JPH06215280A - System for monitoring intrusion of environmental substance into transmission line - Google Patents

Abstract

PURPOSE:To attain the variety of cable structure, to complicate installed environment and to reduce maintenance cost by heating a heating body, measuring its temperature and detecting the intrusion of an environ-metal substance into a transmission line from a change in temperature distribution. CONSTITUTION:The heating body 2 and a temperature measuring optical fiber 3 are built in the transmission line 1 in its longitudinal direction and the body 2 and the fiber 3 are respectively connected to a temperature control device 4 and a Raman scattered light temperature measuring equipment 5. When the heating quantity of the body 2 is changed and the temperature distribution in the longitudinal direction of the fiber 3 is always or occasionarily monitored, the existence of an environmental substance intruded into the line 1, the range of intrusion and the sort of the intruded substance can be detected. Since the specific heat or heat conductivity of the intruded substance is different from that of air in the line 1 or the constitutional materials of the line 1, differences in measured temperature and temperature changing status (temperature distribution in a transient state) are generated between an intruded part and a normal part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention online monitors presence or absence of infiltration of environmental substances (water, mud, sand, etc.) into a transmission line such as a cable for communication and electric power, its distribution, and type of infiltrated substance. And a cable with a water immersion sensor used in this system.

[0002]

2. Description of the Related Art Conventionally, as a method of maintaining (mainly inundation detection) a transmission line for information or energy having high social and public characteristics,
The following are used: Gas (dry air) is inserted into the cable to detect abnormalities due to a decrease in gas pressure and prevent water from entering (gas filled type). An insulated electric wire with a hole in the insulator is installed inside the cable, and water leakage is detected by utilizing the decrease in insulation resistance due to water leakage (leakage detection wire composite type). A sensor module equipped with a mechanism for applying micro-bending to the optical fiber at the time of flooding is installed in the cable connection part (inside the closure), and an abnormality is detected by an increase in the loss of the optical fiber (optical fiber leak sensor type). Use a cable with a waterproof mixture (jelly) filled in the gap (jelly filling type).

On the other hand, in recent years, as a technique for laying an optical fiber, a hollow tube made of plastic or a tube cable in which a plurality of tubes are collected is laid in advance, and the optical fiber unit is pneumatically fed into the tube later. The air blown fiber (ABF) method has been devised, and has rapidly spread around transmission lines in buildings and the like because of the following features. Even if an initial investment is not made in advance for an optical fiber reserve core, it is possible to add an optical fiber or upgrade to a new optical fiber of higher performance, etc., simply by providing a spare tube. Even if the cable length is short, if the tubes are connected to the series with an airtight connector in advance, the optical fiber unit can be pumped in series over a long distance, and the number of optical fiber connections can be reduced. . By opening and closing the tube connector, you can freely switch the installation route and drop. If branch connection is expected in the future, if a connector is provided on the tube in advance, branch connection of the optical fiber can be easily performed as needed in the future.

Recently, there has been a demand for utilizing such an advantage in a wider area outdoor communication network and the like, and it has become necessary to lay a tube cable in a more severe outdoor environment than ever. However, especially in the case of a tube cable of the direct embedding method using a metal corrugated sheath, after installation,
If a cable is cut due to an unexpected accident, or if a part of it is damaged and inundated, the ingress of water tends to run in the longitudinal direction more than with an ordinary optical cable, and the damage is likely to spread. is there. In addition, in public works,
Since there are many cases where tube cables are laid in advance as infrastructure and the optical fiber unit is pumped later if necessary after the next fiscal year, even if a damage accident occurs during the pumping period, it will not be detected at all. There is a risk that the damage will spread.

[0005]

For this reason, it is necessary to perform some type of flood detection to perform maintenance of the transmission line.
Among the conventional maintenance methods, the gas-filled type requires a gas pressure monitoring device and a gas supply device, and is expensive in terms of initial investment and running cost. Further, the water leakage detection electric wire composite type cannot be adopted due to the problem of inductive interference when there is an extra-high voltage electric wire running in parallel with the transmission line (which is often encountered in wide area transmission lines). That is, since an electric wire that is not partially insulated is used, there is a risk of cable burning due to an induced current. Further, since it is a metallic type sensor, the monitoring system is apt to be damaged or malfunction due to the induced current. Further, the optical fiber leak sensor type cannot detect unless the discretely distributed connection parts are flooded, which delays the detection and makes it difficult to specify the damaged position. In addition, since the increase in transmission loss is used, the measurement dynamic range is narrowed by the addition of the microbend, and the measurement location and length are easily restricted. On the other hand, the jelly filling type cannot be used because the connection workability is poor and the tube for the air blown fiber cannot be filled. Further, there is a problem that it is difficult to find out when the cable is partially damaged or the reserve core is damaged. Under the above technical background, an object of the present invention is to provide a monitoring system capable of performing satisfactory maintenance in response to demands for diversification of cable structure, complication of installation environment, and reduction of maintenance cost. is there.

[0006]

The feature is that a temperature monitoring optical fiber connected to a Raman scattered light temperature measuring device and a heating element for heating the optical fiber are provided in the longitudinal direction in the transmission line. This is to detect the infiltration of environmental substances into the transmission line from the change in the temperature distribution by making the temperature of the generated heat to measure the temperature. A cable used in such a system is characterized by having a heating element and an optical fiber for temperature monitoring built therein.

A specific example will be described below with reference to the drawings.
FIG. 1 shows a schematic configuration of a specific example of the present invention. A heating element 2 and an optical fiber 3 for temperature measurement are built in the transmission line 1 in the longitudinal direction, and the heating element 2 is connected to a temperature control device 4 and an optical fiber 3.
Is connected to the Raman scattered light temperature measuring device 5. The configuration of each part is described below.

(Transmission line) This includes all those used as transmission lines for information and energy, such as electric wires, cables, optical cables, ABF tube cables, and composite cables of these. In the figure, 1a is a transmission line sheath or armor, and 1b is a transmission line core.

(Raman scattered light temperature measuring system) This is known as a technique capable of continuously measuring the temperature along the sensor using the optical fiber itself as a sensor. Generally, an optical fiber (sensor) for temperature measurement is used. And a measuring device and a computer for system control, calculation and display. A basic principle and a configuration example will be described with reference to FIGS. 2 and 3. First, an LD (laser diode) is driven and an optical pulse is incident on an optical fiber for temperature measurement. The incident light pulse causes light scattering in each part of the optical fiber, and part of the scattered light returns to the incident end (backscattered light), and this is extracted via the directional coupler. Since the light velocity in the optical fiber is known, the generation position of the backscattered light can be obtained by measuring the time from the incidence of the light pulse until the backscattered light returns to the incident end. Here, since the intensity ratio of the two components (Stokes light and anti-Stokes light) of the Raman scattered light included in the back scattered light is a function of temperature, detection is performed via the light receiving element APD (avalanche photodiode). By processing the signal, the temperature distribution in the longitudinal direction of the optical fiber can be obtained.

(Heating element and temperature control device) These are for heating the temperature measuring optical fiber and its surroundings in order to detect the difference in temperature change between the environmental substance infiltration part and the normal part in the transmission line. Heat is generated by energizing a linear metal body. Specifically, a heating element is a metal body such as copper, aluminum or steel, or a linear body made of an insulating metal body having an insulating coating (including coating) applied thereto. Further, the temperature control device 4 may be an electric heating device or the like that can control the amount of heat generation (temperature) by controlling the voltage applied to the heating element.

[0011]

With the system having such a structure, if the temperature is measured without causing the heating element to generate heat, even if environmental substances enter due to damage to the outer cover, stirrup, or terminal of the transmission line, It is not always possible to reliably detect the infiltrated portion. This is because, if the temperature of the infiltrating substance is close to the environment temperature of the transmission line and the internal temperature of the transmission line is close to the environment temperature, a significant difference in temperature between the infiltrated portion and the normal portion cannot be found.

However, if the temperature distribution in the longitudinal direction of the optical fiber is constantly or constantly monitored by changing the amount of heat generated by the heating element,
When environmental substances have infiltrated into the transmission line, the presence or absence of infiltration, the infiltrated range, or the type of infiltrated substance can be detected. Since the specific heat or the thermal conductivity of the infiltrated environmental substance and the air in the transmission line or the constituent material of the transmission line is different, the measured temperature and the way of temperature change (temperature distribution in the transient state) are different between the infiltrated part and the normal part. Is. For example, if the temperature distribution is measured while it is heated to a predetermined temperature and this distribution is recorded as a normal value, and if there is infiltration of environmental substances, the infiltration part will be compared with this normal value to see where the temperature differs. Can be detected as Alternatively, in the transient state of heating to a predetermined temperature, the infiltration portion can be detected also because the way the temperature changes is different.

In the above specific example, each one heating element and one optical fiber for temperature measurement (a temperature control device corresponding to these,
An example in which Raman scattered light temperature measuring devices are also used one by one and these are arranged from one end of the transmission line is shown, but the present invention is not limited to such a configuration. For example, a plurality of heating elements and / or temperature measurement optical fibers may be used, and a temperature control device, a Raman scattered light temperature measurement device, and a heating element and temperature measurement connected to these from the relay connection part of the transmission line. An optical fiber for use may be arranged. further,
The heating element and / or the temperature-measuring optical fiber may be incorporated in the transmission line, but it is not always necessary to arrange the heating element and the temperature measurement optical fiber uniformly in the longitudinal direction of the transmission line. These may be intermittently arranged at intervals such that the location where the environmental substance enters can be specified to some extent. Further, the heating element may be arranged so as to reciprocate between the objects to be measured.

[0014]

EXAMPLE An example applied to a metal corrugated stirrup ABF pipe cable for direct burying will be described below. FIG. 4 shows a cross section of the example cable, in which a 600 V cross-linked polyethylene insulated wire 12 (conductor size 22 sq) is used as a heating element, and one optical fiber element wire constituting the optical fiber unit 16 in the air blown pipe is used for temperature measurement. It is used as an optical fiber.

The cable structure has four PE tubes 11 (inner diameter 6 mm) around the tension member 10.
φ, outer diameter 8 mmφ) and two cross-linked polyethylene insulated wires
12 is surrounded, LAP sheath 13 and further metal corrugated sheath 14 are formed on them, and an anticorrosion layer 15 is formed on the outermost layer.
Is provided. The optical fiber unit 16 is pressure-fed to one of the PE tubes 11. The cross-sectional structure of this unit is shown in FIG. As shown, the rip cord 17 and the 6-core optical fiber UV strand 18 (0.25 mm
φ), on which a primary coating 19 and a secondary coating 20 are applied.

When monitoring the infiltration of environmental substances, one end of the two insulated wires 12 is connected to a voltage control / supply device (temperature control device) for applying a DC voltage between them, and the other end is connected. Short the two cores. As a temperature measuring optical fiber, one core of a multimode GI type optical fiber element wire (manufactured by Sumitomo Electric Industries, Ltd.) in a 6-core optical fiber unit is used, and one end of this is a Raman scattered light temperature measuring device ( The other end of the SUT-200 manufactured by Sumitomo Electric Industries, Ltd. was fusion-bonded to a non-reflective connector.

[0017]

[Test Example] Next, in order to simulate a long-distance transmission line, FIG.
As shown in (3), a model having a total length of 10 km was constructed by providing a test section with a dummy insulated wire 31 connected to the electric heating device 30 and an optical fiber 33 connected to the Raman scattered light temperature measuring device 32. Each test section has optical fiber 33 and insulated wire
By inserting 31 into the pipe 34 and immersing it in water,
For the cables of sections A and C, to prevent water from entering the pipe,
Both ends of the pipe were exposed to the air, and the cables in the sections B and D imitated the inundated part, so both ends of the pipe were immersed in water to fill the water. The optical fiber length of the sections A and B is 5 m, that of the sections C and D is 10 m, and the ends of the insulated wires are folded and connected. Also, the temperature of water is adjusted to about 25 ° C to simulate an average underground burial condition, and the temperature in the air is about 10
It was ℃.

In this state, the test cable was left standing for 1 hour or more to confirm that the temperature of the test cable became substantially the same as the ambient temperature, and then a voltage of 600 V was applied to the insulated wire 31 by the electric heating device 30 for 15 minutes. The current flowing at this time is about 70A
Met.

FIG. 6 shows the results of measurement of the elapsed time from the start of voltage application and the temperature rise at the center points of sections A, B, C, and D. As shown in the figure, a clear difference was observed in the absolute value of the rising temperature and the temperature gradient in the normal sections A and C and the inundation sections B and D, which proved that the present invention can detect the inundation.

Further, FIG. 7 shows the temperature distribution in the longitudinal direction of the optical fiber 10 minutes after the start of applying the voltage. The difference in inundation length was clearly observed between the inundation sections B and D, and it was also verified that the inundation length can be measured.

[0021]

As described above, when the monitoring system or cable of the present invention is used, environmental substances such as muddy water, seawater, sewage, sand and chemical substances may enter the transmission line due to an accident. However, it is possible to grasp in real time the status of damage such as the occurrence and location of the damage. Therefore, immediate maintenance can be taken, damage is minimized,
And it can be quickly restored.

Further, in the system of the present invention, it is not necessary to provide a monitoring facility in the middle of each transmission line for monitoring, and a long-distance transmission line can be monitored by one system. The system cost per unit length can be reduced.

Further, since the optical fiber having the non-metallic structure is used for the sensor which is generally considered to be weak against inductive interference, problems such as inductive interference from extra high voltage electric wires running in parallel in the vicinity can be avoided. For the heating element, for example, the core of an insulated wire for wiring based on the existing standard is used, and if a surge-proof measure equivalent to that of a normal low-voltage or high-voltage distribution line is taken, problems such as induction failure can be solved.

Therefore, the principle and cable of this system are
It can be applied not only to ABF cables, general optical cables, power cables, and composite cables of these, but also to various substances such as sensor cables, pipelines, common grooves, caverns, and tunnels, as well as environmental substance intrusion monitoring. Also, the environmental substances to be detected are water, seawater, sewage,
Not limited to sand and chemical substances, it is conceivable to target all substances having different specific heat and thermal conductivity from the constituent material of the transmission line.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of a system of the present invention.

FIG. 2 is an explanatory diagram showing the principle of a Raman scattered light temperature measurement system.

FIG. 3 is a graph showing a wavelength distribution of backscattered light in a Raman scattered light temperature measurement system.

FIG. 4 is a sectional view showing the cable of the present invention, (A) is a sectional view of the entire cable, and (B) is a sectional view of an optical fiber unit used therein.

FIG. 5 is a configuration diagram showing an outline of an apparatus used in a test example of the present invention.

FIG. 6 is a graph showing the measurement results of the elapsed time from the start of voltage application and the temperature rise at the center points of sections A, B, C, and D in the test example.

FIG. 7 is a graph showing the temperature distribution in the longitudinal direction of the optical fiber 10 minutes after the start of voltage application.

[Explanation of symbols]

 1 transmission line 1a stirrup 1b core 2 heating element 3 temperature measuring optical fiber 4 temperature control device 5 Raman scattered light temperature measuring device 10 tension member 11 PE tube 12 PE insulated wire 13 LAP sheath 14 metal corrugated sheath 15 anticorrosion layer 16 optical Fiber unit 17 Lip cord 18 Optical fiber UV strand 19 Primary coating 20 Secondary coating 30 Electric heating device 31 Insulated wire 32 Raman scattered light temperature measuring device 33 Optical fiber 34 Pipe

Claims (2)

[Claims] 1. A temperature monitoring optical fiber connected to a Raman scattered light temperature measuring device and a heating element for heating the optical fiber are provided in the longitudinal direction of the transmission line, and the temperature is measured by causing the heating element to generate heat. A system for monitoring the infiltration of environmental substances into a transmission line, which detects the intrusion of environmental substances into the transmission line based on changes in temperature distribution. 2. A cable with a water immersion sensor, which has a built-in heating element and an optical fiber for temperature monitoring.