Temperature measurement method

Abstract

To provide a method for measuring the temperature of a power cable in which the temperature of a cable conductor can be measured over the entire length with good response.SOLUTION: An optical fiber and a first measuring conductor are arranged along a power cable around a cable conductor of the power cable, a second measuring conductor is connected to the first measuring conductor to form a loop circuit, the temperature of the first measuring conductor is measured by using the optical fiber, and the temperature of the cable conductor is calculated based on the measured temperature of the first measuring conductor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the temperature of a power cable. [Background technology]

[0002] Conventionally, optical fiber sensors have been used to evaluate the soundness of laid power cables (see, for example, Patent Document 1). Patent Document 1 discloses that partial discharge occurring in a power cable is detected by using an optical fiber that is combined with the power cable over its entire length.

[0003] Also known is an optical fiber sensor that places an optical fiber along an object to be measured and detects continuous distributed information (temperature, strain, vibration, etc.) along the optical fiber based on changes in the transmission characteristics (intensity, phase, frequency, wavelength, etc.) of light propagating through the optical fiber. Such optical fiber sensors are called "distributed." Distributed optical fiber sensors measure the temperature of the cable conductor over the entire length of a power cable, and based on the measured temperature, it is possible to determine the current flowing through the cable and, ultimately, the amount of power consumed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-298154 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, an optical fiber is disposed inside a power cable, specifically between the cable shielding layer and the cable insulator. When this optical fiber is used as a distributed optical fiber sensor to detect the temperature of the cable conductor, the temperature of the cable conductor is transmitted to the optical fiber via the cable insulator. As a result, the response of the optical fiber to temperature changes in the cable conductor is delayed, making it difficult to grasp temperature changes in real time. In particular, the thicker the cable insulator of a high-voltage cable, the worse the response of the optical fiber sensor is thought to be.

[0006] An object of the present invention is to provide a method for measuring the temperature of a power cable, which is capable of measuring the temperature of the cable conductor over its entire length with good response. [Means for solving the problem]

[0007] The temperature measurement method according to the present invention comprises: an optical fiber and a first measuring conductor are arranged around a cable conductor of a power cable along the power cable; a second measuring conductor is connected to the first measuring conductor to form a loop circuit; measuring a temperature of the first measurement conductor using the optical fiber; The temperature of the cable conductor is calculated based on the measured temperature of the first measurement conductor. [Effects of the Invention]

[0008] According to the present invention, the temperature of a cable conductor can be measured with good responsiveness. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing a method for measuring the temperature of a cable conductor according to an embodiment. [Figure 2] 2A and 2B are diagrams showing an example of an optical fiber composite wire. [Figure 3] FIG. 3 is a diagram showing the configuration of a power cable. [Figure 4]4A and 4B are diagrams showing an example of an arrangement of a loop circuit relative to a power cable. [Figure 5] FIG. 5 is a diagram showing another example of the arrangement of a loop circuit relative to a power cable. [Figure 6] FIG. 6 is a diagram showing another example of the arrangement of the loop circuit relative to the power cable. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] FIG. 1 is a conceptual diagram showing a method for measuring the temperature of a cable conductor according to one embodiment of the present invention.

[0012] As shown in FIG. 1, an optical fiber 11 is arranged along a power cable 20. A loop circuit 40 consisting of a first measurement conductor 41 and a second measurement conductor 42 is arranged around the power cable 20. The optical fiber 11 and the first measurement conductor 41 are arranged, for example, as shown in FIG. 1, by being wound spirally along the outer circumferential surface of the power cable 20 over the entire length. Alternatively, for example, the optical fiber 11 and the first measurement conductor 41 may be incorporated inside the power cable 20. In this embodiment, a distributed optical fiber sensor consisting of the optical fiber 11, a light source 31, and a detector 32 is used to continuously measure the temperature distribution of the cable conductor 21 (see FIG. 3) over the entire length of the power cable 20.

[0013] Specifically, light is emitted from a light source 31 into the optical fiber 11. The emitted light propagates through the optical fiber 11, and scattered light is generated during the propagation process. By detecting this scattered light with a detector 32, it is possible to measure the temperature around the optical fiber 11 and the deformation (strain) of the optical fiber 11. The principle of the distributed optical fiber sensor is well known, so a detailed description thereof will be omitted.

[0014] In this embodiment, instead of directly measuring the temperature of the cable conductor 21, the temperature of the first measurement conductor 41 is measured using the optical fiber 11, taking advantage of the fact that temperature changes in the cable conductor 21 are reflected in temperature changes in the first measurement conductor 41, and the temperature of the cable conductor 21 is indirectly measured based on the temperature of the first measurement conductor 41.

[0015] The first measurement conductor 41 is disposed along the optical fiber 11. The first measurement conductor 41 is disposed, for example, parallel to the optical fiber 11 so that the relative positional relationship with the optical fiber 11 does not change.

[0016] The second measurement conductor 42 is connected to the first measurement conductor 41 and forms a loop circuit 40 together with the first measurement conductor 41. The second measurement conductor 42 is connected to both ends of the first measurement conductor 41, for example.

[0017] The first measurement conductor 41 and the second measurement conductor 42 are elongated members made of a conductive material such as copper, aluminum, a copper alloy, or an aluminum alloy. The materials of the first measurement conductor 41 and the second measurement conductor 42 may be the same or different. Furthermore, the cross-sectional areas of the first measurement conductor 41 and the second measurement conductor 42 may be the same or different.

[0018] The positions of the first measurement conductor 41 and the second measurement conductor 42 can be set individually so as to increase the induced electromotive force generated in the loop circuit 40 when current is passed through the cable conductor 21. In other words, the first measurement conductor 41 and the second measurement conductor 42 may be arranged at different distances from the cable conductor 21 in the cross section of the power cable 20.

[0019] It is preferable that the first measurement conductor 41 has a higher electrical resistance than the second measurement conductor 42. In this case, the first measurement conductor 41 generates more heat when current is applied to the cable conductor 21, so that a change in the temperature of the cable conductor 21 is significantly reflected in a change in the temperature of the first measurement conductor 41.

[0020] For example, when the first measurement conductor 41 and the second measurement conductor 42 have the same cross-sectional area, the first measurement conductor 41 may be made of a material with a higher resistivity than the second measurement conductor 42. For example, the first measurement conductor 41 may be made of iron and the second measurement conductor 42 may be made of copper or aluminum. Furthermore, when the first measurement conductor 41 and the second measurement conductor 42 are made of the same material, the cross-sectional area of ​​the first measurement conductor 41 may be made smaller than the cross-sectional area of ​​the second measurement conductor 42. The electrical resistances of the first measurement conductor 41 and the second measurement conductor 42 can be adjusted, for example, by appropriately setting the material and cross-sectional area of ​​the first measurement conductor 41.

[0021] The optical fiber 11 and the first measuring conductor 41 may be incorporated into, for example, the composite optical fiber wire 10 (see FIGS. 2A and 2B). A known configuration in which a linear member or a tubular member is arranged around the optical fiber 11 as a reinforcing wire can be applied to the composite optical fiber wire 10 shown in FIGS. 2A and 2B.

[0022] 2A, the composite optical fiber wire 10 is composed of a composite stranded optical fiber wire in which optical fibers 11 and solid first measurement conductors 41 are stranded together. In FIG. 2A, the composite optical fiber wire 10 has two optical fibers 11 and seventeen first measurement conductors 41.

[0023] 2A, two optical fibers 11 are disposed, but one or more may be disposed, and it is preferable that the optical fiber 11 be disposed in the outermost layer of the twisted wire. In the case of a twisted optical fiber wire, if the optical fiber 11 is disposed in the center, heat is trapped and the temperature of the first measurement conductor 41 is not easily reflected in the optical fiber 11, which may result in a decrease in responsiveness. In contrast, if the optical fiber 11 is disposed in the outermost layer of the twisted wire, heat dissipation is improved, so that the temperature of the first measurement conductor 41 is quickly reflected in the optical fiber 11, improving responsiveness.

[0024] 2B, the composite optical fiber wire 10 has a configuration in which an optical fiber 11 is disposed in a hollow portion of a tubular first measurement conductor 41. In FIG. 2B, one optical fiber 11 is disposed in the hollow portion of the first measurement conductor 41.

[0025] 2A and 2B, a first measurement conductor 41 is arranged along the optical fiber 11. In the composite optical fiber wire 10, the relative positional relationship between the optical fiber 11 and the first measurement conductor 41 is substantially fixed over the entire length. Note that, in the composite optical fiber wire 10, the number of optical fibers 11 and the number of first measurement conductors 41 arranged is not particularly limited.

[0026] FIG. 3 is a diagram showing the configuration of a power cable.

[0027] 3, a power cable 20 includes, in order from the center, a cable conductor 21, a cable insulator 22, a cable shielding layer 23, and a cable sheath 24. Although not shown, an inner semiconductive layer may be interposed between the cable conductor 21 and the cable insulator 22, and an outer semiconductive layer may be interposed between the cable insulator 22 and the cable shielding layer 23.

[0028] 4A and 4B are diagrams showing an example of an arrangement of a loop circuit 40 relative to a power cable 20. In FIGS. 4A and 4B, a composite optical fiber 10 having an optical fiber 11 and a first measuring conductor 41 is applied.

[0029] In FIG. 4A, the composite optical fiber 10 (including the optical fiber 11 and the first measuring conductor 41) and the second measuring conductor 42 are arranged along the power cable 20 and outside the power cable 20. In FIG.

[0030] The composite optical fiber 10 and the second measurement conductor 42 may be arranged, for example, so as to be in contact with the power cable 20, or may be arranged apart from the power cable 20. In either case, the composite optical fiber 10 is arranged along the longitudinal direction of the power cable 20. The second measurement conductor 42 may be arranged in any manner as long as it forms the loop circuit 40 together with the first measurement conductor 41.

[0031] When the composite optical fiber 10 is arranged away from the power cable 20, it is possible to reduce the influence on the cable sheath 24 of the temperature rise of the first measurement conductor 41 caused by the passage of current through the cable conductor 21, and to prevent damage to the power cable 20. Note that, since the second measurement conductor 42 may also generate heat when current is passed through the cable conductor 21, the second measurement conductor 42 may also be arranged away from the power cable 20.

[0032] The first measurement conductor 41 and the second measurement conductor 42 may be positioned at a position where a temperature change in the cable conductor 21 is reflected in a temperature change in the first measurement conductor 41, i.e., where an induced current flows in the loop circuit 40 when current is applied to the cable conductor 21, causing the temperature of the first measurement conductor 41 to rise.

[0033] The example of the arrangement of the loop circuit 40 shown in Fig. 4A can also be applied to the case where the loop circuit 40 is arranged in a triplex power cable in which three power cables 20 are twisted together, as shown in Fig. 4B. In this case, the composite optical fiber 10 is arranged, for example, near the contact portion of the two power cables 20.

[0034] 4A and 4B, in a cross section perpendicular to the longitudinal direction of the power cable 20, it is preferable that the first measurement conductor 41 is disposed closer to the cable conductor 21 in the radial direction than the second measurement conductor 42. This is because a temperature change in the cable conductor 21 is more likely to be reflected in a temperature change in the first measurement conductor 41.

[0035] 5 and 6 are diagrams showing another example of the arrangement of the loop circuit 40 relative to the power cable 20. In Fig. 5 and Fig. 6, a composite optical fiber 10 having an optical fiber 11 and a first measuring conductor 41 is applied.

[0036] 5, the composite optical fiber 10 (including the optical fiber 11 and the first measurement conductor 41) is arranged inside the power cable 20 along the power cable 20, and the second measurement conductor 42 is arranged outside the power cable 20. The arrangement of the second measurement conductor 42 is as described with reference to FIG. 4A etc.

[0037] 5, the composite optical fiber 10 is disposed, for example, in a cable shielding layer 23. In FIG. 5, a part of the shield wire (wire shield) forming the cable shielding layer 23 is replaced with the composite optical fiber 10. The first measuring conductor 41 of the composite optical fiber 10 is electrically insulated from the cable shielding layer 23.

[0038] When the composite optical fiber 10 is disposed inside the power cable 20, heat generated by the first measuring conductor 41 may impair the insulating performance of the power cable 20, so it is preferable to dispose the composite optical fiber 10 away from the cable insulator 22. For example, the composite optical fiber 10 may be disposed between the cable shielding layer 23 and the cable sheath 24. The composite optical fiber 10 may also be disposed by being embedded in the cable sheath 24. In particular, when the cable shielding layer 23 is formed of a copper tape instead of a wire shield as shown in FIG. 5, the composite optical fiber 10 may be disposed around the copper tape (between the cable shielding layer 23 and the cable sheath 24).

[0039] 6, the composite optical fiber 10 (including the optical fiber 11 and the first measurement conductor 41) is arranged outside the power cable 20 along the power cable 20, and the second measurement conductor 42 is arranged inside the power cable 20. The arrangement of the composite optical fiber 10 is as described with reference to FIG. 4, for example.

[0040] 6, the second measurement conductor 42 is disposed, for example, on the cable shielding layer 23. In Fig. 6, a part of the shield wire (wire shield) forming the cable shielding layer 23 is replaced with the second measurement conductor 42. The second measurement conductor 42 is electrically insulated from the cable shielding layer 23.

[0041] When the second measurement conductor 42 is disposed inside the power cable 20, heat generated by the second measurement conductor 42 may impair the insulating performance of the power cable 20, so it is preferable to dispose the second measurement conductor 42 away from the cable insulator 22. For example, the second measurement conductor 42 may be disposed between the cable shielding layer 23 and the cable sheath 24. The second measurement conductor 42 may also be disposed embedded in the cable sheath 24. In particular, when the cable shielding layer 23 is formed of copper tape instead of a wire shield as shown in FIG. 5, the second measurement conductor 42 may be disposed on the outer periphery of the copper tape (between the cable shielding layer 23 and the cable sheath 24).

[0042] When measuring the temperature distribution in the longitudinal direction of the power cable 20, it is preferable that the optical fiber 11 (composite optical fiber 10) is closer to the cable conductor 21 as in the embodiment of FIG. 5 compared to the embodiment of FIG.

[0043] 5 and 6, the number of the composite optical fiber wires 10 to be arranged is not particularly limited. The composite optical fiber wires 10 and the second measurement conductor 42 may both be arranged inside the power cable 20. In this case, however, the composite optical fiber wires 10 (first measurement conductor 41) and the second measurement conductor 42 must be arranged as far apart as possible in the radial direction so that their distances from the cable conductor 21 are different in a cross section perpendicular to the longitudinal direction of the power cable 20. For example, if the composite optical fiber wires 10 are arranged in the cable shielding layer 23, the second measurement conductor 42 may be embedded as far outward as possible in the radial direction inside the cable sheath 24. The exemplary arrangement of the loop circuit 40 shown in FIGS. 5 and 6 can also be applied to the case where the loop circuit 40 is arranged in a triplex power cable.

[0044] In the temperature measurement method of this embodiment, the loop circuit 40 is arranged around the cable conductor 21 of the power cable 20. When an AC current is passed through the cable conductor 21, the cable conductor 21 generates heat due to the current flow, increasing its temperature, and a magnetic field is generated around the cable conductor 21. As the magnetic field changes, an induced electromotive force is generated in the loop circuit 40 (the first measurement conductor 41 and the second measurement conductor 42) placed in this magnetic field, causing an induced current to flow. The induced current causes the first measurement conductor 41 to generate heat, increasing its temperature. In other words, a change in the temperature of the cable conductor 21 is reflected in a change in the temperature of the first measurement conductor 41. The change in temperature of the cable conductor 21 is also reflected in the second measurement conductor 42.

[0045] By detecting the transmission characteristics of the optical fiber 11, the temperature of the first measurement conductor 41 can be measured, and the temperature of the cable conductor 21 can be calculated based on the temperature of the first measurement conductor 41. For example, the relationship between the temperature of the first measurement conductor 41 and the temperature of the cable conductor 21 may be experimentally obtained in advance.

[0046] As described above, the power cable temperature measuring method according to the embodiment has the following features either alone or in appropriate combination.

[0047] That is, in the power cable temperature measurement method according to the embodiment, an optical fiber 11 and a first measurement conductor 41 are arranged around a cable conductor 21 of a power cable 20 along the power cable 20, a second measurement conductor 42 is connected to the first measurement conductor 41 to form a loop circuit 40, the temperature of the first measurement conductor 41 is measured using the optical fiber 11, and the temperature of the cable conductor 21 is calculated based on the measured temperature of the first measurement conductor 41.

[0048] According to the temperature measurement method of this embodiment, the temperature distribution of the cable conductor 21 can be measured over the entire length using a distributed optical fiber sensor. Furthermore, the temperature of the cable conductor 21 is reflected in the first measurement conductor 41 in a short time, which improves responsiveness compared to when the temperature of the cable conductor 21 is measured directly using an optical fiber. Therefore, the temperature of the cable conductor 21 can be measured over the entire length with good responsiveness. Furthermore, the current flowing through the cable conductor 21 can be estimated from the temperature distribution of the cable conductor 21, and the amount of power consumption can be monitored, which is suitable for demand control.

[0049] Furthermore, since the temperature of the first measurement conductor 41 is measured using the optical fiber 11, it is sufficient to arrange the first measurement conductor 41 and the optical fiber 11 so that the temperature change of the cable conductor 21 is reflected in the temperature change of the first measurement conductor 41, and the temperature measurement equipment can be constructed relatively freely.

[0050] In this embodiment, the first measurement conductor 41 and the second measurement conductor 42 are arranged at different distances from the cable conductor 21 in a cross section perpendicular to the longitudinal direction of the power cable 20. The positions of the first measurement conductor 41 and the second measurement conductor 42 can be set individually, which increases the degree of freedom in arrangement so that the induced electromotive force generated in the loop circuit 40 when current is passed through the cable conductor 21 is large.

[0051] In this embodiment, the first measurement conductor 41 may have a higher electrical resistance than the second measurement conductor 42. For example, the first measurement conductor 41 and the second measurement conductor 42 are formed of different materials. Furthermore, for example, the cross-sectional area of ​​the first measurement conductor 41 is smaller than the cross-sectional area of ​​the second measurement conductor 42. This allows the first measurement conductor 41 to generate heat efficiently when current is applied to the cable conductor 21, and allows the temperature change of the cable conductor 21 to be reflected in the first measurement conductor 41 in a short time.

[0052] In this embodiment, a composite optical fiber cable 10 is used, which includes a first measurement conductor 41 and an optical fiber 11. This allows the relative positional relationship between the optical fiber 11 and the first measurement conductor 41 to be fixed over the entire length, thereby improving measurement accuracy.

[0053] In this embodiment, the composite optical fiber 10 may be arranged along the outer peripheral surface of the cable sheath 24 of the power cable 20 (see FIGS. 4A, 4B, and 6). This makes it possible to easily install a temperature measurement device for the cable conductor 21 in an existing cable facility.

[0054] In the present embodiment, the composite optical fiber 10 may be embedded in the power cable 20. This allows a temperature measurement means for the cable conductor 21 to be built into the power cable 20 using known cable manufacturing techniques, thereby simplifying the temperature measurement equipment.

[0055] The invention made by the inventor has been specifically described above based on an embodiment, but the present invention is not limited to the above embodiment and can be modified within the scope of the gist thereof.

[0056] For example, in the embodiment, the composite optical fiber cable 10 is used in which the optical fiber 11 and the first measurement conductor 41 are integrated, but the optical fiber 11 and the first measurement conductor 41 may be arranged separately with respect to the power cable 20.

[0057] In the embodiment, the temperature distribution of the cable conductor 21 is measured by the distributed optical fiber sensor, but in addition to the temperature distribution of the cable conductor 21, distortion of the power cable 20 and vibrations in the surrounding environment can also be detected and used for the maintenance and inspection of cable facilities. For example, by using the optical fiber 11 laid along the power cable 20, it is possible to monitor deformation of the power cable 20 due to thermal expansion and contraction after installation, movement of the power cable 20 due to slippage, etc., and abnormal axial force. In this way, when detecting distortion and deformation of the power cable 20 using the optical fiber 11, it is preferable to arrange a plurality of composite optical fiber wires 10. Furthermore, for example, the optical fiber 11 laid along the power cable 20 can also detect discharge sounds to detect failures in the cable facility in advance, or detect and warn of vibrations associated with excavation for underground installation.

[0058] Furthermore, for example, in the embodiment, the optical fiber 11 is arranged on the first measurement conductor 41 side, but an optical fiber may be arranged not only on the first measurement conductor 41 side but also on the second measurement conductor 42 side.

[0059] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0060] 10 Optical fiber composite wire 11 Optical Fiber 20 Power Cable 21 Cable conductor 22 Cable insulator 23 Cable shielding layer 24 Cable sheath 40 Loop Circuit 41 First measuring conductor 42 Second measuring conductor

Claims

1. an optical fiber and a first measuring conductor are arranged around a cable conductor of a power cable along the power cable; a second measuring conductor is connected to the first measuring conductor to form a loop circuit; measuring a temperature of the first measurement conductor using the optical fiber; calculating the temperature of the cable conductor based on the measured temperature of the first measurement conductor; Temperature measurement method.

2. the first measurement conductor and the second measurement conductor are arranged so as to be at different distances from the cable conductor in a cross section perpendicular to the longitudinal direction of the power cable. The temperature measurement method according to claim 1 .

3. The first measurement conductor has a higher resistance than the second measurement conductor. The temperature measurement method according to claim 1 .

4. the first measuring conductor and the second measuring conductor are formed of different materials; The temperature measurement method according to claim 3 .

5. The cross-sectional area of ​​the first measurement conductor is smaller than the cross-sectional area of ​​the second measurement conductor. The temperature measurement method according to claim 3 .

6. a composite optical fiber wire including the first measuring conductor and the optical fiber; The temperature measurement method according to claim 1 .

7. The optical fiber composite wire is arranged along an outer peripheral surface of a cable sheath of the power cable. The temperature measurement method according to claim 6.

8. The composite optical fiber is embedded in the power cable. The temperature measurement method according to claim 6.

Images