JP2839809B2 - Optical fiber composite power cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber composite power cable in which an optical fiber for measuring a temperature distribution of a cable is composited.

[0002]

2. Description of the Related Art In recent years, overhead cables in urban areas have become
Regardless of the power cable or communication cable, undergrounding is being promoted from the viewpoint of traffic and aesthetics. In particular, overhead power cables may hinder firefighting activities in building areas, and there is a strong demand for underground cables. For this reason, the undergrounding of power cables in major cities has been progressing remarkably recently. However, if the power cable goes underground, it takes a lot of time to recover from the accident if a cable accident occurs, so monitoring the power cable and detecting abnormalities early,
There is an increasing need for safety measures such as preventing damage to other attached cables. It is also important to locate cable fault points after an accident in a short time.

In general, power cables are often designed and laid with a margin for the current capacity. In response to the recent rapid increase in power demand, the permissible temperature is monitored while monitoring the temperature of the actual cable operating state. It is important to manage the current that can be transmitted below. From the above background, an optical fiber composite power cable in which an optical fiber cable having a temperature distribution detecting function is combined with a power cable to manage the allowable current of the power cable and to search for an abnormal point of the cable may be used. It has become.

An OTDR (optical time domain) is used for temperature distribution measurement using this optical fiber.
Reflectometry) method is used,
The principle of the temperature distribution measurement will be described with reference to FIG.

The frequency of a light pulse incident on an optical fiber is ωo, and the frequency of light corresponding to the difference ΔE between the ground level of the energy level of the fiber constituent material (for example, SiO ₂ ) and the excitation level is ωf (ωf = ΔE / H, h; Planck constant). When a strong light pulse is incident on the optical fiber, energy is transferred between the incident photon and the constituent material of the optical fiber, and is mixed with Rayleigh scattered light having the same frequency as the incident light (ωo) and is called Raman scattered light. Higher frequency (ωo + ωf) and lower frequency (ωo-
ωf) is observed.

This is because a photon (ω
o) is absorbed by the fiber constituent material in the ground state, and the Stokes light (ωo−ω) when the material is in an excited state having a higher energy level than the original ground state when photons are emitted.
f) is emitted, and vice versa.
+ Ωf) is released.

The frequency deviation ωf of the Raman scattered light is a value inherent to the substance and is proportional to the difference ΔE between the thermal energy levels as described above.
0 ¹² ) Hz.

The intensity of the Stokes light and the anti-Stokes light has a temperature dependence shown in FIG. 7, and the temperature dependence of the anti-Stokes light is relatively large. The distributed optical fiber temperature sensor measures the light by observing the temporal change in the intensity ratio of the Stokes light and the anti-Stokes light of the backward Raman scattered light scattered in the optical fiber and transmitted in the direction opposite to the traveling direction of the incident light. Is converted to the distance from the incident point to the reflection point, and the temperature distribution in the longitudinal direction of the cable is measured.

Next, the configuration of the temperature measurement system will be described. FIG. 5 is a block diagram of a distributed temperature measurement system using an optical fiber. The measuring system is roughly divided into an optical fiber core 7, a measuring unit 20, a digital averaging unit 29, and a computer 30 including a display unit.
Consists of

[0010] The optical fiber core has a function of temperature detection based on the above-described principle and a transmission path of the temperature detection information. The measurement unit 20 includes an optical unit 21 and a photoelectric conversion unit 24. The optical unit 21 receives a trigger signal from the digital averaging unit 29 and causes the pulse light source 22 (for example, a laser diode or the like) of monochromatic light to emit light. Optical fiber core wire 7 through spectral device 23
Incident on. Further, the optical unit 21 separates the reflected light from the optical fiber core wire 7 into Stokes light and anti-Stokes light by the spectral device 23. The photoelectric conversion unit 24 converts the separated Stokes light and anti-Stokes light into electric signals by light receiving elements 25 and 26 (for example, silicon avalanche photodiodes; Si-APDs).
The signal is amplified by the amplifiers 27 and 28 and sent to the digital averaging unit 29.

[0011] Digital averaging unit 29, a number of times above the measurement at a high speed is performed (e.g., 10 ⁹ times), is designed to remove noises by averaging process converts the measurement signal into a digital signal. The computer 30 controls the entire measurement and also controls the digital averaging unit 2.
The data is downloaded from 9 and converted into a temperature and a distance and displayed on a display screen or printed out.

From the pulse light source 22 to the optical fiber core 7
Is t = 2Lo / v (where Lo is the optical fiber cord from the incident end of the pulsed light to the point where backscattering occurs). 7 and v are the speed of light in the optical fiber.) Since the digital averaging unit 29 triggers the pulse light source 22 to emit pulse light, the light receiving elements 25 and 26 By measuring the time t until the detection signal is output, the position where the backscattered light is generated can be located, and as a result, the position where the temperature abnormality of the power cable 1 occurs can be obtained.

The optical fiber distribution type temperature measuring system described above has already been commercialized and sold by the applicant of the present invention as "optical fiber distribution type temperature sensor DFS-1000 type". An example of the measurement performance of this system is shown below. Temperature measurement accuracy ± 1 ° C Temperature measurement range -20 to + 150 ° C Measurable distance 2km (maximum 10km) Distance resolution 1m Measurement time required about 10 seconds Also, Fig. 8 shows an example of Raman backscattering measurement of the above system. 9 shows an example in which data of the measurement example in FIG. 8 is converted into temperature.

Further, an optical fiber composite power cable in which an optical fiber and a power cable, which are adapted to the above-described optical fiber distribution type temperature measuring system, are combined, has already been applied for a patent by the applicant of the present invention (Japanese Patent Application No. Sho 63). -28669
8 and Japanese Patent Application No. 63-296101; "Method of measuring power cable and its temperature distribution").

[0015]

However, such a conventional technique is satisfactory as a temperature distribution measurement for the purpose of managing the allowable current of a cable.
Has sufficient detection capability for local temperature rises (hot spots) that occur in relatively short sections of cables such as cable ground faults and that occur in a non-rotationally symmetric manner about the cable axis. There was a problem that not.
In other words, the above-mentioned local temperature can be accurately measured with an optical fiber core.
In order to detect the ascending point, if you think about it,
The fiber core will be wrapped around the fiber
Complex power cable with too much fiber
Problem that the price is too high and it is not economical
There is a point. On the other hand, optical fiber
When the core wire is wound, the local temperature rise
The optical fiber cable is too far away from the location and is easily located for detection
There is a problem that the accuracy becomes extremely poor. In view of the above, the present invention is capable of detecting a ground fault accident early and reliably, and winding an optical fiber core.
It is an object of the present invention to provide an optical fiber composite power cable having an appropriate amount and high economic efficiency .

[0016]

According to the optical fiber composite power cable of the present invention, the cable center conductor is insulated by an insulator,
A shield layer including an outer conductor is provided on the outer periphery of the insulator, and in a power cable having an outer jacket provided on the outer periphery of the shield layer, an optical fiber core wire is provided on a part of the shield layer substantially along the longitudinal direction thereof, The twist rate of the optical fiber is 1.0 to 1.5.
Wrap the optical fiber core around the insulator so that
An object of the present invention is to solve the problem by being able to detect a power cable accident based on the Raman scattered light intensity of the optical fiber core.

Further, the present invention relates to a power cable in which a cable center conductor is insulated by an insulator, and a jacket is provided on the outer periphery of the insulator. An optical fiber is provided, and the optical fiber is wound around the outer periphery of the insulator so that the twisting rate of the optical fiber is 1.0 to 1.5, based on the Raman scattered light intensity of the optical fiber. Power cable accidents can be detected.

[0018]

The present inventor has developed a method for simulating a ground fault in a power cable as shown in FIG. Development of Cable Fault Point Evaluation Method by Temperature Detection ”, Amano et al.). In this method, a test power cable in which a defect (0.1 mmφ conductor) is buried in an insulator during the power cable manufacturing process is created, and a high voltage is applied to the test power cable to reduce the power in the event of a ground fault. It measures the temperature distribution of the cable. This way
Fig. 10 shows the power cable temperature distribution at the time of the ground fault.
The range is the temperature around the ground fault point as well as the ground fault point.
Exists in a certain range. The inventor has discovered that this high temperature
Local temperature rise if fiber core is located within range
To detect ground faults, etc.
This is what we focused on. By measuring the temperature distribution, if the optical fiber core is wound around the insulator so that the twisting rate of the optical fiber is 1.0 to 1.5, the above-mentioned local portion can be obtained.
Optical fiber core in high temperature range due to thermal temperature rise
Thus, it has been found that accurate cable temperature distribution measurement can be performed according to various voltage classes and various nominal cross-sectional areas.

In the present invention, the optical fiber core provided on the shielding layer or the sheath of the power cable is connected to the optical fiber so that the twisting rate of the optical fiber is 1.0 to 1.5. By wrapping around the insulator circumference and measuring the time change of the intensity ratio of Stokes light and anti-Stokes light of backward Raman scattered light when pulsed light enters the optical fiber,
By detecting a local temperature rise that is asymmetrical with respect to the cable center axis in a short section of the cable, a ground fault accident of the power cable can be detected early, and the distance from the cable terminal to the accident point can be calculated. The location of the accident can be located.

[0020]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a sectional view of an optical fiber composite power cable according to the first embodiment of the present invention. As shown in the figure, an optical fiber composite power cable 1 has an inner semiconductive layer 3 and a cross-linked polyethylene insulating layer (insulator) on the outer periphery of a cable center conductor 2 in which a plurality of copper strands are twisted to form a divided conductor.
4, an outer semiconductive layer 5 is provided in order, and usually, the inner semiconductive layer 3, the polyethylene insulating layer 4 and the outer semiconductive layer 5 are formed by a co-extrusion method, and a gap between the inner semiconductive layer 3 and the polyethylene insulating layer 4 is formed. And the crosslinked polyethylene insulating layer 4 and the outer semiconductive layer 5 are integrated.

On the outer periphery of the outer semiconductive layer 5, a shielding layer 8 is provided by a number of copper wires, and a cable sheath (outer jacket) 9 made of plastic, metal or the like is coated thereon.

Further, four optical fiber cores 7 are provided in a part of the shielding layer 8 in the circumferential direction along the longitudinal direction, and the optical fiber cores 7 are optical fibers as shown in FIG. The element wire 7a is covered with a metal layer 7c of copper, aluminum, stainless steel or the like, and a gap between the metal layer 7c and the optical fiber element wire 7a is lubricated with a ceramic powder such as alumina (Al ₂ O ₃ ) or a powder lubrication such as talc powder. The agent 7b is enclosed.

In the first embodiment, the optical fiber core 7
Are provided on the outer periphery of the insulating layer 4, but the invention is not limited to this, and at least one or more may be provided. When the optical fiber core is covered with the metal layer 7c, the number of optical fiber cores in the metal layer 7c is not limited to one, and two or more optical fiber cores may be provided.

FIG. 1 is a partially exploded view showing the shape of a shielding layer 8 in which the cable sheath 9 of the optical fiber composite power cable 1 of the first embodiment is removed. In this embodiment, the twisting rate of the optical fiber core wire 7 which is a part of the shielding layer 8 is 1.3.
However, the present invention is not limited to this, and the twisting ratio of the optical fiber core wire may be any value in the range of 1.0 to 1.5.

The optical fiber combined with the power cable as described above is connected to the distributed temperature measurement system shown in FIG. 5 described in the prior art, and the pulse light is made incident on the optical fiber to reduce the intensity of the Raman scattered light. By measuring the time change, a continuous temperature distribution in the longitudinal direction of the cable can be measured, and a temperature rise in a cable ground fault can be detected.

Next, FIG. 4 shows a sectional view of an optical fiber composite power cable 1A according to a second embodiment of the present invention, and the same parts as those in the first embodiment are described with the same reference numerals.
In the second embodiment, the insulating layer 4 of the power cable 1 shown in FIG.
An optical fiber composite power cable 1A is provided by providing an optical fiber core wire 7 shown in FIG. 3 around the outer periphery of the optical fiber, winding the optical fiber core wire 7 around the outer circumference of the insulating layer 4, and providing a jacket 9 on the outer circumference. It is. The winding of the optical fiber core wire 7 may have an arbitrary value when the twisting ratio of the optical fiber core wire is 1.0 to 1.5. This optical fiber composite power cable 1A
5 can be connected to the distributed temperature measurement system of FIG. 5 similarly to the first embodiment to measure a continuous temperature distribution in the longitudinal direction of the cable, and detect a temperature rise due to a cable ground fault. The preferred embodiment has been described above, but this does not limit the scope of the invention. The scope of the invention should be limited only by the appended claims. From the above description, many modifications within the spirit and scope of the invention will be apparent to those skilled in the art.

[0027]

As described above, in the present invention, the optical fiber core of the optical fiber composite power cable is
By wrapping the twisted rate of the optical fiber core around the outer periphery of the shielding layer or the insulating layer so as to be 1.0 to 1.5, the Stokes light of the backward Raman scattered light when the pulsed light enters the optical fiber By measuring the time change of the intensity ratio with anti-Stokes light, a local temperature rise that is asymmetric with respect to the cable central axis in a short section of the cable can be detected, and a ground fault accident in the power cable can be detected early. Along with
The amount of winding of the optical fiber is appropriate and economical. Ma
In addition, in determining the twist rate of an optical fiber,
After conducting tests on force cables and deciding,
Although the previous labor is enormous and the cost is enormous, the present invention
Since the twist rate can be properly determined at the design stage,
And manufacture of optical fiber composite power cable at low cost
Can be. In addition, the distance from the cable terminal to the accident location can be calculated, and the location of the accident location can be located.

[Brief description of the drawings]

FIG. 1 is a partially exploded view of an optical fiber composite power cable according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the optical fiber composite power cable according to the first embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional view of an optical fiber.

FIG. 4 is a sectional view of an optical fiber composite power cable according to a second embodiment of the present invention.

FIG. 5 is a block diagram of a distributed temperature measurement system.

FIG. 6 is an explanatory diagram of the principle of Raman scattering.

FIG. 7 is a diagram showing the temperature dependence of Raman scattered light intensity.

FIG. 8 is a measurement example of Raman scattered light intensity.

FIG. 9 is an example of temperature measurement by measuring the intensity of Raman scattered light.

FIG. 10 is a diagram illustrating an outline of a cable ground fault pseudo fault test method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical fiber composite power cable (first embodiment) 1A optical fiber composite power cable (second embodiment) 2 cable center conductor 3 inner semiconductive layer 4 crosslinked polyethylene insulating layer 5 outer semiconductive layer 7 optical fiber core 7a Optical fiber strand 7b Powder lubricant 7c Metal layer 8 Shielding layer 9 Cable sheath (jacket) 20 Measurement unit 21 Optical unit 22 Pulse light source 23 Spectral device 24 Photoelectric conversion unit 25, 26 Light receiving element 27, 28 Amp (amplifier) 29 Digital averaging unit 30 Computer

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Kazuo Watanabe 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Co., Ltd. (56) References JP-A-2-144810 (JP, A)

Claims (2)

(57) [Claims] 1. A power cable comprising: a cable center conductor insulated by an insulator; a shield layer including an outer conductor provided on an outer periphery of the insulator; and a jacket provided on an outer periphery of the shield layer. An optical fiber core wire is provided substantially along the longitudinal direction of the optical fiber, and the optical fiber core wire is wound around the outer periphery of the insulator so that the twisting rate of the optical fiber core is 1.0 to 1.5. An optical fiber composite power cable capable of detecting an accident of a power cable based on Raman scattered light intensity of a core wire. 2. A power cable in which a cable center conductor is insulated by an insulator, and a jacket is provided on the outer periphery of the insulator. And the twist rate of the optical fiber is 1.
An optical fiber composite, comprising: wrapping an optical fiber core around an insulator so as to be 0 to 1.5, and detecting a power cable accident based on Raman scattered light intensity of the optical fiber core. Power cable.