JP2019158672A - Abnormal current detector for three-phase AC cable - Google Patents

Abstract

To provide an abnormal current detector for three-phase AC cable with which it is possible to detect an abnormal current of the three-phase AC cable without the need for finding a correction coefficient in advance.SOLUTION: Provided is an abnormal current detector for three-phase AC cable 13 which detects an abnormal current of the three-phase AC cable connected to an electric apparatus. This abnormal current detector comprises: a magnetism detection unit 15 brought into contact with the outer circumferential surface of conduit tube of the three-phase AC cable and detecting a magnetic field; a frequency analysis unit 16 for analyzing the frequency of a magnetic field detection signal detected by the magnetism detection unit; and an abnormal current detection unit 17 for detecting an abnormal current on the basis of the amplitude of a fundamental frequency component and the amplitude of a frequency component other than the fundamental frequency component among the frequency components of the frequency analysis result of the frequency analysis unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an abnormal current detection device for a three-phase AC cable that detects an abnormal current flowing through a three-phase AC cable that is connected to an electric device and is energized.

  At substations, factories, etc., efforts are being made to measure the frequency component of the current flowing in the power cable for the purpose of reducing loss and detecting anomalies in each component. As an example of loss reduction, a high-voltage inverter manages harmonic components of the output current waveform to ensure power quality. The level of the harmonic component varies depending on the switching element of the inverter and the switching frequency. The larger the harmonic component, the larger the loss and the larger the voltage load (bounce voltage) to each device. In recent years, the harmonic component level is also regulated as a guideline for ensuring system power quality (a guideline for suppressing harmonics of customers receiving high voltage or extra high voltage).

Three-phase AC cables such as substations and factories, which are current measurement targets, are connected together to bundle three cables in order to protect the cables and prevent incorrect wiring. For these three-phase AC cables, a three-core cable in which three conductors are insulated from each other and a single-core cable containing three single-core cables are used.
Therefore, in order to measure the current flowing through each cable, it is necessary to attach a current sensor to each phase at the connection between the cable and the distribution board or electrical equipment in a power failure state. In order to measure the current of each phase in a live state, it is necessary to directly attach a clamp type current sensor to a single phase at a site where the cable is separated, which is difficult to implement from a safety aspect in a high voltage facility.
When a clamp type current sensor is attached to a three-phase AC cable in a lump, the three-phase balanced current cancels out the magnetic fields generated by the respective phase currents, and the current cannot be detected from an external magnetic field. In this case, only the zero-phase current component that becomes a three-phase unbalance is detected.

A current sensor described in Patent Document 1 has been proposed as a current sensor capable of measuring a current value of a current flowing through a desired core wire of such a multicore cable in a non-contact manner.
The current sensor described in Patent Document 1 detects a partial magnetic field around the wire to be measured by a magnetic sensor module having a built-in magnetic sensor element, and performs full-wave rectification processing and an average current in an analog signal processing unit. After performing integration processing and low-pass filter processing to obtain a digital signal by the digital signal processing unit, the current value of the current to be measured is calculated from the voltage signal value converted to the digital signal by the current calculation unit I am doing so. Here, the calculation of the current value of the current to be measured by the current calculation unit is performed by multiplying the integral value V of the voltage signal by the correction coefficient K. The correction coefficient K is determined by the sensitivity of the magnetic sensor element and the positional relationship between each core wire and the magnetic sensor module.

Japanese Patent Laid-Open No. 2006-148597

However, in the prior art described in Patent Document 1, the correction coefficient determined by the sensitivity of the magnetic sensor element and the positional relationship between each core wire and the magnetic sensor module after integrating the detection voltage detected by the magnetic sensor module is calculated. The current flowing through the core wire to be measured is calculated by multiplication.
For this reason, it is necessary to obtain a correction coefficient in advance for each multi-core cable to be measured. That is, there is a problem that the correction coefficient K needs to be obtained each time when the distance between the core wire and the magnetic sensor module and the physical property value of the intervening material are different even if the types of the three-core cable and the conduit are the same.

  Therefore, the present invention has been made paying attention to the problems of the above prior art, and can detect an abnormal current of a three-phase AC cable without detecting a correction coefficient in advance. The object is to provide a device.

  In order to achieve the above object, an abnormal current detection device for a three-phase AC cable according to the present invention is an abnormal current detection device for a three-phase AC cable that detects an abnormal current of a three-phase AC cable connected to an electrical device. . The abnormal current detection device includes a magnetic detection unit that detects the magnetic field by contacting the outer peripheral surface of the conduit of the three-phase AC cable, a frequency analysis unit that performs frequency analysis of the magnetic field detection signal detected by the magnetic detection unit, Among the frequency components of the frequency analysis result of the frequency analysis unit, an abnormal current detection unit that detects an abnormal current based on the amplitude of the fundamental frequency component and the amplitude of a frequency component other than the fundamental frequency component is provided.

  According to one aspect of the present invention, the magnetic field detection signal detected by the magnetic detection unit is subjected to frequency analysis, and the presence or absence of occurrence of abnormal current in the three-phase AC cable is detected from the amplitude of the fundamental frequency component and other frequency components. It is possible to detect the presence or absence of abnormal current without obtaining a correction coefficient in advance.

It is a schematic block diagram which shows 1st Embodiment of the abnormal current detection apparatus of the three-phase alternating current cable which concerns on this invention. It is sectional drawing which shows the three-phase alternating current cable and magnetic detection part in which a three-phase core wire is arrange | positioned equally. It is a wave form diagram which shows the detection signal waveform of a magnetic detection part in case a three-phase core wire is equally arrange | positioned to a three-phase current waveform and a three-phase alternating current cable. It is sectional drawing which shows the three-phase alternating current cable and magnetic detection part in which a three-phase core wire is arrange | positioned unevenly. It is a wave form diagram which shows the waveform of the detection signal of a magnetic detection part in case a three-phase core wire is unevenly arrange | positioned in a three-phase current waveform and a three-phase alternating current cable. It is a wave form diagram which shows the relationship between the frequency which shows the frequency analysis result of the detection signal of a magnetic detection part, and an amplitude. It is a schematic block diagram which shows 2nd Embodiment of the abnormal current detection apparatus of the three-phase alternating current cable which concerns on this invention.

Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.
Further, the embodiment described below exemplifies an apparatus and a method for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, The layout is not specified as follows. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

First, a first embodiment of an abnormal current detection device for a three-phase AC cable representing one aspect of the present invention will be described with reference to the drawings.
First, a rotating electrical machine as an electrical apparatus to which the present invention can be applied will be described. Although not shown, the rotating electrical machine 10 includes a rotating electrical machine main body 11 that incorporates a rotor and a stator, and a terminal box 12 that supplies a three-phase alternating current to a stator coil formed on the outer peripheral surface of the rotating electrical machine main body 11. Yes.
One end of a three-phase AC cable 13 is internally connected to the terminal box 12, and the other end of the three-phase AC cable 13 is connected to an inverter that drives a rotating electrical machine (not shown). In particular, in the case of a high voltage, the three-phase AC cable 13 is wired while being stored in the protective conduit 14.

  As shown in the figure, the three-phase AC cable 13 is a state in which three wires, ie, a U-phase electric wire Wu, a V-phase electric wire Wv, and a W-phase electric wire Ww, which are each covered with insulation, are housed in a protective conduit 14. It is wired with. The conduit 14 is properly used depending on the usage environment, and a metal or synthetic resin pipe is used. A connector made of a synthetic resin is mainly used because flexibility is required at a connection portion with an electric device. FIG. 2 shows a state in which a three-phase AC cable is stored inside a synthetic resin conduit 14. A three-core cable or a three-core set of single-core cables is applied to the three-phase AC cable 13 inside the conduit 14.

A magnetic detection unit 15 is attached to an arbitrary outer peripheral surface of the conduit 14. As shown in FIG. 2, the magnetic detection unit 15 includes a V block 15 a formed in a V shape in which an inner surface and an outer surface are parallel. The V block 15a is formed with a through hole 15b penetrating from a valley portion on the inner surface to a mountain portion on the outer surface. The through-hole 15b includes a large-diameter hole portion 15c having a large inner diameter on the inner surface side and a small-diameter hole portion 15d having an inner diameter on the outer surface side smaller than that of the large-diameter hole portion 15c.
A magnetic sensor 15e is disposed in the large diameter hole portion 15c, and a signal line 15f of the magnetic sensor 15e protrudes from the outer peripheral surface of the V block 15a through the small diameter hole portion 15d. In the magnetic sensor 15e, the magnetic detection surface protrudes from the valley portion of the V block 15a, and when the inner surface of the V block 15a is brought into contact with the outer peripheral surface of the conduit 14, the magnetic detection surface becomes the outer peripheral surface of the conduit 14. Touched.

As the magnetic sensor 15e, a magnetoresistive element whose electric resistance changes with application of a magnetic field, a magnetic impedance element whose electric impedance changes with application of a magnetic field, a Hall element that detects a magnetic field using the Hall effect, Alternatively, a flux gate element or the like can be applied. In short, any magnetic detection element can be applied as long as a magnetic field detection signal corresponding to the magnetic field on the outer peripheral surface of the conduit 14 can be output.
The magnetic sensor 15e preferably has a flat gain characteristic in a frequency band of 30 to 3000 Hz. Moreover, it is preferable that the magnetic sensor 15e is attached to the large-diameter hole 15c so that the amount of protrusion can be adjusted.

The magnetic field detection signal output from the magnetic sensor 15e of the magnetic detection unit 15 is supplied to a frequency analysis unit 16 such as a fast Fourier transform (FFT) analyzer. The frequency analysis unit 16 performs frequency analysis on the detection signal output from the magnetic detection unit 15 and supplies the frequency analysis result to the abnormal current detection unit 17.
The abnormal current detector 17 determines the presence or absence of abnormal current based on the amplitude of the fundamental frequency component and the amplitude of other frequency components based on the frequency analysis result of the frequency analyzer 16.
Here, the principle of detecting an abnormal current according to the present invention will be described. First, the relationship between the current flowing through the three-phase AC cable 13 and the detection signal output from the magnetic detection unit 15 will be described.

If each phase current flowing through the three-phase AC cable 13 is a three-phase balanced current having an amplitude of I ₀ , a frequency of f, a phase difference of 120 degrees, and a time of t, the U-phase current Iu, the V-phase current Iv, and The W-phase current Iw can be expressed by the following formulas (1) to (3).
Iu = I ₀ × Sin (2π × f × t) (1)
Iv = I ₀ × Sin (2π × f × t−2 / 3 × π) (2)
Iw = I ₀ × Sin (2π × f × t−4 / 3 × π) (3)

When the distance between the center of each phase wire and the magnetic detection unit 15 is set such that the U phase is Lu, the V phase is Lv, and the W phase is Lw, the magnetic phase Hu and V phase generated by the U phase in the magnetic detection unit 15 are magnetized. The magnetic field Hv generated by the detection unit 15 and the magnetic field Hw generated by the W phase in the magnetic detection unit 15 can be expressed by the following equations (4) to (6).
Hu = Iu / (2 × π × Lu) (4)
Hv = Iv / (2 × π × Lv) (5)
Hw = Iw / (2 × π × Lw) (6)
Since the magnetic field H detected by the magnetic detector 15 is the sum of all phases,
H = Hu + Hv + Hw (7)
It becomes.

  Here, FIG. 3 shows detection signal waveforms when the circumferential position of the three-phase AC cable 13 of the magnetic detection unit 15 shown in FIG. 2 is changed counterclockwise from the center of the conduit 14. Show. The detection signal becomes the largest at the mounting angles of 0 degrees, 120 degrees, and 240 degrees. The angle 60 degrees is a detection signal synchronized with the current waveform of the V phase, the angle of 180 degrees is the U phase, and the angle of 300 degrees is synchronized with the current waveform of the W phase. At other mounting angles, the phases of the detection signal and the phase current are not synchronized because of the influence of magnetic fields from a plurality of phases, and the distance between the magnetic detection unit 15 and each phase wire Wu, Wv, and Ww is also increased. The magnetic field detection signal becomes small.

Therefore, there are three attachment points of the magnetic detection unit 15 where the magnetic field detection signal of the magnetic detection unit 15 becomes the maximum, and at these three points, the magnetic field detection signal becomes a waveform synchronized with the nearby phase current waveform. When the diameter of the conduit 14 is increased, the relationship between the mounting angle and the magnetic field detection signal waveform does not change, and the distance between the wire and the magnetic detection unit 15 increases, so that the detection level of the magnetic detection unit 15 is overall. To drop.
A description will be given of detection signals when the three-phase cables are scattered in the conduit 14 as shown in FIG. The current waveform in this case is as shown in FIG. 5, and the attachment position of the magnetic detection unit 15 where the detection signal is maximum is not necessarily three points, and the phase of the detection signal and the phase current is also at the position where the detection signal is maximum. Does not necessarily match. When the magnetic field H detected by the magnetic detection unit 15 is obtained from the above-described equations (1) to (7), the following equation (8) is obtained.

H = Hu + Hv + Hw
= (Iu / (2 × π × Lu)) + (Iv / (2 × π × Lv)) + (Iw / ((2 × π × rw))
= (I ₀ / (2 × π)) × ((sin (2π × f × t)) / Lu)
+ ((Sin (2π × f × t−2 / 3 × π)) / Lv)
+ ((Sin (2π × f × t−4 / 3 × π)) / Lw)
= (I ₀ / (2 × π)) × (A ² + B ² ) ^0.5 × (sin (2π × f × t + α)) (8)
Here, A = (1 / Lu) − (1 / (2Lv)) − (1 / (2Lw))
B =-(√3 / 2Lv) + (√3 / 2Lw)
Cos (α) = A / (A ² + B ² ) ^0.5 )
Sin (α) = B / (A ² + B ² ) ^0.5

As shown in Expression (8), even when the position of the electric wire in the conduit 14 is indefinite, the same frequency component as the balanced current flowing in the three-phase AC cable 13 is detected as the magnetic field detection signal of the magnetic detection unit 15. It will be. That is, in Expression (8), the phase is shifted by α, but this is a shift on the time axis, and no shift occurs in the frequency domain.
Here, when focusing on each frequency component, the frequency component is classified into a fundamental wave frequency desired to flow to the target electric device and other frequencies. Other frequencies may reduce the efficiency of the target electrical device or cause malfunction or failure.

Therefore, if the amplitude level of the other frequency component becomes so large that it cannot be ignored with respect to the amplitude level of the fundamental frequency component, it can be determined that an abnormal current that adversely affects the electrical device is generated.
Therefore, the magnetic field detection signal output from the magnetic detection unit 15 is subjected to frequency analysis by the frequency analysis unit 16, and the frequency analysis result is supplied to the abnormal current detection unit 17. The presence / absence of an abnormal current can be determined based on the amplitude and the amplitude of frequency components other than the fundamental frequency component.

Next, a specific procedure for detecting an abnormal current will be described. First, the magnetic detection unit 15 is brought into contact with the outer peripheral surface of the conduit tube 14, and the detection level on the circumference is measured. Three points at which the detection level is maximized are obtained on the same circumference, and the positions are plotted.
Next, at each plot position, the first magnetic field detection signal, the second magnetic field detection signal, and the third magnetic field detection signal of the magnetic detection unit 15 are acquired, and the signals are individually analyzed by the frequency analysis unit 16 such as an FFT analyzer. . By performing this frequency analysis, the frequency analysis result shown in FIG. 6 is obtained. In this frequency analysis result, the horizontal axis represents frequency (Hz) and the vertical axis represents amplitude (p, u).

According to this frequency analysis result, for example, a frequency component of an integral multiple of 120 Hz (second harmonic), 180 Hz (third harmonic), 240 Hz (fourth harmonic) with respect to the fundamental frequency component having the largest amplitude, for example, 60 Hz. Wave) and 300 Hz (fifth harmonic), the amplitude increases. In addition, the amplitude of the sideband components on both sides of the fundamental frequency component also increases. In FIG. 6, although up to 300 Hz, which is the fifth harmonic component, is described, actually, recording is performed up to 2400 Hz, which is the 40th harmonic component.
For this purpose, it is preferable that the detection time of the magnetic field detection signal detected by the magnetic detection unit 15 is 5 seconds or more and the sampling frequency is 6.5 kHz or more. By measuring the magnetic field detection signal under this measurement condition, frequency analysis with a frequency range of 2400 Hz and a frequency resolution of 0.2 Hz can be performed. Accordingly, when the fundamental frequency is 60 Hz, the harmonic component can be calculated up to a step size of 40 Hz, and the sideband can be calculated up to a step size of 0.2 Hz.

By inputting the frequency analysis result to the abnormal current detection unit 17, the abnormal current detection unit 17 uses the amplitude Q (n) (n = 1, 2,... 40) of each harmonic component other than the fundamental frequency component. Is divided by the amplitude P of the fundamental frequency component and the value of distortion rate Q (n) / P exceeds a preset threshold value Th determined by, for example, contract power, it is determined that an abnormal current has occurred. This abnormal current detection is performed at three points of the plot points, and the current abnormal mode (any one of single-phase failure, interphase failure and all-phase failure) can be estimated from the difference in distortion rate at the three points.
Thus, according to the above embodiment, the magnetic detection unit 15 is arranged in the conduit 14 of the three-phase AC cable 13 in the energized state, the frequency analysis unit 16 performs frequency analysis on the detected magnetic field detection signal, and the frequency analysis result The abnormal current can be determined based on the amplitude P of the fundamental frequency component and the amplitude Q (n) of the harmonic component other than the frequency component. Therefore, it is possible to provide an abnormal current detection device for a three-phase AC cable that can accurately detect an abnormal current without being affected by the type or material of the three-phase AC cable 13 to be measured.

Moreover, as shown in the above equation (8), even when the phase wires in the conduit 14 are arranged unevenly, the amplitudes of the first to forty-order harmonic components are accurately determined by frequency analysis. Therefore, it is possible to accurately detect the presence or absence of current abnormality in a live line state.
Further, by determining the presence / absence of an abnormal current with a frequency component that is an integral multiple of the reference frequency component, it is possible to detect the presence / absence of a harmonic current from the power supply system.
Furthermore, the detection time of the magnetic field detection signal in the magnetic detection unit 15 is set to 5 seconds or more, and the sampling frequency is set to 6.6 kHz or more. The sideband wave can be evaluated in 0.2 Hz increments.

  In the above embodiment, the case where the abnormal current is detected based on the amplitude P of the fundamental frequency component and the amplitude Q (n) of other harmonic components, for example, has been described. However, the present invention is not limited to this. Alternatively, the abnormal current can be detected based on the amplitude of the fundamental frequency component and the amplitude of the sideband frequency component. That is, for example, when the rotor bar of a squirrel-cage induction motor is broken, it is known that a frequency component of power source frequency ± slip frequency × 2, that is, a sideband frequency component is generated, and the amplitude of this sideband frequency component When the value exceeds a preset threshold value, it is possible to detect an abnormality in current due to breakage of the rotor bar.

Next, a second embodiment of the present invention will be described with reference to FIG.
In the second embodiment, the amplitude of the frequency analysis result is converted into an effective current value to detect the occurrence of an abnormal current.
That is, in the second embodiment, as shown in FIG. 7, the effective value S of the phase current flowing in the three-phase AC cable 13 is detected by the current measuring device 21, and the effective value of the phase current S detected by the current measuring device 21 is detected. Is supplied to the abnormal current detector 17.

  In this abnormal current detector 17, the amplitude P of the reference frequency component f0 of the frequency analysis result input from the frequency analyzer 16, the amplitude Q (1) of the first harmonic frequency component f1, and the second harmonic frequency component The amplitude Q (2) of f2..., the amplitude Q (40) of the 40th harmonic frequency component f40 is obtained. The abnormal current detector 17 calculates the conversion ratio k by dividing the effective value S of the phase current by the amplitude P of the reference frequency component f0 (k = S / P). Then, the current effective value I (n) for each harmonic frequency component f (n) is calculated by multiplying the calculated conversion ratio k by the amplitude Q (n) of each harmonic frequency component f (n). The presence / absence of abnormal current is determined based on the calculated current effective value I (n) of each harmonic frequency component f (n).

For example, in the “Guidelines for Harmonic Suppression Measures for Consumers Receiving Power at High Voltage or Extra High Voltage”, the harmonic outflow current upper limit value [mA / kW] per contracted power of 1 kW at a receiving voltage of 6.6 kW is regulated. This regulation value [mA / kW] is 3.5 for the fifth component, 2.5 for the seventh component, 1.0 for the eleventh component, 1.3 for the thirteenth component, 1.0 for the seventeenth component, The 19th order component is set to 0.90, the 23rd order component is set to 0.76, and the 25th order component is set to 0.7.
Therefore, by grasping the current effective value I (n) of each harmonic frequency component f (n), the harmonic current level generated in the individual device can be grasped and compared with the harmonic outflow current upper limit value. Thus, an abnormal current at each harmonic frequency component f (n) can be detected.

In the first and second embodiments, the case where the occurrence of abnormal current is detected based on the distortion rate and current effective value of each harmonic frequency component f (n) has been described. However, the present invention is not limited to this. is not.
That is, the analysis results obtained by frequency analysis of the magnetic field detection signals detected at the three points by the frequency analysis unit 16 are compared, and the harmonic frequency components that have peaks in the common frequency region in the frequency analysis results of the three points are compared with the common mode signal. The frequency component that peaks only at a specific point is classified as a normal mode signal.

The common mode signal is a signal that is stably and repeatedly generated in all phases, and is likely to reflect changes in power supply facilities and aging of target devices. However, the normal mode signal is a signal that is intermittently generated in a specific phase, and is highly likely to reflect a sudden failure or failure of the power supply facility or the target device.
Therefore, when the normal mode signal is detected, it can be determined that the current is an abnormal current due to a sudden failure or failure of the power supply facility or the target device. For this reason, by accumulating the relationship between the frequency component of the normal mode signal and the cause of the abnormality, it becomes possible to detect a sudden malfunction or failure of the power supply facility or the target device.

Moreover, although the said 1st and 2nd embodiment demonstrated the case where a magnetic field detection signal was measured in three points where the magnetic field on the circumference of the conduit 14 becomes large, it is not limited to this, A magnetic field is The magnetic field detection signal may be measured at one or two points that increase.
Moreover, although the said 1st and 2nd embodiment demonstrated the case where a rotary electric machine was used as an electric equipment, it is not limited to this, The electricity which supplies three-phase electric power using a three-phase alternating current cable The present invention can be applied to any device.

  DESCRIPTION OF SYMBOLS 10 ... Rotating electric machine, 11 ... Rotating electric machine main body, 12 ... Terminal box, 13 ... Three-phase alternating current cable, 14 ... Conduit, 15 ... Magnetic detection part, 15a ... V block, 15b ... Through-hole, 15e ... Magnetic sensor, 15f ... Signal line, 16 ... Frequency analyzer, 17 ... Abnormal current detector, 21 ... Current measuring instrument

Claims (9)

An abnormal current detection device for a three-phase AC cable that detects an abnormal current of a three-phase AC cable connected to an electrical device,
A magnetic detector for detecting a magnetic field in contact with the outer peripheral surface of the conduit of the three-phase AC cable;
A frequency analysis unit for frequency analysis of the magnetic field detection signal detected by the magnetic detection unit;
A three-phase alternating current provided with an abnormal current detector that detects an abnormal current based on the amplitude of a fundamental frequency component and the amplitude of a frequency component other than the fundamental frequency component among the frequency components of the frequency analysis result of the frequency analyzer Cable abnormal current detection device.   The abnormal current detection unit is a frequency at which a distortion rate obtained by dividing an amplitude of a fundamental frequency component having the largest amplitude among frequency components analyzed by the frequency analysis unit by dividing an amplitude of a frequency component other than the fundamental frequency component is equal to or greater than a threshold value. The abnormal current detection device for a three-phase AC cable according to claim 1, wherein occurrence of abnormal current is detected when a component is present.   The abnormal current detection device for a three-phase AC cable according to claim 2, wherein the frequency component to be compared with the fundamental frequency component is a frequency component that is an integral multiple of the fundamental frequency component.   The abnormal current detection device for a three-phase AC cable according to claim 2, wherein the frequency component to be compared with the fundamental frequency component is a sideband component formed on both sides of the fundamental frequency component. A measuring device for detecting the effective value of the phase current of the three-phase AC cable;
The abnormal current detection unit uses a value obtained by dividing the phase current effective value detected by the measuring instrument by the amplitude of the fundamental frequency component as a conversion coefficient, and multiplies the amplitude of each frequency component other than the fundamental frequency component by the conversion coefficient. The abnormal current detection device for a three-phase AC cable according to any one of claims 2 to 4, wherein the presence / absence of an abnormal current is determined based on the calculated current effective value.   The magnetic detection unit detects the first magnetic field detection signal, the second magnetic field detection signal, and the third magnetic field detection signal at three points where the magnetic field detection level on the same circumference of the conduit tube is higher than that of the other part. The frequency conversion unit converts the first magnetic field detection signal, the second magnetic field detection signal, and the third magnetic field detection signal into a first frequency component, a second frequency component, and a third frequency component, respectively, and performs the abnormal operation. The abnormal current detection device for a three-phase AC cable according to any one of claims 2 to 5, wherein the current detection unit detects a current abnormality based on the first frequency component, the second frequency component, and the third frequency component.   The magnetic detection unit generates a frequency component of a peak detection signal that is common to all of the first frequency component, the second frequency component, and the third frequency component as a common mode signal, and generates only one of the frequency components. The abnormal current detection device for a three-phase AC cable according to claim 6, wherein the presence / absence of an abnormal current is determined using a frequency component of the peak detection signal to be a normal mode signal.   The abnormality of the three-phase AC cable according to claim 6, wherein the abnormal current detection unit determines an abnormal mode by comparing distortion rates of the first frequency component, the second frequency component, and the third frequency component. Current detection device.   The abnormal current detection device for a three-phase AC cable according to claim 8, wherein the abnormal mode is any one of single-phase failure, interphase failure, and all-phase failure.

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