Fluxgate-type leakage current detection device and method for controlling it

Abstract

The present invention relates to a fluxgate-type leakage current detection device, characterized in that it has the following features: an oscillation unit that generates a pulse current with a predetermined frequency; a core unit comprising at least a first core wound with at least a first coil, one end of which is connected to the oscillation unit, and which is magnetized in response to the pulse current; a second core wound with a second coil, one end of which is grounded; and a third coil wound around the first core and the second core, to which a compensation current is applied.and a control unit which, based on at least one of the properties of the at least one first core, determines a frequency of the pulse current, which detects a DC leakage current of a conductor to be measured by filtering out a component with a frequency from a voltage signal of a current induced in the at least one first core, and which applies a reverse current corresponding to the detected DC leakage current as a compensation current to the third coil.

Description

Flux gate type leakage current detection device and control method thereof

[0001] The present invention relates to a leakage current detection device for detecting leakage current or residual current (hereinafter referred to as leakage current), and more particularly, to a flux gate type leakage current detection device for detecting leakage current components in a non-contact manner and a control method thereof.

[0002] Recently, the demand for DC power sources such as electric vehicles and charging systems is expected to increase, and the spread of new and renewable energy sources such as solar power and fuel cells and energy storage devices is expected to expand. Accordingly, in the field of solar power generation facilities, the technical standards and judgment criteria for the work processing method of DC ground fault circuit interrupters for solar power generation facilities have been revised (Ministry of Trade, Industry and Energy Notice No. 2020-659 (December 3, 2020)). According to the revised notice, the installation of a device that automatically cuts off the DC circuit when a ground fault occurs in the DC circuit of solar cell power generation facilities is recommended. Accordingly, regardless of the type of power conversion device (transformer type or transformerless type), it is recommended to install a Type B Residual Current Detector (RCD) or Type B Earth Leakage Breaker (ELB), which can detect not only the AC component leakage current but also the DC component leakage current.

[0003] Meanwhile, many flux gate type detection devices are being used as detection devices for detecting such leakage current. The flux gate type leakage current detection device is also called a zero flux type, and the conductor to be measured is placed so as to penetrate a magnetized core (magnetic core), and the current flowing in the conductor to be measured is measured based on the secondary current induced by the magnetic flux generated in the magnetic core due to the current flowing in the placed conductor to be measured, and is attracting attention because it can accurately detect the current flowing in the conductor to be measured in a non-contact manner.

[0004] Meanwhile, in the case of the flux gate method, as described above, the current of the conductor to be measured is detected based on the magnetic flux induced in the magnetized core, i.e., the magnetic core. However, the magnitude of the magnetic flux density that increases in the core as the external magnetic field increases has a limit depending on the characteristics of the core, and the core state when the maximum magnetic flux density that can be induced in the core occurs is called magnetic saturation. In addition, when the core is magnetically saturated and the magnetic flux density becomes maximum, the magnetic flux density may not change even if the external magnetic field increases. In this case, since the magnetic flux density does not change according to the external magnetic field, the detection of the external magnetic field, i.e., the current flowing in the conductor to be measured, may become impossible.

[0005] However, when an AC current flows in the conductor to be measured, due to the nature of the AC current with alternating polarity, a current that increases the magnetic flux density in the forward direction (e.g., positive current) is applied, and then a current that increases the magnetic flux density in the reverse direction (e.g., negative current) is applied. Therefore, since a magnetic field that increases the magnetic flux density in the reverse direction is formed after the magnetic flux density has increased in the forward direction, the magnetic flux can be cancelled out. Therefore, even if the core reaches magnetic saturation, the magnetic flux density of the core can naturally decrease below the maximum magnetic flux density as the magnetic flux is cancelled out by the reverse current due to the polarity change of the current. However, in the case of a DC current without polarity change, a magnetic field that forms the magnetic flux density in only one direction is continuously formed, so the magnetic flux can increase without being cancelled as the external magnetic field increases, and the magnetic flux can continue to accumulate. In this case, the core can reach magnetic saturation and the magnetic flux density can reach the maximum magnetic flux density.

[0006] In order to prevent the core from reaching a state of magnetic saturation when detecting a direct current, a method has emerged of applying a pulse current having a frequency, i.e., a current in which a positive or negative direct current of a certain magnitude is switched at a certain time cycle, to a coil wound around the core. When a pulse current is applied in this way, the polarity of the magnetic field forming the magnetic flux density in the magnetic core is switched according to the frequency of the pulse current, so that, similar to an alternating current, the core can be prevented from entering a state of magnetic saturation.

[0007] Meanwhile, as described above, the flux gate type leakage current detection device detects leakage current by utilizing the change in magnetic flux density induced in the magnetic core, so theoretically, leakage current can be detected only when the saturation state has not been reached. Therefore, in the case of the flux gate type leakage current detection device, the measurable current can be determined according to the magnetic saturation characteristic of the core. In other words, the accuracy and precision of the flux gate type leakage current detection device can be determined according to the magnetic saturation characteristic of the core. Therefore, when a pulse current having a frequency matching the magnetic saturation characteristic of the core is applied, the efficiency of the flux gate type leakage current detection device can be maximized.

[0008] Meanwhile, the maximum magnetic flux density of the core may vary depending on the shape or material of the core, the number of turns of the coil wound on the core, the material of the coil, the winding spacing, etc. The maximum magnetic flux density that varies depending on the shape or material of the core or the structural characteristics is called the magnetic saturation characteristic of the core. In addition, since the maximum magnetic flux density of the core varies depending on the shape or material of the core, the structure, the material of the coil wound on the core, the number of turns of the coil wound on the core, the winding spacing, etc., it is difficult for physically completely identical cores to exist, and the magnetic saturation characteristics may differ for each core.

[0009] In addition, pulse signals are typically generated using a resonant circuit. When generating a pulse signal (pulse current) using a resonant circuit in this way, a pulse current according to a fixed frequency is applied. In this case, as the time for which a current of a specific polarity is applied increases (as the frequency decreases), the amount of current applied to the coil increases, which can increase the magnetizing force. In other words, the magnitude of the current applied to the coil wound on the core can vary depending on the frequency of the pulse current, and accordingly, when a pulse signal having a frequency that can form a current suitable for the magnetic saturation characteristics of the core is applied, the efficiency of a flux gate type leakage current detection device can be maximized.

[0010] However, as described above, since the magnetic saturation characteristics of each core are different, there is a problem in that it is difficult to detect a pulse signal having a frequency that matches the magnetic saturation characteristics of the core to be installed. Furthermore, even if the frequency of the pulse signal that matches the magnetic saturation characteristics of the core can be known, there is a problem in that the design of the resonant circuit itself must be changed in order to change the frequency of the pulse signal in the conventional method of generating a pulse current using a resonant circuit as described above. Therefore, it is difficult to apply a pulse signal frequency that matches the magnetic saturation characteristics of the core, and thus there is a problem in that the flux gate type leakage current detection device cannot be used efficiently.

[0011] Furthermore, when generating a pulse signal using a resonant circuit, there is a problem that the pulse signal may be distorted or its frequency may change due to external shocks such as radiated susceptibility (RS) or conducted susceptibility (CS) or disturbances such as radio noise such as a radio, and such distortion or change in frequency is likely to cause measurement errors.

[0012] The present invention aims to solve the above-mentioned problems and other problems, and provides a flux gate type leakage current detection device and a control method thereof in which accuracy and precision are further improved and efficiency is maximized by applying a frequency matching the magnetic saturation characteristics of the core to a coil wound on the core.

[0013] In addition, the present invention aims to provide a flux gate type leakage current detection device and a control method thereof, which can easily apply a pulse current having a frequency matching the magnetic saturation characteristics of the replaced core to the replaced core when the core is replaced in the flux gate type leakage current detection device.

[0014] In addition, the present invention aims to provide a flux gate type leakage current detection device capable of accurately and stably measuring leakage current regardless of external impact, radio noise or disturbance by generating a pulse current considering core characteristics and applying it to a coil wound around a core, and a control method of the device.

[0015] In order to achieve the above or other purposes, according to one aspect of the present invention, a leakage current detection device according to an embodiment of the present invention is characterized by including an oscillator for generating a pulse current having a preset frequency, at least one first core having at least one first coil connected at one end to the oscillator and magnetized according to the pulse current, a second core having a second coil wound at one end grounded, and a core unit for applying a third coil wound around the first core and the second core and to which a compensation current is applied, and a control unit for determining a frequency of the pulse current according to at least one of the characteristics of the at least one first core, filtering a component having a frequency from a voltage signal of a current induced in the at least one first core to detect a DC component leakage current of a conductor to be measured, and applying a reverse current corresponding to the detected DC component leakage current to the third coil as the compensation current.

[0016] In one embodiment, the characteristics of the at least one first core are characterized by at least one of the shape or thickness of the core, the diameter or material of the core, the diameter of the hollow portion inside the core, the material or number of turns of the coil wound around the core, the winding spacing of the coil, the manufacturer and manufacturing number of the core, and the type of the conductor to be measured.

[0017] In one embodiment, the device further includes a memory storing a plurality of detection frequencies according to different characteristics of the at least one first core, and the control unit is characterized in that it determines one of the plurality of detection frequencies as the frequency of the pulse current based on the characteristic of the at least one first core.

[0018] In one embodiment, the control unit is characterized in that, when a DC component leakage current of the measured conductor is detected according to one of the plurality of detection frequencies, the control unit changes the frequency of the pulse current to another of the plurality of detection frequencies and re-detects the DC component leakage current of the measured conductor according to the changed frequency of the pulse current, and determines whether the at least one first core is magnetically saturated to detect the frequency of the pulse current according to the magnetic saturation characteristic of the at least one first core.

[0019] In one embodiment, the control unit is characterized in that it determines whether the at least one first core is magnetically saturated based on whether a voltage signal detected from the at least one first core generates a square wave.

[0020] In one embodiment, the control unit is characterized in that it determines whether the voltage signal detected from the at least one first core generates a square wave based on whether there is a voltage change of a certain level or more for a certain period of time when the polarity of the voltage signal detected from the at least one first core is switched.

[0021] In one embodiment, the control unit is characterized in that, when a magnetic saturation frequency of a pulse current that magnetically saturates the at least one first core is detected, a frequency close to the magnetic saturation frequency among frequencies of pulse currents that do not magnetically saturate the at least one first core is determined as a pulse current frequency according to the magnetic saturation characteristic of the at least one first core.

[0022] In one embodiment, the measured conductor is characterized in that it is a test conductor through which a leakage current of a direct current component and an alternating current component of a preset size flow.

[0023] In one embodiment, the oscillator receives a pulse digital signal in which a state of outputting a specific voltage and a state of not outputting a voltage are repeated at a preset time cycle, and generates a pulse current in which a positive current and a negative current alternate at a preset time cycle in synchronization with the pulse digital signal, and the control unit is characterized in that it applies the pulse digital signal in which the pulse current is repeated at a preset time cycle to the oscillator based on a frequency of the pulse current determined according to a characteristic of the at least one first core.

[0024] In one embodiment, the oscillator comprises a comparator having a preset reference voltage, and the comparator outputs a current having a positive voltage of a preset magnitude when a pulse digital signal having a voltage higher than the reference voltage is input, and outputs a current having a negative voltage of a preset magnitude when a pulse digital signal having a voltage lower than the reference voltage is input.

[0025] In one embodiment, the reference voltage has a size of half of the specific voltage, and the positive and negative voltages of the preset size are characterized by being positive and negative voltages corresponding to the reference voltage.

[0026] According to another embodiment of the present invention for achieving the above or other purposes, a leakage current detection device comprises: an oscillator for generating a pulse current having a preset frequency; at least one first core having at least one first coil wound around one end connected to the oscillator and magnetized according to the pulse current; a second core having a second coil wound around one end grounded; and a core unit for applying a third coil wound around the first core and the second core and applying a compensation current; a leakage current detection unit connected to the other end of the at least one first core and the other end of the second core and adding a voltage signal detected in the first core and a voltage signal detected in the second core; an amplifier unit for inverting and amplifying a voltage signal according to a result of adding the voltage signals of the leakage current detection unit and generating a compensation current applied to the third coil; and a control unit for determining a frequency of the pulse current according to at least one of the characteristics of the at least one first core and detecting a DC component leakage current flowing in a conductor to be measured based on the compensation current.

[0027] In one embodiment, the leakage current detection unit includes a differential amplifier having a non-inverting input terminal connected to the other end of the second coil and an inverting input terminal connected to the other end of the first coil, and adding a voltage signal corresponding to a DC component leakage current of the measured conductor and a voltage signal corresponding to an AC component leakage current, wherein the differential amplifier is characterized in that an output terminal is connected to the non-inverting input terminal via a resistor and a capacitor that serve as a noise filter, so that an output of the differential amplifier is fed back to the non-inverting input terminal.

[0028] In one embodiment, the amplification unit includes an operational amplifier having a first input terminal connected to ground and a second input terminal connected to an output terminal of the differential amplifier via a first resistor of a preset size, and the output terminal of the operational amplifier is connected to the second input terminal via a second resistor of a preset size and is connected to a non-inverting input terminal of the differential amplifier such that an output of the operational amplifier is fed back to the differential amplifier.

[0029] In one embodiment, the at least one first core is characterized by including a first core having a first-first coil wound around which the pulse current is applied, an inverting amplifier that inverts the polarity of the pulse current, a first core having a first-second coil wound around which the pulse current, the polarity of which is inverted by the inverting amplifier, is applied, and a summing amplifier that synthesizes voltage signals corresponding to secondary currents induced in the first-first coil and the first-second coil, respectively.

[0030] In one embodiment, the device further includes a memory storing a plurality of detection frequencies according to different characteristics of the at least one first core, and the control unit is characterized in that it determines one of the plurality of detection frequencies as the frequency of the pulse current based on the characteristic of the at least one first core.

[0031] In one embodiment, the control unit is characterized in that, when a DC component leakage current of the measured conductor is detected according to one of the plurality of detection frequencies, the control unit changes the frequency of the pulse current to another of the plurality of detection frequencies and re-detects the DC component leakage current of the measured conductor according to the changed frequency of the pulse current, and determines whether the at least one first core is magnetically saturated to detect the frequency of the pulse current according to the magnetic saturation characteristic of the at least one first core.

[0032] In one embodiment, the control unit is characterized in that, when a magnetic saturation frequency of a pulse current that magnetically saturates the at least one first core is detected, a frequency close to the magnetic saturation frequency among frequencies of pulse currents that do not magnetically saturate the at least one first core is determined as a pulse current frequency according to the magnetic saturation characteristic of the at least one first core.

[0033] The effects of the flux gate type leakage current detection device and the control method thereof according to the present invention are described as follows.

[0034] According to at least one of the embodiments of the present invention, the present invention generates a pulse current applied to a coil wound on a core of a leakage current detection device through a control unit that intermittently outputs a current of a constant magnitude according to a preset time interval, changes the frequency of the pulse current by adjusting the preset time interval, and detects the frequency of the pulse current that matches the magnetic saturation characteristic of the core based on the changed frequency of the pulse current. In addition, by applying a pulse current of the detected frequency to the coil wound on the core, the measurement efficiency of the flux gate type leakage current detection device can be maximized, and the precision and accuracy can be maximized.

[0035] Furthermore, the present invention can detect the frequency of a pulse signal that matches the characteristics of a replaced core when the core of a flux gate type leakage current detection device is replaced. Therefore, the frequency of the pulse current can be easily changed to a frequency that matches the magnetic saturation characteristics of the replaced core. Therefore, regardless of the core change, the measurement efficiency, precision, and accuracy of the leakage current detection device can be stably maintained at maximum levels.

[0036] Furthermore, the present invention can apply a pulse current to a coil wound around a flux gate core based on a digital pulse signal of a constant voltage level intermittently output at preset time intervals generated by a control unit. Therefore, since a resonant circuit is not used to generate the pulse current, it can have a leakage current detection effect that is robust to external shocks, radio noise, or disturbances.

[0037] FIG. 1 is a circuit diagram showing the circuit configuration of a leakage current detection device that compensates for a direct current component compensation current according to a first embodiment of the present invention.

[0038] FIG. 2 is a circuit diagram showing the circuit configuration of a leakage current detection device that applies a compensation current according to a detected leakage current according to a second embodiment of the present invention.

[0039] Figures 3 to 5 are exemplary diagrams showing the configuration of a core part provided in a leakage current detection device according to embodiments of the present invention.

[0040] FIG. 6 is a flowchart illustrating an operation process for detecting a frequency of a pulse current that matches the magnetic saturation characteristics of a core in a leakage current detection device according to embodiments of the present invention.

[0041] Figure 7 is a graph showing a hysteresis loop illustrating the magnetic saturation characteristics of the core and a graph showing the magnetic flux density characteristics of the core according to the current in the core.

[0042] FIG. 8 is a flowchart illustrating an operation process of applying a DC component compensation current detected when detecting a leakage current of a measured conductor to each core in a leakage current detection device according to a first embodiment of the present invention.

[0043] FIG. 9 is a flowchart illustrating an operation process for initializing a core according to a magnetic saturation state of the core in a leakage current detection device according to a first embodiment of the present invention.

[0044] FIG. 10 is an exemplary diagram showing the output waveform of a DC component detection core according to the state of the core in a leakage current detection device according to embodiments of the present invention.

[0045] It should be noted that the technical terms used herein are used merely to describe specific embodiments and are not intended to limit the present invention. Furthermore, singular expressions used herein include plural expressions unless the context clearly dictates otherwise. The suffixes "module" and "part" used in the following description for components are assigned or used interchangeably solely for the convenience of writing the specification, and do not in themselves have distinct meanings or roles.

[0046] In this specification, the terms “comprises” or “includes” should not be construed to necessarily include all of the components or steps described in the specification, and some of the components or steps may not be included, or additional components or steps may be included.

[0047] In addition, when describing the technology disclosed in this specification, if it is determined that a detailed description of a related known technology may obscure the gist of the technology disclosed in this specification, the detailed description is omitted.

[0048] In addition, the attached drawings are only intended to facilitate easy understanding of the embodiments disclosed in this specification, and the technical ideas disclosed in this specification are not limited by the attached drawings, and should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention. In addition, not only each embodiment described below, but also a combination of embodiments may correspond to the spirit and technical scope of the present invention as modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

[0049] FIG. 1 is a circuit diagram showing the circuit configuration of a flux gate type leakage current detection device that compensates for a direct current component compensation current according to a first embodiment of the present invention.

[0050] Referring to FIG. 1, a leakage current detection device according to an embodiment of the present invention may be configured to include a control unit (Micro Controller Unit, MCU) (100), an oscillator (110) connected to the control unit (100) and controlled by the control unit (100), an output unit (not shown), and a core unit (120) including at least one core whose magnetic flux changes according to a DC component leakage current or an AC component leakage current flowing in a conductor. The components illustrated in FIG. 1 are not essential for implementing a flux gate type leakage current detection device, and thus, the leakage current detection device described in this specification may have more or fewer components than the components listed above.

[0051] First, the control unit (100) can intermittently output a current having a specific voltage according to a preset time interval. That is, the control unit (100) can output a current having the specific voltage (e.g., 3.3 V) for a certain period of time in a cycle of the preset time, and not output the current for a subsequent period of time. Accordingly, a pulse digital signal (111) in which a state of outputting the specific voltage (e.g., 3.3 V) and a state of outputting 0 V (a state in which no current is output) are repeated in a cycle of the preset time can be output from the control unit (100).

[0052] Meanwhile, the control unit (100) can determine the frequency of the pulse digital signal (111) by changing the preset time interval. For example, the control unit (100) can output a current of the specific voltage for 1 / 3600 second. Then, after stopping the current output for 1 / 3600 second, the current of the specific voltage can be output again for 1 / 3600 second. In this case, the state in which the current of the specific voltage is output and the state in which 0 V is output can alternate in a cycle of 1 / 1800 second. That is, a pulse digital signal (111) having a frequency of 1.8 KHz can be generated.

[0053] A pulse digital signal (111) generated in the control unit (100) can be applied to an oscillator (110) that generates a pulse current from the applied pulse digital signal (111).

[0054] In this case, the oscillator (110) can generate a pulse current synchronized with the pulse digital signal (111) applied from the control unit (100). To this end, the oscillator (110) can include a comparator (113) in which a preset voltage is set as a reference voltage. In this case, the comparator (113) can output a current having a positive (+) voltage when a pulse digital signal having a voltage higher than the reference voltage is input, and can output a current having a negative (-) voltage when a pulse digital signal having a voltage lower than the reference voltage is input. Therefore, a pulse current in which positive and negative currents alternate according to the frequency of the pulse digital signal (111) can be generated. In this case, the reference voltage can be half the voltage of the specific voltage.

[0055] For example, if the specific voltage is 3.3 V as in the example described above, the reference voltage can be set to 1.65 V. Then, when the pulse digital signal (111) output from the control unit (100) is 3.3 V, a positive voltage (+1.65 V) of 1.65 V can be generated, and when the pulse digital signal output is 0 V, a negative voltage (-1.65 V) of 1.65 V can be generated. That is, a pulse voltage (112) in which positive and negative voltages of 1.65 V alternate for each cycle can be generated.

[0056] And the oscillation unit (110) can apply a pulse current according to the generated pulse voltage (112) to a coil wound on at least one core for detecting a DC component leakage current among the cores constituting the core unit (120). In this case, among the cores of the core unit (120), a core for detecting an AC component leakage current can induce a current corresponding to a magnetic flux due to an AC component of a current (Ip) flowing in a conductor to be measured.

[0057] Meanwhile, the oscillation unit (110) may further include a resistor (114) for determining the magnitude of the current to be applied to the core unit (120). Here, the polarity and magnitude of the pulse current may be determined (I=V / R) according to the polarity of the pulse voltage (112) and the magnitude of the resistance (114) for the pulse voltage (112). In addition, when the pulse current is applied, the core may be magnetized based on the magnetizing force according to the magnitude of the applied current, and a magnetic flux may be formed around the magnetized core.

[0058] Meanwhile, the core unit (120) may include at least one DC component detection core for detecting a DC component leakage current and at least one AC component detection core for detecting an AC component leakage current. In this case, each core may have a ring structure or a loop structure having a hole formed in the center so that a conductor to be measured can pass through. In addition, a first coil (N1) for magnetizing the core may be wound around the at least one DC component detection core, and a second coil (N2) for magnetizing the core may be wound around the AC component detection core. In addition, a third coil (N3) for applying a compensation current may be wound around both the at least one DC component detection core and the AC component detection core.

[0059] When a conductor to be measured for detecting a leakage current is inserted through the central hole of the cores formed in this manner, a magnetic flux can be generated in each core due to the current (Ip) flowing in the conductor to be measured. Then, a current (secondary current) to cancel out the generated magnetic flux can be induced in the coil wound around each core. In addition, the control unit (100) can detect a voltage signal corresponding to an AC component leakage current flowing in the conductor to be measured and a voltage signal corresponding to a DC component leakage current according to the magnitude of the secondary current induced in each core.

[0060] Meanwhile, the voltage signals detected in the core unit (120) may be of such a small size that they are difficult to detect in the control unit (100). Therefore, the control unit (100) may include an amplifier unit (101) that can amplify the voltage signals detected in the core unit (120) to a range that can be recognized by the control unit (100). In addition, the control unit (100) may include a low pass filter (LPF) (not shown) for removing the pulse signal applied from the oscillator unit (110) and noise of the core, and may include an analog-to-digital converter (ADC) (not shown) for converting the voltage signal amplified to a range that can be recognized by the control unit (100) into a digital signal.

[0061] Meanwhile, if the leakage current is AC, the magnetic flux can be automatically canceled by reversing the current's polarity. However, if the leakage current is DC, the current's polarity does not change, and thus the magnetic flux cannot be canceled. Consequently, the magnetic flux can accumulate.

[0062] When the magnetic flux that is not offset in this way accumulates, the accumulated magnetic flux component can be added up as a leakage current of the DC component. And the accumulated magnetic flux component can be measured as a leakage current. Therefore, the control unit (100) can apply a compensation current to the coil wound on the DC component detection core to offset the accumulated magnetic flux component. In this case, in order to offset the magnetic flux, a current capable of generating a magnetic flux in the opposite direction must be applied. Therefore, a current having the same magnitude as the measured DC component leakage current but opposite in polarity, i.e., a reverse current, can be applied to the core unit (120) as the compensation current.

[0063] Meanwhile, when a DC component leakage current flows through the measured conductor, an AC component leakage current may increase due to the DC component leakage current. Therefore, the third coil (N3) may be wound on both the AC component detection core and the at least one DC component detection core. Accordingly, the magnetic flux according to the error component (DC component leakage current component) included in the AC component leakage current may be offset by the compensation current.

[0064] To apply this compensation current, the control unit (100) can detect a voltage signal corresponding to the secondary current induced in at least one DC component detection core through a resistor (R7).

[0065] Here, the DC component detection core may be a core that is magnetized by a first coil (N1) wound around the DC component detection core. And, a pulse current generated from the oscillation unit (110) may be applied to the first coil (N1). Accordingly, the secondary current induced in the at least one DC component detection core may include an AC component according to the pulse current applied to the first coil (N1).

[0066] In this case, the control unit (100) may include a filter unit (103) for filtering out the AC component from the secondary current induced in the DC component detection core. For example, the filter unit (103) may filter out a component having a frequency from a voltage signal of the secondary current induced in the DC component detection core. Then, a voltage signal corresponding to a pure DC component leakage current with a component according to a pulse current removed from the secondary current induced in the DC component detection core may be detected.

[0067] Then, the control unit (100) can apply a reverse current corresponding to the DC component leakage current detected through the filter unit (103) as a compensation current to the core unit (120), more specifically, to the third coil (N3) for applying the compensation current. Accordingly, the magnetic flux due to the DC component leakage current flowing in the measured conductor can be canceled not only in the DC component detection core but also in the AC component detection core.

[0068] Here, the compensation current may be a microcurrent that is difficult for the control unit (100) to directly control. Accordingly, the control unit (100) may further include an attenuation unit (102) for attenuating the current output from the control unit (100). In addition, the control unit (100) may control the attenuation amount of the attenuation unit (102) to apply the compensation current, which is attenuated to a microlevel lower than the level that the control unit (100) can control, to the third coil (N3).

[0069] Meanwhile, when the magnetic flux according to the DC component leakage current flowing in the measured conductor is canceled by the compensation current, the control unit (100) can detect a voltage signal corresponding to the secondary current induced in the AC component detection core through the resistor (R4). Then, the voltage signal corresponding to the secondary current induced in the AC component detection core can be detected as the AC component leakage current. Then, the control unit (100) can calculate the amount of the total leakage current (Ip) flowing in the measured conductor by adding the voltage signal (DC component leakage current) detected by filtering the secondary current induced in the DC component detection core and the voltage signal (AC component leakage current) detected from the secondary current induced in the AC component detection core. Then, the output unit can be controlled according to the calculated leakage current amount to output the amount of the detected leakage current. In addition, a signal related to the detection of the leakage current can be output.

[0070] Here, the signal related to the detection of the leakage current may be a trip signal for controlling a circuit breaker. In this case, the circuit breaker receiving the trip signal from the output unit can isolate the internal circuit connected to the leakage current detection device from the line, thereby preventing leakage current from flowing into the internal circuit or into the line.

[0071] Alternatively, the signal related to the detection of the leakage current may be a notification signal that notifies a preset system of the occurrence of the leakage current. In this case, the system may be a control system that controls an internal circuit connected to a leakage current detection device. Then, the control system may control a circuit breaker to isolate the internal circuit from the line based on the notification signal. Alternatively, the control system may transmit information to at least one other device or apparatus to notify the occurrence of the leakage current, or may initiate a process to deal with the occurrence of the leakage current.

[0072] Meanwhile, the density of the magnetic flux formed in the core can be determined according to the magnetizing force that magnetizes the core. In addition, the magnetizing force can vary in magnitude depending on the magnetizing current that magnetizes the core, i.e., the current flowing in the coil wound around the core. In this case, if the current flowing in the coil is an alternating current in which the cathodes and anodes alternate, the flow of current can be limited depending on the frequency due to the inductive reactance of the coil. In other words, even for the same magnitude of alternating current, the higher the frequency, the more limited the current flow in the coil can be, and accordingly, the magnitude of the magnetizing current can also vary.

[0073] However, as described above, since the pulse current also has the characteristics of an alternating current in which the cathode and anode alternate at regular intervals, the flow of current may be limited depending on the frequency of the pulse current due to the inductive reactance of the coil. That is, the higher the frequency, the smaller the magnetizing current, and the lower the frequency, the larger the magnetizing current. In addition, as the magnitude of the magnetizing current increases, the magnitude of the magnetic flux density may increase in proportion to it.

[0074] Therefore, in the case of the present invention in which a pulse current according to a specific frequency is generated according to a pulse digital signal generated by the control unit (100), the magnetizing current flowing in the coil can be changed by only changing the frequency of the pulse digital signal applied to the oscillation unit (110) by the control unit (100) without having to change the resistance of the oscillation unit (110) and the voltage of the pulse digital signal, thereby changing the magnetic flux density formed around the DC component detection core. That is, in the case of the present invention, the control unit (100) changes the time interval at which a current having the specific voltage is output according to the frequency of different pulse currents, thereby changing the magnetic flux density formed around the core without having to change the circuit configuration of the oscillation unit (110).

[0075] Meanwhile, as described above, when the magnetic saturation characteristic of the core, i.e., the magnetizing current that forms the maximum magnetic flux density, is generated, the accuracy and precision of the flux gate type leakage current detection device can be maximized, and the efficiency of the flux gate type leakage current detection device can be maximized. Accordingly, the present invention can detect the frequency of the pulse digital signal at which the magnetizing current that forms the maximum magnetic flux density of the DC component detection core is generated while the control unit (100) changes the frequency of the pulse digital signal.

[0076] For example, the control unit (100) can detect the DC component leakage current detected from the test conductor while changing the frequency of the pulse current when a test conductor through which a preset DC component leakage current flows is passed through each core. In this case, when the frequency of the pulse current decreases, the magnetizing current of the DC component detection core increases due to the inductive reactance of the first coil (N1), and when the magnetizing current increases, the magnetic flux density increases, and more secondary current can be induced in the DC component detection core. Accordingly, more DC component leakage current can be detected. In this case, when the magnetizing current increases and the magnetic flux reaches the maximum magnetic flux density, a secondary current of the same size is induced in the DC component detection core regardless of the change in the frequency of the pulse current, and thus the same DC component leakage current can be detected. That is, the pulse current frequency when the DC component leakage current is maintained constant even when the frequency of the pulse current increases or decreases may be the frequency of the pulse current that generates the magnetizing current that forms the maximum magnetic flux density, i.e., the frequency of the pulse current corresponding to the magnetic saturation characteristic of the core.

[0077] Meanwhile, in order to shorten the time for detecting the frequency of the pulse current corresponding to the magnetic saturation characteristic of the core, the control unit (100) can set a specific frequency range according to the structural characteristics of the core, such as the shape or material of the core, the material of the coil, the number of turns, or the winding spacing.

[0078] To this end, the leakage current detection device according to an embodiment of the present invention may have a memory (not shown) in which different detection frequency ranges are stored according to at least one of the diameter, material, shape, or characteristics of the coil wound on the core of the DC component detection core. Alternatively, the memory may store different detection frequency ranges according to the type of the conductor to be measured for which the DC component leakage current is to be detected, or the manufacturer or serial number of the core. In this case, the control unit (100) may detect the frequency of the pulse current matching the magnetic saturation characteristic of the core based on a detection frequency range according to at least one of the structural characteristics of the core, such as the diameter, material, or shape, or the type of the conductor to be measured, and the manufacturing information, such as the manufacturer or serial number of the core, among the different detection frequency ranges stored in the memory.

[0079] In this case, the control unit (100) can detect the frequency of the pulse current matching the magnetic saturation characteristic of the DC component detection core according to the preset frequency change unit corresponding to each detection frequency range. For example, the control unit (100) can determine the detection frequency range corresponding to 1.3 KHz or more and less than 1.8 KHz based on at least one of the structural characteristics of the core, the type of the conductor to be measured, and the manufacturing information of the core. Then, the frequency of the pulse current corresponding to the magnetic saturation characteristic of the core can be detected while changing the frequency at preset units within the determined detection frequency range. In this case, the frequency change unit corresponding to the detection frequency range of 1.3 KHz or more and less than 1.8 KHz may be 0.05 KHz. In this case, if the detection frequency range changes, the frequency change unit may also change.

[0080] Meanwhile, the control unit (100) can detect whether the DC component detection core is in a magnetic saturation state based on the waveform of the secondary current detected from the DC component detection core. In addition, if the DC component detection core is in a magnetic saturation state, the DC component compensation current can be amplified to a size according to the magnetic saturation characteristics of the core and applied to the third coil (N3).

[0081] In this case, since the DC component detection core cannot be magnetized beyond the maximum magnetic flux density state due to the magnetic saturation characteristics of the core, when a compensation current corresponding to the current that forms the magnetizing force that causes the DC component detection core to reach the magnetic saturation state, i.e., a reverse current, is applied, the magnetic flux of the magnetically saturated core is canceled, so that the DC component detection core can be demagnetized.

[0082] Then, the control unit (100) can apply a pulse current having a frequency according to the magnetic saturation characteristics of the core to the coil wound around the DC component detection core, thereby magnetizing the DC component detection core according to the magnetic saturation characteristics of the core.

[0083] Meanwhile, Fig. 1 describes a structure in which a control unit (100) detects a DC component leakage current and applies a compensation current based on the detected DC component leakage current. However, in the case of a pulse current, since it has the characteristic of an AC current in which the polarity is reversed at regular intervals, it is of course possible to apply a compensation current based on a leakage current obtained by adding a DC component leakage current having an AC characteristic according to the AC component leakage current and the applied pulse current, and to detect the summed leakage current based on the applied compensation current.

[0084] FIG. 2 is a circuit diagram showing a circuit configuration of a flux gate type leakage current detection device that applies a compensation current according to a detected leakage current, according to a second embodiment of the present invention.

[0085] Referring to FIG. 2, a leakage current detection device according to a second embodiment of the present invention may be configured to include a leakage current detection unit (130) and an amplifier unit (160). In addition, it may be configured to include a reset unit (170) including the entire burden resistance and a measuring unit (140) that amplifies the compensation current and inputs it to the control unit (100).

[0086] In more detail, the leakage current detection unit (130) may include a differential amplifier (131). And the output terminal of the differential amplifier (131) via the resistor (R6) may be fed back to the non-inverting input terminal (V+) of the differential amplifier (131) via the resistor (R5) and the capacitor (C1) that serve as a noise filter. And the other end of the first coil (N1) which is connected to the oscillator (110) to receive the pulse current may be connected to the inverting input terminal (V-) of the differential amplifier (131) via the resistor (R7), and the other end of the second coil (N2) which is grounded may be connected to the non-inverting input terminal (V+) of the differential amplifier (131) via the resistor (R4).

[0087] Accordingly, the differential amplifier (131) can differentially amplify a voltage signal corresponding to a DC component leakage current of a conductor to be measured inputted through an inverting input terminal (V-) and a voltage signal corresponding to an AC component leakage current of a conductor to be measured inputted through a non-inverting input terminal (V+). That is, the differential amplifier (131) can amplify by adding a voltage signal corresponding to a DC component leakage current detected in a conductor to be measured and a voltage signal corresponding to an AC component leakage current.

[0088] Here, the DC component detection core may be a core that is magnetized by a first coil (N1) to which a pulse current is applied. Therefore, the voltage signal corresponding to the DC component leakage current may be a voltage signal whose polarity is reversed according to the frequency of the pulse current applied to the first coil (N1). That is, the voltage signal detected by the DC component detection core, although it corresponds to the DC component leakage current of the conductor to be measured, has the characteristics of an AC current according to the applied pulse current. Therefore, unlike a DC current to which only a current of a specific polarity is applied, since the polarity is reversed, the magnetic flux of the core can be canceled according to the frequency of the pulse current. Therefore, as shown in the first embodiment of the present invention illustrated in the above-described FIG. 1, instead of separately compensating for the DC component leakage current, as shown in FIG. 2, the voltage signal detected in the AC component detection core and the voltage signal detected in the DC component detection core are added (leakage current detection unit (130)), and a compensation current corresponding to the total added voltage signal can be generated.

[0089] Meanwhile, the amplifier (160) may be configured to include an operational amplifier (161) to invert and amplify the voltage signal attenuated by the resistors (R4, R7, R6) and the filter (R5, C1) using the resistors (R8, R9). The operational amplifier (161) may invert and amplify the voltage signal output from the differential amplifier (131) output terminal of the leakage current detection unit (130), i.e., the DC voltage signal (corresponding to the DC component leakage current) and the AC voltage signal (corresponding to the AC component leakage current) added in the leakage current detection unit (130).

[0090] Here, the non-inverting input terminal (V+) of the operational amplifier (161) can be grounded, and the output terminal of the differential amplifier (131) of the leakage current detection unit (130) via the resistor (R8) and the resistor (R6) can be connected to the inverting input terminal (V-). In addition, the output terminal of the operational amplifier (161) can be fed back to the non-inverting input terminal (V+) of the differential amplifier (131) of the leakage current detection unit (130). Therefore, through the inverting amplification of the amplification unit (160), the reverse voltage of the DC voltage signal and the AC voltage signal added in the leakage current detection unit (130), i.e., the compensation current, can be output from the output terminal of the differential amplifier (131) of the leakage current detection unit (130).

[0091] Meanwhile, the output terminal of the differential amplifier (131) of the leakage current detection unit (130) may be connected to one end of a third coil (N3) wound around both the AC component detection core and at least one DC component detection core. Accordingly, the compensation current may be applied to the third coil (N3). Accordingly, an error due to leakage current may be compensated for.

[0092] Then, the compensation current can be output in the form of a voltage signal generated according to the total burden resistance (171) of the reset unit (170) connected to the other end of the third coil (N3). In this case, the voltage signal may include a pulse signal applied from the oscillator (110) and noise of the core. Accordingly, the measuring unit (140) may include a low pass filter (LPF) (141) connected to the other end of the third coil (N3), and may include an amplifier (142) that amplifies the voltage signal into a range that the control unit (100) can recognize using a preset reference voltage (Vref). Then, the voltage signal amplified into a range that the control unit (100) can recognize through the amplifier (142) can be input to an ADC (Analog Digital Converter) channel of the control unit (100).

[0093] Then, the size of the compensation current can be detected through the ADC (not shown) provided in the control unit (100). Here, the compensation current is the reverse current of the current obtained by adding the AC component leakage current and the DC component leakage current of the conductor to be measured, and may be equal to the size of the leakage current of the conductor to be measured. Therefore, by detecting the size of the compensation current, the leakage current of the conductor to be measured can be detected.

[0094] Meanwhile, the reset unit (170) is placed between the other end of the third coil (N3) and the measurement unit (140), and may be configured to include a reset switch (172) that initializes and demagnetizes the cores of the core unit (120) according to a reset signal applied from the overall burden resistance (171) and the control unit (100).

[0095] Meanwhile, FIGS. 3 to 5 are exemplary diagrams showing different configurations of the core part (120) provided in the leakage current detection device according to the first and second embodiments of the present invention described above.

[0096] First, referring to FIG. 3, an example in which a core part (120) of a leakage current detection device according to embodiments of the present invention is composed of a first core (121) for detecting a DC component leakage current and a second core (122) for detecting an AC component leakage current (dual core structure) is illustrated. In this case, a first coil (N1) for magnetizing the first core (121) may be wound around the first core (121), and a second coil (N2) for magnetizing the second core (122) may be wound around the second core (122). In addition, a third coil (N3) for applying a compensation current may be wound around both the first core (121) and the second core (122).

[0097] In this case, when the core part (120) is configured to include two cores, the DC component leakage current and the AC component leakage current can be detected respectively according to secondary currents induced in different cores. In this case, the leakage current detection device according to an embodiment of the present invention can detect the DC component leakage current by removing the AC component having the frequency from the secondary current detected through the first core (121), and detect the AC component leakage current from the secondary current detected through the second core (122) after compensating for an error according to the detected DC component leakage current. In addition, the total leakage current flowing in the conductor to be measured can be detected by adding up the detected DC component leakage current and the AC component leakage current (first embodiment of the present invention). Alternatively, the leakage current detection device according to an embodiment of the present invention may add up the voltage signal of the secondary current detected through the first core (121) and the voltage signal of the secondary current detected through the second core (122), and apply a compensation current corresponding to the added voltage signal to the third coil (N3) wound around both the first core (121) and the second core (122). And, based on the compensation current, the total leakage current flowing in the conductor to be measured may be detected (second embodiment of the present invention).

[0098] Meanwhile, as shown in Fig. 3, in addition to a structure including two cores, it is also possible to detect leakage current of a direct current component and leakage current of an alternating current component through a single core. Fig. 4 illustrates an example in which a core portion is configured with a single core in this manner.

[0099] Referring to Fig. 4, the core section (120) is configured as a single core for detecting direct current and alternating current components (single core structure). In this case, a second coil (N2) having one end grounded may be wound around the core. In addition, a first coil (N1) having one end connected to an oscillator (110) that applies a pulse current may be wound around the core. In addition, a third coil (N3) for applying a compensation current may be wound around the core.

[0100] In this case, a secondary current corresponding to the leakage current of the AC component flowing in the conductor to be measured can be induced in the first coil (N1). And, a secondary current corresponding to the leakage current of the DC component flowing in the conductor to be measured can be induced in the second coil (N2). In addition, a compensation current according to the secondary current corresponding to the leakage current of the AC component and the secondary current corresponding to the leakage current of the DC component can be applied to the third coil (N3). And, based on the compensation current, the total amount of the leakage current flowing in the conductor to be measured can be detected.

[0101] Meanwhile, in the description according to the first embodiment of the present invention described above, a configuration was described in which the control unit (100) filters the AC component having a frequency from the voltage signal of the secondary current induced from the first core (121) in order to detect the DC component leakage current. However, in contrast to this, when two identical cores that are magnetized with opposite polarities are used, it goes without saying that the DC component of the leakage current can be detected even without filtering the AC component.

[0102] Fig. 5 illustrates an example in which the core part (120) is configured as a triple core structure having two cores for detecting direct current component leakage current and one core for detecting alternating current component leakage current.

[0103] When the core part (120) has a triple core structure as shown in Fig. 5, the first-first core (121-1) and the first-second core (121-2) may be cores that detect direct current component leakage current. In addition, the second core (122) may be a core that detects alternating current component leakage current.

[0104] In this case, a second coil (N2) having one end grounded may be wound around the second core (122). In addition, a first-first coil (N1-1) may be wound around the first-first core (121-1), and a first-second coil (N1-2) may be wound around the first-second core (121-2). In addition, pulse currents having the same magnitude and frequency but different polarities may be applied to the first-first coil (N1-1) and the first-second coil (N1-2). That is, a pulse current output from the oscillator (110) may be applied to one end of either the first-first coil (N1-1) or the first-second coil (N1-2), while a pulse current whose sign is inverted through an inverting amplifier or the like may be applied to the other end.

[0105] And when the measured conductor is inserted through the hole inside each core of the core part (120), a secondary current corresponding to the leakage current of the direct current component flowing in the measured conductor can be induced in the first-first coil (N1-1) and the first-second coil (N1-2), respectively. In this case, since pulse currents having opposite polarities are applied to the first-first coil (N1-1) and the first-second coil (N1-2), the secondary currents applied to the first-first coil (N1-1) and the first-second coil (N1-2) can have opposite polarities.

[0106] Meanwhile, the other ends of each of the first-first coil (N1-1) and the first-second coil (N1-2) can be connected in parallel to the inverting input (V-) of the summing amplifier whose non-inverting input (V+) is grounded. Accordingly, voltage signals corresponding to the secondary currents induced in the first-first coil (N1-1) and the first-second coil (N1-2) can be synthesized in the summing amplifier. Then, through the synthesis, the frequency component according to the pulse current can be canceled, and accordingly, the DC component leakage current in the form of a pure DC can be detected.

[0107] Meanwhile, in the case of the leakage current detection device according to the second embodiment of the present invention, the DC component leakage current calculated according to the synthesis result of the summing amplifier can be applied to the third coil (N3) to compensate for the error according to the DC component leakage current. In addition, the AC component leakage current can be detected based on the secondary current induced from the second core (122), and the total leakage current of the measured conductor can be calculated based on the detected DC component leakage current and AC component leakage current. In addition, based on the calculated total leakage current, the output unit (not shown) can be controlled to output the result of determining the leakage current, and when the leakage current is detected, a signal related to the detection of the leakage current can be output.

[0108] Alternatively, in the case of the leakage current detection device according to the second embodiment of the present invention, the output terminal of the summing amplifier may be connected to one end of the input terminal (e.g., inverting input terminal (V-)) of the differential amplifier (131) of the leakage current detection unit (130). And the other end of the second coil (N2) may be connected to the other end of the input terminal (e.g., non-inverting input terminal (V+)) of the differential amplifier (131). Accordingly, the differential amplifier (131) may add and amplify the voltage signal of the DC component leakage current detected from the 1-1 core (121-1) and the 1-2 core (121-2) and the voltage signal of the AC component leakage current detected from the second core (122). And the added voltage signal may be applied to the amplifier (160) to be inverted and amplified. And the compensation current corresponding to the added voltage signal may be applied to the third coil (N3). And the control unit (100) can calculate the total leakage current of the measured conductor by measuring the compensation current through the measuring unit (140).

[0109] Meanwhile, in the above FIGS. 3 to 5, the configuration of the core part (120) having different structures has been described. However, regardless of the structure of the core part (120), a pulse current generated by the oscillator (110) can be applied to a core among the cores of the core part (120) that detects a DC component leakage current. Here, the oscillator (110) determines the frequency of the pulse current according to the frequency of the pulse digital signal output from the control part (100), and the control part (100) can detect the frequency of the pulse current that matches the magnetic saturation characteristic of the core that detects the DC component leakage current by changing the frequency of the pulse digital signal. Therefore, the present invention can maximize the accuracy, precision, and efficiency of the leakage current detection device by applying a pulse current according to the optimal frequency that matches the magnetic saturation characteristic of the core regardless of the structure of the core part (120).

[0110] Meanwhile, in the above description, the circuit structures of the flux gate type leakage current detection device according to embodiments of the present invention were examined in detail.

[0111] In the following description, the operation process of detecting the leakage current of a conductor to be measured by applying a pulse current at an optimal frequency matching the magnetic saturation characteristics of the core in a flux gate type leakage current detection device according to the first or second embodiment of the present invention will be examined in detail.

[0112] First, FIG. 6 is a flowchart illustrating an operation process for detecting a frequency of a pulse current that matches the magnetic saturation characteristics of a core in a leakage current detection device according to embodiments of the present invention. FIG. 7 is a graph illustrating a hysteresis loop illustrating the magnetic saturation characteristics of a core and a magnetic flux density characteristic of a core according to the current in the core.

[0113] First, referring to FIG. 6, the control unit (100) of the leakage current detection device according to embodiments of the present invention can first determine a detection frequency range for detecting a pulse current frequency that matches the magnetic saturation characteristics of the core (S700).

[0114] For example, the detection frequency range may vary depending on various characteristics of the core to which the pulse current is applied. For example, different detection frequency ranges may be determined based on physical characteristics of the core, such as the shape of the core (e.g., ring shape or open ring shape), thickness, diameter of the core, material of the core, diameter of the inner hollow of the core, etc. Alternatively, different detection frequency ranges may be determined based on characteristics of the coil, such as the material of the coil wound on the core, the number of turns of the coil, and the winding spacing of the coil. Alternatively, different detection frequency ranges may be determined based on characteristics of the conductor to be measured, such as the type of the conductor to be measured, the manufacturer or manufacturing number (serial number) of the core, or manufacturing information of the core. The control unit (100) may determine any one of a plurality of different detection frequency ranges that are pre-stored based on at least one of the physical characteristics of the core, the characteristics of the coil, the type of the conductor to be measured, and manufacturing information of the core.

[0115] Here, the plurality of different detection frequency ranges can be stored in the memory (not shown) of the leakage current detection device, and the detection frequency ranges of each pulse current determined according to the physical characteristics of the core, the characteristics of the coil, the type of the conductor to be measured, and the manufacturing information of the core can be obtained from the results of magnetic saturation characteristic experiments on a plurality of cores having different physical characteristics of the core, characteristics of the coil, the type of the conductor to be measured, and the manufacturing information of the core.

[0116] To this end, the control unit (100) may, in step S700, receive various information about the core to which the pulse current will be applied. For example, the control unit (100) may receive information about the core from a preset input device connected via wire or wireless connection. Furthermore, one of the plurality of detection frequency ranges may be determined based on at least one of the input core information.

[0117] Once the detection frequency range is determined, the control unit (100) can intermittently output a specific voltage at a predetermined time interval according to the initial frequency within the determined detection frequency range to generate a pulse digital signal. Then, the generated pulse digital signal can be applied to the oscillator (110) (S702). Then, the oscillator (110) can generate a pulse current having a frequency according to the predetermined time interval based on the reference frequency preset in the comparator (113). Then, the generated pulse current can be applied to a coil (e.g., a first coil (N1)) wound around at least one core constituting the core unit (120), for example, at least one DC component detection core. Then, the DC component detection core can be magnetized according to the pulse current.

[0118] Meanwhile, when the DC component detection core is magnetized according to the pulse current, a test conductor can be inserted into the core portion (120). In this case, the test conductor can be a conductor through which a preset leakage current, for example, a DC leakage current, flows. Then, the control unit (100) can detect the leakage current for the test conductor inserted into the core portion (120) (S704). And, the detection result of the leakage current can be output.

[0119] In the above step S704, if a leakage current is detected for the test conductor, the control unit (100) can change the time interval at which a specific voltage is output according to the frequency change unit generated according to the currently determined detection frequency range. For example, if the initial frequency is 1.8 KHz, the control unit (100) can output a specific voltage to the oscillator (110) every 1 / 3600 second in the above step S702 to apply a pulse digital signal having a period of 1.8 KHz to the oscillator (110). In this state, if the frequency change unit corresponding to the currently determined detection frequency range is 0.1 KHz, the control unit (100) can change the period at which the specific voltage is output to the oscillator to 1 / 3400 second to apply a pulse digital signal having a period of 1.7 KHz to the oscillator (110). Therefore, the frequency of the pulse current applied to the coil wound on the core can be changed.

[0120] Meanwhile, when a pulse current is applied to the core, the magnetized core exhibits magnetic saturation characteristics, such as the hysteresis loop shown in (a) of Fig. 7. That is, when a positive current is applied, the magnetic flux density may increase as the magnetizing force (H) increases. Conversely, when a negative current is applied while the magnetic flux has a positive value, the magnetic flux may be canceled out and the magnetic flux density may decrease.

[0121] However, as shown in (b) of Fig. 7, the core has a characteristic in which the magnetic flux density increases as the magnetizing force (H / M) increases up to a certain level, but when the increased magnetic flux density reaches the maximum magnetic flux density (Bm), it becomes magnetically saturated and the magnetic flux density no longer increases. In this way, the magnetizing force (H / M) that reaches the maximum magnetic flux density is different for each core because the shape, material, physical characteristics, or coil characteristics of the core are different. Therefore, the magnetizing force (H / M) that reaches the maximum magnetic flux density (Bm) may be one of the magnetic saturation characteristics of the core.

[0122] Accordingly, when an alternating current with reversed polarity is applied to a coil wound around a magnetized core, the magnetic flux of the core can continue to increase until the magnetizing force (H) according to the magnetic saturation characteristics of the core is reached. However, when the core reaches magnetic saturation due to the increasing magnetizing force, the magnetic flux no longer increases and remains at a constant size even if the magnetizing force increases.

[0123] However, in the case of the flux gate type leakage current detection device as described above, the leakage current can be detected based on the secondary current induced from the magnetic flux generated from the leakage current flowing in the conductor to be measured. Therefore, when the core is saturated, a problem may occur in which the leakage current flowing in the conductor to be measured is not detected if the magnetic flux of the core does not change. Therefore, the flux gate type leakage current detection device can generate a reverse magnetic flux by applying a pulse current whose polarity is periodically reversed to the coil as described above, thereby reversing the polarity of the magnetized core at regular intervals, thereby canceling out the magnetic flux of the core.

[0124] Therefore, as shown in (a) of Fig. 7, when a positive current is applied, the magnetizing force (H) may gradually increase according to the time for which the positive current is applied. In addition, when the polarity of the current applied to the coil is reversed, a magnetic flux having a negative value may be generated, and a magnetic flux having a positive value may be offset. In this case, the maximum value of the magnetic flux density according to the positive current applied to the coil may be +Bm, and the magnetizing force that forms the maximum value of the magnetic flux density (+Bm) according to the positive current of the pulse current may be the maximum magnetization point (+Hm) according to the positive current.

[0125] Meanwhile, as the polarity of the pulse current is reversed, the magnetic flux of the core may gradually decrease and reach points b and c. And the magnetizing force (H) may gradually decrease depending on the time that the negative current is applied, so that the magnetizing force may have a negative value. And when the polarity of the current applied to the coil is reversed again, a magnetic flux with a positive value may be generated, and the magnetic flux with a negative value may be canceled out. In this case, the minimum value of the magnetic flux density according to the negative current applied to the coil may be -Bm, and the magnetizing force that forms the maximum value of the magnetic flux density (-Bm) according to the negative current of the pulse current may be the maximum magnetization point (-Hm) according to the negative current. Therefore, during one cycle of the frequency of the pulse current having the characteristics of an AC signal, the magnetic flux of the core may pass through points a, b, and c to reach point d, and then pass through points e and f to reach point a again.

[0126] Meanwhile, in the case of the flux gate type leakage current detection device as described above, the leakage current can be detected according to the change in magnetic flux. And since the magnetic flux varies depending on the magnetization state of the core, the higher the magnetization degree of the core, the more precise the leakage current measurement can be. In this case, the magnetization degree of the core is determined by the magnetizing force, and as shown in Fig. 7 (a), the smaller the maximum magnetizing force (+Hm, -Hm) is, the smaller the change in magnetic flux (between points b and e) can be. Therefore, the amount of change in magnetic flux can be limited, and thus the accuracy of the leakage current detection device can be limited. On the other hand, the larger the maximum magnetizing force (+Hm, -Hm) is, the larger the change in magnetic flux (between points b and e) can be, and therefore the greater the amount of change in magnetic flux can be. Therefore, the greater the magnetizing force, the higher the accuracy of the leakage current detection device can be.

[0127] However, as shown in (b) of the above-described Fig. 7, the core has a limit to the magnetic flux that can increase as the magnetizing force increases, and the state where the magnetic flux density is saturated when the magnetic flux increases to the limit is called the maximum magnetic flux density. In addition, when the magnetizing force exceeds the magnetization point corresponding to the maximum magnetic flux density, the magnetic flux is saturated and does not change, so detection of leakage current may not be possible. Therefore, as the maximum magnetic flux density of the core is formed closer to the magnetization point that forms the maximum magnetic flux density value (+Bm, -Bm) of Fig. 7a, the efficiency and precision of the flux gate type leakage current detection device can increase. That is, the current that generates the magnetizing force that magnetizes the core so that the magnetic flux of the core does not exceed the maximum magnetic flux density but is as close to the maximum magnetic flux density as possible may be a current that is optimized for the magnetic saturation characteristics of the core, and matches the magnetic saturation characteristics of the core.

[0128] However, if the coil to which the pulse current is applied is wound on a core and the current applied to the coil has an AC characteristic in which the polarity is periodically reversed, the current flow applied to the coil may be limited as in the following mathematical expression 1 depending on the inductive reactance of the coil.

[0129]

[0130] Here, I is the current flowing in the coil, X L where is the inductive reactance of the coil (ohm), V is the AC voltage, f is the frequency, and L is the inductance of the coil.

[0131]

[0132] In the above mathematical expression 1, V may be the voltage of the pulse current, and f may be the frequency of the pulse current. In addition, L is the inductance of the coil, which may be a value included in the core information, for example, the coil information, or determined according to the type of core, etc. In other words, it may be a preset value.

[0133] Therefore, as shown in the above mathematical expression 1, the amount of current flowing in the coil wound on the core can be determined according to the frequency of the pulse current applied. In addition, since the magnetizing force (H) of the core is directly proportional to the current (I) flowing in the coil, the magnetizing force of the core can be determined according to the frequency of the pulse current applied to the coil. That is, as the frequency of the pulse current decreases, the magnetizing force (H) of the core increases, and the magnetic flux can increase. On the other hand, as the frequency of the pulse current increases, the magnetizing force (H) of the core decreases, and the magnetic flux can decrease.

[0134] Therefore, the frequency of the pulse current that causes the current to flow so as to generate a magnetizing force that magnetizes the core so that the magnetic flux of the core does not exceed the maximum magnetic flux density but is as close as possible to the maximum magnetic flux density may be a frequency that is optimized for the magnetic saturation characteristics of the core and matches the magnetic saturation characteristics of the core.

[0135] Meanwhile, as described above, if the core is not in a state of magnetic saturation, the magnetization of the core may increase when the current flowing in the coil increases as the frequency of the pulse current decreases. Therefore, even if the leakage current flowing in the conductor to be measured is the same, the magnetic flux density may increase according to the increased magnetic flux. On the other hand, if the magnetization of the core forms the maximum magnetic flux density according to the frequency of the pulse current, that is, if the core is magnetically saturated according to the changed frequency of the pulse current, it may be difficult to detect the leakage current flowing in the conductor to be measured because the magnetic flux density is already in a state of maximum saturation.

[0136] Therefore, when the frequency of the pulse current is changed, if the core is not magnetically saturated by the changed frequency of the pulse current, even if the test conductor has the same leakage current flowing, the leakage current of the test conductor may be detected normally, or may be different from the leakage current detection result detected from the frequency of the pulse current before the change. On the other hand, when the frequency of the pulse current is changed, if the core is magnetically saturated by the changed frequency of the pulse current, even if the test conductor has the same leakage current flowing, the leakage current of the test conductor may not be detected normally, or only the same leakage current detection result detected from the frequency of the pulse current before the change may be output regardless of the change in frequency. That is, when the frequency of the pulse current is changed, it is possible to detect whether the core has entered a magnetic saturation state depending on the frequency of the currently applied pulse current based on the change in the leakage current detection result of the control unit (100) for the test conductor.

[0137] Alternatively, the control unit (100) can detect a voltage signal including a pulse current component and a DC component leakage current from a secondary current induced in the DC component detection core. Then, it can be determined whether the DC component detection core is in a magnetic saturation state depending on whether the detected voltage signal generates a square wave.

[0138] For example, if the core is not saturated, i.e., if the core is in a normal state, the detected voltage signal may form a wave shape. However, if the core is in a magnetic saturation state, since leakage current is not detected, the voltage signal may generate a square wave according to the form of the pulse current. Accordingly, the control unit (100) can determine whether the DC component detection core is in a magnetic saturation state based on whether the voltage signal generates a square wave.

[0139] In this case, the control unit (100) can detect whether the voltage signal is a square wave based on the change in voltage detected in the state where the polarity is switched from the detected voltage signal. For example, in the case of a square wave, the voltage signal may not change more than a certain level in voltage for a certain period of time in the state where the polarity is switched. On the other hand, if the core is not saturated, a voltage change more than a certain level may occur for a certain period of time after the polarity is switched. In this way, the control unit (100) can determine whether the DC component detection core is saturated based on whether there is a voltage change more than a certain level for a certain period of time when the polarity is switched.

[0140] Accordingly, when the frequency of the pulse current is changed according to the frequency change unit in step S706, the control unit (100) can check whether the core to which the pulse current is applied has reached a magnetic saturation state based on the result of detecting the leakage current of the test conductor (S708).

[0141] And if it is determined as a result of the check at step S708 that the core has reached a state of magnetic saturation, the control unit (100) can determine that the frequency of the currently changed pulse current and the previous frequency are the frequencies at which the core can maintain the maximum magnetic flux without becoming magnetically saturated.

[0142] That is, the frequency of the pulse current matching the magnetic saturation characteristics of the core can be determined. And the determined pulse current frequency can be stored (S710). In addition, when the frequency of the pulse current matching the magnetic saturation characteristics of the core is determined, the test conductor can be removed from the core section (120).

[0143] Meanwhile, if a frequency of a pulse current matching the characteristics of the core is detected, the control unit (100) can apply a pulse current according to the determined frequency to a coil wound around the core (S712). Accordingly, the control unit (100) can detect a leakage current of a direct current component flowing in a conductor to be measured penetrating into the core unit (120) based on the frequency of the pulse current matching the magnetic saturation characteristics of the direct current component detection core.

[0144] Here, the core part (120) may be configured as a triple core structure. In this case, the DC component detection core may be configured with two physically identical cores. Meanwhile, according to the operation process of FIG. 7 described above, based on the change in the DC component leakage current of the test conductor detected by the two cores, the frequency of the pulse current that allows the cores to have the maximum magnetic flux without being magnetically saturated, i.e., the magnetizing force that can maximize the area of ​​the hysteresis loop illustrated in FIG. 7 (a), can be formed can be detected.

[0145] Therefore, even if the core part (120) is configured as a triple core structure, the present invention can apply a pulse current having an optimized frequency according to the magnetic saturation characteristics of the cores detecting the DC component leakage current to the cores detecting the DC component leakage current.

[0146] Meanwhile, FIG. 8 is a flowchart illustrating an operation process of applying a DC component compensation current detected to each core when detecting a leakage current of a measured conductor other than a test conductor in a leakage current detection device according to a first embodiment of the present invention.

[0147] Referring to FIG. 8, when a pulse current having an optimized frequency matching the magnetic saturation characteristics of a core (e.g., a DC component detection core) is applied and the core is magnetized, the control unit (100) can detect a voltage signal corresponding to a leakage current of a DC component based on a secondary current induced from the magnetized core and an intermediate resistance (S800). In this case, the secondary current is induced in the core magnetized by the pulse current, and the voltage signal may include not only a leakage current component of a DC component but also the applied pulse current component. The detected voltage signal may be received by the control unit (100).

[0148] In order to receive the voltage signal, the control unit (100) can amplify the voltage signal to a level that the control unit (100) can recognize through an amplifier unit (101) provided in the control unit (100). In addition, the control unit (100) can remove noise from the voltage signal before the amplification through a low-pass filter. In addition, the amplified voltage signal can be converted into a digital signal through an ADC.

[0149] Meanwhile, the control unit (100) can remove the pulse current component included in the voltage signal through filtering (S802). To this end, the control unit (100) can remove the AC component having a frequency from the voltage signal through a filter (e.g., filter unit (103)). In this case, the pulse current has the characteristics of an AC current whose polarity periodically changes, and thus can be removed through the filtering.

[0150] Then, the voltage signal may only include the leakage current component of the pure direct current component detected from the measured conductor. Then, the control unit (100) may determine a compensation current corresponding to the leakage current component of the direct current component. Then, the determined compensation current may be applied to the third coil (N3) that applies the core (S804). In this case, the compensation current may be a direct current having a polarity opposite to that of the leakage current of the direct current component and having the same magnitude.

[0151] Here, the compensation current may be a current of a micro level that is difficult for the control unit (100) to output. For example, it may be a current of a micro level that the control unit (100) cannot recognize. In this case, the control unit (100) may control the attenuation unit (102) to apply the compensation current of the micro level, and may apply the compensation current attenuated to the micro level by the attenuation unit (102) to the third coil (N3).

[0152] Meanwhile, due to the DC current compensation of step S804, the magnetic flux according to the DC component leakage current of the conductor to be measured can be canceled. Then, the control unit (100) can receive a voltage signal corresponding to the secondary current induced in the coil wound on the AC component detection core through the intermediate resistor. In this case, the voltage signal can have noise removed through a low-pass filter and can be amplified to a level that the control unit (100) can recognize. Then, it can be converted into a digital signal through the ADC of the control unit (100), and the AC component leakage current can be detected based on the voltage signal converted into the digital signal (S806).

[0153] Then, the control unit (100) can detect the total leakage current of the measured conductor by adding the magnitude of the DC component leakage current and the AC component leakage current. And, it can determine whether the total leakage current is greater than or equal to the preset operating current (S810).

[0154] If the total amount of leakage current calculated as a result of the determination in step S810 is less than the preset operating current, the control unit (100) can proceed to step S800 again and perform a process of detecting the DC component leakage current from the DC component core. Then, the following process can be repeated to detect the total amount of leakage current detected in the measured conductor.

[0155] However, if the total amount of leakage current calculated as a result of the determination in step S810 is greater than or equal to the preset operating current, the control unit (100) can start a process related to the generation of leakage current (S812).

[0156] In the above step S812, the control unit (100) may output a control signal, for example, a trip signal, for controlling the circuit breaker when a leakage current exceeding the operating current is detected. Alternatively, the control unit may output notification information notifying at least one other system or device related to the leakage current of the occurrence of the leakage current. In this case, whether or not to operate the circuit breaker may be determined through the other system or device.

[0157] Meanwhile, in the leakage current detection device according to an embodiment of the present invention, when an external magnetic field is formed due to an unexpected overcurrent or the like, the core may fall into a state of magnetic saturation due to the influence of the external magnetic field.

[0158] Accordingly, the control unit (100) of the leakage current detection device according to an embodiment of the present invention can demagnetize the core that has fallen into the magnetic saturation state through reset.

[0159] FIG. 9 is a flowchart illustrating an operation process for initializing a core according to a magnetic saturation state of the core in a leakage current detection device according to a first embodiment of the present invention. FIG. 10 is an exemplary diagram illustrating an output waveform of a DC component detection core according to a state of the core in a leakage current detection device according to embodiments of the present invention.

[0160] First, referring to FIG. 9, when step S800 of FIG. 8, which detects a DC component leakage current, is performed, the control unit (100) can detect a voltage signal including a pulse current component and a DC component leakage current from a secondary current induced to the DC component detection core through an intermediate resistor (S900). Then, it can be determined whether the detected voltage signal generates a square wave (S902).

[0161] For example, when the core is not saturated, i.e., when the core is in a normal state, the detected voltage signal may form a wave shape as shown in (a) of Fig. 10. However, when the core is in a magnetic saturation state, since the leakage current is not detected, the voltage signal may generate a square wave according to the form of the pulse current. Accordingly, the control unit (100) can determine whether the DC component detection core is in a magnetic saturation state based on whether the voltage signal generates a square wave.

[0162] In this case, the control unit (100) can detect a change in voltage detected in a state where the polarity is switched from the detected voltage signal. For example, as shown in (b) of Fig. 10, in the case of a square wave, the voltage signal may not cause a voltage change of a certain level or more for a certain period of time in a state where the polarity is switched.

[0163] On the other hand, if the core is not saturated, as shown in (a) of Fig. 10, a voltage change greater than a certain level may occur for a certain period of time after the polarity is switched. In this way, the control unit (100) can determine whether the DC component detection core is saturated in step S902 based on whether a voltage change greater than a certain level occurs for a certain period of time when the polarity is switched.

[0164] Meanwhile, if the determination result of the above step S902 indicates that the DC component detection core is not magnetically saturated, the control unit (100) can proceed to step S802 of FIG. 8 and continue the process of detecting the leakage current of the measured conductor.

[0165] However, if the determination result of the above step S902 indicates that the DC component detection core is in a magnetic saturated state, the control unit (100) can demagnetize the core in the magnetic saturated state by initializing the core (S904).

[0166] In the above step S904, the control unit (100) can amplify the compensation current to a preset size and apply it to the third coil (N3) to which the compensation current is applied. In this case, since the DC component detection core cannot be magnetized beyond the maximum magnetic flux density state due to the magnetic saturation characteristic of the core, the preset size may be a size corresponding to a current that forms a magnetizing force that allows the DC component detection core to reach the magnetic saturation state (for example, a current size that generates a magnetizing force of +Hm when the maximum magnetic flux density is +BM in a of FIG. 7). Then, since the magnetic flux is reduced by the amplified compensation current, i.e., the reverse current, the DC component detection core can be demagnetized.

[0167] Meanwhile, when core initialization is performed through the core demagnetization, the control unit (100) may proceed to step S712 of FIG. 7, and apply a pulse current having a frequency according to the magnetic saturation characteristics of the currently stored core to the coil wound on the DC component detection core. Then, according to the operation process illustrated in FIG. 8, the initialized core may be re-magnetized according to the pulse current having a frequency according to its magnetic saturation characteristics, and the leakage current of the conductor to be measured may be detected.

[0168] Meanwhile, in the above description, a configuration for applying a compensation current or detecting a leakage current through the core portion (120) has been described, but it may be obvious in the technical field to which the present invention pertains that the number of turns of the coil wound on each core may be reflected in the application of the compensation current and detection of the leakage current.

[0169] In addition, according to the description of the above-described FIG. 7, the present invention can detect the frequency of the pulse current that matches the magnetic saturation characteristics of the core by changing the frequency of the pulse digital signal before detecting the leakage current from the measured conductor.

[0170] In addition, by changing the time interval at which the control unit (100) outputs a specific voltage as described above, thereby changing the frequency of the pulse digital signal, it is possible to change the frequency of the pulse current applied to the coil wound on the DC component detection core without changing the circuit elements such as resistors or capacitors. Therefore, when the core of the leakage current detection device is replaced for reasons such as maintenance or change of use, the replaced core can be magnetized according to the pulse current having a frequency matching the magnetic saturation characteristics of the replaced core without changing the internal configuration of the circuit.

[0171] The present invention described above can be implemented as computer-readable code on a medium having a program recorded thereon. Computer-readable media include all types of recording devices that store data that can be read by a computer system. Examples of computer-readable media include hard disk drives (HDDs), solid-state disks (SSDs), silicon disk drives (SDDs), ROMs, RAMs, CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, etc., and also include media implemented in the form of carrier waves (e.g., transmission via the Internet). Therefore, the above detailed description should not be construed as limiting in any respect, but rather as illustrative. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all changes within the equivalent scope of the present invention are intended to be included in the scope of the present invention.

Claims

1. An oscillator that generates a pulse current having a preset frequency; At least one first core having at least one first coil wound at one end connected to the oscillating section and magnetized according to the pulse current, a second core having a second coil wound at one end grounded, and a core section having a third coil wound around the first core and the second core and to which a compensation current is applied; and A leakage current detection device characterized by comprising a control unit that determines the frequency of the pulse current according to at least one of the characteristics of the at least one first core, filters out a component having the frequency from a voltage signal of a current induced in the at least one first core, detects a DC component leakage current of a conductor to be measured, and applies a reverse current corresponding to the detected DC component leakage current to the third coil as the compensation current.

2. In the first paragraph, the characteristics of at least one first core are: A leakage current detection device characterized by at least one of the following: the shape or thickness of the core, the diameter or material of the core, the diameter of the hollow space inside the core, the material or number of turns of the coil wound on the core, the winding spacing of the coil, the manufacturer and manufacturing number of the core, and the type of the conductor to be measured.

3. In paragraph 2, Further comprising a memory in which a plurality of detection frequencies are stored according to different characteristics of at least one of the first cores, The above control unit, A leakage current detection device characterized in that one of the plurality of detection frequencies is determined as the frequency of the pulse current based on the characteristics of at least one of the first cores.

4. In the third paragraph, the control unit, When the DC component leakage current of the measured conductor is detected according to any one of the plurality of detection frequencies, the frequency of the pulse current is changed to another one of the plurality of detection frequencies, and the DC component leakage current of the measured conductor is detected again according to the frequency of the changed pulse current. A leakage current detection device characterized in that it detects the frequency of a pulse current according to the magnetic saturation characteristic of the at least one first core by determining whether the at least one first core is magnetically saturated.

5. In paragraph 4, the control unit, A leakage current detection device characterized in that it determines whether the magnetic saturation of the at least one first core is achieved based on whether a voltage signal detected from the at least one first core generates a square wave.

6. In paragraph 5, the control unit, A leakage current detection device characterized in that it is determined whether the voltage signal detected from the at least one first core generates a square wave based on whether there is a voltage change of a certain level or more for a certain period of time when the polarity of the voltage signal detected from the at least one first core is switched.

7. In paragraph 4, the control unit, A leakage current detection device characterized in that, when a magnetic saturation frequency of a pulse current that magnetically saturates at least one first core is detected, a frequency close to the magnetic saturation frequency among the frequencies of pulse currents that do not magnetically saturate the at least one first core is determined as a pulse current frequency according to the magnetic saturation characteristic of the at least one first core.

8. In paragraph 4, the conductor to be measured is, A leakage current detection device characterized by being a test conductor through which a leakage current of a direct current component and an alternating current component of a preset size flow.

9. In paragraph 1, The above rash area is, A pulse digital signal is input that repeats a state of outputting a specific voltage and a state of not outputting voltage at a preset time cycle, and a pulse current is generated in which a positive current and a negative current alternate at a preset time cycle in synchronization with the pulse digital signal. The above control unit, A leakage current detection device characterized in that it applies a pulse digital signal that is repeated at a predetermined time cycle to the oscillator based on the frequency of the pulse current determined according to the characteristics of at least one first core.

10. In paragraph 9, The above rash area is, It has a comparator with a preset reference voltage, The above comparator is, A leakage current detection device characterized in that when a pulse digital signal having a voltage higher than the reference voltage is input, a current having a positive voltage of a preset size is output, and when a pulse digital signal having a voltage lower than the reference voltage is input, a current having a negative voltage of a preset size is output.

11. In paragraph 10, The above reference voltage has a size of half of the above specific voltage, The positive and negative voltages of the above preset sizes are A leakage current detection device characterized by positive and negative voltages corresponding to the above reference voltage.

12. An oscillator that generates a pulse current having a preset frequency; At least one first core having at least one first coil wound at one end connected to the oscillating section and magnetized according to the pulse current, a second core having a second coil wound at one end grounded, and a core section having a third coil wound around the first core and the second core and to which a compensation current is applied; and A leakage current detection unit connected to the other end of at least one first core and the other end of the second core and adding a voltage signal detected from the first core and a voltage signal detected from the second core; An amplifier unit that generates a compensation current applied to the third coil by inverting and amplifying a voltage signal according to the result of summing the voltage signals of the leakage current detection unit; and A leakage current detection device characterized by including a control unit that determines the frequency of the pulse current according to at least one of the characteristics of the at least one first core and detects a DC component leakage current flowing in the measured conductor based on the compensation current.

13. In the 12th paragraph, the leakage current detection unit, A differential amplifier is provided with a non-inverting input terminal connected to the other end of the second coil and an inverting input terminal connected to the other end of the first coil, and which adds a voltage signal corresponding to a DC component leakage current of the measured conductor and a voltage signal corresponding to an AC component leakage current. The above differential amplifier, A leakage current detection device characterized in that the output terminal is connected to the non-inverting input terminal via a resistor and capacitor that act as a noise filter, and the output of the differential amplifier is fed back to the non-inverting input terminal.

14. In the 13th paragraph, the amplifying unit, An operational amplifier having a first input terminal connected to ground and a second input terminal connected to the output terminal of the differential amplifier via a first resistor of a preset size, The output terminal of the above operational amplifier is, A leakage current detection device characterized in that it is connected to the second input terminal via a second resistor of a preset size and is connected to the non-inverting input terminal of the differential amplifier so that the output of the operational amplifier is fed back to the differential amplifier.

15. In the 12th paragraph, at least one first core, A first core in which a first coil to which the pulse current is applied is wound; An inverting amplifier that inverts the polarity of the pulse current; A first-second core having a first-second coil wound thereon, to which a pulse current having a polarity reversed by the above-described inverting amplifier is applied; and A leakage current detection device characterized by including an adding amplifier that synthesizes voltage signals corresponding to secondary currents induced in the first-1 coil and the first-2 coil.

16. In paragraph 12, Further comprising a memory in which a plurality of detection frequencies are stored according to different characteristics of at least one of the first cores, The above control unit, A leakage current detection device characterized in that one of the plurality of detection frequencies is determined as the frequency of the pulse current based on the characteristics of at least one of the first cores.

17. In paragraph 16, the control unit, When the DC component leakage current of the measured conductor is detected according to any one of the plurality of detection frequencies, the frequency of the pulse current is changed to another one of the plurality of detection frequencies, and the DC component leakage current of the measured conductor is detected again according to the frequency of the changed pulse current. A leakage current detection device characterized in that it detects the frequency of a pulse current according to the magnetic saturation characteristic of the at least one first core by determining whether the at least one first core is magnetically saturated.

18. In paragraph 17, the control unit, A leakage current detection device characterized in that, when a magnetic saturation frequency of a pulse current that magnetically saturates at least one first core is detected, a frequency close to the magnetic saturation frequency among the frequencies of pulse currents that do not magnetically saturate the at least one first core is determined as a pulse current frequency according to the magnetic saturation characteristic of the at least one first core.

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