JP2005274351A - Wire defect detection method and conductor defect detection sensor - Google Patents

Abstract

The present invention relates to a conductor current of a twisted conductor in which a plurality of conductor strands are twisted and a defect of any of the plurality of strands in an insulation coated electric wire in which an insulation coating layer is provided on the twisted conductor. In the case of detecting from the distribution change of the peripheral circuit magnetic field based on the distribution of the peripheral circuit magnetic field when there is no wire defect, the defect is detected from the change of the peripheral circuit magnetic field distribution in a sufficiently narrow range to simplify the work.
[Solution]
A change in the circumferential circuit magnetic field distribution at a location isolated from the defective location or a change in the circumferential circuit magnetic field distribution in a range of approximately one pitch of twist of the twisted conductor is detected. The sensor to be used is, for example, two magneto-impedance effect elements separated by an angle of 180 ° around the electric wire and equidistant from the electric wire center, and the magnetic sensing direction is a direction perpendicular to the circumference concentric with the electric wire. The sensors are connected in series so that the direction of magnetic sensitivity is reversed, and the output from this series-connected magneto-impedance effect element is used as the sensor output.
[Selection figure] None

Description

  The present invention relates to a method for detecting a conductor defect in a wire and a sensor for detecting a conductor defect, and is useful for inspecting defects such as disconnection, scratches, non-conductivity, and deterioration such as stress corrosion cracking in a current-carrying / hot-wire state. .

  As one of the methods for inspecting defects (defects) such as disconnection, scratches, non-conductivity, and deterioration such as stress corrosion cracking, the load current that is actually applied causes flow disturbance at the defective part, which is caused by that. A method for detecting a change in a magnetic field is known.

If a defect occurs in any of the conductor strands of the stranded conductor of the electric wire, the contour of the conductor cross section at that location is made non-circular, and the center of the current path of the cross section is shifted. As a result, the distribution of the circumferential circuit magnetic field based on the conductor current Will change.
Therefore, an experiment has been conducted in which a wire having a twisted conductor of an electric wire sample is artificially scratched, a search coil is scanned along the electric wire, and a deviation of the current path center of the conductor cross section is detected. (Non-Patent Document 1)

Takashi Nonaka and two others, “Fundamental study on non-destructive magnetic flaw detection of distribution lines” T, IEEEjapan, Vol, 121-A, No. 3,2001, p282-287

任意座標点ｐ1(x1,y1)における磁束密度(Ｂｘ1，Ｂy1)及びｐ2(x2,y2)における磁束密度(Ｂｘ2，Ｂy2)をサーチコイルにより測定し、これらの測定値から電流路断面の中心座標Ｃ1(Cx1,Cy1)を計算し、この中心座標の変位から撚線導体の欠陥を評価しようとしている。 That is, as shown in FIG. 8, the center C1 (Cx1, Cy1) of the current path cross section has arbitrary coordinate points p1 (x1, y1) and p2 (x2, y2) and these arbitrary coordinate points p1 (x1, y1) and p2 ( From the magnetic flux density (Bx1, By1) and (Bx2, By2) at x2, y2)

The magnetic flux density (Bx1, By1) at the arbitrary coordinate point p1 (x1, y1) and the magnetic flux density (Bx2, By2) at p2 (x2, y2) are measured by the search coil, and the center coordinates of the current path cross section are obtained from these measured values. C1 (Cx1, Cy1) is calculated, and the defect of the stranded wire conductor is evaluated from the displacement of the central coordinates.

  The wire sample used in this experiment is a new wire, and the contact resistance between the strands of the twisted conductor is extremely low. Therefore, even if the center of the current path cross section shifts at the artificially scratched spot, it is presumed that the current flows uniformly in the cross section of the conductor at some distance from the scratched spot. Then, scanning along the electric wire of the search coil is necessary.

  Defects in the conductors of the insulated insulated wires that are erected occur in an oxidizing environment under rainwater intrusion inside the insulation coating layer. Therefore, when the defects occur, the contact resistance between the conductor wires of the stranded conductor is reduced. Extremely high due to oxide film. Assuming that the contact resistance between the strands can completely interrupt the current conduction between the strands, the state where the current of the defective conductor strand is lower than that of the other healthy strands extends to the entire length of the wire. A shift in the center of the cross section occurs over the entire length of the electric wire. On the other hand, if the contact resistance between the strands is assumed to be zero, the displacement of the center of the conductive path cross section occurs only in the vicinity of the defective portion, and the non-patent document 1 assumes the latter.

  Therefore, in the present inventor, in the defect in which one of the outer strands in the direction of the seven stranded wires is disconnected, the disconnection location is determined by the result of earnest experiment of the defect detection of the actually insulated insulation wire. The deviation of the center of the conductive path cross section could be confirmed in the range from 1 to several tens of meters on the left and right. Therefore, it is reasonable to presuppose that the state where the current of the conductor wire in which the defect is generated is lower than that of other healthy wires occurs in a wide range from the defective portion and the shift of the center of the conductive path cross section occurs over a wide range.

An object of the present invention is to detect a defect of any conductor wire of a twisted conductor in an electric wire from a change in distribution of the peripheral circuit magnetic field based on the energization current of the twisted conductor with respect to the peripheral circuit magnetic field when there is no wire defect. Based on the above knowledge, the defect is detected from the change in the distribution of the magnetic field in the peripheral circuit in a sufficiently narrow range, and the work is simplified.
Furthermore, it is providing the magnetic sensor which can detect the change of the surrounding circuit magnetic field distribution with high sensitivity.

  In the method for detecting a conductor defect of an electric wire according to claim 1, a defect of any one of the strands of a twisted conductor in an electric wire obtained by twisting a plurality of conductor strands is used as an energization current of the twisted conductor. It is a method of detecting from a distribution change with respect to a peripheral circuit magnetic field when there is no strand defect of the peripheral circuit magnetic field based on detecting a change in the magnetic field distribution at a location isolated from a location where the conductor strand is defective Features.

  The method for detecting a conductor defect in an electric wire according to claim 2 is based on an energization current of the twisted conductor based on a defect in the conductor wire of any of the twisted conductor wires in the electric wire obtained by twisting a plurality of conductor strands. A method of detecting from a change in distribution of a peripheral circuit magnetic field with respect to a peripheral circuit magnetic field when there is no wire defect, and detecting a change in the peripheral circuit magnetic field distribution in a range of approximately one pitch of twist of the twisted conductor. To do.

  A sensor for detecting a conductor defect in an electric wire according to claim 3 is a sensor used in the method for detecting a conductor defect in an electric wire according to claim 1 or 2, with an angle of 180 ° around the electric wire and from the center of the electric wire, etc. Two magneto-impedance effect elements that are separated by a distance and have a magnetosensitive direction perpendicular to the circumference concentric with the electric wire are connected in series so that the magnetosensitive direction has a reverse polarity. The output is a sensor output.

In an electric wire with a defect, the contact resistance between the conductor wires is extremely high due to the oxide film, and the change in the circumferential circuit magnetic field distribution due to the deviation of the center of the cross section of the conductive path at the defective part is considerably different from the defective part. Even a remote location is apparent, and in the present invention, a conductor defect is detected from a change in the circumferential circuit magnetic field distribution at the remote location.
The change in the circumferential circuit magnetic field distribution is detected from the magnetic field component perpendicular to the circumferential direction of the concentric circle with the wire, and this detected magnetic field component is sufficiently smaller than the circumferential magnetic field in the vicinity of the outer circumference of the wire and within the measurement limit. Yes, the sensor element can be disposed close to the outer periphery of the electric wire, and the sensor can be made compact. The high detection capability of the magneto-impedance effect element and the removal of external noise by the pair arrangement of the magneto-impedance effect element separated by 180 ° or the removal of internal and external noise by using a differential amplifier circuit or a subtraction circuit are high. Sensitivity can be detected, and the change in the circumferential circuit magnetic field distribution at the separated location can be detected with high sensitivity.
Therefore, it is not necessary to scan the magnetic sensor along the entire length of the electric wire, and the detection work can be simplified.

FIG. 1 shows an example of an insulation-coated electric wire that is a target of conductor defect detection according to the present invention, and a synthetic resin such as polyethylene or polyvinyl chloride on a twisted conductor b obtained by twisting a conductor wire a such as a hard copper wire. c is extrusion coated.
It is assumed that a defect has occurred in any conductor wire of the twisted conductor of this electric wire. Assuming that the contact resistance between the strands is high enough to completely interrupt the current conduction between the strands, the deviation of the current center of the conductor cross section due to the defect occurs over the entire length of the wire, and therefore A change in the circumferential circuit magnetic field distribution based on the conductor current occurs over the entire length of the wire.
In FIG. 2, the strength H of the reference peripheral circuit magnetic field at the distance r from the wire center o when no deviation of the current center of the conductive path cross section occurs.

  H = I / (2πr)

Given in.
1a and 1a ′ are magneto-impedance effects in which the distance from the center of the wire is r and they are separated by 180 ° on a circle concentric with the center of the wire, and the axial direction (maximum magnetosensitive direction) is a direction perpendicular to the concentric circle. The element is shown and is not sensitive to the reference circuit magnetic field. If the angle between the axial direction of the magneto-impedance effect element and the direction of displacement is α and the displacement distance is ΔL,

x ² = r ² + (ΔL) ² −2r · ΔL cos α
sinγ / ΔL = sinα / x

And the magnetosensitive component of the magneto-impedance effect element 1a at the circumferential circuit magnetic field strength H ′ = I / (2πx) at the distance x under the conductive path cross-sectional center o ′, that is, the maximum magnetosensitive direction component ha. Is

  ha = H’sinγ

Given in.
When ha is obtained from the above equations,

[Formula 1] ha≈H (ΔL / r) sin α / [1-2 (ΔL / r) cos α]

Is established.
The magnetosensitive component ha ′ of the other magneto-impedance effect element 1a ′ takes into account that α is (π + α) in the ha and the direction of the circumferential circuit magnetic field is opposite.

[Formula 2] ha′≈H (ΔL / r) sin α / [1 + 2 (ΔL / r) cos α]

Given in.

  The present invention detects a small magnetosensitive component in a direction perpendicular to the circumferential circuit magnetic field caused by a change in the circumferential circuit magnetic field distribution with high detectability of the magneto-impedance effect element, and reverses the polarity of the magneto-sensitive direction of the paired magneto-impedance effect element. Or by subtraction or in-phase cancellation in differential amplification to detect noise with a high sensitivity and detect a change in the circumferential circuit magnetic field distribution based on the conductor defect. It is possible to detect changes in the distribution of the magnetic field of the peripheral circuit even at locations far away from each other.

FIG. 3 shows a basic configuration of a magnetic sensor using a magneto-impedance effect element.
In FIG. 3, reference numeral 1 denotes a magneto-impedance effect element, which has a zero magnetostriction or a negative magnetostriction having an outer shell portion in which magnetic domains whose spontaneous magnetization directions are opposite to each other in the circumferential direction of the wire are alternately separated by domain walls. An amorphous alloy wire is used. The inductance voltage component in the output voltage between both ends of the wire generated when a high-frequency excitation current is passed through an amorphous magnetic wire having zero magnetostriction or negative magnetostriction is obtained by the circumferential magnetic flux generated in the cross section of the wire. This occurs due to the magnetization of the easily magnetizable outer shell in the circumferential direction. Therefore, the circumferential magnetic permeability mu _theta depends on the circumferential direction of magnetization of Dosotokara portion. Therefore, when a detected magnetic field is applied in the axial direction (maximum magnetosensitive direction) of the energized amorphous wire, the circumferential direction magnetic flux and the detected magnetic field magnetic flux generated by the energization are combined in the circumferential direction. The direction of the magnetic flux acting on the easily magnetized outer shell part is deviated from the circumferential direction, and the magnetization in the circumferential direction is less likely to occur, the circumferential permeability μ _θ changes, and the inductance voltage changes. Will do. This fluctuation phenomenon is called a magnetic inductance effect, which can be said to be a phenomenon in which the high-frequency excitation current (carrier wave) is modulated by a detected wave (signal wave). Further, when the frequency of the energization current is in the order of MHz, a high-frequency skin effect appears greatly, and the skin depth δ = (2ρ / wμ _θ ) ^1/2 (μ _θ is the circumferential permeability, ρ as described above. electrical resistivity, w is shows the angular frequency, respectively) is changed by mu _theta, as the mu _theta is the so changed by the detected magnetic field, the resistance voltage division also be detected magnetic field in the wire between both ends output voltage It will fluctuate with. This fluctuation phenomenon is called a magneto-impedance effect, which can be said to be a phenomenon in which the high-frequency excitation current (carrier wave) is modulated by a detected wave (signal wave).

  In FIG. 3, 2 is a high-frequency power source for applying a high-frequency excitation current to the magneto-impedance effect element, and 3 is a modulation of the high-frequency excitation current (carrier wave) by a detected magnetic field (signal wave) acting in the axial direction of the magneto-impedance effect element. Demodulation circuit for demodulating the modulated wave thus generated, 4 an amplification circuit for amplifying the demodulated wave, 5 an output terminal, 6 a negative feedback coil, and 7 a bias magnetic field coil. For the magneto-impedance effect element 1, an amorphous ribbon, an amorphous sputtered film, or the like can be used in addition to zero magnetostrictive or negative magnetostrictive amorphous wires.

In the magneto-impedance effect element, as described above, the direction of the magnetic flux acting on the outer shell portion that is easily magnetized in the circumferential direction is obtained by combining the circumferential magnetic flux based on the excitation current and the axial magnetic flux due to the detected magnetic field. Due to the deviation from the circumferential direction, the circumferential magnetic permeability μ _θ changes, the inductance is changed, and the impedance is changed by the change of the skin depth of the high frequency skin effect of the circumferential magnetic permeability μ _θ . Accordingly, although even the circumferential direction positional shift phi by the synthesized magnetic field by ± of the detected magnetic field becomes ± phi, the circumferential direction of the magnetic field reduction ratio cos (± phi) is unchanged, the degree of reduction in thus mu _theta is of the detected magnetic field It does not change depending on the direction. Accordingly, the detected magnetic field-output characteristics are substantially bilaterally symmetric with respect to the y axis when the detected magnetic field is on the x axis and the output is on the y axis as shown in FIG. This detected magnetic field-output characteristic is non-linear. With non-linear characteristics, it is difficult to measure with high sensitivity. Therefore, negative feedback is applied by a negative feedback coil to linearize the characteristics as shown in FIG. In FIG. 4B, Δw is a linear range in which the gain A without negative feedback is very large and the gain is determined only by the feedback rate β. However, with this output characteristic, since the polarity of the magnetic field to be detected cannot be determined, a bias magnetic field is applied by the bias coil 7 so that the polarity can be determined as shown in FIG. That is, the characteristic of (b) in FIG. 4 is moved in the negative direction of the x-axis by the bias magnetic field, and the maximum range of the detected magnetic field −Hmax to + Hmax is within the range of the single oblique line region. Further, as shown in FIG. 4D, a linear characteristic passing through the origin is obtained by adjusting the zero point. Therefore, in FIG. 4D, if the detected magnetic field is + He, the output is + Eo, and if the detected magnetic field is -He, the output is -Eo, and the detected magnetic field can be accurately measured based on polarity discrimination. .

As shown in FIG. 5, an operational amplifier (negative feedback path insertion impedance Z ₂ , input side insertion impedance Z ₁ ) in which negative feedback is applied to the inverting input terminal from the output is used to obtain the linear output characteristics capable of discriminating the polarity. You can also In this case, if the resistance inserted in the negative feedback coil is R, the number of turns of the coil is n, the length is L, the gain of the demodulation amplifier B is A, the detected magnetic field is Hex, and the output is Eout,

A >> Z ₁ RL / (Z ₂ n)

Under

Eout = RLZ ₁ Hex / (nZ ₂ ) + VccZ ₁ R / [Z ₂ (Z ₂ + R)]

Is established, and the output characteristics can be shifted in the ± direction of the x-axis by adjusting various constants (Z ₁ , Z ₂ , resistance R, coil turns n, etc.), and the diagonal straight line portion whose polarity can be discriminated by the adjustment Can be positioned within the range of the maximum detected magnetic field ± Hmax, and the linearity output characteristics capable of discriminating the polarity as shown in FIG. 4 (d) can be obtained by adjusting the zero point in the y-axis direction. it can.

  As the high frequency excitation current, a normal high frequency such as a continuous sine wave, a pulse wave, or a triangular wave can be used. As the high frequency excitation current source, for example, a Hartley oscillation circuit, a Colpitts oscillation circuit, a collector tuning oscillation circuit, a base tuning oscillation circuit can be used. In addition to the normal oscillation circuit, a rectangular wave generator that integrates the square wave output of the crystal oscillator through a DC cut capacitor with an integration circuit and amplifies the triangular wave of the integration output with an amplification circuit, and the COMS-IC as an oscillation unit The used triangular wave generator etc. can be used.

The demodulating circuit includes, for example, a configuration in which a modulated wave is half-wave rectified by an operational amplifier circuit, and this half-wave rectified wave is processed by a parallel RC circuit or an RC low-pass filter to obtain an envelope output of the half-wave rectified wave. A configuration in which the modulated wave is half-wave rectified by a diode and the half-wave rectified wave is processed by a parallel RC circuit or an RC low-pass filter to obtain an envelope output of the half-wave rectified wave can be used.
In the above embodiment, the detected amount is extracted by demodulating the modulated wave. However, the present invention is not limited to this, and the detected amount corresponding to the detected magnetic field is detected from the magnetic field detection signal by the detected magnetic field acting on the magneto-impedance effect element. Any suitable circuit configuration can be used.
The negative feedback coil and the bias magnetic field coil can be wound around a magneto-impedance effect element. Further, as shown in FIG. 6, a negative feedback coil and a bias magnetic field coil can be wound around an iron core constituting a magneto-impedance effect element and a loop magnetic circuit.

6 (a) is a side view showing an example of a magnetic impedance effect unit with an iron core, FIG. 6 (b) is a bottom view, and FIG. 6 (c) is a cross-sectional view of FIG. FIG.
In FIG. 6, reference numeral 100 denotes a substrate chip, and for example, a ceramic plate can be used. Reference numeral 101 denotes an electrode provided on one surface of the substrate piece, and includes an element connecting projection 102. This electrode can be provided by printing and baking a conductive paste, for example, a silver paste. 1x is a magneto-impedance effect element connected between the protrusions 102 and 102 of the electrodes 101 and 101 by soldering or welding. As described above, an amorphous wire, amorphous ribbon, sputtered film or the like having zero or negative magnetostriction can be used. 103 is a C-type iron core, 6x is a negative feedback coil wound around the C-type iron core, 7x is also a bias magnetic field coil, and the magneto-impedance effect element 1x and the C-type iron core 103 constitute a loop magnetic circuit. Thus, both ends of the C-shaped iron core 103 are fixed to the other surface of the substrate piece 100 with an adhesive or the like. The iron core material may be a magnetic material having a small residual magnetic flux density. Examples thereof include permalloy, ferrite, iron, amorphous magnetic alloy, magnetic powder mixed plastic, and the like.

FIG. 7 (a) is a drawing showing an embodiment of a sensor for detecting a conductor defect of an insulated wire according to claim 3, and FIG. 7 (b) is a circuit diagram of the sensor.
In FIG. 7, 8 is an insulation coating electric wire. Reference numeral 9 denotes a sensor board, which has a wire insertion slot 91, and the two magneto-impedance effect elements 1 and 1 'are separated from each other by an angle of 180 ° around the wire 8 and equidistant from the center of the wire. The magnetic direction is arranged so as to be perpendicular to the circumference concentric with the electric wire.
These magneto-impedance effect elements 1 and 1 'are connected in series so that the direction of magnetic sensing is reversed, and a demodulating circuit 3 is connected to the output terminal of the series-connected magneto-impedance effect element, and an amplifier 4 is connected to the demodulating circuit. Are connected to each other, and the output characteristic is a linear characteristic capable of discriminating the polarity by the negative feedback through the negative feedback coil 6 and the magnetic field shift by the bias magnetic field coil 7.
If the magnetic field component that one magneto-impedance effect element 1 senses due to the change in the circumferential circuit magnetic field distribution is ha and the magneto-sensitivity component against external noise such as geomagnetism is Na, the magnetic field that this magneto-impedance effect element 1 senses magnetically. The strength Ha is Ha = ha + Na.
On the other hand, the magnetic field strength Ha ′ that the other magneto-impedance effect element 1 ′ senses magnetically has the opposite direction of the magnetosensitive direction when the magnetic field component to be magnetized is ha ′. -(Ha '+ Na).
Therefore, the magnetic field strength (Ha + Ha ′) that the magneto-impedance effect elements connected in series have a magnetic sensitivity is (Ha + Ha ′) = (ha−ha ′), and external noise can be eliminated due to the reverse polarity. The magnetic field strength (Ha + Ha ′) is obtained from the equations (1) and (2).

(Ha−ha ′) ≈4H (ΔL / r) ² sinαcosα = 2H (ΔL / r) ² sin2α

Given in.
This magnetic sensitivity (ha−ha ′) is small because ΔL << r, and the sensor can be made small. Even if the detected amount (ha-ha ′) is small, high-precision detection is possible because of the high detection resolution of the magneto-impedance effect element.
Therefore, even if the deviation ΔL of the current center of the conductor cross-section of the conductor becomes small from the defective portion of the insulated wire, it can be detected for high sensitivity detection, and the location is several tens of meters away from the conductor defective portion. Even with this magnetic field detection, it is possible to detect defects.

In the sensor for detecting a conductor defect in an insulated wire according to the present invention, the magnetosensitive strength changes in a waveform of sin 2α (or sin α), and α is 0, 90 ° and 180 ° (or 0, 180 ° and 360 °). ) Becomes 0.
Thus, the twisted conductor is twisted, α changes from 0 to 180 ° during a half pitch, α is 0, 90 ° and 180 ° (or α is 0, 180 ° and 360). Since the above detection cannot be satisfactorily performed at a position of (°), in the conductor defect detection method according to claim 2, the sensor is scanned by several pitches of twisted conductors of the wire, preferably 3-5 pitches. I am letting.
The present invention can also be implemented using four or more magneto-impedance effect elements.

It is sectional drawing which shows an insulation coating electric wire. 2 is a view showing a magnetosensitive component of a magneto-impedance effect element separated by 180 ° in the present invention. It is drawing which shows the basic circuit of the magnetic field detection using a magnetic field impedance effect element. It is drawing which shows the output characteristic of the magnetic field detection using a magnetic field impedance effect element. It is drawing which shows another example of the basic circuit of the magnetic field detection using a magnetic field impedance effect element. It is drawing which shows a magnetic impedance effect element with a C type iron core. It is drawing which shows one Example of the sensor which concerns on Claim 3. 1 is a diagram showing the contents of Non-Patent Document 1.

Explanation of symbols

1, 1 ′ 180 ° -separated magnetoimpedance effect element 1a, 1a ′ 180 ° -separated magneto-impedance effect element 1b, 1b ′ 180 ° -separated magneto-impedance effect element Dm Differential amplifier Ad Adder or superposition circuit 8 Insulation Sheathed wire

Claims (3)

A defect of any one of the strands of a twisted conductor in an electric wire in which a plurality of conductor strands are twisted together is determined as an element of a peripheral circuit magnetic field based on an energization current of the twisted conductor having a defect in the conductor strand. A method for detecting a conductor defect in an electric wire, comprising: detecting from a change in distribution with respect to a circumferential circuit magnetic field when no line defect is present; and detecting a change in the magnetic field distribution at a location isolated from the defective location. A defect of any one of the strands of the twisted conductor in an electric wire in which a plurality of conductor strands are twisted together is defined as a circumference when there is no strand defect in the circumferential circuit magnetic field based on the energization current of the twisted conductor. A method for detecting a defect in a conductor of an electric wire, wherein the change is detected from a distribution change with respect to a circuit magnetic field, and a change in a peripheral circuit magnetic field distribution in a range of approximately several pitches of twist of the twisted conductor is detected. A sensor for use in the method for detecting a conductor defect in an electric wire according to claim 1 or 2, wherein the magnetic sensing direction is a circle concentric with the electric wire at an angle of 180 ° around the electric wire and at an equal distance from the center of the electric wire. Two magneto-impedance effect elements that are perpendicular to the circumference are connected in series so that the magnetosensitive direction is opposite in polarity, and the output from this series-connected magneto-impedance effect element is used as the sensor output. Conductor defect detection sensor for electric wires.

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