JP4520188B2 - Method for detecting conductor defects in electric wires - Google Patents

Description

The present invention relates to a sensor used in a method for detecting a conductor defect portion of an electric wire, and is useful for detecting defects (defects) such as wire conductor breakage, flaws, non-conductor formation, and deterioration such as stress corrosion cracking.

One of the methods to detect defects and defects such as wire breakage, scratches, non-conductivity, and deterioration due to stress corrosion cracking, etc., the actual load current is disturbed in the defective part, and the change in the generated magnetic field is A method of detecting is known.
When the defect occurs, the contour of the conductor cross section at that location becomes non-circular, the center of the current path of the cross section shifts, and the distribution of the peripheral circuit magnetic field based on the conductor current changes. It has been proposed to detect a defective part by paying attention to this fact. (Patent Document 1, Non-Patent Document 1)

Japanese Patent Laid-Open No. 10-73631 Takashi Nonaka and two others, “Fundamental study on non-destructive magnetic flaw detection of electric wires” T, IEEEjapan, Vol, 121-A, No. 3,2001, p282-287

In Patent Document 1, as shown in FIG. 11, search coils 1o and 1o ′ are arranged around the electric wire at a position equidistant from the center of the electric wire by a plurality of pairs separated by 180 °, and the search coil core direction and the electric wire are arranged. The tangential direction of the concentric circles is matched, and the difference between the outputs of both search coils of each pair is used as the sensor output.
In FIG. 11, when the displacement of the center of the current path cross section of the stranded conductor is zero, that is, there is no change in the circumferential circuit magnetic field distribution, the outputs of both coils are equal and the sensor output is 0, indicating no defect. When the peripheral circuit magnetic field distribution change occurs, the outputs of both coils are not equal and a sensor output is generated, and it is determined that there is a defect.

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箇所を評価している。 In Non-Patent Document 1, as shown in FIG. 12, 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 magnetic flux density (Bx1, By1) and (Bx2, By2) at p2 (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 defective portion of the stranded conductor is evaluated from the displacement of the center coordinates.

  However, in the above conventional example, while the magnetic sensor is moved along the electric wire, the magnetic sensor is inevitably shaken with respect to the axis of the electric wire, and this shake causes a relative shift of the center of the current path cross section of the conductor. Therefore, it is difficult to accurately detect the defective part of the conductor.

When the conductor current is I, the magnetic field strength H at a distance r from the conductor center is
H = I / (2πr)
Given in.
A current of several tens of A to several hundreds of A is passed through the wired wire, and the magnetic flux density on the outer periphery of the wire is extremely high. For example, if the current value is 150 A and the wire radius is 15 mm, the magnetic flux density on the wire surface is as high as 1600 A / m. The magnetic field sensor has a measurement limit, and it is difficult to measure a high magnetic field of 1600 A / m.
However, in the above-described conventional example, the search coil is arranged with its magnetic sensing direction directed to the direction of the circumferential circuit magnetic field of the electric wire. It is necessary to arrange them at positions that are considerably separated from each other.
Furthermore, in the conventional example described in Patent Document 1, two search coils are arranged around the electric wire at positions spaced equidistant from the center of the electric wire in pairs separated by 180 °, and the current center of the conductor path cross section of the stranded wire conductor is arranged. The sensor output is the difference between the outputs of the two search coils at the time of deviation, but the change ΔH in the ambient magnetic field strength H with respect to the deviation ΔL is given by ΔH = HΔL / r, and the search coil is located far away from the center of the wire. If r is increased by arranging it, the output difference between the two search coils is reduced accordingly, the sensor output is lowered, and it is difficult to guarantee sufficient detection sensitivity.

  Recently, magneto-impedance effect elements have been developed as magnetic field sensor elements with high magnetic field detection resolution and micro dimensions.

  An object of the present invention is to easily detect a defective portion in an electric wire with sufficiently high accuracy with a small magnetic sensor by using a magnetic field component in the longitudinal direction of the electric wire generated due to current disturbance at the defective portion of the conductor of the electric wire. Enable.

  In the method for detecting a conductor defect portion of an electric wire according to claim 1, the two magneto-impedance effect elements using amorphous wires are sandwiched in the center so that the magnetic sensing direction and the longitudinal direction of the electric wire are parallel to each other. While detecting the positive / negative reversal point of the magnetic field for detecting the longitudinal direction of the electric wire based on the defect of the electric wire conductor by disposing the element at an angle of 180 ° in the circumferential direction and moving both the elements along the longitudinal direction of the electric wire. The detected output of both elements during the movement is a sinusoidal wire length generated by the wire circuit magnetic field swells and fluctuates due to the conductor wire twist based on the current difference between the defective conductor wire and the healthy conductor wire. The differential amplification or subtraction is performed so as to cancel the directional magnetic field component.

At the defective portion of the wire conductor, the conductor cross section is deviated unevenly, and in order to narrow the current as shown in FIG. 1 (a) in the conductor cross section, the ± current as shown in FIG. The poles p and p ′ can be virtualized. The magnetic field component in the longitudinal direction of the wire along the wire longitudinal direction path aa ′ based on the ± current poles, as shown in FIG. Pattern.
In the present invention, this sudden change point is detected to find the defective portion e of the conductor, and the current value of the ± current pole is extremely small compared to the conductor current. Is a pattern that can be kept within the limit range of the magnetic sensor, and the distribution pattern of the magnetic field component in the longitudinal direction of the wire is a pattern that inverts positively and negatively at the defect point e as shown in FIG. In addition, since this pattern is sufficiently retained even if the magnetic sensor is slightly moved, a defective portion of the electric wire can be found accurately and easily.

In addition, a magnetic sensor with the magneto-impedance effect element oriented in the longitudinal direction of the wire and the magneto-impedance effect element close to the surface of the wire can be used. Can be easily performed with high sensitivity.
In addition, the magnetic field effect component in the longitudinal direction of the sine wave generated due to the fluctuation of the circumferential circuit magnetic field generated based on the electric current of the electric wire due to the influence of the twisting of the conductor, the two elements of the magneto-impedance effect element It is possible to eliminate noise by canceling the output of the signal with a method of differential amplification or subtraction.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 shows the basic configuration of the magnetic sensor used in the present invention.
In FIG. 2, 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. 2, 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 an amorphous wire having zero magnetostriction or negative magnetostriction.

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. Therefore, the detected magnetic field-output characteristics are almost symmetrical with respect to the y axis when the detected magnetic field is taken on the x axis and the output is taken 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 the negative feedback coil 6 to linearize the characteristics as shown in FIG. In FIG. 3B, 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, the polarity of the magnetic field to be detected cannot be determined, so that 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. 3 is moved in the negative direction of the x-axis by the bias magnetic field, and the maximum range −Hmax to + Hmax of the detected magnetic field is within the range of the single oblique line region. Further, as shown in FIG. 3D, linear characteristics passing through the origin are obtained by adjusting the zero point. Therefore, in FIG. 3D, when the detected magnetic field is + He, the output is + Eo, and when 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. 4, an operational amplifier Q (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. It can also be used. 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 34 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. 3 (d) can be obtained by adjusting the zero point in the y-axis direction. it can.

In order to detect a defective portion of a conductor by the method for detecting a defective portion of a conductor according to the present invention, the magnetic sensor is moved along the electric wire with the magnetic sensing direction of the magnetic sensor directed in the longitudinal direction of the electric wire. In this case, the wheel that holds the electric wire can be attached to the magnetic sensor, and the magnetic sensor can be pulled by the wire.
When the magnetic sensor passes through a defective portion of the conductor, based on the detected magnetic field-output characteristic (proportional coefficient is k) with the electric wire longitudinal direction Hx of the generated magnetic field based on the current disturbance of the defective portion as the detected magnetic field. , Eout = kHx is output, and it can be known that this is a defective part by detecting this output kHx.
Considering the pattern of the magnetic field generated in the longitudinal direction of the generated magnetic field based on the current disturbance of the defective portion, in FIG. 5, the distance between the longitudinal direction moving path aa ′ of the magnetic sensor element, for example, the magneto-impedance effect element, and the defective portion e. As d increases, the crest value decreases, but the pattern itself hardly changes.
Thus, if a magnetic sensor element, for example, a magneto-impedance effect element is disposed with the electric wire sandwiched between the magnetic impedance effect element and the magneto-impedance effect element is more defective than the other magneto-impedance effect element. Because it will take a wire longitudinal direction path that is close to the location, the output on one side of the magneto-impedance effect element is larger than the output on the side of the other magneto-impedance effect element, and both outputs have positive and negative polarity, If both outputs are differentially amplified or subtracted to obtain a sensor output, a sensor output having a high peak value can be obtained.

According to the present inventors' earnest study results, when a defect occurs in the twisted conductor of the electric wire, a difference occurs in the current flowing between the defective strand and the healthy strand, and the circumferential circuit magnetic field based on the conductor energization current is twisted in the conductor. As a result, a sine wave-like magnetic field component that changes in a sine wave shape may be generated (as a result, the conductor becomes twisted and the pitch becomes a fraction of the twist pitch).
Thus, in the method using the two magneto-impedance effect elements sandwiching the above-described electric wires and differentially amplifying or subtracting the output signals of both elements to obtain the sensor output, the sinusoidal electric wire longitudinal magnetic field is used. The ingredients can be countered.

  The length of the magnetic sensor element, for example, the magneto-impedance effect element is small compared to the pitch of the magnetic field component in the longitudinal direction of the sinusoidal electric wire, and the two magneto-impedance effect elements are several times less than the magneto-impedance effect element. Even if the sensor output is obtained by differential amplification or subtraction by shifting the distance in the longitudinal direction of the electric wire, the sinusoidal electric wire longitudinal direction magnetic field component can be sufficiently canceled.

In the method for detecting a conductor defect portion of an electric wire according to the present invention, a magnetic sensor or a fluxgate sensor using a magnetoresistive element or a Hall element can be used as the magnetic sensor, in addition to the magnetic impedance effect type sensor.
Next, the Example of the magnetic sensor for a conductor defect location detection of the electric wire which concerns on this invention is described.

FIG. 6 (a) is a drawing showing an embodiment of the magnetic sensor according to the present invention and the state of use thereof, wherein Se is a sensor, Ca is an electric wire, and M is a ground measuring instrument. An electric wire holding wheel is attached to the sensor, and the sensor is moved by pulling the wire, but these configurations are not shown.
FIG. 6B is a circuit diagram of the sensor Se.
In FIG. 6, P is a substrate. Reference numeral 1 denotes a magneto-impedance effect element, which is provided with a negative feedback coil 6 for making the output characteristics linear and a bias coil 7 for making it possible to determine the polarity of the output characteristics.

7 is a side view showing an example of the magneto-impedance effect element with a coil, FIG. 7B is a bottom view, and FIG. 7C is a cross-sectional view of FIG.
In FIG. 7, 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, and an amorphous wire, amorphous ribbon, sputtered film, or the like having zero or negative magnetostriction can be used as described above. 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. 104 and 104 are lead conductors joined to the electrodes 102 and 102 by welding or the like.

In FIG. 6, u is a magneto-impedance effect element with a coil. P is a substrate, and the magneto-impedance effect element u with coil is supported by the lead conductor 104, and the lead conductor 104 is bent so that the magnetosensitive direction (axial direction) of the magneto-impedance effect element is directed to the longitudinal direction of the electric wire.
Reference numeral 2 denotes a high-frequency current source for exciting the magneto-impedance effect element 1, and a detected magnetic field (a longitudinal component of a magnetic field generated based on current disturbance at a defective portion of the conductor) is used as a signal wave, and a high-frequency excitation current is generated. A modulated wave as a carrier wave appears at the output end of the magneto-impedance effect element 1. Reference numeral 3 denotes a demodulation circuit, which demodulates the modulated wave and outputs the signal wave. Reference numeral 4 denotes an amplifier. The output is negatively fed back to the magneto-impedance effect element 1 through the negative feedback coil 6 and the output is linearized. In addition, a bias magnetic field is applied to the magneto-impedance effect element 1 through the bias coil 7 with the + Vcc power source, and the polarity of the output characteristics can be discriminated.
The high-frequency current source 2, the demodulation circuit 3, and the amplifier 4 are mounted on the substrate P.

FIG. 8 (a) is a drawing showing another embodiment of the magnetic sensor according to the present invention and the state of use thereof, wherein Se is a sensor, Ca is an electric wire, and M is a ground measuring instrument. An electric wire holding wheel is attached to the sensor, and the sensor is moved by pulling the wire, but these configurations are not shown.
FIG. 8B is a circuit diagram of the sensor Se.
In FIG. 8, P is a board | substrate and the notch part h for electric wire insertion is provided. u and u are magneto-impedance effect elements with two coils, and the one shown in FIG. 7 can be used, and the lead conductor 104 is bent so that the electric wire Ca is sandwiched and the magnetic sensing direction is oriented in the longitudinal direction of the electric wire Ca. Are supported on the substrate P. 2 is a high-frequency current source for exciting both magneto-impedance effect elements, 3a and 3b are demodulator circuits connected to the output terminals of the respective magneto-impedance effect elements 1a and 1b, and 4d is a differential amplifier. It is installed.
The two magneto-impedance effect elements are separated by an angle of 180 ° with the electric wire in the center, and as shown in FIG. 9, the magnetic field generated based on the current disturbance at the defective portion e of the conductor is generated by, for example, one magnetic field. The impedance effect element 1a is a wire longitudinal path aa ', and the other magnetic impedance effect element 1b is a wire longitudinal path that is separated from the wire longitudinal path aa' by a distance w / 2 that is substantially a half circumference of the wire. It is moved by bb ′. The detected magnetic field (wire longitudinal magnetic field component) along these two paths can be estimated to have substantially the same waveform except that the polarity is positive and negative and the peak value is different. Therefore, the absolute values of the detection signals of both magneto-impedance effect elements are added to form a sensor output.

  As described above, when a defect occurs in the conductor of the electric wire, a current difference is generated between the defective conductor wire and the healthy wire, and the circumferential circuit magnetic field based on the conductor current is swelled and fluctuated due to the twist of the twisted conductor. A sinusoidal electric wire longitudinal direction magnetic field component is generated. The sine wave can be regarded as a harmonic with respect to the twist of the conductor, and the pitch is shorter than the twist pitch of the twisted conductor, but is extremely longer than the length of the magneto-impedance effect element. Therefore, the sinusoidal wire longitudinal magnetic field component acts as a substantially identical magnetic field on both magneto-impedance effect elements, cancels out for differential amplification, and does not appear as a sensor output. In addition, internal noise generated by the influence of temperature or the like in each demodulating circuit is canceled out due to differential amplification and does not appear as a sensor output.

  When amplification is performed by differential amplification as in the second embodiment, the direction of the bias magnetic field Hb applied to one magnetoimpedance effect element and the direction of the bias magnetic field Hb applied to the other magnetoimpedance effect element as shown in FIG. Is reversed, and the demodulated outputs (magnetic field detection signals) with opposite phases are represented by E + and E−, and the difference approaches a straight line as indicated by E ±, so negative feedback can be omitted. is there.

  In the first and second embodiments, 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, and the Hartley oscillation circuit, Colpitts oscillation circuit, collector tuned oscillation can be used as the high frequency excitation current source, for example. In addition to a normal oscillation circuit such as a circuit and a base tuned oscillation circuit, a triangular wave generator that integrates a square wave output of a crystal oscillator through an integration circuit via a DC component cut capacitor, and amplifies the triangular wave of the integration output by an amplification circuit, COMS -A triangular wave generator using an IC as an oscillator can be used.

  As a demodulator circuit, for example, a configuration in which a modulated wave is half-wave rectified by an operational amplifier circuit 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, the modulated wave The half-wave rectified wave is processed 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.

  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 circuit configuration can be used as long as the amount can be extracted.

It is drawing used for description of the effect of the conductor defect location detection method of the electric wire which concerns on this invention. It is drawing which shows the magneto-impedance effect type sensor used in this invention. It is drawing which shows the output characteristic of the magneto-impedance effect type sensor used in this invention. It is drawing which shows another example of the magneto-impedance effect type sensor used in this invention. It is drawing which shows the movement path | route of the sensor in one Example of the conductor defect location detection method of the electric wire which concerns on this invention. It is drawing which shows one Example of the sensor which concerns on this invention. FIG. 5 shows a magnetoimpedance effect element with a coil in the sensor of FIG. It is drawing which shows another Example of the sensor which concerns on this invention. It is drawing which shows the movement path | route of the sensor in another Example of the conductor defect location detection method of the electric wire which concerns on this invention. It is drawing used in order to demonstrate the principal part of another Example of the sensor which concerns on this invention. It is drawing which shows a prior art example. It is drawing which shows the prior art example different from the above.

DESCRIPTION OF SYMBOLS 1 Magneto-impedance effect element 1a Magneto-impedance effect element 1b Magnet-impedance effect element 2 Current source 3 for high frequency excitation Demodulation circuit 3a Demodulation circuit 3b Demodulation circuit 4 Amplifier 4d Differential amplifier Ca Electric wire e Defect location of conductor

Claims (1)

Two magneto-impedance effect elements using amorphous wires are arranged at an angle of 180 ° in the circumferential direction of the electric wire with the electric wire sandwiched in the center so that the magnetic sensing direction and the longitudinal direction of the electric wire are parallel to each other, By moving both the elements along the longitudinal direction of the electric wire, the positive and negative reversal points of the magnetic field for detecting the longitudinal direction of the electric wire based on the defect of the electric wire conductor are detected, and the detection outputs of the both elements during the movement are detected as defects. Differential amplification or subtraction so as to cancel the sinusoidal wire longitudinal magnetic field component generated by the wire gyrating magnetic field wandering due to twisting of the conductor wire based on the current difference between the conductor wire and the healthy conductor wire A method for detecting a conductor defect in an electric wire.

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