JP2013096961A - Earth fault detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an earth fault detection device capable of identifying an earth-fault steel tower in an extra-high-voltage transmission system whose neutral point on a transmission side is directly grounded.SOLUTION: Surge absorbers 140 and 142 are provided with, besides a function for suppressing outputs of detecting coil parts 1 and 2 that have detected a fault current in earth fault, a function of reducing magnetic saturation of the first and second detecting coil parts 1 and 2, and are configured to have nonmagnetic air core parts between a core 7 and a coil 9 wound around the core 7. When the output waveforms of the first and second detecting coil parts 1 and 2 are distorted, the earth fault detection device improves the distortion of a fault current in the earth fault on the basis of the outputs of the nonmagnetic air core parts of the first and second detecting coil parts 1 and 2 so as to enable phase detection.

Description

  The present invention relates to detection of a ground fault in a power transmission tower, and more particularly to a ground fault detection device that detects a ground fault in a power transmission tower in an ultra high voltage power transmission system.

  As a device for detecting a ground fault in a power transmission tower, for example, there is a ground fault point display device described in Patent Document 1 previously proposed by the present applicant. When such a ground fault display device described in Patent Document 1 is applied to detection of a ground fault in a transmission tower in an ultrahigh voltage transmission line having a transmission voltage of 187 kV or higher, the neutral point on the transmission side has a resistance. Because it is directly grounded without any grounding, if a ground fault occurs, a large fault current of several tens of kA or more may be shunted to the overhead ground wire, which may damage the circuit for detecting the ground fault. Not only that, the fault current at the time of ground fault becomes extremely large, and depending on the interruption timing of the ground fault fault relay, the DC component is superimposed on the current flowing through the overhead ground wire, etc., detection that detected the fault current There is a risk that the output waveform of the coil is distorted, and it becomes difficult to detect a ground fault.

Japanese Patent No. 3458123

  Such a ground fault point display device described in Patent Document 1 functions effectively for detecting a ground fault in a resistance grounding transmission line having a transmission voltage of 154 kV or less. As described above, there is a risk of damage to the detection circuit, the fault current at the time of the ground fault becomes extremely large, and the overhead ground Since a direct current component may be superimposed on the current flowing through the line, there has been a problem that the detection output waveform is distorted and a ground fault cannot be detected.

  The present invention has been made based on such a viewpoint, and can prevent the detection circuit from being damaged due to a large amount of fault current, increase the fault current during a ground fault, and A ground fault that can identify the ground fault tower of an ultra-high voltage transmission system with the neutral point of the transmission side directly grounded without causing any trouble in fault detection due to the DC component superimposed on the current flowing through the ground line An object is to provide a failure detection apparatus.

  In the present invention, a first and a first are provided for detecting a fault current that is attached to an overhead ground wire of an ultrahigh-voltage power transmission line with a neutral point directly grounded with a power transmission tower sandwiched between them and is shunted to the overhead ground wire in the event of a ground fault. Two detection coil units; and a detection unit that detects a power transmission tower in which a ground fault has occurred from a phase of a fault current detected at the time of the ground fault detected by the first and second detection coil units, and the detection unit However, a surge absorber made of a zinc oxide element is inserted in parallel on the output side of each of the first and second detection coil units, and the outputs of the first and second detection coil units are directly input, In addition to the function of suppressing the output of the detection coil at the time of ground fault current detection to a predetermined voltage, the first and second detection coil sections are configured to detect the phase of the fault current at the time. A function to reduce magnetic saturation And the first and second detection coil portions are configured to have a non-magnetic air-core portion in addition to the core between the core and the coil wound around the core. When the output waveforms of the first and second detection coil sections are distorted, the fault current is distorted during a ground fault based on the outputs of the nonmagnetic air core portions of the first and second detection coil sections. The above-mentioned object is achieved by a ground fault detection device that improves the above-mentioned and enables phase detection.

  According to such a configuration, since a neutral point is directly grounded, even when a large fault current flows at the time of a ground fault, the surge absorber can suppress the voltage to a predetermined voltage and prevent damage to the detection circuit. be able to.

  Further, according to such a configuration, the surge absorber made of a zinc oxide element has a function of reducing the magnetic saturation of the cores of the first and second detection coil portions. That is, the voltage induced in these detection coil portions from the fault current flowing through the overhead ground wire is suppressed to a predetermined voltage by the surge absorber. In order to maintain the output voltage from the first and second detection coil portions at the above-mentioned predetermined voltage, a large amount of current flows in the surge absorber in the direction to cancel the magnetic flux of the core of the first and second detection coil portions. As a result, the magnetic saturation of the first and second detection coil portions is reduced, and the distortion of the output waveform of these detection coil portions can be improved.

  Further, according to the above configuration, since the fault current at the time of the ground fault becomes large and the DC component is superimposed on the fault current depending on the interruption timing of the ground fault fault relay, the first and second detections Even if the cores of the first and second detection coil portions are magnetically saturated, the nonmagnetic air-core portion between the cores is magnetically fluxed. Will penetrate. For this reason, since the air core portion has no magnetic saturation, the larger the current flowing through the overhead ground wire, the greater the distortion-free output from the air core portion, which is superimposed on the outputs of the first and second detection coil units. Waveform distortion is improved and phase detection becomes possible.

  Further, in the present invention, the detection means is inserted in parallel with the surge absorber circuit including the two surge absorbers inserted in parallel with the coils of the first and second detection coil sections, and the surge absorber circuit. The phase detection circuit includes two bidirectional Zener diodes connected in series, and a rectification circuit that full-wave rectifies the output of the phase detection circuit.

  Further, in the present invention, the detection means further inputs a full-wave rectified output of the rectifier circuit, gives a predetermined constant current, a charging circuit charged with a constant current by the constant current circuit, And a detection circuit that provides a detection output indicating a ground fault when the charging voltage of the charging circuit becomes equal to or higher than a predetermined value.

  Furthermore, in this invention, it can comprise so that a magnetic gap may be formed in the said core of the said 1st and 2nd detection coil part.

  According to the present invention, it is possible to detect a ground fault tower of an ultra high voltage power transmission system with a neutral point directly grounded, and it is possible to prevent damage to a detection circuit due to a very large ground fault current and to detect a fault current. Thus, distortion of the output waveform of the detection coil section can be improved.

  Further, according to the present invention, by performing constant current charging, it is possible to prevent malfunctioning with respect to lightning having a current waveform similar to that of a half cycle of a commercial frequency, and the output of the detection coil unit by a DC component. Even when the waveform is distorted, constant current charging can be performed.

FIG. 1 is a diagram showing an embodiment of a ground fault detection apparatus according to the present invention. FIG. 2 is a diagram showing an embodiment of the ground fault detection device according to the present invention. Input terminals a and b are connected to output terminals a and b having the same reference numerals in FIG. FIG. 3 is a diagram showing a ground fault detection device according to the present invention attached to a transmission tower of an ultra-high-voltage transmission line whose neutral point is directly grounded. It shows a ground fault tower. FIG. 4 is a diagram illustrating a state of the transmission tower of the healthy tower adjacent to the ground fault tower of FIG. 3 when a ground fault occurs. FIG. 5 is a diagram showing the configuration of the first and second detection coil units. FIG. 6 is an experimental result showing the relationship between the first (second) detection coil unit and the magnetic saturation of the core, and shows the output of the first (second) detection coil unit in the magnetic saturation state. FIG. 7 is an experimental result showing the relationship between the first (second) detection coil section and the magnetic saturation of the core, and the first (second) detection coil whose peak voltage is limited through the surge absorber circuit and the phase detection circuit. The output of the part is shown. FIG. 8 is an experimental result showing the relationship between the first (second) detection coil unit and the magnetic saturation of the core, and the output from the air core part of the core is superimposed on the output of the first (second) detection coil unit. Shows the case. FIG. 9 is an experimental result showing the relationship between the first (second) detection coil unit and the magnetic saturation of the core. The output from the air core part of the core is further superimposed on the output of the first (second) detection coil unit. Shows the case. FIG. 10 is an experimental result showing an example of an operation waveform diagram of the ground fault detector when a DC component is superimposed on the current flowing through the overhead ground wire.

  An embodiment of the present invention will be described below as a mode for carrying out the present invention.

  FIG. 1 and FIG. 2 are diagrams showing an embodiment of a ground fault detection device according to the present invention. Output terminals a and b in FIG. 1 are connected to input terminals a and b having the same reference numerals in FIG.

  As shown in FIGS. 1 and 2, the ground fault detection device includes a first detection coil unit 1, a second detection coil unit 2, a detection unit 3, and a display unit 4. And such a ground fault detection device is attached to the tower of an ultra high voltage power transmission line as described below.

  FIG. 3 is a diagram showing a ground fault detection device according to the present invention attached to a steel tower of an ultra high voltage transmission line with a neutral point directly grounded on the power transmission side. This shows the case where this occurs. That is, in FIG. 3, the power transmission tower 5 is a faulty tower in which a ground fault has occurred.

  The power transmission tower 5 is one of the power transmission towers that form an ultrahigh-voltage power transmission line having a power transmission voltage of 187 kV or higher. In a transmission line of a resistance grounding system with a transmission voltage of 154 kV or less, the neutral point on the power transmission side is grounded via a resistor, and a fault current at the time of a ground fault is adjusted by the resistor. On the other hand, since the neutral point of the ultra high voltage transmission line is directly grounded, a fault current of several tens of kA or more larger than that of the resistance grounding system flows to the overhead ground wire 6.

  In FIG. 3, the first and second detection coil units 1 and 2 are respectively attached to the young number side and the old number side of the aerial ground wire 6 that sandwiches the power transmission tower 5. When a ground fault occurs in the power transmission tower 5 due to lightning or birds and beasts, a fault current Ia that flows toward the ground and fault currents Ib1 and Ib2 that are shunted to the overhead ground wire 6 flow. The fault currents Ib1 and Ib2 diverted to the overhead ground wire 6 flow in opposite directions around the steel tower 5, and the current Ic1 is induced in the first detection coil unit 1 by one fault current Ib1 of the overhead ground wire 6. The current Ic2 having the same phase as the current Ic1 is induced in the two detection coil units 2 by the other fault current Ib2. In the detection means 3, since the induced currents Ic1 and Ic2 are in the same phase, the power transmission tower 5 in which the ground fault has occurred is determined and displayed on the display unit 4.

  FIG. 4 is a diagram illustrating a state of the transmission tower of the healthy tower adjacent to the ground fault tower of FIG. 3 when a ground fault occurs. That is, in FIG. 4, the power transmission tower 5 is a healthy tower in which no ground fault has occurred. When a ground fault occurs in another power transmission tower, fault currents Ib1 and Ib2 flow in the same direction from the power transmission tower in which the ground fault has occurred in the overhead ground wire 6 with the power transmission tower 5 interposed therebetween. A current Ic1 is induced in the first detection coil unit 1 by one fault current Ib1, and a current Ic2 having a phase opposite to that of the current Ic1 is induced in the second detection coil unit 2 by the other fault current Ib2. In the detection means 3, the induced currents Ic 1 and Ic 2 are canceled out because they are in opposite phases, and no display output is given to the display unit 4.

  FIG. 5 is a diagram showing the configuration of the first and second detection coil units.

  The 1st and 2nd detection coil parts 1 and 2 have the I-shaped core 7 and the U-shaped core 8 which were formed with the ferrite in this example. The first and second detection coil units 1 and 2 are used for the overhead ground wire by moving the U-shaped core 8 up and down or by rotating one side portion 8a or 8b of the U-shaped core 8 as a fulcrum. 6 is configured to be detachable.

  The I-shaped core 7 includes a non-magnetic bobbin 10 between the coil 9, a non-magnetic rubber member 11 surrounding the outer periphery of the I-shaped core 7, a space between the rubber member 11 and the bobbin 10, and a rubber member 11. It has a non-magnetic air core part constituted by a space part 12 between the I-shaped core 7 and the like. As will be described later, such a non-magnetic air core portion is such a non-magnetic air core portion even when the I-shaped core 7 and the U-shaped core 8 are magnetically saturated and the output waveform is distorted. Without magnetic saturation, a non-distorted output is given from the air core portion according to the increase of the fault current and is superimposed on the outputs of the first and second detection coil units 1 and 2, and the output of the detection coil units 1 and 2 Waveform distortion is improved.

  Further, the first and second detection coil portions 1 and 2 have two gaps 13 in this example between the I-shaped core 7 and the U-shaped core 8. The magnetic saturation of the core 8 is reduced. In this example, the width of the gap 13 can be adjusted by inserting a nonmagnetic member having a desired thickness, such as a brass plate, between the I-shaped core 7 and the U-shaped core 8. .

  Returning to FIG. 1 and FIG. 2, the detection means 3 includes a surge absorber circuit 14, a phase detection circuit 15, a rectifier circuit 16, a constant current circuit 17, a charging circuit 18 and a detection circuit 19.

  The surge absorber circuit 14 has two surge absorbers 140 and 142 made of zinc oxide elements. One surge absorber 140 is inserted in parallel on the output side of the first detection coil unit 1 and is configured to directly input the output of the first detection coil unit 1 without interposing other elements. Yes. Similarly, the other surge absorber 142 is inserted in parallel on the output side of the second detection coil unit 2 so as to directly input the output of the second detection coil unit 2 without interposing other elements. It is configured. Further, one surge absorber 140 is connected in parallel to one bidirectional Zener diode 150 of the phase detection circuit 15 having serially connected bidirectional Zener diodes 150 and 151 via a protective resistor 141, and the other surge absorber 142. Is connected in parallel to the other bidirectional Zener diode 151 via a protective resistor 143.

  Even when a large fault current flows in the system in which the neutral point is directly grounded by such a surge absorber circuit 14, the output from the detection coil units 1 and 2 is output by the surge absorbers 140 and 142. The voltage is suppressed to a predetermined voltage, and damage to a circuit for detection can be prevented.

  In the present invention, the first and second detection coils in addition to the function of suppressing the output at the time of the ground fault from the first and second detection coil sections 1 and 2 to the surge absorbers 140 and 142 made of zinc oxide elements. A function of reducing the magnetic saturation of the parts 1 and 2 is provided. That is, the voltage induced in the first and second detection coil sections 1 and 2 from the fault current flowing through the overhead ground wire 6 is suppressed to a predetermined voltage by the surge absorbers 140 and 142, and the first and second detection coil sections In order to suppress the detection outputs from 1 and 2 to this predetermined voltage, the surge absorbers 140 and 142 have a large amount of current in a direction to cancel the magnetic fluxes of the cores 7 and 8 of the first and second detection coil portions 1 and 2. Thus, the magnetic saturation of the cores 7 and 8 of the first and second detection coil units 1 and 2 is reduced, and the distortion of the output waveforms of the first and second detection coil units 1 and 2 is prevented. be able to.

  The output of the phase detection circuit 15 is given to the rectifier circuit 16, and after full-wave rectification by the diodes 161 to 164 through the protective resistor 160 that prevents inflow of a current exceeding the rated current, the output to the constant current circuit 17 of FIG. Given.

  The constant current circuit 17 includes a capacitor 170 that smoothes the rectified output of the rectifier circuit 16, a constant voltage regulator 171, a resistor 172 that determines a current value to a subsequent circuit, and a capacitor 173 that prevents noise associated with oscillation of the regulator 171. And supplying a predetermined constant current to the charging circuit 18. In this way, constant current charging is performed so that it does not operate for currents with a duration less than a certain value, and for lightning with a current waveform similar to that of a half cycle of the commercial frequency. Malfunction can be prevented. At the same time, the smoothing capacitor 170 smoothes the rectified output from the rectifier circuit 16 so as to suppress the pulsation of the rectified output, and the first and second detection coil units 1 and 2 are superimposed by superimposing the DC component. Even when the output waveform is distorted, it can be charged with a predetermined constant current.

  The charging circuit 18 includes a charging capacitor 180 and a resistor 181 inserted in parallel thereto, and the charging capacitor 180 is charged with a predetermined constant current according to a time constant with the resistor 181. The detection circuit 19 includes a series connection of a resistor 190, a Zener diode 191, and a trigger resistor 192, a noise prevention capacitor 193 inserted in parallel with the trigger resistor 192, and a thyristor 194. The trigger resistor 192 applies a gate voltage to the gate of the thyristor 194, and the noise prevention capacitor 193 prevents malfunction due to noise. The detection circuit 19 having such a configuration monitors the charging voltage of the charging circuit 18 and turns on the thyristor 194 when the charging voltage becomes equal to or higher than a predetermined value, and gives an output indicating a ground fault to the display unit 4.

  6, 7, 8, and 9 are experimental results showing the relationship between the first (second) detection coil unit 1 (2) and the magnetic saturation of the cores 7 and 8. FIG. 6 shows the magnetic saturation state. FIG. 7 shows the output of the first (second) detection coil unit 1 (2), and FIG. 7 shows the first (second) detection coil unit 1 (with the peak voltage limited through the surge absorber circuit 14 and the phase detection circuit 15). FIG. 8 shows a case where the output of the air core portion of the I-shaped core 7 is superimposed on the output of the first (second) detection coil unit 1 (2), and FIG. The case where the output by the air core part of the I-shaped core 7 is further superimposed on the output of the (second) detection coil unit 1 (2) is shown.

  In the ultra high voltage transmission line having a transmission voltage of 187 kV or more, the neutral point on the power transmission side is directly grounded. Therefore, when a ground fault occurs, an extremely large failure current of several tens of kA or more flows. Although magnetic saturation is reduced by the surge absorbers 140 and 142 made of zinc oxide elements, the fault current flowing through the overhead ground wire 6 is large, and the I-shaped cores 7 of the first and second detection coil sections 1 and 2 and As shown in FIG. 6, the U-shaped core 8 is in a magnetic saturation state, and the output waveforms of the first and second detection coil units 1 and 2 are distorted.

  Reduction of magnetic saturation of the cores 7 and 8 by the surge absorbers 140 and 142 is performed as follows. As described above, the voltage induced in the first and second detection coil sections 1 and 2 from the fault current flowing in the overhead ground wire 6 is suppressed to a predetermined voltage by the surge absorbers 140 and 142, and the first and second In order to maintain the detection output from the detection coil units 1 and 2 at the above-mentioned predetermined voltage, the surge absorbers 140 and 142 cancel the magnetic fluxes of the cores 7 and 8 of the first and second detection coil units 1 and 2. The direction current increases, thereby reducing the magnetic saturation of the cores 7 and 8 of the first and second detection coil sections 1 and 2, and the first and second detection coils as shown in FIG. The output waveforms of the parts 1 and 2 become a waveform that approaches a square wave from a distorted waveform such as a differential wave, and the surge absorbers 140 and 142 cause distortion of the output waveforms of the first and second detection coil parts 1 and 2. Acting in the direction of reducing It can be seen.

  Even if the fault current flowing through the overhead ground wire 6 further increases and the cores 7 and 8 of the first and second detection coil units 1 and 2 are magnetically saturated, the non-contact between the I-shaped core 7 and the coil 9 is not achieved. Nonmagnetic bobbin 10 between the magnetic air core portion, that is, the coil 9, nonmagnetic rubber member 11 surrounding the outer periphery of the I-shaped core 7, between the rubber member 11 and the bobbin 10, and the rubber member 11 As shown in FIGS. 8 and 9, since the magnetic flux penetrates the non-magnetic air core portion formed by the space portion 12 between the I-shaped core 7 and the I-shaped core 7 and the air core portion is not magnetically saturated. As the fault current flowing through the ground wire 6 increases, the distortion-free output increases from the air core portion and is superimposed on the outputs of the first and second detection coil units 1 and 2, and the output waveforms of the detection coil units 1 and 2 The phase can be detected by improving the distortion. Thus, in the present invention, a large fault current is detected, and the output waveforms of the first and second detection coil units 1 and 2 are caused by the magnetic saturation of the cores 7 and 8 of the first and second detection coil units 1 and 2. Can be detected even if the current is distorted.

  FIG. 10 is an experimental result showing an example of an operation waveform diagram of the ground fault detector when a direct current component is superimposed on the current flowing in the overhead ground wire 6, and (a) shows an overhead ground wire 6 on which the direct current component is superimposed. (B) shows the output waveform of the 1st (2nd) detection coil part 1 and 2 which detected the electric current of the overhead ground wire 6 on which the DC component was superimposed, (c) shows the constant current circuit 17. The voltage waveform of the smoothing capacitor 170 is shown, and (d) shows the voltage waveform of the charging capacitor 181 of the charging circuit 18.

  When the current flowing through the overhead ground wire 6 is increased, the cores 7 and 8 of the first and second detection coil units 1 and 2 are magnetically saturated as shown in FIG. The output waveforms of the detection coil units 1 and 2 are distorted. In addition, in an ultra-high-voltage transmission line whose neutral point is directly grounded, a DC component due to inductance between the transmission line and the ground may be superimposed on the failure current depending on the interruption timing of the failure current. At this time, as shown in FIG. 10A, the fault current flowing in the overhead ground wire 6 has a current waveform that does not change around the zero point. Therefore, the detection coil unit 1 is caused by the magnetic saturation of the cores 7 and 8. 2 will be further distorted. However, even if the cores 7 and 8 are magnetically saturated, the nonmagnetic air core part between the I-shaped core 7 and the coil 9, that is, the nonmagnetic bobbin 10 between the coil 9 and the I-shaped core. A nonmagnetic air core portion formed by a nonmagnetic rubber member 11 that surrounds the outer periphery of 7, a space portion 12 between the rubber member 11 and the bobbin 10, and between the rubber member 11 and the I-shaped core 7. Magnetic flux will penetrate. Since these air core portions are not magnetically saturated, as the fault current flowing through the overhead ground wire 6 increases, the output without distortion from the air core portion increases, and the outputs of the first and second detection coil units 1 and 2 are increased. The phase is detected by superimposing and improving the distortion of the waveform of the fault current. Thus, according to the present invention, the outputs of the first and second detection coil units 1 and 2 are superimposed by the magnetic saturation of the cores 7 and 8 of the first and second detection coil units 1 and 2 with the direct current component superimposed. Even if the waveform is distorted, phase detection can be performed. Note that time S in FIG. 10D is the operating point of the detection means 3.

  INDUSTRIAL APPLICABILITY The present invention can be effectively used as a detection device for detecting a ground fault in a transmission tower in an ultra-high-voltage transmission line in which a neutral point on a power transmission side is directly grounded, and a large fault current at the time of a ground fault The circuit of the fault current can be prevented, and the phase detection of the fault current can be performed regardless of the magnetic saturation of the cores of the first and second detection coil sections accompanying the detection of a large fault current. The present invention can be used as a detection device for detecting a ground fault in a transmission tower on a track.

DESCRIPTION OF SYMBOLS 1 1st detection coil part 2 2nd detection coil part 3 Detection means 5 Power transmission tower 6 Overhead ground wire 7 I-shaped core 8 U-shaped core 9 Coil 10 Bobbin 11 Rubber member 12 Space part 13 Gap 14 Surge absorber circuit DESCRIPTION OF SYMBOLS 15 Phase detection circuit 16 Rectifier circuit 17 Constant current circuit 18 Charging circuit 19 Detection circuit 140, 142 Surge absorber 150, 151 Bidirectional Zener diode

Claims (4)

First and second detection coil portions that are respectively attached to an overhead ground wire of an ultra-high-voltage transmission line with a neutral point directly grounded with a transmission tower interposed therebetween and detect a fault current that is diverted to the overhead ground wire in the event of a ground fault When,
Detecting means for detecting a power transmission tower in which a ground fault has occurred from a phase of a fault current at the time of a ground fault detected by the first and second detection coil units;
The detection means inserts a surge absorber made of a zinc oxide element in parallel on the output side of each of the first and second detection coil units and directly inputs the outputs of the first and second detection coil units. In addition to the function of suppressing the output from the detection coil unit to the surge absorber, the magnetic saturation of the first and second detection coil units is detected. While having a function to reduce,
The first and second detection coil portions are configured to have a non-magnetic air core portion between a core and a coil wound around the core,
When the output waveforms of the first and second detection coil sections are distorted due to magnetic saturation, a fault at the time of a ground fault is based on the output from the nonmagnetic air core portion of the first and second detection coil sections. A ground fault detection apparatus characterized by improving current distortion and enabling phase detection. The detection means is
A surge absorber circuit including two of the surge absorbers inserted in parallel to the coils of the first and second detection coil parts;
A phase detection circuit including two bidirectional Zener diodes connected in series inserted in parallel with the surge absorber circuit;
The ground fault detection device according to claim 1, further comprising: a rectifier circuit that full-wave rectifies the output of the phase detection circuit. The detection means further comprises:
A constant current circuit for inputting a full-wave rectified output of the rectifier circuit and providing a predetermined constant current;
A charging circuit charged at a constant current by the constant current circuit;
The ground fault detection device according to claim 2, further comprising: a detection circuit that provides a detection output indicating a ground fault when a charging voltage of the charging circuit becomes equal to or higher than a predetermined value.   The ground fault detection device according to claim 1, wherein a magnetic gap having a predetermined width is formed in the cores of the first and second detection coil portions.

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