JPH09281146A - Power cable line with current detector using giant magnetostrictive alloy and giant magnetostrictive alloy sensor - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To generate a large strain in a sensor made of giant magnetostrictive alloy to detect a current with high sensitivity, and to accurately detect an accident point by using a sensor made of giant magnetostrictive alloy. When a current flows through a power device, a power cable, or the like, a uniform magnetic field is generated in the axial direction of the curved surface of the giant magnetostrictive alloy plate 3, and the magnetic field causes magnetostriction in the giant magnetostrictive alloy plate 3. Since both ends of the giant magnetostrictive alloy plate 3 are restrained from moving by the protrusions 2a of the giant magnetostrictive alloy plate fixing adapter 2,
The giant magnetostrictive alloy plate 3 expands and deforms in the circumferential direction. The deformation of the giant magnetostrictive alloy plate 3 is detected by the strain gauge 5 and sent to the strain measuring instrument 7 via the lead wire 6 to measure the strain amount. Further, by attaching a giant magnetostrictive alloy sensor to an ultrahigh voltage power cable or the like and detecting the strain of the giant magnetostrictive alloy by the strain sensor, it is possible to determine the ground fault accident occurrence section or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power cable line equipped with a current detector using a giant magnetostrictive alloy and a giant magnetostrictive sensor. In particular, the present invention relates to detecting a current flowing through a power cable or various power devices. The present invention relates to a suitable current detector and a power cable line capable of detecting a fault point in an ultra high voltage power cable.

[0002]

2. Description of the Related Art As a general method for detecting a ground fault in an ultra-high-voltage power cable, a current transformer (CT) is attached to the ground wire that cross-bonds each cable connection, and the current that flows in each ground wire when an accident occurs. There is known a method of determining by determining the size, direction, phase distribution, and the like. The above method has a problem that the work is complicated and a large equipment cost is required. Therefore, a method has also been considered in which an optical fiber type distributed temperature sensor is provided along the cable to measure the cable temperature change during a ground fault.

However, recently, the performance of the circuit breaker has improved, and the duration of the ground fault is as short as about 1/10 second.
Since the heat capacity of the ultra high voltage power cable is large, it is not easy to detect the cable temperature change at the time of a ground fault from the outside. If the optical temperature sensor fiber is built into the cable, it is possible to detect the temperature change during a ground fault in a relatively short time, but the cable structure becomes complicated and it is also possible to take the sensor signal out of the cable. Not easy.

FIG. 11 is a diagram showing a cross-bonded three-phase line. In a power cable line of 275 kVA or more, normally, every other two normal connecting portions NJ are arranged in the longitudinal direction of the line. Then, the cable metal sheath 3 and the ground are grounded by the ground wire 5. In addition, the middle two connecting portions are insulated cylinders 7 such that the sheath circuit is once interrupted.
Is incorporated into the insulation connection section IJ. Here, the three-phase sheath circuits of the cable are replaced with each other by the ground wire and cross-bond connection is performed. This prevents the generation of unbalanced induced current in the three-phase sheath circuit under constant power transmission.

In FIG. 11, when a ground fault occurs at the P point of the A phase of the cable, the ground fault current I0 flowing through the conductor from the power source side moves to the A phase metal sheath 3 at the fault point P and further insulation connection is made. From the cross bond portion of the section IJ, the B-phase or C-phase metal sheath 3 is returned to the ground (the return current is I
1 or I2). Generally, the ground fault current of a 275 kV class cable is predicted to be about 30 kA and that of a 500 kV class cable is about 60 kA.
A current of several tens of times that of (00A) instantaneously flows. This huge ground fault current flows to the sheath return path outside the conductor as described above, and generates a large magnetic field in the periphery.

FIG. 12 shows a magnetic field H (A / m) generated when a current I flows through a cable 11 placed in a straight line, and a distance r (m) on a plane perpendicular to the cable 11.
The magnetic field at the position of is calculated by the following formula. H = I / (2πr) (A / m) That is, by detecting the magnetic field generated around the cable 11, a current such as a ground fault current can be detected. Therefore, a method has been proposed in which a magnetostrictive material M that changes the length according to the magnitude of the magnetic field is installed around the cable, and the change in the strain is monitored to detect the location of the ground fault.

Ferromagnetic materials such as ferrite have conventionally existed as the magnetostrictive material, but the maximum strain of the conventional magnetostrictive material is about 40 μm no matter how large the magnetic field is placed. Since the size is the same level as the expansion and contraction strain generated by temperature change, it cannot be distinguished,
It did not reach practical use. However, recently, a magnetostrictive material M that generates a strain having a level of expansion / contraction strain that is approximately two orders of magnitude higher than that of the conventional one has been developed, and these are called a giant magnetostrictive material in distinction from the conventional magnetostrictive material. .

As a representative of the giant magnetostrictive material, terbium,
Tb _0.3 Dy _0.7 Fe _1.9 which is an alloy of dysprosium and iron
Has been put into practical use, and a strain of about 1000 μm can be generated in a magnetic field of several tens kA / m at room temperature.
If this level of strain can be generated, it can be accurately evaluated by pasting an existing resistance wire strain gauge on the surface of a giant magnetostrictive alloy and measuring the strain, and it is also sufficiently distinguished from the strain due to the thermal expansion of the giant magnetostrictive alloy. It is possible.

[0009]

In an ultra-high-voltage power cable, the fault current at ground fault reaches several tens of kA, so if a giant magnetostrictive alloy is placed near the cable, a sufficiently detectable magnetostriction will occur and the ground fault current will be detected. be able to. Therefore, in the ultra-high voltage power cable, if a ground fault current is detected using the giant magnetostrictive alloy and transmitted to a center or the like,
The point of occurrence of a ground fault can be detected. On the other hand, 15
Ground fault current is 1 for cables of low voltage class of 4 kV or less.
It will be a small number of digits or less, and there is a high possibility that magnetostriction that can detect this will not occur even in the event of an accident. Further, in various electric power devices and the like, the current flowing at the time of an accident is smaller than the current flowing at the time of the ground fault of the above-mentioned ultra-high voltage power cable, and it is also difficult to measure with the conventional giant magnetostrictive alloy.
Therefore, it is considered necessary to provide a method of generating a larger magnetostriction with the same magnetic field and the same giant magnetostrictive alloy.

The present invention has been made in consideration of the above circumstances, and a first object thereof is to generate an even larger strain using an existing giant magnetostrictive alloy, and to provide an extra high voltage power cable. An object of the present invention is to provide a current detector capable of detecting not only a ground fault current but also a ground fault current in an electric line having a small normal current, a current flowing in various electric power devices, and the like. A second object of the present invention is to easily attach the sensor unit from outside the power cable, and
It is an object of the present invention to provide a power cable line capable of transmitting a sensor output with a simple system and further accurately detecting an accident point.

[0011]

[Means for Solving the Problems] By precurving a giant magnetostrictive alloy and restraining the extension of its ends, when a magnetostriction occurs in the giant magnetostrictive alloy due to a magnetic field, a large bending strain is induced, and it is originally generated. The magnitude of elongation due to magnetostriction can be increased. Further, if the giant magnetostrictive alloy is formed of a thin plate curved in an arc shape and the thin plate is placed in a magnetic field generated by an electric current flowing through an electric line, the curved surface axis of the giant magnetostrictive alloy 3 as shown in FIG. A uniform magnetostriction occurs in the direction.

As shown by the solid line in FIG. 2, when the radius of curvature of the arc portion of the giant magnetostrictive alloy is R and the curvature is θ, δL at each arc end portion due to the uniform magnetostriction ε generated on the curved surface. =
An elongation of εRθ occurs. Therefore, when the both ends of the giant magnetostrictive alloy are constrained by a strong resistance force so as not to move due to this elongation, the giant magnetostrictive alloy plate swells and deforms in the circumferential direction as shown by the dotted line in FIG.

At this time, the bending strain ε 0 generated at the top of the circular plate having the thickness t is given by the following equation based on the strain deformation theory of the curved beam in material mechanics. ε0 = ε {1+ [sinθ−θ ・ cos (θ / 2)] t / [θ / 2 + (
sin2θ) / 4− (sin ² θ) / θ] R} If the second term of the above equation is increased significantly, this bending strain ε0
The value of can be made much larger than the expansion strain ε due to the magnetic field uniformly generated in the giant magnetostrictive alloy plate when the arc portion is unconstrained.

FIG. 3 shows the internal angle of the arc (θ in FIG. 2) and the strain amplification factor (ε0 / ε) obtained from the above equation. If the internal angle is less than about 78 °, the strain amplification factor is 1.
It becomes 0 or more, and the distortion amplification factor can be increased as the internal angle is decreased, and can be increased from approximately 25 ° or less to 10 times or more. However, it should be noted that as the internal angle becomes smaller, the length L (L = ε × R × θ) of the giant magnetostrictive alloy becomes shorter, the terminal effect is likely to occur, and the strain measurement error may increase. is there.

FIG. 4 is a diagram showing the relationship between the magnetic field direction and the strain generated in the giant magnetostrictive alloy. As is clear from the figure,
The strain generated in the giant magnetostrictive alloy is larger in the same direction as the direction of the magnetic field (difference in a direction in the figure), and is larger in the direction orthogonal to the magnetic field (difference in b direction in the figure). A little small. For this reason, the amount of deformation of the giant magnetostrictive alloy is larger when the giant magnetostrictive alloy is arranged in parallel with the magnetic field, but even if the giant magnetostrictive alloy is arranged orthogonally to the magnetic field, the amount of deformation is small by about 20 to 30%. However, it is sufficiently practical when high sensitivity is not required.

On the other hand, in the case of an ultra-high voltage cable of 275 kV class cable or more, a constant current (1
Since a huge current several tens times (000 to 1500 A) flows instantaneously, the fault current can be detected without using the above-mentioned means for expanding the magnitude of elongation due to magnetostriction.
That is, if a giant magnetostrictive element is attached to a cable or the like, when a ground fault occurs in the cable or the like, a large strain change can be generated in the giant magnetostrictive element, and the strain generated in the giant magnetostrictive element can be detected. This makes it easy to detect the occurrence of an accident and locate the accident point. As a method of detecting the strain generated in the giant magnetostrictive element M, for example, a strain gauge using a metal resistance wire is attached to the surface of the giant magnetostrictive element, or an optical fiber is fixed to the surface of the giant magnetostrictive element to make it A strain change equivalent to that of the magnetostrictive element is generated in the optical fiber, and the strain transmitted to the optical fiber can be detected by, for example, a measuring method applying Brillouin scattering described later.

The present invention solves the above-described problems based on the above principle as follows. (1) disposing a giant magnetostrictive alloy in a magnetic field generated by an electric current,
The giant magnetostrictive alloy is formed into a plate-like body that is curved in an arc shape, and both ends of the plate-like body are restrained from expansion and contraction by restraint bodies. (2) An adapter for fixing a sensor made of a giant magnetostrictive alloy, which is provided with a sensor made of a giant magnetostrictive alloy, which is curved in an arc shape, and a strain sensor is attached to the apex of the arc, and constraint bodies for restraining both ends of the sensor made of the giant magnetostrictive alloy A current detector is constituted by and the above giant magnetostrictive alloy sensor is placed in a magnetic field generated by an electric current, and both ends thereof are engaged with a restraining body provided on the adapter. (3) In the above (2), a fiber Bragg grating type optical fiber sensor is fixed to the surface of the arc top, and the strain is measured by the optical fiber sensor. (4) A giant magnetostrictive element is installed close to the abnormal current path, a strain detection sensor is fixed to the giant magnetostrictive element, and an abnormal current flowing through the abnormal current path is detected. (5) In the above (4), the strain detection sensor is composed of an optical fiber fixed to the giant magnetostrictive element and a means for detecting the strain of the giant magnetostrictive element transmitted to the optical fiber. (6) The abnormal current detectors of (4) and (5) above are installed along the power cable, and the output of the strain detection sensor of the abnormal current detector is transmitted to the fault point detection means to cause an accident in the power cable. Orient the points.

In the invention of claim 1 of the present invention, since it is configured as in the above (1), expansion and contraction of the giant magnetostrictive alloy sensor due to magnetostriction can be expanded, and a cable of a low voltage class of 154 kV or less can be obtained. Accidental current flowing, or
It becomes possible to detect the current flowing through various electric power devices by the giant magnetostrictive alloy sensor. According to the second and third aspects of the present invention, since it is configured as described in (2) and (3) above, it is possible to easily attach the giant magnetostrictive alloy sensor to the object to be measured. The expansion and contraction of the giant magnetostrictive alloy sensor due to magnetostriction can be expanded. Since the invention of claim 4 of the present invention is configured as in the above (4), the abnormal current flowing in the abnormal current path can be detected by a simple system, and the sensor unit including a giant magnetostrictive element is provided. Since it can be attached from the outside such as a cable, it can be easily applied to a cable line after being laid. Since the invention of claim 5 of the present invention is configured as in the above (5), it is possible to detect a ground fault or the like simply by laying an optical fiber along a cable or the like, and to supply power to each sensor or There is no need to provide an amplifier. Since the invention of claim 6 of the present invention is configured as in the above (6), the ground fault accident point of the power cable or the like can be accurately located with a simple system.

[0019]

1 is a diagram showing an embodiment of the invention. In the figure, 11 is a power cable having a diameter of about 120 mm, and a giant magnetostrictive alloy plate fixing adapter 12 made of stainless steel or the like which is non-magnetic and excellent in mechanical strength is attached to the outer peripheral surface of the cable with an adhesive or the like. Install. The giant magnetostrictive alloy plate 13 is a curved plate-shaped member having a thickness of about 4 mm and a width of about 10 mm, and has a radius of about 70 mm and a slightly larger radius of curvature than the cable.
And is attached to the end of the adapter 12 with a fixing bolt 14. The giant magnetostrictive alloy plate 13 is preliminarily subjected to compressive deformation, and is integrated with the adapter 12 by its spring reaction force. In addition, the giant magnetostrictive alloy plate 13
The end portion of the magnetostrictive alloy plate 13 is constrained by the protrusion 12a of the adapter so that the end portion of the magnetostrictive alloy plate 13 cannot be expanded or contracted.

Reference numeral 15 is a strain gauge, and the strain gauge 15
Is attached to the arc top of the giant magnetostrictive alloy plate 13,
It is connected to a strain measuring instrument 17 via a lead wire 16. In the figure, when a current such as a ground fault current flows through the conductor of the power cable 11 or the metal sheath, a uniform magnetic field is generated in the axial direction of the curved surface of the giant magnetostrictive alloy plate 13, and the magnetic field causes the giant magnetostrictive alloy plate. Magnetostriction occurs in 3. Since both ends of the giant magnetostrictive alloy plate 13 are constrained from moving by the protrusions 12a of the adapter 12, the giant magnetostrictive alloy plate 13 has the same structure as in FIG.
It deforms as shown by the dotted line. The bending strain ε0 generated at the arc top of the giant magnetostrictive alloy plate 13 is proportional to the magnetostriction amount ε of the giant magnetostrictive element. Therefore, by detecting the bending strain ε0 by the strain gauge 15, the magnetic field generated around the power cable 11 is detected. Can be detected. Therefore, by detecting this change in the amount of strain with the strain measuring device 17, it is possible to detect the current flowing through the conductor of the power cable 11, the metal sheath, or the like.

Conductor size 2000mm ² class 154kV
When the ground fault occurs on the cable, the ground fault current is usually 3
It is about kA, and if the distance between the center of the cable conductor and the surface of the giant magnetostrictive alloy is about 70 mm, it is
= 3 / 0.07 = 43 kA / m magnetic field is generated. On the other hand, the measured strain change of a giant magnetostrictive alloy having a rectangular parallelepiped shape (length 40 mm, width 10 mm, thickness 5 mm) having a material composition of Tb _0.3 Dy _0.7 Fe _1.9 is ± ± under an alternating magnetic field of 80 kA / m.
It became 0.06%. Therefore, it is considered that the strain change of about 1/2 is generated at the time of the ground fault, and it is a size that can be detected by using the existing strain gauge. Therefore, as in the present invention, a giant magnetostrictive alloy plate is used as the inner corner 4
If the distortion is amplified to 0 ° or less so that the generated distortion can be amplified, the measurement can be performed with higher accuracy.

FIG. 5 is a diagram showing an embodiment in which an optical fiber strain sensing element 21 of fiber Bragg grating type is used in place of the strain gauge 15 in FIG. 1, and the same one as shown in FIG. The same reference numerals are attached. An optical fiber is usually composed of a core having a large refractive index for propagating transmitted light and a clad having a refractive index smaller than that of the core in order to prevent light leakage. Fiber Bragg Grinding (FBG)
As shown in FIG. 6A, “ating” is a waveguide in which the core is provided with periodic unevenness to form a diffraction grating to reflect light in a specific wavelength band. It is known that when strain is applied to the FBG, the spacing between the diffraction gratings changes, and the peak wavelength of the reflected light spectrum changes as shown in FIG. 6B (see, for example, JP-A-61-500052). .
Since the amount of change in the peak wavelength is proportional to the magnitude of load strain, the amount of strain can be detected by measuring the amount of change.

In FIG. 5, the transmitted light from the light source 24 passes through the optical branching device 22 and reaches the FBG 21 fixed to the giant magnetostrictive alloy plate 3 with an adhesive agent via the lead fiber. At this time, only the light in the region where the distance between the diffraction gratings corresponds to an integral multiple of 1/2 of the wavelength is reflected to the incident end side. This reflected light is transmitted from the optical splitter 22 to the optical spectrum analyzer 23.
To find the peak wavelength of the spectrum. When strain occurs in the giant magnetostrictive element due to the electromagnetic field, the F
Since the peak wavelength of the reflected light spectrum of BG21 changes, the current can be detected by detecting this.

It is possible to change the reflected light spectrum band by slightly changing the distance between the diffraction gratings of the FBG 21. Therefore, it is also possible to arrange the FBGs 21 having different reflected light bands in series in this way and detect the change in each reflected light spectrum with one set of measurement system. When a ground fault occurs in a 154 kV cable with a conductor size of 2000 mm ^2, the ground fault current is usually 3 kA.
If the distance between the center of the cable conductor and the surface of the giant magnetostrictive alloy is about 70 mm, H =
A magnetic field of 3 / (2π × 0.07) = 7 kA / m is generated.

On the other hand, the measured strain change of a giant magnetostrictive alloy having a rectangular parallelepiped shape (length 40 mm, width 10 mm, thickness 5 mm) having a material composition of Tb _0.3 Dy _0.7 Fe _1.9 is 80 kA / m as shown in FIG. Under an alternating magnetic field of 0.06%. From these experimental results, it is 0.00 at a ground fault current of 3 kA.
It is considered that a strain change of 5% or more occurs. Strain detection sensitivity of fiber Bragg grating type is 0.00
It is about 3%, and the ground fault current can be detected even with the rectangular parallelepiped giant magnetostrictive alloy used in the experiment, but as described in this embodiment, the giant magnetostrictive alloy plate is used as the giant magnetostrictive sensor with an internal angle of 40 ° or less. If the distortion is generated so that the generated distortion can be amplified, the measurement can be performed more reliably.

In the above embodiment, the giant magnetostrictive alloy plate 13 is used.
Although the case of arranging in parallel with the magnetic field is shown, it is not always necessary to dispose the giant magnetostrictive alloy in parallel with the magnetic field.
That is, as shown in FIG. 4, even if the giant magnetostrictive alloy is arranged orthogonally to the magnetic field, the amount of deformation is reduced by about 20 to 30%. Therefore, when high sensitivity is not required, it is parallel to the magnetic field. Even if it is not placed in, it is sufficiently practical. Also,
In the description of the above embodiment, the case where the present invention is applied to the detection of the ground fault current in the power cable has been described, but the above embodiment is not limited to the detection of the ground fault current in the power cable as described above, and for example, various power devices. It can be used for various kinds of current detection, such as accident current / overcurrent detection in, and detection of lightning current flowing in a transmission tower at the time of a lightning strike.

Next, an embodiment for detecting a ground fault point in an ultrahigh voltage power cable using a giant magnetostrictive alloy will be described. FIG. 7 is a diagram showing an example of the mounting position of the sensor in the cross-bonded three-phase cable line.
In order to detect an accident point in the above-mentioned electric line, as shown in the figure, the giant magnetostrictive elements 1a to 1h, 1a, 1h, 1a, 1h having strain gauges attached to the cable surfaces on both sides of each connection portion NJ, IJ of each phase
b ′ to 1c ′ and 1b ″ to 1g ″ are attached, and the strain generated in the giant magnetostrictive element is constantly monitored.

In FIG. 7, when a ground fault occurs at point P of the A phase of the cable, the large ground fault current I0 flowing through the conductor 2 from the power source side as described above causes the metal sheath 3 of the A phase at the fault point. Then, from the cross bond portion of the IJ, the B-phase or C-phase metal sheath is returned to the ground as a return route. Therefore, from IJ next to the accident point, the ground fault current does not flow in either the A-phase conductor 2 or the metal sheath 3 and almost no strain occurs from 1f of the giant magnetostrictive element, but until the accident section. A large ground fault current flows through either the conductor 2 or the metal sheath 3, and the amount of strain generated in the giant magnetostrictive elements 1a to 1e up to that point becomes significantly large.

FIG. 8 (a) shows a model of the time history of strain appearing in the giant magnetostrictive element attached to the cable in the section where the ground fault current flows in the conductor or metal sheath, and is constant up to t1 before the accident. Distortion change of the sine waveform of the wave height occurred, but with the occurrence of the ground fault accident, a remarkably large attenuating waveform of the wave height occurs for several cycles until the fault current interruption t2. Such a distorted waveform causes an A-phase giant magnetostrictive element 1a in which a ground fault has occurred.
The other phase giant magnetostrictive element generated in 1e and having a return current flowing in the metal sheath 3, here, 1b′1c ′ or 1f ″
Occurs in 1 g ".

On the other hand, in the super strained element after 1h attached to the A phase, the ground fault current does not flow in any of the conductor 2 and the metal sheath 3, so that as shown in FIG. The sinusoidal waveform disappears. In this way, the ground fault accident occurrence section can be determined by knowing which portion of the accident occurrence cable and which section of the other phase cable the large distortion waveform has changed when the ground fault occurs.

FIG. 9 is a diagram showing an example of a system for detecting the strain generated in the giant magnetostrictive element. As a method of detecting the strain generated in the giant magnetostrictive elements 1a to 1h, 1b 'to 1c', and 1b "to 1g", a method using a strain gauge using a metal resistance wire as shown in FIG. it can.
That is, a length of 50 mm near the power cable 11,
A rectangular parallelepiped giant magnetostrictive element 1 having a width of 10 mm and a thickness of 5 mm
A protective case (not shown here) accommodating a and 1b is installed close to each other with a cable before and after each connecting portion.

A strain gauge 31 is attached to the surface of each of the giant magnetostrictive elements 1a and 1b, the output of which is amplified by an amplifier 32 and is constantly transmitted to a detector 33 by a multicore cable 34. In addition,
As described above, the deformation amount becomes larger when the mounting directions of the giant magnetostrictive elements 1a and 1b are arranged in parallel with the magnetic field, but even if the giant magnetostrictive alloy is arranged orthogonally to the magnetic field, high sensitivity is not required. In some cases, it is sufficiently practical. If the cable is transmitted normally, only a small alternating strain is generated, but at the same time as the occurrence of the ground fault, an extremely large ground fault current also flows in the metal sheath, and following this, the giant magnetostrictive elements 1a, 1b. A large distortion change appears.

This strain change is detected by the strain gauge 31 attached to the giant magnetostrictive elements 1a and 1b, and the strain gauge 31
Is amplified by the amplifier 32. The output of the amplifier 32 is transmitted to the detector 33 through the multi-core cable 34, and the detector 33 detects the position where the distortion change occurs, so that the point of occurrence of the ground fault accident can be detected as described above. it can. Although FIG. 9 shows an example in which the giant magnetostrictive element 1a is attached to the power cable 11, the giant magnetostrictive element 1 is shown.
The a can be applied to the detection of other abnormal currents, for example, by mounting the power transmission line in the vicinity of an overhead ground wire or on a power transmission tower to detect a lightning current.

The above-mentioned method using the resistance wire strain gauge is the most general method, but a major drawback is that an amplifier for amplifying the strain output and a power source for the amplifier are required near each measurement point. Therefore, a method may be considered in which an optical fiber line is fixed along the strain generation direction of the giant magnetostrictive element by adhesion or the like so that a strain change equivalent to that of the giant magnetostrictive element occurs in the optical fiber, and this is constantly monitored. For the strain generated in the optical fiber, a known measurement method applying Brillouin scattering can be used. When the light beams from two lasers are sent from both ends of the fiber, it uses the amplification effect of the beams obtained by adjusting the frequency difference between the two beams called "Brillouin frequency shift". The strain change can be obtained by measuring the power. The strain detection system using Brillouin scattering can measure the strain change of all lines over a long distance with one optical fiber, and does not require a power source for each measurement point.

Next, an embodiment of the strain detection system using the above Brillouin scattering will be described. Figure 10 above is Bril
It is a figure which shows the structural example of the accident point detection system using a giant magnetostrictive element and an optical fiber which utilizes louin scattering. In the figure, 11 is a power cable, and the power cable 11
A rectangular parallelepiped giant magnetostrictive element 1a is installed in the vicinity of, and the sensing fiber 46 (hereinafter referred to as a sensor fiber) is bonded to the giant magnetostrictive element 1a. 45
Is a transmission fiber, and the transmission fiber 45 may be the same as the sensing fiber 46, but in the case of a long-distance line, a fiber with less transmission loss is used, and the sensor fiber 46 and the measurement fiber are fused at each measurement point. Is effective.

Reference numeral 41 denotes a laser light source, and light is continuously sent from the single laser light source 41 to the transmission fiber 45. The light sent from the laser light source 41 is the first
The optical fiber directional coupler 42 divides the power into two, one of which is sent to the Brillouin scattering generator 43 and the other of which is sent to the optical switch 47. The Brillouin scattering generator 43 produces light that travels in the opposite direction (the direction of the arrow in the figure) at a different frequency than the light produced by the laser light source 41. The light beam in the opposite direction is transmitted to the sensor fiber 46.
Signal beam 44 for

On the other hand, the optical switch 47 includes the sensor fiber 4
A pulsed pump beam 49 that is input to the opposite end of 6 is created. The signal beam 44 is amplified by the interaction with the pump beam 49, and the amplified signal beam 44 is split by the second optical fiber directional coupler 48 to measure the signal beam.
0, where the amount of strain change generated in the giant magnetostrictive element 1a is detected.

The giant magnetostrictive element 1a to which the sensor fiber 46 is attached is attached to the cable line as shown in FIG. 7, and the signal beam 44 and the pump beam 49 are given to each sensor fiber 46 through the transmission fiber 45. As a result, as described above, it is possible to detect the place where the strain change occurs on the power cable line, and it is possible to detect the accident point. According to this embodiment, it is possible to detect the strain change occurring in the giant magnetostrictive element without using an amplifier as shown in FIG. 9, so that it is not necessary to provide a power source for each measurement point. The current detector shown in FIGS. 1 and 5 may be used for detecting the ground fault point of the ultra high voltage power cable. Thereby, the detection sensitivity can be further improved.

[0039]

As described above, the following effects can be obtained in the present invention. (1) A sensor made of a giant magnetostrictive alloy is arranged in a magnetic field generated by an electric current, the sensor made of a giant magnetostrictive alloy is formed into a plate-like body curved in an arc shape, and both ends of the plate-like body are restrained from expanding and contracting by restraining bodies. Therefore, even when the current is relatively small, the strain generated in the giant magnetostrictive alloy can be increased, and it can be useful for accurate fault point detection of electric lines, fault current of various power equipment, detection of overcurrent, etc. it can. (2) A current detector is composed of an adapter for fixing a sensor made of a giant magnetostrictive alloy and a sensor made of a giant magnetostrictive alloy having a strain gauge attached to the arc top of a plate body curved in an arc shape. The current detector of the present invention can be easily attached to various electric power equipment by attaching both ends of the current detector to the restraining body provided on the adapter.

(3) Since the giant magnetostrictive element to which the strain detection sensor is fixed is installed close to the abnormal current passage to detect the abnormal current flowing in the abnormal current passage, the sensor unit can be easily attached from the outside. You can Therefore, it is possible to easily attach it to a cable or the like after installation. (4) Since the strain detecting sensor is composed of the optical fiber fixed to the giant magnetostrictive element and the means for detecting the strain of the giant magnetostrictive element transmitted to the optical fiber, the optical fiber is laid along the cable or the like. It is possible to detect a ground fault accident by itself, and it is not necessary to provide a power source or an amplifier for each sensor unit. (5) A plurality of giant magnetostrictive elements are installed along the power cable, the output of the strain detection sensor fixed to the plurality of giant magnetostrictive elements is transmitted to the fault point detection means, and the fault point generated in the power cable is located. Therefore, the ground fault point can be accurately measured with a simple system.

[Brief description of drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating deformation of a giant magnetostrictive alloy formed in an arc shape.

FIG. 3 is a diagram showing a relationship between an internal angle and a distortion amplification rate in FIG.

FIG. 4 is a diagram showing a relationship between a magnetic field direction and strain generated in a giant magnetostrictive alloy plate.

FIG. 5 is a diagram showing an embodiment in which an optical fiber strain sensing element is used as the strain sensing element.

FIG. 6 is a diagram illustrating a fiber Bragg grating.

FIG. 7 is a diagram showing an example of a mounting position of a sensor on a three-phase cable line.

FIG. 8 is a diagram showing a strain change that appears in a giant magnetostrictive element when a ground fault current flows.

FIG. 9 is a diagram showing an example of an accident point detection system using a strain gauge.

FIG. 10 is a diagram showing a configuration example of an accident point detection system using Brillouin scattering.

FIG. 11 is a diagram showing a current flowing through a power cable line at the time of a ground fault.

FIG. 12 is a diagram showing a magnetic field generated when a current flows through a cable.

[Explanation of symbols]

 1a-1g "Giant Magnetostrictive Element 2 Conductor 3 Metal Sheath 4 NJ External Copper Tube 5 Ground Wire 6 IJ External Copper Tube 7 IJ Insulation Tube 11 Power Cable 12 Giant Magnetostrictive Alloy Plate Fixing Adapter 13 Giant Magnetostrictive Alloy Plate 14 Fixing Bolt 15 Strain gauge 16 Lead wire 17 Strain measuring instrument 21 Fiber Bragg grating element 22 Optical branching device 23 Optical spectrum analyzer 24 Light source 25 Optical fiber 31 Strain gauge 32 Amplifier 33 Detector 34 Multi-core cable 41 Laser light source 42, 48 Optical fiber directional coupling 43 Brillouin Scattering generator 44 Signal beam 45 Transmission optical fiber 46 Sensor fiber 47 Optical switch 49 Pump beam 50 Photodetector P Accident occurrence point

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G01R 33/02 G01R 15/02 Z

Claims (6)

[Claims] 1. A current detector comprising a giant magnetostrictive alloy which is arranged in a magnetic field generated by an electric current and detects the electric current by detecting the magnetostriction generated by the magnetic field, wherein the giant magnetostrictive alloy has an arc shape. A current detector characterized in that it is a curved plate-like body, and both ends of the plate-like body are restrained from expanding and contracting by restraining bodies. 2. A giant magnetostrictive alloy sensor, which is curved in an arc shape and has a strain sensor attached to the top of the arc, and a constraint body for restraining both ends of the giant magnetostrictive alloy sensor. The above-mentioned giant magnetostrictive alloy sensor is arranged in a magnetic field generated by an electric current, and both ends of the sensor are engaged with a restraining body provided on the adapter. 3. The current detector according to claim 2, wherein a fiber Bragg grating type optical fiber sensor is fixed to the surface of the arc top, and the optical fiber sensor measures strain. 4. An abnormal current characterized in that a giant magnetostrictive element is installed close to the abnormal current path, a strain detection sensor is fixed to the giant magnetostrictive element, and an abnormal current flowing in the abnormal current path is detected. Detector. 5. The strain detection sensor comprises an optical fiber fixed to the giant magnetostrictive element and a means for detecting the strain of the giant magnetostrictive element transmitted to the optical fiber. 4 abnormal current detector. 6. The abnormal current detector according to claim 4 or 5 is installed along the power cable, and the output of the strain detection sensor of the abnormal current detector is transmitted to the fault point detection means to generate on the power cable. Power cable line characterized by locating the accident point.