Fluxgate type earth leakage current detection device and control method for the device

Abstract

The present invention relates to a fluxgate type leakage current detection device, characterized by including: an oscillator unit that generates a pulse current having a predetermined frequency; at least one first core wound with at least one first coil having one end connected to the oscillator unit and magnetized by the pulse current; a second core wound with a second coil having one end grounded; and a core unit that supplies a third coil wound around the first core and the second core and supplied with a compensation current; and a control unit that determines the frequency of the pulse current in accordance with at least one feature of the at least one first core, filters out a frequency component 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 supplies a reverse current corresponding to the detected DC component leakage current to the third coil as the compensation current.

Description

[Technical Field]

[0001] The present invention relates to a leakage current detection device for detecting leakage current or residual current (hereinafter referred to as leakage current (Residual 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 method for controlling the device. [Background technology]

[0002] In recent years, demand for DC power sources, such as electric vehicles and charging systems, is expected to grow, along with the widespread adoption of renewable energy sources such as solar panels and fuel cells, as well as energy storage devices. Accordingly, in the field of solar power generation equipment, the technical standards and criteria for DC ground fault interrupter procedures for solar power generation equipment have been revised (Ministry of Trade, Industry and Energy Announcement No. 2020-659 (December 3, 2020)). The revised announcement recommends the installation of a device that automatically interrupts the DC circuit when a ground fault occurs in the DC circuit of solar power generation equipment. The announcement also recommends the installation of a Type B Residual Current Detector (RCD) or Type B Earth Leakage Breaker (ELB), which can detect not only AC component leakage current but also DC component leakage current, regardless of the type of power conversion equipment (transformer type or transformerless type).

[0003] On the other hand, many fluxgate type detectors are used as detectors for detecting such leakage currents.Fluxgate type leakage current detectors are also called zero-flux type detectors, and measure the current flowing in a conductor under test based on a secondary current induced by magnetic flux generated in the magnetic core when a current flows through the conductor under test.Fluxgate type leakage current detectors are attracting attention because they can accurately detect the current flowing in the conductor under test without contact.

[0004] On the other hand, as mentioned above, the fluxgate method detects the current in the conductor under test based on the magnetic flux induced in a magnetized core, i.e., a magnetic core. However, the amount of magnetic flux density that increases in the core as the external magnetic field increases is limited by the core's characteristics, and the core's state when the maximum magnetic flux density induced in the core is reached is called a magnetic saturation state. Furthermore, when the core is magnetically saturated and the magnetic flux density reaches its maximum, the magnetic flux density does not change even when the external magnetic field increases. In this case, the magnetic flux density does not change with the external magnetic field, making it impossible to detect the external magnetic field, i.e., the current flowing in the conductor under test.

[0005] However, when an AC current flows through a conductor under test, due to the alternating polarity of the AC current, a current that increases the magnetic flux density in the positive direction (e.g., a positive (+) current) is supplied, followed by a current that increases the magnetic flux density in the reverse direction (e.g., a negative (-) current). Therefore, after the magnetic flux density increases in the positive direction, a magnetic field that increases the magnetic flux density in the reverse direction is formed, canceling out the magnetic flux. Even if the core reaches magnetic saturation, when the polarity of the current switches, the magnetic flux is canceled out by the reverse current, and the magnetic flux density in the core naturally decreases below its maximum magnetic flux density. However, with DC current, which does not switch polarity, a magnetic field that forms magnetic flux density in only one direction continues to be formed. As the external magnetic field increases, the magnetic flux increases without being canceled out, and the magnetic flux continues to accumulate. In this case, the core reaches magnetic saturation, and the magnetic flux density reaches its maximum.

[0006] Thus, to prevent the core from reaching magnetic saturation when detecting DC current, a method has emerged in which a pulse current having a predetermined frequency is supplied to the coil wound around the core, where the polarity of the magnetic field that forms the magnetic flux density in the magnetic core switches according to the frequency of the pulse current.

[0007] As described above, since a fluxgate leakage current detector detects leakage current by utilizing changes in magnetic flux density induced in a magnetic core, it is theoretically unable to detect leakage current unless the core is in a saturated state. Therefore, in a fluxgate leakage current detector, the measurable current is determined according to the magnetic saturation characteristics of the core. That is, the accuracy and precision of the fluxgate leakage current detector are determined according to the magnetic saturation characteristics of the core. Therefore, the efficiency of the fluxgate leakage current detector can be maximized by supplying a pulse current having a frequency that matches the magnetic saturation characteristics of the core.

[0008] Meanwhile, the maximum magnetic flux density of a core varies depending on the shape and material of the core, the number of turns of the coil wound around the core, the material, and the winding spacing. The maximum magnetic flux density, which varies depending on the shape, material, or structural characteristics of the core, is called the magnetic saturation characteristic of the core. Furthermore, since the maximum magnetic flux density of a core varies depending on the shape, material, and structure of the core, the material of the coil wound around the core, the number of turns, and the winding spacing, it is difficult to create cores that are completely identical physically, and the magnetic saturation characteristics differ for each core.

[0009] In addition, pulse signals are typically generated using a resonant circuit. When a pulse signal (pulse current) is generated using such a resonant circuit, the pulse current is supplied at a fixed frequency. In this case, the longer the time that a current of a specific polarity is supplied according to the frequency (the shorter the frequency), the greater the amount of current supplied to the coil, and the greater the magnetizing force. In other words, since the magnitude of the current supplied to the coil wound around the core varies depending on the frequency of the pulse current, applying a pulse signal having a frequency that generates a current suitable for the magnetic saturation characteristics of the core can maximize the efficiency of the fluxgate leakage current detection device.

[0010] However, as mentioned above, because the magnetic saturation characteristics differ for each core, 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 is known, as mentioned above, in the conventional method of generating a pulse current using a resonant circuit, the design of the resonant circuit itself must be changed to change the frequency of the pulse signal. Therefore, since it is difficult to apply a pulse signal frequency that matches the magnetic saturation characteristics of the core, there is a problem that the fluxgate type leakage current detector cannot be used efficiently.

[0011] Furthermore, when generating a pulse signal using a resonant circuit or the like, the pulse signal may be distorted or its frequency may change due to external disturbances such as electromagnetic radiation (RS: Radiated Susceptibility), electromagnetic conduction (CS: Conducted Susceptibility), radio wave noise, etc., and such distortions and frequency changes are likely to cause measurement errors. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made to solve the above problems and other problems, and aims to provide a fluxgate type leakage current detection device and a control method for the device in which a frequency that matches the magnetic saturation characteristics of the core is supplied to a coil wound around the core, thereby further improving accuracy and precision and maximizing efficiency.

[0013] Another object of the present invention is to provide a fluxgate type earth leakage current detection device and a control method for the device that, when a core is replaced in the fluxgate type earth leakage current detection device, can easily supply a pulse current having a frequency that matches the magnetic saturation characteristics of the replaced core to the replaced core.

[0014] Furthermore, the present invention aims to provide a fluxgate type leakage current detection device and a control method for the device, which can measure leakage current accurately and stably, regardless of external impacts, radio wave noise, or disturbances, by generating a pulse current that takes into account the core characteristics and supplying it to a coil wound around the core. [Means for solving the problem]

[0015] In order to achieve the above or other objects, in one aspect of the present invention, a leakage current detection device according to one embodiment of the present invention is characterized by including: an oscillator unit that generates a pulse current having a predetermined frequency; at least one first core wound with at least one first coil having one end connected to the oscillator unit and magnetized by the pulse current; a second core wound with a second coil having one end grounded; and a core unit that supplies a third coil wound around the first core and the second core and supplied with a compensation current; and a control unit that determines the frequency of the pulse current in accordance with at least one feature of the at least one first core, filters out a frequency component 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 supplies 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 at least one of the shape and thickness of the core, the diameter and material of the core, the diameter of the hollow interior of the core, the material and number of windings of the coil wound around the core, the winding spacing of the coil, the manufacturer and serial number of the core, and the type of conductor to be measured.

[0017] In one embodiment, the device further includes a memory in which a plurality of detection frequencies corresponding to various characteristics of the at least one first core are stored, and the control unit determines one of the plurality of detection frequencies as the frequency of the pulse current based on the characteristics of the at least one first core.

[0018] In one embodiment, when the control unit detects a DC component leakage current of the conductor under measurement at one of the plurality of detection frequencies, it changes the frequency of the pulse current to another of the plurality of detection frequencies, detects the DC component leakage current of the conductor under measurement again at the changed frequency of the pulse current, determines whether the at least one first core is magnetically saturated, and detects the frequency of the pulse current according to the magnetic saturation characteristics of the at least one first core.

[0019] In one embodiment, the control unit 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 rectangular wave.

[0020] In one embodiment, the control unit determines whether the voltage signal detected from the at least one first core generates a rectangular wave based on whether there is a voltage change of a predetermined level or more in a predetermined time when the polarity of the voltage signal detected from the at least one first core switches.

[0021] In one embodiment, when the control unit detects a magnetic saturation frequency of a pulse current that magnetically saturates the at least one first core, it determines a frequency of a pulse current that does not magnetically saturate the at least one first core and that is close to the magnetic saturation frequency as the pulse current frequency corresponding to the magnetic saturation characteristics of the at least one first core.

[0022] In one embodiment, the conductor to be measured is a test conductor through which a DC component leakage current and an AC component leakage current of a predetermined magnitude 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 in a predetermined time period, and generates the pulse current in which positive and negative currents alternate in the predetermined time period in synchronization with the pulse digital signal, and the controller applies the pulse digital signal in which the pulse current is repeated in the predetermined time period 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 includes a comparator having a predetermined reference voltage set thereto, the comparator outputting a current having a positive voltage of a predetermined magnitude when a pulse digital signal having a voltage higher than the reference voltage is input, and outputting a current having a negative voltage of a predetermined 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 magnitude that is half the magnitude of the specific voltage, and the positive voltage and negative voltage of the predetermined magnitude are positive voltages and negative voltages that correspond to the reference voltage.

[0026] In order to achieve the above or other objects, another embodiment of the leakage current detection device of the present invention is characterized by including: an oscillator unit that generates a pulse current having a predetermined frequency; at least one first core around which at least one first coil having one end connected to the oscillator unit is wound and which is magnetized by the pulse current; a second core around which a second coil having one end grounded is wound; and a core unit that supplies a third coil wound around the first core and the second core and to which a compensation current is supplied; a leakage current detection unit that is connected to the other end of the at least one first core and the other end of the second core and that adds up a voltage signal detected from the first core and a voltage signal detected from the second core; an amplifier unit that inverts and amplifies a voltage signal corresponding to the addition result of the voltage signals from the leakage current detection unit to generate a compensation current to be supplied to the third coil; and a control unit that determines the frequency of the pulse current according to at least one feature of the at least one first core and detects 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 the DC component leakage current of the conductor under test and a voltage signal corresponding to the AC component leakage current, the output terminal of the differential amplifier being connected to the non-inverting input terminal via a resistor and a capacitor that act as a noise filter, and the output of the differential amplifier being 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 the output terminal of the differential amplifier via a first resistor of a predetermined magnitude, and the output terminal of the operational amplifier is connected to the second input terminal via a second resistor of a predetermined magnitude 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.

[0029] In one embodiment, the at least one first core includes a 1-1 core around which a 1-1 coil to which the pulse current is supplied is wound, an inverting amplifier that inverts the polarity of the pulse current, a 1-2 core around which a 1-2 coil to which the pulse current of which polarity is inverted by the inverting amplifier is supplied is wound, and a summing amplifier that combines voltage signals corresponding to the secondary currents induced in the 1-1 coil and the 1-2 coil, respectively.

[0030] In one embodiment, the device further includes a memory in which a plurality of detection frequencies corresponding to various characteristics of the at least one first core are stored, and the control unit determines one of the plurality of detection frequencies as the frequency of the pulse current based on the characteristics of the at least one first core.

[0031] In one embodiment, when the control unit detects a DC component leakage current of the conductor under measurement at one of the plurality of detection frequencies, it changes the frequency of the pulse current to another of the plurality of detection frequencies, detects the DC component leakage current of the conductor under measurement again at the changed frequency of the pulse current, determines whether the at least one first core is magnetically saturated, and detects the frequency of the pulse current according to the magnetic saturation characteristics of the at least one first core.

[0032] In one embodiment, when the control unit detects a magnetic saturation frequency of a pulse current that magnetically saturates the at least one first core, it determines a frequency of a pulse current that does not magnetically saturate the at least one first core and that is close to the magnetic saturation frequency as the pulse current frequency corresponding to the magnetic saturation characteristics of the at least one first core. [Effects of the Invention]

[0033] The effects of the fluxgate type earth leakage current detection device and the control method for the device according to the present invention will be described below.

[0034] According to at least one embodiment of the present invention, a pulse current to be supplied to a coil wound around a core of a leakage current detector is generated by a control unit that intermittently outputs a current of a predetermined magnitude at a predetermined time interval, the frequency of the pulse current is changed by adjusting the predetermined time interval, and the frequency of the pulse current that matches the magnetic saturation characteristics of the core is detected based on the changed frequency of the pulse current.Furthermore, by supplying a pulse current of the detected frequency to the coil wound around the core, it is possible to maximize the measurement efficiency, precision, and accuracy of the fluxgate leakage current detector.

[0035] Furthermore, when replacing the core of a fluxgate leakage current detector, the present invention can detect a pulse signal frequency that matches the characteristics of the replaced core. 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, the measurement efficiency, precision, and accuracy of the leakage current detector can be stably maintained at the highest level regardless of core replacement.

[0036] Furthermore, the present invention can supply a pulse current to a coil wound around a fluxgate core based on a digital pulse signal with a predetermined voltage level that is generated by a control unit and output intermittently at predetermined time intervals. Therefore, since no resonant circuit is used to generate the pulse current, leakage current detection is possible that is resistant to external impacts, radio noise, or disturbances. [Brief explanation of the drawings]

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

[0038] [Figure 2] FIG. 10 is a circuit diagram showing the circuit configuration of a leakage current detection device that supplies a compensation current based on a detected leakage current according to a second embodiment of the present invention.

[0039] [Figure 3] 2 is a diagram showing an example of the configuration of a core unit provided in the leakage current detection device according to the embodiment of the present invention; FIG. [Figure 4] 10A and 10B are diagrams illustrating another example of the configuration of the core unit provided in the leakage current detection device according to the embodiment of the present invention. [Figure 5] 10 is a diagram showing yet another example of the configuration of the core unit provided in the leakage current detection device according to the embodiment of the present invention. FIG.

[0040] [Figure 6] 4 is a flowchart showing an operation process of detecting a frequency of a pulse current that matches the magnetic saturation characteristics of a core in the leakage current detection device according to the embodiment of the present invention.

[0041] [Figure 7] 1 is a graph showing a hysteresis loop indicating the magnetic saturation characteristics of a core and a magnetic flux density characteristic of the core depending on the current in the core;

[0042] [Figure 8] 5 is a flowchart showing an operation process of supplying a detected DC component compensation current to each core when detecting a leakage current in a conductor to be measured in the leakage current detector according to the first embodiment of the present invention.

[0043] [Figure 9] 5 is a flowchart showing an operation process of initializing a core in accordance with a magnetic saturation state of the core in the leakage current detection device according to the first embodiment of the present invention.

[0044] [Figure 10] 5A to 5C are diagrams showing examples of output waveforms of a DC component detection core according to the state of the core in the earth leakage current detection device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0045] The technical terms used in this specification are merely used to describe specific embodiments and are not intended to limit the present invention. Furthermore, singular expressions used in this specification include plural expressions unless otherwise specified. The suffixes "module" and "section" for components used in the following description are given or mixed together to facilitate the preparation of the specification and do not have any significance or utility in themselves.

[0046] In this specification, the terms "comprise," "include," and the like should not be construed as necessarily including all of the various components or steps in this specification, but rather as including none of the components or steps, or including additional components or steps.

[0047] Furthermore, when describing the technology disclosed in this specification, if it is determined that a specific description of related publicly known technology would obscure the gist of the technology disclosed in this specification, that detailed description will be omitted.

[0048] Furthermore, the accompanying drawings are merely for the purpose of making it easier to understand the embodiments disclosed in this specification, and the accompanying drawings do not limit the technical ideas disclosed in this specification, and should be understood to include any modifications, equivalents, or alternatives within the spirit and technical scope of the present invention. Furthermore, it goes without saying that not only the embodiments described below, but also combinations thereof are included within the spirit and technical scope of the present invention as modifications, equivalents, or alternatives within the spirit and technical scope of the present invention.

[0049] FIG. 1 is a circuit diagram showing the circuit configuration of a fluxgate type leakage current detection device for compensating for a DC component compensation current according to a first embodiment of the present invention.

[0050] 1, the earth leakage current detection device according to the embodiment of the present invention includes a control unit (microcontroller unit, MCU) 100, an oscillator unit 110 connected to 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 depending on a DC component leakage current or an AC component leakage current flowing through a conductor. The components shown in FIG. 1 are not essential for realizing a fluxgate type earth leakage current detection device, and the earth leakage current detection device described in this specification may include more or fewer components than those described above.

[0051] First, the control unit 100 intermittently outputs a current having a specific voltage at a predetermined time interval. That is, the control unit 100 outputs a current having the specific voltage (e.g., 3.3V) for a predetermined time in the predetermined time period, and does not output a current for the next predetermined time. Therefore, the control unit 100 outputs a pulse digital signal 111 in which a state in which the specific voltage (e.g., 3.3V) is output and a state in which 0V is output (a state in which no current is output) are repeated in the predetermined time period.

[0052] Meanwhile, the control unit 100 determines the frequency of the pulse digital signal 111 by changing the predetermined time interval. For example, the control unit 100 outputs a current of the specific voltage for 1 / 3600 seconds. Then, the current output is stopped again for 1 / 3600 seconds, and then the current of the specific voltage is output again for 1 / 3600 seconds. In this case, a state in which the current of the specific voltage is output and a state in which 0V is output alternate with a cycle of 1 / 1800 seconds. That is, a pulse digital signal 111 having a frequency of 1.8 kHz is generated.

[0053] A pulse digital signal 111 generated by the control unit 100 is supplied to an oscillator 110 that generates a pulse current from the applied pulse digital signal 111 .

[0054] In this case, the oscillator 110 generates a pulse current synchronized with the pulse digital signal 111 applied from the controller 100. To this end, the oscillator 110 includes a comparator 113 having a predetermined voltage set as a reference voltage. In this case, the comparator 113 outputs a current having a positive (+) voltage when a pulse digital signal having a voltage higher than the reference voltage is input, and outputs a current having a negative (-) voltage when a pulse digital signal having a voltage lower than the reference voltage is input. Thus, a pulse current in which positive and negative currents alternate according to the frequency of the pulse digital signal 111 is generated. In this case, the reference voltage is half the voltage of the specific voltage.

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

[0056] The oscillator 110 also supplies a pulse current due to the generated pulse voltage 112 to a coil wound around at least one core for detecting a DC component leakage current among the cores constituting the core unit 120. In this case, a current corresponding to a magnetic flux due to the AC component of the current (Ip) flowing through the conductor under measurement is induced in the core for detecting an AC component leakage current among the cores of the core unit 120.

[0057] Meanwhile, the oscillator 110 further includes a resistor 114 for determining the magnitude of the current supplied to the core 120. Here, the polarity and magnitude of the pulse current are determined according to the polarity of the pulse voltage 112 and the magnitude of the resistance 114 to the pulse voltage 112 (I=V / R). When the pulse current is supplied, the core is magnetized based on a magnetizing force according to the magnitude of the supplied current, and a magnetic flux is formed around the magnetized core.

[0058] Meanwhile, the core unit 120 includes 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 has a ring structure with a hole formed in the center so that a conductor to be measured can pass through. A first coil N1 is wound around the at least one DC component detection core for magnetizing the core, and a second coil N2 is wound around the AC component detection core for magnetizing the core. Furthermore, a third coil N3 is wound around both the at least one DC component detection core and the AC component detection core for supplying a compensation current.

[0059] When a conductor to be measured for detecting leakage current is inserted through the central hole of the core thus formed, a magnetic flux is generated in each core due to the current (Ip) flowing through the conductor. Then, a current (secondary current) to offset the generated magnetic flux is induced in the coil wound around each core. Furthermore, the control unit 100 detects a voltage signal corresponding to the AC component leakage current flowing through the conductor and a voltage signal corresponding to the DC component leakage current according to the magnitude of the secondary current induced in each core.

[0060] On the other hand, the voltage signal detected from core unit 120 is so small that it is difficult for control unit 100 to detect it. Therefore, control unit 100 includes amplifier unit 101 that amplifies the voltage signal detected from core unit 120 to a range that can be recognized by control unit 100. Control unit 100 also includes a low pass filter (LPF) (not shown) for removing the pulse signal applied from oscillator unit 110, core noise, etc., and an ADC (Analog Digital Converter) (not shown) for converting the voltage signal amplified to a range that can be recognized by control unit 100 into a digital signal.

[0061] On the other hand, if the leakage current is AC, the magnetic flux is automatically cancelled by switching the polarity of the current. However, if the leakage current is DC, the polarity of the current is not switched, so the magnetic flux is not cancelled. Therefore, the magnetic flux accumulates.

[0062] When uncancelled magnetic flux accumulates, the accumulated magnetic flux component is added as a DC component leakage current. The accumulated magnetic flux component is measured as a leakage current. Therefore, the control unit 100 supplies a compensation current to the coil wound around the DC component detection core to cancel out the accumulated magnetic flux component. In this case, to cancel out the magnetic flux, a current that generates a magnetic flux in the opposite direction must be supplied. Therefore, a current with the same magnitude as the measured DC component leakage current but with the opposite polarity, i.e., a reverse current, is supplied to the core unit 120 as the compensation current.

[0063] On the other hand, when a DC component leakage current flows through the conductor under test, the DC component leakage current increases the AC component leakage current. Therefore, the third coil N3 is wound not only around the at least one DC component detection core but also around the AC component detection core. Therefore, the magnetic flux due to the error component (DC component leakage current component) contained in the AC component leakage current is canceled out by the compensation current.

[0064] To supply such a compensation current, the control unit 100 detects a voltage signal corresponding to the secondary current induced in the at least one DC component detection core via a resistor R7.

[0065] Here, the DC component detection core is a core that is magnetized by a first coil N1 wound around the DC component detection core. The first coil N1 is supplied with a pulse current generated by the oscillator 110. Therefore, the secondary current induced in the at least one DC component detection core includes an AC component due to the pulse current supplied to the first coil N1.

[0066] In this case, the control unit 100 includes a filter unit 103 for filtering the AC component from the secondary current induced in the DC component detection core. For example, the filter unit 103 filters a component having a frequency from the voltage signal of the secondary current induced in the DC component detection core. As a result, a voltage signal corresponding to a pure DC component leakage current is detected, with components due to pulse current removed from the secondary current induced in the DC component detection core.

[0067] Then, the control unit 100 supplies a reverse current corresponding to the DC component leakage current detected by the filter unit 103 as a compensation current to the core unit 120, more specifically, to the third coil N3 for supplying the compensation current. Thus, the magnetic flux caused by the DC component leakage current flowing through the conductor under measurement is canceled out not only in the DC component detection core but also in the AC component detection core.

[0068] Here, the compensation current is a minute current that is difficult for the control unit 100 to directly control. Therefore, the control unit 100 further includes an attenuation unit 102 for attenuating the current output from the control unit 100. Furthermore, the control unit 100 controls the attenuation amount of the attenuation unit 102, and supplies the compensation current attenuated to a minute level below the level controllable by the control unit 100 to the third coil N3.

[0069] On the other hand, when the magnetic flux caused by the DC component leakage current flowing in the conductor under test is canceled out by the compensation current, the control unit 100 detects a voltage signal corresponding to the secondary current induced in the AC component detection core via resistor R4. The control unit 100 also detects the voltage signal corresponding to the secondary current induced in the AC component detection core as the AC component leakage current. The control unit 100 then adds the voltage signal (DC component leakage current) detected by filtering the secondary current induced in the DC component detection core to the voltage signal (AC component leakage current) detected from the secondary current induced in the AC component detection core to calculate the total leakage current (Ip) flowing in the conductor under test. The control unit 100 then controls the output unit based on the calculated leakage current amount to output the detected leakage current amount. The control unit 100 also outputs a signal related to the detection of the leakage current.

[0070] Here, the signal related to the detection of the earth 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 separates an internal circuit connected to the earth leakage current detection device from the line, thereby preventing the earth leakage current from flowing into the internal circuit or the line.

[0071] Alternatively, the signal regarding the detection of the ground fault current may be a notification signal that notifies a predetermined system of the occurrence of the ground fault current. In this case, the system is a control system that controls an internal circuit connected to the ground fault current detection device. The control system then controls a circuit breaker to isolate the internal circuit from the line based on the notification signal. Alternatively, the control system transmits information to at least one other device or equipment to notify the occurrence of the ground fault current, or performs a process to deal with the occurrence of the ground fault current.

[0072] Meanwhile, the density of the magnetic flux formed in the core is determined by the magnetizing force that magnetizes the core. The magnitude of the magnetizing force varies depending on the magnetizing current that magnetizes the core, i.e., the current flowing through the coil wound around the core. In this case, if the current flowing through the coil is an alternating current that alternates between negative and positive polarities, the inductive reactance of the coil limits the flow of current depending on the frequency. That is, even for the same magnitude of AC current, the higher the frequency, the more the current flow in the coil is limited, and the magnitude of the magnetizing current also varies.

[0073] However, as mentioned above, since pulse current also has the characteristics of an alternating current in which the negative and positive poles alternate at a predetermined time period, the current flow is limited by the inductive reactance of the coil according to the frequency of the pulse current. That is, the higher the frequency, the smaller the magnetizing current, and the lower the frequency, the larger the magnetizing current. Furthermore, as the magnitude of the magnetizing current increases, the magnitude of the magnetic flux density increases proportionally.

[0074] Therefore, in the present invention, in which a pulse current is generated in accordance with a specific frequency by a pulse digital signal generated by the control unit 100, the magnetizing current flowing through the coil can be changed and the magnetic flux density formed around the DC component detection core can be changed simply by changing the frequency of the pulse digital signal applied by the control unit 100 to the oscillator 110, without changing the resistance of the oscillator 110 or the voltage of the pulse digital signal. That is, in the present invention, the control unit 100 changes the time interval at which a current having the specific voltage is output in accordance with the frequency of various pulse currents, thereby changing the magnetic flux density formed around the core without changing the circuit configuration of the oscillator 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 fluxgate type earth leakage current detector are maximized, and the efficiency of the fluxgate type earth leakage current detector is maximized. Therefore, in the present invention, the control unit 100 can detect the frequency of the pulse digital signal that generates the magnetizing current that forms the maximum magnetic flux density of the DC component detection core while changing the frequency of the pulse digital signal.

[0076] For example, when a test conductor carrying a predetermined DC component leakage current passes through each core, the control unit 100 detects the DC component leakage current detected from the test conductor while changing the frequency of the pulse current. In this case, as the frequency of the pulse current decreases, the magnetizing current in the DC component detection core increases due to the inductive reactance of the first coil N1. As the magnetizing current increases, the magnetic flux density increases, and a larger secondary current is induced in the DC component detection core. Therefore, a larger DC component leakage current is detected. In this case, when the magnetizing current increases and the magnetic flux reaches its maximum magnetic flux density, a secondary current of the same magnitude is induced in the DC component detection core regardless of changes in the pulse current frequency, and the same DC component leakage current is detected. In other words, the pulse current frequency at which the DC component leakage current remains constant despite an increase or decrease in the pulse current frequency is the pulse current frequency that generates the magnetizing current that forms the maximum magnetic flux density, i.e., the pulse current frequency that corresponds to the magnetic saturation characteristic of the core.

[0077] On the other hand, in order to shorten the time required to detect the frequency of the pulse current corresponding to the magnetic saturation characteristics of the core, the control unit 100 sets a specific frequency range according to the structural characteristics of the core, such as the core shape, material, coil material, number of windings, and winding spacing.

[0078] To this end, the leakage current detector according to an embodiment of the present invention includes a memory (not shown) storing various detection frequency ranges corresponding to at least one of the diameter, material, and shape of the DC component detection core and the characteristics of the coil wound around the core. Alternatively, the memory may store various detection frequency ranges corresponding to the type of conductor to be measured for which DC component leakage current is to be detected, the core manufacturer, or the sequence number. In this case, the control unit 100 detects the frequency of the pulse current that matches the magnetic saturation characteristics of the core based on a detection frequency range corresponding to at least one of the structural characteristics of the core, such as the diameter, material, and shape, the type of conductor to be measured, the core manufacturer, and the sequence number, among the various detection frequency ranges stored in the memory.

[0079] In this case, the control unit 100 detects the frequency of the pulse current that matches the magnetic saturation characteristics of the DC component detection core in a predetermined frequency change increment corresponding to each detection frequency range. For example, the control unit 100 determines the detection frequency range to be 1.3 kHz or higher and less than 1.8 kHz based on at least one of the structural characteristics of the core, the type of conductor to be measured, and the core's manufacturing information. Then, the control unit 100 detects the frequency of the pulse current that corresponds to the magnetic saturation characteristics of the core while changing the frequency in predetermined increments within the determined detection frequency range. In this case, the frequency change increment corresponding to the detection frequency range of 1.3 kHz or higher and less than 1.8 kHz is 0.05 kHz. In this case, when the detection frequency range is changed, the frequency change increment is also changed.

[0080] The control unit 100 detects whether the DC component detection core is magnetically saturated based on the waveform of the secondary current detected by the DC component detection core, and if the DC component detection core is magnetically saturated, amplifies the DC component compensation current to a level according to the magnetic saturation characteristics of the core and supplies it to the third coil N3.

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

[0082] Then, the control unit 100 again supplies 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, and magnetizes the DC component detection core according to the magnetic saturation characteristics of the core.

[0083] 1, a structure has been described in which the control unit 100 detects a DC component leakage current and supplies a compensation current based on the detected DC component leakage current. However, since a pulse current has the characteristics of an AC current whose polarity reverses at predetermined time intervals, it goes without saying that a compensation current may be supplied based on a leakage current obtained by adding an AC component leakage current and a DC component leakage current having AC characteristics due to the supplied pulse current, and the added leakage current may be detected based on the supplied compensation current.

[0084] FIG. 2 is a circuit diagram showing the circuit configuration of a fluxgate type leakage current detection device that supplies a compensation current based on a detected leakage current according to a second embodiment of the present invention.

[0085] 2, the leakage current detection device according to the second embodiment of the present invention includes a leakage current detection unit 130 and an amplifier unit 160. It also includes a reset unit 170 including a full burden resistor, and a measurement unit 140 that amplifies the compensation current and inputs it to the control unit 100.

[0086] More specifically, the leakage current detection unit 130 includes a differential amplifier 131. An output terminal of the differential amplifier 131 via a resistor R6 is fed back to a non-inverting input terminal V+ of the differential amplifier 131 via a resistor R5 and a capacitor C1, which function as a noise filter. One end of a first coil N1, which is connected to the oscillator 110 and to which a pulse current is supplied, is connected to an inverting input terminal V− of the differential amplifier 131 via a resistor R7, and one end of a second coil N2, which is grounded at its other end, is connected to the non-inverting input terminal V+ of the differential amplifier 131 via a resistor R4.

[0087] Therefore, the differential amplifier 131 differentially amplifies the voltage signal corresponding to the DC component leakage current of the conductor under measurement input from the inverting input terminal V- and the voltage signal corresponding to the AC component leakage current of the conductor under measurement input from the non-inverting input terminal V+. That is, the differential amplifier 131 adds and amplifies the voltage signal corresponding to the DC component leakage current detected in the conductor under measurement and the voltage signal corresponding to the AC component leakage current.

[0088] Here, the DC component detection core is a core magnetized by the first coil N1 to which a pulse current is supplied. Therefore, the voltage signal corresponding to the DC component leakage current is a voltage signal whose polarity reverses according to the frequency of the pulse current supplied to the first coil N1. That is, even if the voltage signal detected by the DC component detection core corresponds to the DC component leakage current of the conductor under test, it has the characteristics of an AC current due to the supplied pulse current. Therefore, unlike a DC current supplied with only a specific polarity, the polarity reverses, and the magnetic flux in the core is canceled out according to the frequency of the pulse current. Therefore, instead of separately compensating for the DC component leakage current as in the first embodiment of the present invention shown in FIG. 1, as shown in FIG. 2, the voltage signal detected by the AC component detection core and the voltage signal detected by the DC component detection core may be added (by the leakage current detection unit 130) to generate a compensation current corresponding to the sum of all voltage signals.

[0089] On the other hand, the amplifier 160 inverts and amplifies the voltage signal attenuated by the resistors R4, R7, R6 and the filter R5, C1 using resistors R8, R9, and includes an operational amplifier 161. The operational amplifier 161 inverts and amplifies the voltage signal output from the output terminal of the differential amplifier 131 of the leakage current detector 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 by the leakage current detector 130.

[0090] Here, the non-inverting input terminal V+ of operational amplifier 161 is grounded, and the inverting input terminal V- is connected to the output terminal of differential amplifier 131 of leakage current detection unit 130 via resistors R8 and R6. The output terminal of operational amplifier 161 is fed back to the non-inverting input terminal V+ of differential amplifier 131 of leakage current detection unit 130. Therefore, the inverse voltage of the DC voltage signal and AC voltage signal added in leakage current detection unit 130 by inverting amplification of amplifier unit 160, i.e., a compensation current, is output from the output terminal of differential amplifier 131 of leakage current detection unit 130.

[0091] Meanwhile, the output terminal of the differential amplifier 131 of the leakage current detector 130 is 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. Thus, the compensation current is supplied to the third coil N3. Thus, the error due to the leakage current is compensated for.

[0092] Then, the compensation current is output in the form of a voltage signal generated by a total burden resistor 171 of the reset unit 170 connected to the other end of the third coil N3. In this case, the voltage signal includes the pulse signal applied from the oscillator 110, core noise, etc. Therefore, the measurement unit 140 includes a low pass filter (LPF) 141 connected to the other end of the third coil N3, and also includes an amplifier 142 that amplifies the voltage signal to a range recognizable by the control unit 100 using a predetermined reference voltage (Vref). In addition, the voltage signal amplified by the amplifier 142 to a range recognizable by the control unit 100 is input to an ADC (Analog Digital Converter) channel of the control unit 100.

[0093] Then, the magnitude of the compensation current is detected by an 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 under test, and has the same magnitude as the leakage current of the conductor under test. Therefore, by detecting the magnitude of the compensation current, the leakage current of the conductor under test can be detected.

[0094] On the other hand, the reset unit 170 is arranged between the other end of the third coil N3 and the measurement unit 140, and includes a total burden resistor 171 and a reset switch 172 that initializes and demagnetizes the core of the core unit 120 in response to a reset signal applied from the control unit 100.

[0095] Meanwhile, FIGS. 3 to 5 are diagrams showing various examples of the configuration of the core unit 120 provided in the leakage current detection devices according to the first and second embodiments of the present invention.

[0096] 3, an example (dual-core structure) is shown in which core unit 120 of the leakage current detection device according to the embodiment of the present invention is configured with first core 121 for detecting DC component leakage current and second core 122 for detecting AC component leakage current. In this case, a first coil N1 for magnetizing first core 121 is wound around first core 121, and a second coil N2 for magnetizing second core 122 is wound around second core 122. In addition, a third coil N3 for supplying a compensation current is wound around both first core 121 and second core 122.

[0097] When the core unit 120 is configured to include two cores, the DC component leakage current and the AC component leakage current are detected by the secondary currents induced in the respective cores. In this case, the leakage current detection device according to the embodiment of the present invention detects the DC component leakage current by removing the AC component having a frequency from the secondary current detected by the first core 121, compensates for the error due to the detected DC component leakage current, and then detects the AC component leakage current from the secondary current detected by the second core 122. The detected DC component leakage current and AC component leakage current are added together to detect the total leakage current flowing through the conductor under test (first embodiment of the present invention). Alternatively, the leakage current detection device according to the embodiment of the present invention adds together the voltage signal of the secondary current detected by the first core 121 and the voltage signal of the secondary current detected by the second core 122, and supplies a compensating current corresponding to the added voltage signal to the third coil N3 wound around both the first core 121 and the second core 122. Furthermore, the total leakage current flowing through the conductor under measurement is detected based on the compensation current (second embodiment of the present invention).

[0098] On the other hand, instead of the structure including two cores as shown in Fig. 3, a single core may be used to detect leakage current of both DC and AC components. Fig. 4 shows an example in which the core section is configured with one core.

[0099] 4 shows an example (single-core structure) in which the core unit 120 is configured with one core for detecting DC and AC current components. In this case, a second coil N2, one end of which is grounded, is wound around the core. A first coil N1, one end of which is connected to the oscillator 110 that supplies a pulse current, is also wound around the core. A third coil N3, for supplying a compensation current, is also wound around the core.

[0100] In this case, a secondary current corresponding to the AC component of the leakage current flowing in the conductor under test is induced in the first coil N1. A secondary current corresponding to the DC component of the leakage current flowing in the conductor under test is induced in the second coil N2. A compensation current is supplied to the third coil N3, consisting of a secondary current corresponding to the AC component of the leakage current and a secondary current corresponding to the DC component of the leakage current. Based on the compensation current, the total amount of leakage current flowing in the conductor under test is detected.

[0101] Meanwhile, in the first embodiment of the present invention, a configuration has been described in which the control unit 100 filters out an AC component having a frequency from the voltage signal of the secondary current induced from the first core 121 in order to detect a DC component of leakage current. However, it goes without saying that, if two identical cores magnetized with opposite polarities are used, the DC component of leakage current can be detected without filtering the AC component.

[0102] FIG. 5 shows an example in which the core section 120 is configured with a triple-core structure having two cores for detecting DC component leakage current and one core for detecting AC component leakage current.

[0103] 5, when the core unit 120 has a triple-core structure, the first core 121-1 and the second core 121-2 are cores that detect a DC component leakage current, and the second core 122 is a core that detects an AC component leakage current.

[0104] In this case, a second coil N2, one end of which is grounded, is wound around the second core 122. A first coil N1-1 is wound around the first core 121-1, and a first coil N1-2 is wound around the first core 121-2. A pulse current having the same magnitude and frequency but opposite polarity is supplied to the first coil N1-1 and the first coil N1-2. That is, a pulse current output from the oscillator 110 is supplied to one end of either the first coil N1-1 or the first coil N1-2, while a pulse current whose sign is inverted by an inverting amplifier or the like is supplied to the other end.

[0105] Furthermore, when the conductor under measurement is inserted into the holes in the cores of the core unit 120, secondary currents corresponding to the DC component leakage current flowing through the conductor under measurement are induced in the first coil N1-1 and the second coil N1-2, respectively. In this case, pulse currents having opposite polarities are supplied to the first coil N1-1 and the second coil N1-2, so the secondary currents supplied to the first coil N1-1 and the second coil N1-2 have opposite polarities.

[0106] Meanwhile, the other ends of the first coil N1-1 and the first coil N1-2 are connected in parallel to the inverting input V- of a summing amplifier whose non-inverting input V+ is grounded. Thus, voltage signals corresponding to the secondary currents induced in the first coil N1-1 and the first coil N1-2 are combined by the summing amplifier. As a result, the frequency components due to the pulse current are canceled out by this combination, and a DC component leakage current in pure DC form is detected.

[0107] On the other hand, in the leakage current detection device according to the second embodiment of the present invention, the DC component leakage current calculated from the combined result of the summing amplifier is supplied to the third coil N3 to compensate for the error due to the DC component leakage current. The AC component leakage current is detected based on the secondary current induced from the second core 122, and the total leakage current of the conductor under measurement is calculated based on the detected DC component leakage current and AC component leakage current. Furthermore, an output unit (not shown) is controlled based on the calculated total leakage current to output a leakage current determination result, and when a leakage current is detected, a signal related to the leakage current detection is output.

[0108] Alternatively, in a leakage current detection device according to a second embodiment of the present invention, the output terminal of the summing amplifier is connected to one terminal (e.g., inverting input terminal V-) of an input terminal of a differential amplifier 131 of the leakage current detection unit 130. The other terminal (e.g., non-inverting input terminal V+) of the input terminal of the differential amplifier 131 is connected to the other terminal of the second coil N2. Thus, the differential amplifier 131 adds and amplifies 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. The added voltage signal is applied to the amplifier 160 and inverted and amplified. Furthermore, a compensation current corresponding to the added voltage signal is supplied to the third coil N3. Furthermore, the control unit 100 calculates the total leakage current of the conductor to be measured by measuring the compensation current using the measurement unit 140.

[0109] 3 to 5 illustrate various configurations of the core unit 120. However, regardless of the structure of the core unit 120, a pulse current generated by the oscillator 110 is supplied to one of the cores of the core unit 120 that detects the 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 controller 100, and the controller 100 detects the frequency of the pulse current that matches the magnetic saturation characteristics 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 supplying a pulse current at an optimal frequency that matches the magnetic saturation characteristics of the core, regardless of the structure of the core unit 120.

[0110] The circuit structure of the fluxgate type earth leakage current detection device according to the embodiment of the present invention has been described in detail above.

[0111] Below, we will explain in detail the operating process of the fluxgate type leakage current detection device according to the first or second embodiment of the present invention, in which a pulse current is supplied at an optimal frequency that matches the magnetic saturation characteristics of the core and leakage current of the conductor being measured is detected.

[0112] 6 is a flowchart showing the operation of detecting the frequency of a pulse current that matches the magnetic saturation characteristics of a core in a leakage current detection device according to an embodiment of the present invention. Also, FIG. 7 is a graph showing a hysteresis loop indicating the magnetic saturation characteristics of the core and the magnetic flux density characteristics of the core as a function of the core current.

[0113] First, as shown in FIG. 6, the control unit 100 of the leakage current detection device according to the embodiment of the present invention determines 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 varies depending on various characteristics of the core supplying the pulse current. For example, various detection frequency ranges are determined depending on the physical characteristics of the core, such as the core's shape (e.g., ring-shaped or open-ring-shaped), thickness, diameter, material, and diameter of the internal cavity. Alternatively, various detection frequency ranges are determined depending on the characteristics of the coil wound around the core, such as the material, number of windings, and winding spacing. Alternatively, various detection frequency ranges are determined depending on the characteristics of the conductor to be measured, such as the type of conductor to be measured, the core manufacturer, and the serial number (sequence number), or the core's manufacturing information. The control unit 100 determines one of a plurality of pre-stored various detection frequency ranges based on at least one of the physical characteristics of the core, the coil characteristics, the type of conductor to be measured, and the core's manufacturing information.

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

[0116] To this end, in step S700, the control unit 100 receives input of various pieces of information related to the core to which the pulse current is supplied. For example, the control unit 100 receives input of the core information from a predetermined input device connected by wire or wirelessly. Furthermore, the control unit 100 determines one of the plurality of detection frequency ranges based on at least one of the input pieces of core information.

[0117] After determining the detection frequency range, the control unit 100 generates a pulse digital signal by intermittently outputting a specific voltage at a first frequency within the determined detection frequency range at a predetermined time interval. The generated pulse digital signal is then applied to the oscillator 110 (S702). The oscillator 110 then generates a pulse current having a frequency at the predetermined time interval based on a reference frequency preset in the comparator 113. The generated pulse current is then supplied to at least one core constituting the core unit 120, for example, a coil (e.g., first coil N1) wound around at least one DC component detection core. The DC component detection core is then magnetized by the pulse current.

[0118] Meanwhile, when the DC component detection core is magnetized by the pulse current, a test conductor is inserted into the core unit 120. In this case, the test conductor is a conductor through which a predetermined leakage current, for example, a DC leakage current, flows. Then, the control unit 100 detects the leakage current in the test conductor inserted into the core unit 120 (S704). The control unit 100 also outputs the leakage current detection result.

[0119] If a leakage current is detected in the test conductor in step S704, the control unit 100 changes the time interval at which the specific voltage is output using the frequency change unit generated in the currently determined detection frequency range. For example, if the initial frequency is 1.8 kHz, the control unit 100 outputs the specific voltage to the oscillator 110 every 1 / 3600 seconds in step S702 and applies 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 changes the period at which the specific voltage is output to the oscillator 110 to 1 / 3400 seconds and applies a pulse digital signal having a period of 1.7 kHz to the oscillator 110. Thus, the frequency of the pulse current supplied to the coil wound around the core is changed.

[0120] On the other hand, when a pulse current is supplied to the core, the magnetized core exhibits magnetic saturation characteristics like the hysteresis loop shown in Figure 7(a). That is, when a positive current is supplied, the magnetic flux density increases as the magnetizing force H increases. Conversely, when a negative current is supplied while the magnetic flux has a positive value, the magnetic flux is canceled out and the magnetic flux density decreases.

[0121] However, as shown in Figure 7(b), the core's magnetic flux density increases as the magnetizing force (H / M) increases up to a certain level, but once the increased magnetic flux density reaches the maximum magnetic flux density (Bm), it enters a magnetic saturation state and the magnetic flux density does not increase any further. Thus, the magnetizing force (H / M) at which the maximum magnetic flux density is reached varies for each core due to differences in core shape, material, physical characteristics, and coil characteristics. Therefore, the magnetizing force (H / M) at which the maximum magnetic flux density (Bm) is reached is one of the magnetic saturation characteristics of that core.

[0122] Therefore, when an alternating current with reversing polarity is supplied to a coil wound around a magnetized core, the magnetic flux in the core continues to increase until it reaches a magnetizing force H that corresponds to the magnetic saturation characteristics of the core. However, once the increasing magnetizing force causes the core to reach magnetic saturation, the magnetic flux no longer increases and remains at a predetermined magnitude, even if the magnetizing force increases.

[0123] However, as mentioned above, a fluxgate leakage current detector detects the leakage current based on a secondary current induced by magnetic flux generated by the leakage current flowing through the conductor under test. Therefore, if the core becomes saturated, the leakage current flowing through the conductor under test cannot be detected unless the magnetic flux in the core changes. Therefore, as mentioned above, a fluxgate leakage current detector supplies a pulse current whose polarity reverses periodically to the coil, reversing the polarity of the magnetized core at predetermined intervals to generate magnetic flux in the opposite direction and canceling the magnetic flux in the core.

[0124] 7(a), when a positive current is supplied, the magnetizing force H gradually increases depending on the time the positive current is supplied. Furthermore, when the polarity of the current supplied to the coil is reversed, a negative magnetic flux is generated, canceling out the positive magnetic flux. In this case, the maximum magnetic flux density value of the positive current supplied to the coil is +Bm, and the magnetizing force that forms the maximum magnetic flux density value +Bm due to the positive current of the pulse current is the maximum magnetization point +Hm due to the positive current.

[0125] Meanwhile, when the polarity of the pulse current is reversed, the magnetic flux in the core gradually decreases, reaching points b and c. Furthermore, the magnetizing force H gradually decreases over time as the negative current is supplied, resulting in a negative magnetizing force. Furthermore, when the polarity of the current supplied to the coil is reversed again, a positive magnetic flux is generated, canceling out the negative magnetic flux. In this case, the minimum magnetic flux density due to the negative current supplied to the coil is -Bm, and the magnetizing force that forms the maximum magnetic flux density value -Bm due to the negative pulse current is the maximum magnetization point -Hm due 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 in the core travels from point a to point d via points b and c, then travels through points e and f, and then returns to point a.

[0126] Meanwhile, as mentioned above, a fluxgate-type leakage current detector detects leakage current according to changes in magnetic flux. Furthermore, since magnetic flux changes according to the magnetization state of the core, the higher the core's magnetization, the more accurate leakage current measurement is possible. In this case, the core's magnetization is determined by the magnetizing force. As shown in Figure 7(a), the smaller the maximum magnetizing force +Hm, -Hm, the smaller the change in magnetic flux (between points b and e). Therefore, the amount of change in magnetic flux is limited, thereby limiting the accuracy of the leakage current detector. On the other hand, the larger the maximum magnetizing force +Hm, -Hm, the larger the change in magnetic flux (between points b and e), resulting in a larger change in magnetic flux. Therefore, the greater the magnetizing force, the more accurate the leakage current detector.

[0127] However, as shown in Figure 7(b) above, the core has a limit to the increase in magnetic flux as the magnetizing force increases, and the state in which the magnetic flux increases to its limit and the magnetic flux density saturates is called the maximum magnetic flux density. Furthermore, if the magnetizing force exceeds the magnetization point corresponding to the maximum magnetic flux density, the magnetic flux saturates and does not change, making leakage current detection impossible. Therefore, the closer the maximum magnetic flux density of the core is to the magnetization points forming the maximum magnetic flux density values ​​+Bm and -Bm in Figure 7(a), the more the efficiency and accuracy of the fluxgate leakage current detector improves. In other words, the current that generates a magnetizing force that magnetizes the core so that the core's magnetic flux does not exceed the maximum magnetic flux density and is as close as possible to the maximum magnetic flux density is the current that is optimized for and matches the magnetic saturation characteristics of the core.

[0128] However, the coil to which the pulse current is supplied is wound around a core, and if the current supplied to the coil has AC characteristics in which the polarity is periodically reversed, the flow of the current supplied to the coil is restricted by the inductive reactance of the coil as shown in Equation 1.

[0129]

number

[0130] where I is the current through the coil and X L 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 Equation 1, V is the voltage of the pulse current, f is the frequency of the pulse current, and L is the inductance of the coil, which is a value determined by core information, such as a value included in the coil information, or the type of core. In other words, it is a predetermined value.

[0133] Therefore, as shown in Equation 1, the amount of current flowing through the coil wound around the core is determined by the frequency of the supplied pulse current. Also, since the magnetizing force H of the core is directly proportional to the current I flowing through the coil, the magnetizing force of the core is determined by the frequency of the pulse current supplied to the coil. In other words, the lower the frequency of the pulse current, the greater the magnetizing force H of the core, and the greater the magnetic flux. Conversely, the higher the frequency of the pulse current, the smaller the magnetizing force H of the core, and the less the magnetic flux.

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

[0135] On the other hand, as mentioned above, if the core is not magnetically saturated, when the current flowing through the coil increases due to a decrease in the frequency of the pulse current, the magnetization of the core increases. Therefore, even if the leakage current flowing through the conductor under test remains the same, the increased magnetic flux increases the magnetic flux density. On the other hand, if the magnetization of the core forms a maximum magnetic flux density according to the frequency of the pulse current, that is, if the core becomes magnetically saturated according to the changed frequency of the pulse current, the magnetic flux density is already at its maximum saturation state, making it difficult to detect the leakage current flowing through the conductor under test.

[0136] Therefore, when the frequency of the pulse current is changed, if the core does not become magnetically saturated at the changed pulse current frequency, even if the same leakage current flows through the test conductor, the leakage current in the test conductor will be detected correctly, or a different result will be detected from the leakage current detection result detected at the previous pulse current frequency. On the other hand, when the frequency of the pulse current is changed, if the core becomes magnetically saturated at the changed pulse current frequency, even if the same leakage current flows through the test conductor, the leakage current in the test conductor will not be detected correctly, or the same leakage current detection result will be output regardless of the leakage current detection result detected at the previous pulse current frequency or the change in frequency. In other words, when the frequency of the pulse current is changed, whether the core has become magnetically saturated according to the frequency of the currently supplied pulse current is detected based on the change in the leakage current detection result of the control unit 100 in the test conductor.

[0137] Alternatively, the control unit 100 detects a voltage signal containing a pulse current component and a DC component leakage current from the secondary current induced in the DC component detection core, and determines whether the DC component detection core is in a magnetically saturated state based on whether the detected voltage signal generates a rectangular wave.

[0138] For example, if the core is not saturated, i.e., if the core is in a normal state, the detected voltage signal will be wavy. However, if the core is in a magnetic saturation state, leakage current detection is not performed, and the voltage signal will generate a square wave in accordance with the form of a pulse current. Therefore, the control unit 100 determines 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 detects whether the detected voltage signal is a square wave based on the change in voltage detected when the polarity is switched. For example, if the voltage signal is a square wave, the voltage signal will not change by more than a predetermined level in a predetermined time when the polarity is switched. In contrast, if the core is not saturated, the polarity will be switched and then a voltage change of more than a predetermined level will occur in a predetermined time. In this way, the control unit 100 determines whether the DC component detection core is saturated based on whether a voltage change of more than a predetermined level occurs in a predetermined time when the polarity is switched.

[0140] Therefore, when the frequency of the pulse current is changed by the frequency change unit in step S706, the control unit 100 checks whether the core to which the pulse current is supplied has reached a magnetic saturation state based on the leakage current detection result of the test conductor (S708).

[0141] Furthermore, if the check in step S708 determines that the core has reached magnetic saturation, the control unit 100 determines the frequency before the currently changed pulse current frequency as the frequency at which the core can maintain the maximum magnetic flux without reaching magnetic saturation.

[0142] That is, the frequency of the pulse current that matches the magnetic saturation characteristics of the core is determined. The determined pulse current frequency is then stored (S710). After the frequency of the pulse current that matches the magnetic saturation characteristics of the core is determined, the test conductor is removed from the core portion 120.

[0143] On the other hand, when the frequency of the pulse current that matches the characteristics of the core is detected, the control unit 100 supplies the pulse current at the determined frequency to the coil wound around the core (S712). Thus, the control unit 100 detects the DC component leakage current flowing through the conductor under test inserted into the core unit 120 based on the frequency of the pulse current that matches the magnetic saturation characteristics of the DC component detection core.

[0144] Here, the core unit 120 has a triple-core structure. In this case, the DC component detection core is composed of two physically identical cores. Meanwhile, according to the operation process of Figure 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 is detected so that the core has a maximum magnetic flux without magnetic saturation, i.e., so that the magnetizing force that maximizes the area of ​​the hysteresis loop shown in Figure 7(a) is formed.

[0145] Therefore, even if the core portion 120 is configured with a triple core structure, the present invention can supply a pulse current having a frequency optimized according to the magnetic saturation characteristics of the core that detects the DC component leakage current to the core that detects the DC component leakage current.

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

[0147] As shown in Figure 8, when a pulse current having an optimized frequency that matches the magnetic saturation characteristics of a core (e.g., a DC component detection core) is supplied to magnetize the core, the control unit 100 detects a voltage signal corresponding to a DC component leakage current based on a secondary current induced in the magnetized core and an intermediate resistance (S800). In this case, the secondary current is induced in the magnetized core by the pulse current, and the voltage signal includes not only a DC component leakage current component but also the supplied pulse current component. The detected voltage signal is received by the control unit 100.

[0148] To receive the voltage signal, the control unit 100 amplifies the voltage signal to a level that can be recognized by the control unit 100 using an amplifier 101 provided in the control unit 100. In addition, the control unit 100 may remove noise from the voltage signal using a low-pass filter before the amplification. The amplified voltage signal is then converted into a digital signal using an ADC.

[0149] Meanwhile, the control unit 100 removes pulse current components contained in the voltage signal by filtering (S802). To do so, the control unit 100 removes AC components having a frequency from the voltage signal by using a filter (for example, the filter unit 103). In this case, the pulse current has the characteristics of AC current in which the polarity switches periodically, and is therefore removed by the filtering.

[0150] Then, the voltage signal contains only the pure DC leakage current component detected from the conductor under test. The control unit 100 then determines a compensation current corresponding to the DC leakage current component. The control unit 100 then supplies the determined compensation current to the third coil N3, which supplies the core (S804). In this case, the compensation current is a DC current having the same magnitude and opposite polarity as the DC leakage current.

[0151] Here, the compensation current is a minute level current that is difficult for the control unit 100 to output. For example, it is a minute level current that cannot be recognized by the control unit 100. In this case, the control unit 100 controls the attenuation unit 102 to supply the minute level compensation current, and supplies the compensation current attenuated to the minute level by the attenuation unit 102 to the third coil N3.

[0152] Meanwhile, the DC current compensation in step S804 cancels out the magnetic flux due to the DC component leakage current of the conductor under test. Then, the control unit 100 receives, via an intermediate resistor, a voltage signal corresponding to the secondary current induced in the coil wound around the AC component detection core. The voltage signal is then subjected to noise removal by a low-pass filter and amplified to a level recognizable by the control unit 100. The voltage signal is then converted into a digital signal by the ADC of the control unit 100, and the AC component leakage current is detected based on the digital voltage signal (S806).

[0153] Then, the control unit 100 adds the magnitude of the DC component leakage current and the AC component leakage current to detect the total leakage current of the conductor under test, and determines whether the total leakage current is equal to or greater than a predetermined operating current (S810).

[0154] If the result of the determination in step S810 is that the calculated total leakage current is less than the predetermined operating current, the control unit 100 proceeds to step S800 again to perform the process of detecting the DC component leakage current from the DC component core, and then repeats the subsequent processes to detect the total leakage current detected from the conductor under test.

[0155] However, if the result of the determination in step S810 is that the calculated total leakage current is equal to or greater than the predetermined operating current, the control unit 100 starts a process related to the occurrence of leakage current (S812).

[0156] In step S812, when a leakage current equal to or greater than the operating current is detected, the control unit 100 outputs a control signal, such as a trip signal, to control the circuit breaker. Alternatively, the control unit 100 outputs notification information to notify at least one other system or device related to the leakage current of the occurrence of the leakage current. In this case, the other system or device determines whether to activate the circuit breaker.

[0157] On the other hand, in the leakage current detection device according to the embodiment of the present invention, if an external magnetic field is generated due to an unexpected overcurrent or the like, the core will be magnetically saturated due to the influence of the external magnetic field.

[0158] Therefore, the control unit 100 of the leakage current detection device according to the embodiment of the present invention may demagnetize the core that has reached the magnetic saturation state by resetting.

[0159] Fig. 9 is a flowchart showing the operation process of initializing the core in accordance with the magnetic saturation state of the core in the leakage current detection device according to the first embodiment of the present invention, and Fig. 10 is a diagram showing an example of the output waveform of the DC component detection core in accordance with the state of the core in the leakage current detection device according to the embodiment of the present invention.

[0160] 9, when step S800 of FIG. 8 for detecting a DC component leakage current is performed, the control unit 100 detects a voltage signal including a pulse current component and a DC component leakage current from the secondary current induced in the DC component detection core by the intermediate resistor (S900), and determines whether the detected voltage signal generates a square wave (S902).

[0161] For example, if the core is not saturated, i.e., if the core is in a normal state, the detected voltage signal will be wavy as shown in Figure 10(a). However, if the core is in a magnetically saturated state, leakage current detection is not performed, and the voltage signal will generate a square wave in accordance with the form of a pulse current. Therefore, the control unit 100 determines whether the DC component detection core is in a magnetically saturated state based on whether the voltage signal generates a square wave.

[0162] In this case, the control unit 100 detects a change in voltage detected when the polarity is switched from the detected voltage signal. For example, as shown in (b) of Fig. 10, if the voltage signal is a square wave, no voltage change of a predetermined level or more occurs in the voltage signal when the polarity is switched.

[0163] On the other hand, if the core is not saturated, the polarity switches, and a voltage change of a predetermined level or more occurs within a predetermined time period, as shown in (a) of Figure 10. In this way, when the polarity switches, the control unit 100 determines in step S902 whether the DC component detection core is saturated, depending on whether a voltage change of a predetermined level or more occurs within a predetermined time period.

[0164] On the other hand, if the result of the determination in step S902 is that the DC component detection core is not magnetically saturated, the control unit 100 proceeds to step S802 and subsequent steps in FIG. 8 to continue the process of detecting leakage current in the conductor under measurement.

[0165] However, if the result of the determination in step S902 is that the DC component detection core is in a magnetically saturated state, the control unit 100 initializes the core and demagnetizes the magnetically saturated core (S904).

[0166] In step S904, the control unit 100 amplifies the compensation current to a predetermined magnitude and supplies it to the third coil N3 to which the compensation current is supplied. In this case, the DC component detection core is not magnetized beyond the maximum magnetic flux density state due to the magnetic saturation characteristics of the core. Therefore, the predetermined magnitude corresponds to a current that generates a magnetizing force that causes the DC component detection core to reach the magnetic saturation state (for example, the magnitude of a current that generates a magnetizing force of +Hm when the maximum magnetic flux density is +BM in FIG. 7(a)). Then, the amplified compensation current, i.e., the reverse current, reduces the magnetic flux, and the DC component detection core is demagnetized.

[0167] Meanwhile, when the core initialization is performed by the core demagnetization, the control unit 100 proceeds to step S712 of Fig. 7 and supplies a pulse current having a frequency corresponding to the current magnetic saturation characteristics of the core, which has been stored in advance, to the coil wound around the DC component detection core. Then, according to the operation process shown in Fig. 8, the initialized core is re-magnetized by a pulse current having a frequency corresponding to the magnetic saturation characteristics of the magnet, and the leakage current of the conductor under measurement is detected.

[0168] On the other hand, in the above explanation, a configuration has been described in which a compensation current is supplied or a leakage current is detected by the core unit 120. However, it is obvious in the technical field to which the present invention pertains that the number of windings of the coil wound around each core, etc., is reflected in the supply of the compensation current and the detection of the leakage current.

[0169] Furthermore, according to the explanation of FIG. 7 above, before detecting the leakage current from the conductor under test, the present invention changes the frequency of the pulse digital signal and detects the frequency of the pulse current that matches the magnetic saturation characteristics of the core.

[0170] Furthermore, as described above, by changing the time interval at which the control unit 100 outputs the specific voltage and changing the frequency of the pulse digital signal, the frequency of the pulse current supplied to the coil wound around the DC component detection core can be changed without changing circuit elements such as resistors and capacitors. Therefore, when the core of the leakage current detection device is replaced for maintenance or a change in application, the replaced core can be magnetized by a pulse current of a frequency that matches the magnetic saturation characteristics of the replaced core without changing the internal configuration of the circuit.

[0171] The present invention described above can be realized as computer-readable code on a program recording medium. Computer-readable media include any type of storage device that stores data readable by a computer system. 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, and the like, as well as media implemented in the form of carrier waves (e.g., transmissions over the Internet). Therefore, the above detailed description should not be construed as limiting in any respect, but should be considered as illustrative. The scope of the present invention should be determined by reasonable interpretation of the claims, and all modifications within the scope of the equivalents of the present invention are encompassed in the present invention.

Claims

1. an oscillator for generating a pulse current having a predetermined frequency; a core unit that supplies at least one first core wound with at least one first coil having one end connected to the oscillator unit and magnetized by the pulse current, a second core wound with a second coil having one end grounded, and a third coil wound around the first core and the second core and supplied with a compensation current; a control unit that determines a frequency of the pulse current according to at least one of the characteristics of the at least one first core, detects a DC component leakage current of the conductor to be measured by filtering a component having a frequency from a voltage signal of a current induced in the at least one first core, and supplies a reverse current corresponding to the detected DC component leakage current to the third coil as the compensation current. Leakage current detection device.

2. The at least one first core is characterized by: The information is at least one of the shape and thickness of the core, the diameter and material of the core, the diameter of the hollow inside of the core, the material and number of windings of the coil wound around the core, the winding interval of the coil, the manufacturer and serial number of the core, and the type of conductor to be measured. The earth leakage current detection device according to claim 1 .

3. a memory storing a plurality of detection frequencies corresponding to various characteristics of the at least one first core; The control unit determining one of the plurality of detection frequencies as the frequency of the pulse current based on the characteristics of the at least one first core; The leakage current detection device according to claim 2.

4. The control unit When a DC component leakage current of the conductor under measurement is detected at any one of the plurality of detection frequencies, the frequency of the pulse current is changed to another detection frequency of the plurality of detection frequencies, and the DC component leakage current of the conductor under measurement is detected again at the changed frequency of the pulse current; The method is characterized in that it determines whether or not the at least one first core is magnetically saturated, and detects a frequency of a pulse current according to the magnetic saturation characteristic of the at least one first core. The leakage current detection device according to claim 3.

5. The control unit and determining 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.

5. The earth leakage current detection device according to claim 4.

6. The control unit When the polarity of the voltage signal detected from the at least one first core is switched, it is determined whether or not the voltage signal detected from the at least one first core generates a square wave depending on whether or not there is a voltage change of a predetermined level or more in a predetermined time. The leakage current detection device according to claim 5.

7. The control unit when a magnetic saturation frequency of a pulse current that magnetically saturates the at least one first core is detected, a frequency of a pulse current that does not magnetically saturate the at least one first core and that is close to the magnetic saturation frequency is determined as a pulse current frequency according to the magnetic saturation characteristics of the at least one first core.

5. The earth leakage current detection device according to claim 4.

8. The conductor to be measured is A test conductor through which a predetermined magnitude of DC component leakage current and AC component leakage current flows.

5. The earth leakage current detection device according to claim 4.

9. The oscillation unit is receiving an input of a pulse digital signal in which a state in which a specific voltage is output and a state in which no voltage is output are repeated in a predetermined time period, and generating the pulse current in which a positive current and a negative current alternate in the predetermined time period in synchronization with the pulse digital signal; The control unit a pulse digital signal that is repeated at the predetermined time period based on a frequency of a pulse current determined according to the characteristics of the at least one first core is applied to the oscillator. The earth leakage current detection device according to claim 1 .

10. The oscillation unit is a comparator to which a predetermined reference voltage is set; The comparator When a pulse digital signal having a voltage higher than the reference voltage is input, a current having a positive voltage of a predetermined magnitude 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 predetermined magnitude is output. The earth leakage current detection device according to claim 9.

11. the reference voltage has a magnitude half that of the specific voltage; The positive voltage and the negative voltage of the predetermined magnitude are A positive voltage and a negative voltage corresponding to the reference voltage, The leakage current detection device according to claim 10.

12. an oscillator for generating a pulse current having a predetermined frequency; a core unit that supplies at least one first core wound with at least one first coil having one end connected to the oscillator unit and magnetized by the pulse current, a second core wound with a second coil having one end grounded, and a third coil wound around the first core and the second core and supplied with 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 configured to add a voltage signal detected from the first core and a voltage signal detected from the second core; an amplifier that inverts and amplifies a voltage signal corresponding to the voltage signal addition result of the leakage current detector to generate a compensation current to be supplied to the third coil; and a control unit that determines a frequency of the pulse current in accordance with at least one of the characteristics of the at least one first core, and detects a DC component leakage current flowing in the conductor to be measured based on the compensation current. Leakage current detection device.

13. The leakage current detection unit 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 together a voltage signal corresponding to a DC component leakage current of the conductor under test and a voltage signal corresponding to an AC component leakage current; The differential amplifier an output terminal is connected to the non-inverting input terminal via a resistor and a capacitor that function as a noise filter, and the output of the differential amplifier is fed back to the non-inverting input terminal; The earth leakage current detection device according to claim 12.

14. The amplifier unit an operational amplifier having a first input connected to ground and a second input connected to the output of the differential amplifier via a first resistor of a predetermined magnitude; The output terminal of the operational amplifier is a second resistor having a predetermined magnitude connected to the second input terminal and a non-inverting input terminal of the differential amplifier, so that the output of the operational amplifier is fed back to the differential amplifier; The earth leakage current detection device according to claim 13.

15. The at least one first core a first-1 core around which a first-1 coil to which the pulse current is supplied is wound; an inverting amplifier that inverts the polarity of the pulse current; a first-second core around which a first-second coil is wound, to which a pulse current of inverted polarity is supplied by the inverting amplifier; and a summing amplifier for combining voltage signals corresponding to the secondary currents induced in the first coil and the second coil, The earth leakage current detection device according to claim 12.

16. a memory storing a plurality of detection frequencies corresponding to various characteristics of the at least one first core; The control unit determining one of the plurality of detection frequencies as the frequency of the pulse current based on the characteristics of the at least one first core; The earth leakage current detection device according to claim 12.

17. The control unit When a DC component leakage current of the conductor under measurement is detected at any one of the plurality of detection frequencies, the frequency of the pulse current is changed to another detection frequency of the plurality of detection frequencies, and the DC component leakage current of the conductor under measurement is detected again at the changed frequency of the pulse current; The method is characterized in that it determines whether or not the at least one first core is magnetically saturated, and detects a frequency of a pulse current according to the magnetic saturation characteristic of the at least one first core.

17. The earth leakage current detection device according to claim 16.

18. The control unit when a magnetic saturation frequency of a pulse current that magnetically saturates the at least one first core is detected, a frequency of a pulse current that does not magnetically saturate the at least one first core and that is close to the magnetic saturation frequency is determined as a pulse current frequency according to the magnetic saturation characteristics of the at least one first core.

18. The earth leakage current detection device according to claim 17.

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