AD converter 317 converts the input analog electric signal into a digital electric signal and sends it to the calculator 32 .

(Calculation unit 32)
A digital electrical signal obtained by the measurement unit 31 is sent to the calculation unit 32 . The calculator 32 calculates the 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 generation state of Rayleigh scattered light generated at each point of the optical fiber 13, and is, for example, the intensity of Rayleigh scattered light or the phase change amount of Rayleigh scattered light. These values change due to vibration/sound propagation to the optical fiber 13, deformation of the optical fiber 13 itself, temperature change, and the like. The calculator 32 calculates Rayleigh scattered light characteristic values that change in the longitudinal direction of the optical fiber 13 . The result calculated by the calculation unit 32 is a plurality of Rayleigh scattered light characteristic values discretized for each distance in the longitudinal direction of the optical fiber 13 corresponding to the individual light pulses sent to the optical fiber 13 by the measurement unit 31. is a repeated data string.

(storage unit 33)
The calculation unit 32 converts the data string of the calculation result into two-dimensional data with respect to the distance in the longitudinal direction of the optical fiber 13 and an arbitrary time interval with 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.

(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 the Rayleigh scattered light characteristic value data in the longitudinal direction of the optical fiber 13 at an arbitrary time temporarily stored in the storage unit 33 and the reference data stored in the information storage unit 34 (step S105 in FIG. 4). ), first, it is determined 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), the location of the occurrence (lightning strike area), specifically, the distance from the measuring device 30, and the occurrence time are calculated (step S107). If necessary, the optical fiber distance range affected by the lightning strike is estimated from the Rayleigh scattered light characteristic value. If it is determined that a lightning strike has not occurred (step S106, No), the flow ends.

(Determination of lightning strike occurrence time)
FIG. 5 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 2 minutes calculated by the calculator 32 .

In FIG. 5, the horizontal axis represents time and the vertical axis represents distance. The distance on the vertical axis has the origin (zero point) as the position where the measuring device 30 is installed. Also, the white portion is a region with a large phase value. The same applies to FIGS. 7 and 9 to 12 below.

FIG. 6 shows temporal changes in the phase value at a point in the distance direction in FIG. 5 (the point indicated by the arrow along the time axis shown in FIG. 5). A phase value is an example of a Rayleigh scattered light characteristic.

In FIG. 6, the dashed line along the time axis indicates the threshold value for determining the phase change due to the occurrence of a lightning strike. In the figure, it can be seen that the phase change exceeds the threshold value at the time of about 30 seconds on the time axis. Therefore, it can be determined that a lightning strike has occurred when the threshold value is exceeded at the position indicated by the arrow along the time axis shown in FIG. This is because the determination in the measuring device 30 is determined in advance with respect to changes in phase or intensity or both phase and intensity of Rayleigh scattered light in the longitudinal direction of the optical fiber 13 at each arbitrarily determined elapsed time. It is an example of determination made by comparison with a threshold value. A time of approximately 30 seconds on the time axis is an example of an arbitrarily determined elapsed time. A threshold is an example of reference data held by the information storage unit 34 .

Characteristics can be seen in the temporal change of the phase of the Rayleigh scattered light when a lightning strike occurs, as shown in FIG. That is, the phase value rises sharply as the temperature of the OPGW 10 rises due to the Joule heat of the discharge caused by the lightning strike, and the phase value drops after a certain time interval (about 10 seconds in the case of FIG. 6). This is because the phase change due to the extension of the optical fiber 13 at the time of temperature rise was detected, but after that, the heat diffused through the aluminum-coated copper wire 11 constituting the OPGW 10, and the extension of the optical fiber 13 stopped. , is thought to be due to a decrease in the phase change.

In other words, it can be seen that in the lightning strike phenomenon to the OPGW, the time change of the Rayleigh scattered light immediately after the lightning strike becomes a characteristic waveform having a sharp rise and a fall after a certain time interval. Therefore, by observing the time waveform of the phase of Rayleigh scattered light, it is possible to determine the presence or absence of a lightning strike.

(Determination of location of lightning strike)
FIG. 7 shows the 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.

FIG. 8 shows the variation of the phase value with respect to distance at a certain time in the time direction in FIG. 7 (the time of the arrow along the distance axis shown in FIG. 7).

In FIG. 8, the dashed line along the distance axis indicates the threshold value for determining the phase change due to the occurrence of a lightning strike. In the figure, it can be seen that the phase change exceeds the threshold value at a position of about 49600 m on the distance axis. Therefore, it can be determined that a lightning strike occurred at a position exceeding the threshold value at the time determined by the arrow along the distance axis shown in FIG. This is determined in advance by the determination in the measuring device 30 as 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 13. This is an example of determination of occurrence of an event by comparison with a threshold value. A position of about 49600 m on the distance axis is an example of a position included in an arbitrarily defined longitudinal section of the optical fiber 13 . A threshold is an example of reference data held by the information storage unit 34 .

A feature can be seen in the distance change of the phase of the Rayleigh scattered light when a lightning strike occurs, as shown in FIG. The waveform differs slightly around 49,600m, which is the location of the lightning strike. It can be seen that the average level of the phase values after the lightning strike position of 49600 m is slightly higher than before the lightning strike position. This is thought to be due to the fact that the rapid change in the optical fiber 13 at the lightning strike position causes a change in the phase of the optical pulse propagating there and the phase of the Rayleigh backscattered light generated in the portion after the lightning strike position.

In other words, in the lightning strike phenomenon to the OPGW 10, the waveform (distance waveform) of the change in the phase of the Rayleigh scattered light before and after the lightning strike position with respect to the distance is a characteristic waveform in which the form of change is different before and after the lightning strike position. Therefore, by observing the distance waveform of the phase of Rayleigh scattered light, the presence or absence of a lightning strike can be determined.

(Determination of location and time of lightning strike)
FIG. 9 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 different from those in FIGS.

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

In FIG. 9, it can be seen that the phase change is larger in region 3 than in regions 1 and 2, and it can be determined that a lightning event has occurred at the time and position within this region. Comparison of regions can be performed by comparing after extracting feature amounts, using a trained model, or the like.

FIG. 10 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 the same two minutes as in FIG.

In FIG. 10, divided regions (regions 1 to 5) determined by an arbitrarily determined elapsed time and a distance in the longitudinal direction of the optical fiber 13 are indicated by dashed frames. By comparing the phase value distribution in each region, it is possible to determine whether or not the target event has occurred. FIG. 10 shows an example of a method of segmenting regions that is different from that in FIG.

In FIG. 10, regions 1-2 are compared with regions 3-5, and it can be seen that changes in phase distribution state are different. Therefore, it can be determined that the position where the target event occurs is the boundary between the regions 2 and 3 .

FIG. 11 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 when a lightning strike occurs, calculated by the calculator 32 . In FIG. 11, a region 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 frame is shown so as to include the position and time when the event occurred within the dashed frame.

FIG. 12 shows the phase value distribution of the Rayleigh scattered light in the longitudinal direction of the optical fiber 13 for 2 minutes when an event other than a lightning strike occurs, calculated by the calculator 32 . In FIG. 12, a region 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 frame is shown so that the position where the event occurred is included in the dashed frame.

11 and 12, it can be seen that in FIG. 11, the phase value increases in the far direction from the event occurrence position. On the other hand, in FIG. 12, although the phase value is large at the event occurrence position, there is no change seen in FIG. 11 in the far direction.

When a lightning strike occurs, Joule heat due to discharge causes a rapid temperature rise. The light pulse from the measuring device 30 propagates through the optical fiber 13, whose temperature has risen sharply, and the backward Rayleigh scattered light generated from the optical fiber far from the event occurrence position also travels through the optical fiber portion whose temperature has risen. It propagates and advances to the measuring device 30 .

When the optical pulse and the Rayleigh scattered light propagate through the portion of the optical fiber 13 where the temperature rises, the phase change occurs in a distant portion of the optical fiber 13 where the temperature should not originally change. It is shown. This phenomenon occurs when a phenomenon such as a sudden change in phase occurs, and the lightning phenomenon also corresponds to this phenomenon.

Therefore, as compared with FIG. 11 and FIG. 12, as a characteristic of the state of distribution in each region, the phase or intensity of the distance section that is far and close to the position where the event is estimated to have occurred as seen from the measuring instrument 30. By comparing, it can be determined whether or not the event is a determination target (lightning strike in this case).

FIG. 13 shows the time change of 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, arrows indicate event occurrence times.

In the method of detecting the phase or intensity of Rayleigh scattered light, the difference between two points on the local optical fiber 13 is obtained. Therefore, if the temperature change rate with respect to time is small, the detected difference will be small, making it difficult to detect the temperature change. As a result of comparing the phase change of Rayleigh scattered light and the temperature change when an event occurs as shown in FIG. 13, it was found that the optimum detection condition is 1° C./second or more. Therefore, the event that accompanies the temperature change that occurs in the object to be measured is preferably an event in which the temperature change has an amount of change of 1° C./second or more with respect to time.

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

The OPGW 10 has a lightning protection function and is installed at the top of a transmission line pylon 20 . Therefore, the OPGW 10 is vibrated by the wind force. 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 FIG. However, as described above, changes in the phase or intensity of Rayleigh scattered light generated by a lightning strike have characteristics different from those of other events, so they can be distinguished from changes due to wind volume or the like.

Therefore, according to the lightning strike location system 1, it is possible to observe the state of the wind force by measuring the change in the phase or intensity of the Rayleigh scattered light at the same time as detecting the lightning strike.

In addition, in the lightning location system 1, the OPGW 10 may be replaced with a transmission line containing an optical fiber.

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

The optical fiber cable 22 installed in the tunnel 21 only has to mount one or more optical fibers, and various types of cables can be used.

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 includes a tension member 222 extending in the longitudinal direction at the center of the cross section and four light beams extending in the longitudinal direction so as to surround the tension member 222. It has a fiber 221 and a coating layer 223 surrounding the outer periphery.

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 includes a plurality of optical fibers 224 extending longitudinally at the cross-sectional center, a coating layer 226 surrounding the outer circumference, and tension members 225 extending longitudinally within the coating layer 226. and have

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 tape core wires 227, a tension member 228, outer covering layers 229a and 229b, and a slot member 230. As shown in FIG. The slot material 230 extends in the longitudinal direction of the optical fiber cable 22c.

The slot member 230 is provided with a plurality of grooves 231 provided at equal intervals in the circumferential direction on its outer circumference. The grooves 231 extend around the axis with an S twist (left twist), a Z twist (right twist), or a combined SZ twist in which the twist direction is reversed at regular intervals in the longitudinal direction. That is, multiple twists are provided in the plurality of grooves 231 . The slot material 230 can be made of synthetic resin material, for example.

FIG. 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 includes two optical fibers 232, a plurality of tension members 233, an inner coating layer 234, an outer coating layer 235, three power lines 236, and a ground line. 237 and .

When a fire breaks out in the tunnel 21, the temperature of the optical fibers in the optical fiber cable 22 near the location of the fire rises. Thereby, the properties (phase, intensity) of the Rayleigh scattered light observed by the measuring device 30 change. It is assumed that the temperature inside the tunnel due to a fire will rise from the ambient temperature in a steady state to several tens of degrees Celsius to about one hundred and several tens of degrees Celsius (Non-Patent Document 3). It is an example of a heat generation phenomenon or an ignition phenomenon, and is an example of an event that accompanies a temperature change that occurs in the tunnel 21 .

As a result, a large temperature change occurs, similar to the temperature rise at the time of lightning strike to the OPGW, which causes a large change in the characteristics of Rayleigh scattered light from the optical fiber.

The fire detection process flow in the measuring instrument 30 in this embodiment is the same as the lightning strike location process flow (FIG. 4) in the first embodiment, so detailed description will be omitted.

In a system for fire detection such as that of the second embodiment, it is most important to quickly detect the occurrence of fire and to more accurately identify the location of the fire. For this purpose, the fire detection system 2 according to the second embodiment can instantly grasp the signs of fire by capturing the characteristics of Rayleigh scattered light from optical fibers, and improves the performance of conventional fire detection. It has superior characteristics.

Although FIG. 14 shows an example of fire detection for a tunnel, embodiments of the fire detection system include embodiments that can be introduced into various facilities and equipment. Such facilities and equipment include, for example, oil and gas plants, power plants, airports, pipelines, and the like.

[Third embodiment]
FIG. 19 is a configuration diagram showing a failure detection system for power cables according to the third embodiment. The failure 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 encloses an optical fiber 402 . Optical fiber 402 is connected to measuring instrument 30 . Failure detection system 3 is an example of an event detection system. The power cable 40 is an example of an object to be measured.

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

In the power cable 40, dielectric breakdown occurs due to the application of shock voltage due to a lightning strike, deterioration of the insulation of the power cable 40, or external damage to the power cable 40, and a large current flows from the portion where the dielectric breakdown occurs to the ground system. An accident may occur and damage the power cable 40 .

In addition, in the power cable 40, if there is an insulation weak point such as a void, a flaw, or an electric field concentrated portion in the insulator, partial discharge occurs inside the void or the like in the operating state of the power cable 40, Problems such as deterioration of the insulation of the equipment of the cable 40 and the like, and eventually dielectric breakdown may occur.

When a fault such as a ground fault or partial discharge occurs, a large current flows from the conductor portion to the insulator or the ground system, causing heat generation in the cable peripheral portion. Therefore, the optical fiber 402 built in the power cable 40 is also heated.

The process flow for fault detection such as ground faults and partial discharges in the measuring instrument 30 in this embodiment is the same as the lightning strike location process flow in the first embodiment (FIG. 4), so detailed description is as follows. omitted.

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

FIG. 19 shows an example of failure detection for a power cable installed underground, but as an embodiment of the failure detection system, there are embodiments that can be introduced to power cables laid in various forms. included. Such power cables include, for example, power transmission cables installed in the sea, overhead power cables, and the like.

An example of the processing procedure in the measuring device 30 in the event detection system shown in the first, second and third embodiments is shown below.

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

First, the calculation unit 32 performs calculations based on the data measured by the measurement unit 31, acquires physical quantities such as the intensity or phase of Rayleigh scattered light, and stores them in the storage unit 33 (step S201). Subsequently, event discrimination is performed (step S202). In event discrimination, for example, based on a learned model stored as a program in the information storage unit 34, output parameters for input parameters are acquired, and the determination unit 35 discriminates events based on the output parameters. Here, the events that can be determined include the presence or absence of a lightning strike, the location of occurrence, the time of occurrence, and the like. This technique can be used not only in the lightning location system but also in the fire detection system shown in the second embodiment. In step S201, there are cases where an entity as a subject of an event that has not been classified by the past trained model, that is, a new entity different from the already classified entity may be classified. Also, the trained model can be obtained by machine learning (step S203), for example, using teacher data in which measurement data measured using a lightning strike orientation system and labels indicating events corresponding to the measurement data are linked. . As a machine learning method, a deep learning method such as a neural network can be used.

Subsequently, the result of executing machine learning is updated or stored in the learned model (step S204). Update is a process of deleting a part of past data corresponding to new data, and accumulation is a process of adding new data without deleting past data.

In addition, the present invention is not limited by the above-described embodiment. The present invention also includes a configuration obtained by appropriately combining the constituent elements of the above-described embodiments. Further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible.

1... Lightning location system 2... Fire detection system 3... Failure detection system 10... OPGW
DESCRIPTION OF SYMBOLS 11...Aluminum-coated copper wire 12...Aluminum tube 13...Optical fiber 20...Steel tower 21...Tunnel 22...Optical fiber cable 22a...Optical fiber cable 22b...Optical fiber cable 22c...Optical fiber cable 22d...Optical fiber cable 30...Measuring instrument 31 Measurement section 32 Calculation section 33 Storage section 34 Information storage section 35 Judgment section 40 Power cable 42 Duct 43 Manhole 221 Optical fiber 222 Tension member 223 Coating layer 224 Optical fiber 225 Tension Member 226 Coating 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 Internal coating layer 235 External coating layer 236 Power line 237 Ground line 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 line 402 Optical fiber 403 Internal coating layer 404 ... outer coating layer

Claims (12)

an optical fiber provided in the object to be measured;
By inputting a light pulse into the optical fiber from one end and receiving the backward Rayleigh scattered light generated in the optical fiber emitted from the one end of the optical fiber, measuring a change in the phase or intensity of the Rayleigh scattered light, calculating temporal or distance changes in the phase or intensity or both phase and intensity of the Rayleigh scattered light, and based on the calculated change, the measurement a measuring instrument that determines the location or time of occurrence of an event that accompanies a temperature change that occurs in an object;
An event detection system comprising: The determination is performed 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 with a predetermined threshold for each arbitrarily determined elapsed time. The event detection system of claim 1, wherein the event detection system is performed by: The determination is based on temporal changes in phase or intensity or both phase and intensity of the Rayleigh scattered light within an arbitrarily defined longitudinal section of the optical fiber and a predetermined threshold value. 2. The event detection system of claim 1, wherein the determination of event occurrence is by comparison. The determination is divided into a plurality of regions defined by an arbitrarily defined elapsed time and a distance in the longitudinal direction of the optical fiber, and the phase or intensity of the Rayleigh scattered light or the phase and intensity of the Rayleigh scattered light in the plurality of regions. 2. The event detection system of claim 1, wherein determination of event occurrence is by comparing both distribution states. Divided into a plurality of regions defined by an arbitrarily defined elapsed time and a distance in the longitudinal direction of the optical fiber, and a distribution state of phase or intensity or both phase and intensity of the Rayleigh scattered light within the plurality of regions When comparing
As a feature of the distribution state in each region, by comparing the phase or intensity of the distance section far and close to the position where the event is estimated to have occurred from the measuring device, it is possible to determine whether the event is an object to be determined. 5. The event detection system of claim 4, wherein the event detection system determines whether the 6. The event detection system according to any one of claims 1 to 5, wherein an event accompanied by a temperature change occurring in the object to be measured has an amount of temperature change of 1°C/second or more with respect to time. The object to be measured is an overhead ground wire or a transmission line in which the optical fiber is housed, and the measuring device locates the location and time of occurrence of a lightning strike occurring in the overhead ground wire or transmission line as the determination. The event detection system of any one of claims 1-6, wherein: 8. The event detection system according to claim 7, wherein the measuring device determines whether or not the lightning strike has occurred, and also determines an ambient environment state and an occurrence event other than the lightning strike occurring in the overhead ground wire or power transmission line. 7. The event detection system according to any one of claims 1 to 6, wherein said measuring device determines, as said determination, the position and time of occurrence of an exothermic phenomenon or an ignition phenomenon in said object to be measured. The object to be measured is a power cable containing the optical fiber, and the measuring instrument determines, as the determination, the location and time of occurrence of a failure occurring in the power cable. An event detection system according to any one of the preceding claims. A light pulse is incident from one end of an optical fiber provided in a measurement object, and the backward Rayleigh scattered light emitted from the one end of the optical fiber is received. a measurement unit that measures changes in the phase or intensity of Rayleigh scattered light occurring at each point in the direction;
Calculate temporal or distance changes in the phase or intensity or both phase and intensity of the Rayleigh scattered light, and based on the calculated change, the occurrence position or the event accompanied by the temperature change occurring in the measurement object a determination unit that determines the occurrence time;
measuring instrument. A light pulse is injected from one end into an optical fiber provided in the object to be measured,
By receiving the backward Rayleigh scattered light generated in the optical fiber emitted from the one end of the optical fiber, the change in the phase or intensity of the Rayleigh scattered light generated at each point in the longitudinal direction of the optical fiber is measured. death,
Calculate temporal or distance changes in the phase or intensity or both phase and intensity of the Rayleigh scattered light, and based on the calculated change, the occurrence position or the event accompanied by the temperature change occurring in the measurement object determine the occurrence time,
Event detection method.

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