Leakage sensor and circuit protection system

Abstract

A leakage sensor for suppressing false detection of leakage in the case of positive-negative asymmetry of an excitation magnetic field. An unbalance determination circuit (15) determines the positive-negative asymmetry of the excitation magnetic field in the state in which a balancing current flows through a measured current line (30) on the basis of the excitation magnetic field and the excitation signal acquired from a magnetic sensor (14) in the state in which the balancing current flows through the measured current line (30), generates a control signal, and an excitation circuit (16) reduces the amplitude of either the positive or the negative of the excitation current to less than the original size or superimposes an offset current of either the positive or the negative on the excitation current on the basis of the control signal.

Description

Technical Field

[0001] This application relates to leakage current sensors and circuit protection systems. Background Technology

[0002] Fluxgate sensors are known as microcurrent sensors that can operate on both AC and DC current. In a fluxgate sensor, a coil is used to AC excite a magnetic core. The current value of the measured magnetic field, i.e., the object being measured, is measured by the difference between the time it takes for the magnetic core to become magnetically saturated and not output to the detection coil, and the time it takes for the magnetic core to become unsaturated and output to the detection coil. In leakage current sensors using fluxgate sensors, high-speed response is ensured by setting the AC excitation frequency to hundreds of Hz or higher (see, for example, Patent Document 1). Existing technical documents Patent documents

[0003] Patent Document 1: Japanese Patent Utility Model No. 59-92532 Summary of the Invention The technical problem that the invention aims to solve

[0004] The current measured by a leakage current sensor using a fluxgate sensor is a balanced two-phase or three-phase current. Therefore, the current-measuring lines passing through the core of the leakage current sensor are two or three. Thus, it is necessary to ensure that the inner diameter of the leakage current sensor core is, for example, more than twice the diameter of the current-measuring lines. Furthermore, when the rated current of the current-measuring lines is large, the diameter of the current-measuring lines needs to be increased, requiring an increase in the inner diameter of the core. If the inner diameter of the core is increased, the cross-sectional area of ​​the core needs to be increased to ensure the mechanical strength of the core; as a result, the core volume increases, making the core larger.

[0005] To achieve full magnetic saturation of a large-scale magnetic core, a large excitation current is required, necessitating a power supply capable of outputting high current. However, when implementing a leakage current sensor within a limited size, the size of the built-in power supply is constrained, and the excitation current sometimes becomes unstable when outputting large currents. Furthermore, when high current and high frequency are required for the excitation current, the current becomes even more unstable, and the excitation magnetic field sometimes exhibits asymmetry. In leakage current sensors using fluxgate sensors, if the excitation magnetic field is asymmetrical, the saturation time of the detection coil output differs in each magnetic field, leading to the problem of falsely detecting leakage even when no leakage has occurred.

[0006] This application was made to solve the above-mentioned problems, and its purpose is to provide a leakage current sensor and circuit protection system that can suppress false detection of leakage current when the excitation current is required to be large current and high frequency and the excitation magnetic field is asymmetrical. Technical means for solving technical problems

[0007] The leakage current sensor disclosed in this application is a leakage current sensor for detecting leakage current in a measured current line, comprising: a magnetic core through which the measured current line passes; an excitation coil wound on the magnetic core; a detection coil wound on the magnetic core; a magnetic sensor for detecting the excitation magnetic field generated by the excitation coil; an oscillation circuit for generating an excitation signal with the excitation frequency as its fundamental frequency; an imbalance determination circuit for generating and outputting a control signal based on the output of the magnetic sensor and the output of the oscillation circuit; an excitation circuit for applying an excitation current to the excitation coil based on the output of the oscillation circuit and the output of the imbalance determination circuit; and a filtering circuit for extracting a component of twice the excitation frequency from the output voltage of the detection coil. The output circuit of the amplification and filtering circuit, when the imbalance judgment circuit detects leakage current, does not determine the asymmetry of the positive and negative excitation magnetic field. Instead, it determines the asymmetry of the positive and negative excitation magnetic field when the balanced current flows through the measured current line based on the excitation magnetic field and excitation signal obtained from the magnetic sensor. It then generates a control signal. The excitation circuit generates the control signal based on the determination of the asymmetry of the positive and negative excitation magnetic field when the balanced current flows through the measured current line. This control signal makes the amplitude of either the positive or negative excitation current smaller than its original value, or adds a positive or negative offset current to the excitation current. Invention Effects

[0008] In the leakage current sensor disclosed in this application, when the imbalance determination circuit detects leakage current, it does not determine the asymmetry of the positive and negative excitation magnetic field. Instead, it determines the asymmetry of the positive and negative excitation magnetic field when the balanced current flows through the measured current line based on the excitation magnetic field and excitation signal obtained from the magnetic sensor. It then generates a control signal. The excitation circuit generates the control signal based on the determination of the asymmetry of the positive and negative excitation magnetic field when the balanced current flows through the measured current line. This makes the amplitude of either the positive or negative excitation current smaller than its original value, or adds a bias current of either the positive or negative value to the excitation current. Therefore, when the excitation current requires a large current and high frequency, resulting in asymmetry of the positive and negative excitation magnetic field, it can suppress false detection of leakage current. Attached Figure Description

[0009] Figure 1 This is a diagram showing the structure of the leakage detection unit of the leakage sensor according to Embodiment 1. Figure 2 This is a diagram illustrating the output voltage of the detection coil when no leakage occurs. Figure 3 This is a diagram illustrating the output voltage of the detection coil when a leakage current occurs. Figure 4This diagram illustrates the first instance of asymmetry between the positive and negative excitation magnetic fields when no leakage occurs. Figure 5 This diagram illustrates a second example of asymmetric excitation magnetic field under conditions where leakage current has not occurred. Figure 6 This is a diagram showing the structure of the leakage current sensor and circuit protection system involved in Embodiment 1. Figure 7 This is a flowchart illustrating the operation of the imbalance determination circuit in Implementation Method 1. Figure 8 This is a graph showing the result of performing a fast Fourier transform on the output signal of the magnetic sensor. Figure 9 This is a graph showing the result of performing a fast Fourier transform on the output signal of the magnetic sensor. Figure 10 This is a diagram showing the configuration of the magnetic sensor of the leakage current sensor according to Embodiment 1. Figure 11 This is a diagram showing the configuration of the magnetic sensor of the leakage current sensor according to Embodiment 1. Figure 12 This is a diagram showing the configuration of the magnetic sensor of the leakage current sensor according to Embodiment 1. Figure 13 This is a diagram showing the structure of the leakage current sensor and circuit protection system involved in Embodiment 2. Figure 14 This is a flowchart illustrating the operation of the imbalance determination circuit in Implementation Method 2. Figure 15 This is a schematic diagram illustrating an example of the hardware of the imbalance determination circuit in Embodiment 1 and Embodiment 2. Detailed Implementation

[0010] Hereinafter, the leakage current sensor and circuit protection system according to the embodiments used in implementing this application will be described in detail with reference to the accompanying drawings. The same reference numerals in the figures indicate the same or equivalent parts.

[0011] Implementation method 1. Figure 1 This diagram illustrates the structure of the leakage detection unit 10 of the leakage current sensor according to Embodiment 1. The leakage detection unit 10 is a fluxgate sensor, including a circular magnetic core 11, an excitation coil 12 wound around the magnetic core 11, and a detection coil 13 wound around the magnetic core 11. Current measurement is performed by passing the measured current line through the magnetic core 11. Figure 1 In this configuration, the windings of the excitation coil 12 and the detection coil 13 are wound only on a portion of the magnetic core 11, but they can also be wound on the entire circumference of the magnetic core 11 respectively.

[0012] use Figure 2 and Figure 3 Explain the operating principle of the fluxgate sensor. Figure 2 This is a diagram illustrating the output voltage of the detection coil 13 under the condition that the balanced current flows through the measured current line, i.e., under the condition that no leakage occurs. Figure 2 The upper left figure shows the magnetization curve of the magnetic core, that is, the BH curve showing the change in magnetic flux density relative to the applied magnetic field. By energizing the excitation coil 12 with a sinusoidal excitation current, a magnetic flux density is applied to the magnetic core 11... Figure 2 The excitation magnetic field is shown in the lower left figure. Because the magnetic core 11 has, for example... Figure 2 The magnetic properties shown in the upper left figure, therefore, as Figure 2 As shown in the upper right figure, the linkage flux of the magnetic core 11, i.e., the core linkage flux, undergoes periodic geomagnetic saturation. In the detection coil 13, a flux linkage flux of the magnetic core 11 induces a magnetic flux resembling... Figure 2 The detection coil induced voltage is shown in the lower right figure. In the detection coil 13, a voltage is generated during the period when the magnetic core 11 is not magnetically saturated, and no voltage is generated during the period when the magnetic core 11 is magnetically saturated. Since the magnetization curve of the magnetic body is the origin object, the state of no voltage being generated on the detection coil 13 is repeated at twice the period of the excitation magnetic field when no leakage occurs.

[0013] Figure 3 This is a diagram illustrating the output voltage of the detection coil 13 when leakage occurs on the measured current line. Figure 3 In the various diagrams, dashed lines represent values ​​indicating no leakage, while solid lines represent values ​​indicating leakage. Figure 3 In the lower left diagram, a magnetic field caused by leakage current is superimposed on the excitation magnetic field due to the leakage current. Figure 3 In the upper right diagram, the difference in magnetic field saturation time between the positive and negative sides is caused by leakage current. As a result, in... Figure 3 In the lower right diagram, there is a difference between the time during which voltage is generated and the time during which no voltage is generated. The period of the time difference is twice the excitation frequency, and the time difference is proportional to the leakage current value.

[0014] When a magnetic sensor for detecting the excitation magnetic field generated by the excitation coil 12 is installed on the leakage current detection unit 10, the magnetic sensor detects the excitation magnetic field rather than the linkage flux of the magnetic core 11. Therefore, the output of the magnetic sensor is independent of the presence or absence of leakage current or the magnetic characteristics of the magnetic core 11, becoming... Figure 2 The waveform shown in the lower left figure.

[0015] Next, the situation where the excitation current supplied to the excitation coil 12 is required to be large and high frequency, and the excitation magnetic field is asymmetrical, is explained, under the condition that the balanced current flows through the measured current line, that is, under the condition that there is no leakage current in the measured current line. Figure 4 This diagram illustrates the first instance of asymmetric excitation magnetic field polarity in the absence of leakage current. Figure 4 In the various diagrams, dashed lines represent the values ​​when the excitation magnetic field is symmetrical, and solid lines represent the values ​​when the excitation magnetic field is asymmetrical. Figure 4 The lower left figure shows an example where the negative magnetic field of the excitation field is smaller than the positive magnetic field. Figure 4 In the upper right figure, the time for the core linkage flux to saturate on the negative side is shorter than the time it takes for the core linkage flux to saturate on the positive side. As a result, in Figure 4 In the lower right figure, the time during which no voltage is generated in the detection coil 13 varies. Since leakage current is detected by measuring the difference between the time when voltage is generated and the time when no voltage is generated in the detection coil 13, leakage current is still considered to have occurred even though no leakage current has occurred. That is, the asymmetry of the excitation magnetic field leads to the measurement error of leakage current.

[0016] Figure 5 This diagram illustrates a second example of asymmetric excitation magnetic field under conditions where a balanced current flows through the measured current line, i.e., without leakage. In Figure 5 In the various diagrams, dashed lines represent the values ​​when the excitation magnetic field is symmetrical, and solid lines represent the values ​​when the excitation magnetic field is asymmetrical. Figure 5 The lower left figure shows an example of a positive offset superimposed on the excitation magnetic field, leading to saturation of the positive excitation magnetic field. This is, for example, a case where the positive excitation magnetic field is limited by the rated maximum value of the excitation power supply. In this case, Figure 5 The core linkage flux shown in the upper right figure is... Figure 3 The same as shown in the upper right image. Figure 5 The detection coil induced voltage shown in the lower right figure is related to... Figure 3 The result is the same as shown in the lower right figure. Therefore, it was determined that leakage current had occurred.

[0017] Figure 6This diagram illustrates the structure of the leakage current sensor 1 and the circuit protection system according to Embodiment 1. The leakage current sensor 1 includes a magnetic core 11, an excitation coil 12, a detection coil 13, a magnetic sensor 14, an imbalance determination circuit 15, an excitation circuit 16, an oscillation circuit 17, a filter circuit 18, and an output circuit 19. The current being measured by the leakage current sensor 1, i.e., the current being measured, is traversed by the magnetic core 11 via the current-measuring line 30. The oscillation circuit 17 generates an excitation signal with the excitation frequency as its fundamental frequency and outputs it to the excitation circuit 16 and the imbalance determination circuit 15. The filter circuit 18 obtains the excitation signal from the oscillation circuit 17, extracts the component with twice the excitation frequency (i.e., the second harmonic component) from the output voltage of the detection coil 13, and outputs it. The output of the filter circuit 18, i.e., the second harmonic component, corresponds to the difference between the time when the detection coil 13 generates voltage and the time when it does not generate voltage. The output circuit 19 amplifies the output of the filter circuit 18 by a factor set according to the sensor specifications and outputs it. Here, the factor set according to the sensor specifications is the sensor output per unit current, which corresponds to the sensor sensitivity.

[0018] The circuit protection system described in Embodiment 1 includes a leakage current sensor 1, a relay unit 20, and a protection circuit 21. The relay unit 20 monitors the output of the output circuit 19 of the leakage current sensor 1 to determine whether leakage current exists. If leakage current is detected, it controls the protection circuit 21, such as a circuit breaker or switch, to disconnect the measured current line 30, protecting the load device connected to the measured current line 30 from the effects of the circuit malfunction. For example, the relay unit 20 determines that leakage current has occurred when the output of the output circuit 19 exceeds a predetermined threshold.

[0019] The magnetic sensor 14 detects the excitation magnetic field generated by the excitation coil 12. The magnetic sensor can be, for example, a device fabricated using semiconductor technology such as a Hall element, a magnetoresistive element, or a magnetoresistive element, or it can be a coil capable of detecting alternating magnetic fields. One factor affecting the excitation magnetic field is the uniformity of the windings in the excitation coil. In the leakage current sensor 1 where the measured current line 30 passes through the magnetic core 11, the excitation coil 12 is called a toroidal coil, which is a coil wound towards the inner or outer side of a circular core. If the windings are wound uniformly, the magnetic flux generated by the excitation current is confined within the coil, thus the excitation magnetic field is proportional to the excitation current flowing through the excitation coil 12, and the excitation magnetic field is uniformly applied to the magnetic core 11. However, if the windings are uneven, resulting in localized gaps in the winding spacing, the magnetic flux leaks out of the coil in the sparse areas, causing the excitation current and excitation magnetic field to be disproportionate, or the excitation magnetic field to be locally uneven in magnitude. Generally, it is difficult to ensure the uniformity of the windings in a toroidal coil, and winding non-uniformity is unavoidable. Therefore, in the leakage current sensor 1, the excitation magnetic field is not predicted based on the excitation current, but is detected by the magnetic sensor 14.

[0020] The imbalance determination circuit 15 determines the asymmetry of the excitation magnetic field when the balanced current flows through the measured current line 30 based on the excitation magnetic field acquired from the magnetic sensor 14 and the excitation signal from the oscillation circuit 17. It then generates a control signal and outputs it to the excitation circuit 16. Based on the output of the imbalance determination circuit 15, the excitation circuit 16 either reduces the amplitude of the signal on either side of the excitation current to less than its original value, or shifts the excitation current in either direction. Thus, the excitation magnetic field becomes symmetrical.

[0021] Next, the operation of the imbalance detection circuit 15 will be explained. When a balanced current flows through the measured current line 30, i.e., when the measured current line 30 is energized with its rated current without leakage, the imbalance detection circuit 15 acquires information about the excitation magnetic field generated by the excitation coil 12 from the magnetic sensor 14 and acquires an excitation signal from the oscillation circuit 17. The excitation magnetic field generated in the excitation coil 12 becomes the differential value of the excitation current generated by the excitation signal; therefore, the excitation signal and the excitation magnetic field have a phase difference of approximately 90 degrees. Thus, in the imbalance detection circuit 15, the excitation magnetic field signal is synchronously detected using a signal that causes a 90-degree phase shift in the excitation signal, thereby determining the positive and negative asymmetry of the excitation magnetic field waveform. The frequency of the excitation magnetic field is uniquely determined by the excitation circuit 16; therefore, in the imbalance detection circuit 15, Fourier transforms or similar methods can be performed on the output of the magnetic sensor 14 to determine waveform distortion based on the intensity of harmonics other than the fundamental frequency, thereby determining the positive and negative asymmetry of the excitation magnetic field waveform. When the imbalance judgment circuit 15 detects leakage current in the leakage current sensor 1, it does not determine the positive or negative asymmetry of the waveform of the excitation magnetic field.

[0022] When the waveform of the excitation current output from the excitation circuit 16 is symmetrical, for example as... Figure 2 As shown in the lower left figure, the waveform of the excitation magnetic field is symmetrical, which can accurately detect leakage current. However, due to the influence of power supply noise and other factors in the excitation circuit 16, the value of either the positive or negative excitation current may sometimes be distorted, resulting in asymmetry of the excitation magnetic field waveform. When the imbalance judgment circuit 15 detects asymmetry in the excitation magnetic field, it outputs a control signal corresponding to the asymmetry of the excitation magnetic field to the excitation circuit 16. Upon receiving the control signal, the excitation circuit 16 reduces the amplitude of either the positive or negative excitation current signal to a smaller value, or shifts the excitation current in either direction. When the leakage current sensor 1 detects leakage current, the excitation circuit 16 does not change the amount by which the amplitude of the excitation current is reduced or the offset amount superimposed on the excitation current.

[0023] use Figure 4An example will be given of a case where the magnitude of the negative magnetic field and the magnitude of the positive magnetic field of the excitation magnetic field are different, which is considered an asymmetry of the excitation magnetic field, detected in the imbalance determination circuit 15. For example, in the imbalance determination circuit 15, such as Figure 4 As shown by the solid line in the lower left figure, when the negative magnetic field of the excitation magnetic field is detected to be smaller than the positive magnetic field, the imbalance determination circuit 15 outputs a control signal to the excitation circuit 16 indicating that the amplitude of the positive side of the excitation current should be smaller than its original value. Upon receiving the control signal indicating that the amplitude of the positive side of the excitation current should be smaller than its original value, the excitation circuit 16 reduces the amplitude of the positive side of the excitation current to its original value. When the imbalance determination circuit 15 confirms that the excitation magnetic field is symmetrical, it maintains the positive and negative symmetry of the excitation magnetic field by fixing the control quantity in the excitation circuit 16.

[0024] use Figure 5 An example will be given of a case where a positive offset is detected as an asymmetry of the excitation magnetic field in the imbalance detection circuit 15. For example, in the imbalance detection circuit 15, such as Figure 5 As shown by the solid line in the lower left figure, a positive offset is superimposed on the excitation magnetic field. When the positive excitation magnetic field is detected to be saturated, the imbalance determination circuit 15 outputs a control signal to the excitation circuit 16 indicating that a negative offset current is superimposed on the excitation current. Upon receiving the control signal indicating that a negative offset current is superimposed on the excitation current, the excitation circuit 16 makes the excitation magnetic field symmetrical by superimposing a negative offset current on the excitation current. When the imbalance determination circuit 15 confirms that the excitation magnetic field is symmetrical, it maintains the symmetry of the excitation magnetic field by fixing the control quantity in the excitation circuit 16.

[0025] Figure 7 This is a flowchart illustrating the operation of the imbalance determination circuit 15 in Embodiment 1. Here, an example is described when the output of the oscillation circuit 17 is a sine wave. In step S01, the imbalance determination circuit 15 acquires the output of the magnetic sensor 14 and the output of the oscillation circuit 17, and proceeds to step S02. In step S02, the imbalance determination circuit 15 acquires the positive and negative amplitudes of the output of the magnetic sensor 14, and proceeds to step S03. In step S02, for example, the frequency of the excitation signal, i.e., the excitation frequency, is determined based on the output of the oscillation circuit 17 acquired in step S01. Within one cycle of the excitation signal, the peak value on the positive side and the peak value on the negative side of the output of the magnetic sensor 14 are determined, and the positive and negative amplitudes of the output of the magnetic sensor 14 are acquired.

[0026] In step S03, the imbalance determination circuit 15 determines whether the difference between the positive and negative amplitudes of the output of the magnetic sensor 14 is below a threshold. If the difference between the positive and negative amplitudes is below the threshold, proceed to step S07; if the difference between the positive and negative amplitudes exceeds the threshold, proceed to step S04.

[0027] In step S04, the imbalance determination circuit 15 determines whether the positive amplitude of the output of the magnetic sensor 14 is greater than the negative amplitude. If the positive amplitude is greater than the negative amplitude, the process proceeds to step S05; if the positive amplitude is less than the negative amplitude, the process proceeds to step S06. In step S05, the imbalance determination circuit 15 outputs a control signal to the excitation circuit 16 to reduce the positive amplitude of the excitation current to its original value, and returns to step S01. Upon receiving the control signal to reduce the positive amplitude of the excitation current to its original value, the excitation circuit 16 reduces the positive amplitude of the excitation current by a predetermined amount. In step S06, the imbalance determination circuit 15 outputs a control signal to the excitation circuit 16 to reduce the negative amplitude of the excitation current to its original value, and returns to step S01. Upon receiving the control signal to reduce the negative amplitude of the excitation current to its original value, the excitation circuit 16 reduces the negative amplitude of the excitation current by a predetermined amount.

[0028] In step S07, the imbalance determination circuit 15 performs a Fast Fourier Transform (FFT) on the output signal of the magnetic sensor 14 for one cycle of the excitation signal to obtain the integer harmonics relative to the excitation frequency, and proceeds to step S08. In step S08, the imbalance determination circuit 15 determines whether the magnitude of the harmonic component of a specific order of the integer harmonics obtained in step S07 is below a threshold. If the magnitude of the harmonic component of the specific order is below the threshold, the operation of the imbalance determination circuit 15 ends; if the magnitude of the harmonic component of the specific order exceeds the threshold, proceeds to step S09.

[0029] Figure 8 This is a graph showing the result of performing a Fast Fourier Transform on the output signal of the magnetic sensor 14. Figure 5 The second example shown is an example of asymmetric excitation magnetic field. Figure 5 The solid line in the lower left figure shows the result of performing a fast Fourier transform on the excitation magnetic field. Figure 8 Is and in Figure 7 The output signal of the magnetic sensor 14, obtained in step S07, is an integer harmonic of the excitation signal over one cycle, relative to the excitation frequency. Figure 8 In the diagram, the horizontal axis represents the harmonic order, and the vertical axis uses a logarithmic axis to represent the intensity of harmonics within each harmonic order. Figure 8In the diagram, black triangles represent cases with a large positive offset superimposed on the excitation magnetic field, white circles represent cases with a medium positive offset superimposed on the excitation magnetic field, and black squares represent cases with a small positive offset superimposed on the excitation magnetic field. The harmonic intensity of each harmonic order changes periodically, but its period varies depending on the magnitude of the offset superimposed on the excitation magnetic field. However, when the offset decreases, the harmonic intensity of harmonics below the 5th order consistently decreases. Therefore, in step S08, by determining whether the magnitude of any harmonic component below the 5th order is below a threshold, the magnitude of the offset superimposed on the excitation magnetic field can be estimated.

[0030] Figure 9 This is a graph showing the result of performing a high-speed Fourier transform on the output signal of the magnetic sensor 14. Figure 4 The first example of positive and negative asymmetry in the excitation magnetic field shown Figure 4 The solid line in the lower left figure shows the result of performing a Fast Fourier Transform on the excitation magnetic field. Figure 9 In the diagram, the horizontal axis represents the harmonic order, and the vertical axis uses a logarithmic axis to represent the intensity of each harmonic order. Figure 9 In the diagram, black triangles indicate a large difference between the positive and negative amplitudes of the excitation magnetic field, white circles indicate a moderate difference, and black squares indicate a small difference. For example... Figure 4 The first example shown illustrates an asymmetrical excitation magnetic field. When the excitation magnetic field is unsaturated and the amplitudes on the positive and negative sides differ, it can be observed that the harmonic intensity tends to decrease monotonically due to the magnitude of the difference between the amplitudes on the positive and negative sides. Therefore, for example, it is also possible to... Figure 7 In step S02, a Fourier transform is performed as shown in step S07. In step S03, it is determined whether the harmonic intensity is monotonically decreasing and whether the harmonic intensity of a specific order is below the threshold.

[0031] exist Figure 7In step S09, the imbalance determination circuit 15 determines whether the positive amplitude of the output of the magnetic sensor 14 is greater than the negative amplitude. If the positive amplitude is greater than the negative amplitude, the process proceeds to step S10; if the positive amplitude is less than the negative amplitude, the process proceeds to step S11. In step S10, the imbalance determination circuit 15 outputs a control signal to the excitation circuit 16 to superimpose a negative offset current onto the excitation current, and returns to step S01. Upon receiving the control signal to superimpose a negative offset current onto the excitation current, the excitation circuit 16 superimposes a negative offset current of a predetermined size onto the excitation current. In step S11, the imbalance determination circuit 15 outputs a control signal to the excitation circuit 16 to superimpose a positive offset current onto the excitation current, and returns to step S01. Upon receiving the control signal to superimpose a positive offset current onto the excitation current, the excitation circuit 16 superimposes a positive offset current of a predetermined size onto the excitation current. Through the above actions, the excitation current output from the excitation circuit 16 is corrected, eliminating the positive and negative asymmetry of the excitation magnetic field applied to the magnetic core 11.

[0032] In steps S02 and S07, the output signal of the magnetic sensor 14 for one cycle of the excitation signal is processed. However, in order to eliminate the influence of electromagnetic noise caused by the measurement environment, a high-speed storage device such as a semiconductor memory can be provided to acquire the output signal of the magnetic sensor 14 for several cycles and process the averaged signal.

[0033] Figure 10 , Figure 11 and Figure 12 This diagram illustrates the configuration of the magnetic sensor 14 in the leakage current sensor 1 according to Embodiment 1. Figure 10 , Figure 11 and Figure 12 The detection coil 13 is omitted; instead, the magnetic core 11, excitation coil 12, and magnetic sensor 14 are shown. The excitation coil 12 is a toroidal coil wound around the magnetic core 11. Within the toroidal coil, the magnetic field does not leak to the outside of the coil. Figure 10 In the example shown, by having a magnetic sensor 14 between the magnetic core 11 and the excitation coil 12, the excitation magnetic field can be detected by the magnetic sensor 14.

[0034] exist Figure 11 In the example shown, an opening is provided in a portion of the magnetic core 11, which is not wound around the excitation coil 12, thus exposing the magnetic core 11. A magnetic sensor 14 is provided in the opening. In a toroidal coil, since the magnetic field leaks through the opening, even if there is not enough space between the magnetic core 11 and the excitation coil 12 to place the magnetic sensor 14, the magnetic sensor can still be placed through the opening to detect the excitation magnetic field.

[0035] exist Figure 12In the example shown, a slit is provided in a portion of the magnetic core 11 to form a magnetic gap. At the slit serving as the magnetic gap, the magnetic field induced by the excitation current in the magnetic core 11 leaks out in a concentrated manner. Therefore, by providing a magnetic sensor 14 at the slit of the magnetic core 11, the excitation magnetic field can be detected. Since a larger magnetic field leaks out as the slit spacing narrows, the excitation magnetic field can be measured with high precision by narrowing the slit spacing.

[0036] As described above, the leakage current sensor 1 according to Embodiment 1 is a leakage current sensor 1 that detects leakage current in the measured current line 30, including: a magnetic core 11 through which the measured current line 30 passes; an excitation coil 12 wound on the magnetic core 11; a detection coil 13 wound on the magnetic core 11; a magnetic sensor 14 that detects the excitation magnetic field generated by the excitation coil 12; an oscillation circuit 17 that generates an excitation signal with the excitation frequency as the basic frequency; an imbalance determination circuit 15 that generates and outputs a control signal based on the output of the magnetic sensor 14 and the output of the oscillation circuit 17; an excitation circuit 16 that applies an excitation current to the excitation coil 12 based on the output of the oscillation circuit 17 and the output of the imbalance determination circuit 15; and a detection coil 13 from the detection coil 13. The output voltage is extracted by a filter circuit 18 that extracts the component of twice the excitation frequency; and the output circuit 19 is an amplification circuit for the output of the filter circuit. The imbalance determination circuit 15 determines the asymmetry of the positive and negative excitation magnetic field when the balanced current flows through the measured current line 30 based on the excitation magnetic field and excitation signal obtained from the magnetic sensor 14. It generates a control signal, and the excitation circuit 16, according to the control signal, makes the amplitude of either the positive or negative excitation current smaller than its original size, or superimposes a bias current of either the positive or negative on the excitation current. Therefore, when the excitation current requires a large current and a high frequency, resulting in an asymmetry of the positive and negative excitation magnetic field, it can suppress the false detection of leakage current.

[0037] Implementation method 2. Figure 13 This is a diagram showing the structure of the leakage current sensor 1a and the circuit protection system according to Embodiment 2. Figure 13 The leakage current sensor 1a involved in Embodiment 2 shown is... Figure 6 Compared with the leakage current sensor 1 of Embodiment 1 shown, the imbalance determination circuit 15 becomes the imbalance determination circuit 15a, the excitation circuit 16 becomes the excitation circuit 16a, and the output circuit 19 becomes the output circuit 19a. The other structures of the leakage current sensor 1a in Embodiment 2 are the same as those in Embodiment 1. Furthermore, the relay unit 20 and the protection circuit 21 are also the same as in Embodiment 1.

[0038] The excitation circuit 16a applies an excitation current to the excitation coil 12 based on the excitation signal from the oscillation circuit 17. The imbalance determination circuit 15a, under the condition that a balanced current flows through the measured current line 30 (i.e., when no leakage occurs in the measured current line 30), determines the asymmetry of the excitation magnetic field obtained from the magnetic sensor 14 and outputs a control signal corresponding to the determined asymmetry to the output circuit 19a. When leakage is detected in the leakage sensor 1a, the imbalance determination circuit 15a does not determine the asymmetry of the waveform of the excitation magnetic field. The output circuit 19a, based on the output of the imbalance determination circuit 15a (i.e., the control signal), corrects the output of the filter circuit 18, calculates the corrected output, amplifies the corrected output according to the factor set by the sensor specifications, and then outputs it.

[0039] Figure 14 This is a flowchart illustrating the operation of the imbalance determination circuit 15a in Embodiment 2. In step S21, the imbalance determination circuit 15a acquires the output of the magnetic sensor 14 and the output of the oscillation circuit 17, and proceeds to steps S22 and S25. In step S22, the imbalance determination circuit 15a acquires the positive and negative amplitudes of the output of the magnetic sensor 14, and proceeds to step S23. In step S23, the imbalance determination circuit 15a determines whether the difference between the positive and negative amplitudes of the output of the magnetic sensor 14 is below a threshold. If the difference is below the threshold, proceeds to step S28; if the difference exceeds the threshold, proceeds to step S24. In step S24, the imbalance determination circuit 15a generates a correction value for the output circuit 19a to correct the output of the filter circuit 18, and proceeds to step S28. In step S24, the output of the output circuit 19a can be predetermined based on the difference between the positive and negative amplitudes of the magnetic sensor 14. Correction values ​​used to correct these changes are stored in a storage device, and the imbalance determination circuit 15a reads the correction value corresponding to the difference between the positive and negative amplitudes from the storage device. Alternatively, in step S24, the imbalance determination circuit 15a can also generate a correction value that makes the output of the output circuit 19a zero.

[0040] In step S25, the imbalance determination circuit 15a performs a Fast Fourier Transform (FFT) on the output signal of the magnetic sensor 14 for one cycle of the excitation signal to obtain the integer harmonics relative to the excitation frequency, and proceeds to step S26. In step S26, the imbalance determination circuit 15a determines whether the magnitude of a specific harmonic component of the integer harmonics obtained in step S25 is below a threshold. If the magnitude of the specific harmonic component is below the threshold, proceeds to step S28; if the magnitude of the specific harmonic component exceeds the threshold, proceeds to step S27. In step S27, the imbalance determination circuit 15a generates a correction value for the output circuit 19a to correct the output of the filter circuit 18, and proceeds to step S28. In step S27, the output of the output circuit 19a can be predetermined based on the values ​​of the harmonic components of a specific order after FFT processing of the output of the magnetic sensor 14. Correction values ​​used to correct these changes are stored in a storage device, and the imbalance determination circuit 15a reads the correction values ​​corresponding to the magnitude of the harmonic components from the storage device. Alternatively, in step S27, the imbalance determination circuit 15a can also generate, for example, a correction value that makes the output of the output circuit 19a zero.

[0041] In step S28, the imbalance determination circuit 15a checks whether a correction value has been generated in at least one of steps S24 and S27. If a correction value has been generated, it outputs the correction value as a control signal to the output circuit 19a, ending the operation of the imbalance determination circuit 15a. The output circuit 19a, receiving the control signal from the imbalance determination circuit 15a, calculates the corrected output of the filter circuit 18 based on the correction value, amplifies the corrected output at a magnification set according to the sensor specifications, and outputs it. The output circuit 19a calculates the corrected output, for example, by adding the correction value to the output of the filter circuit 18, or by multiplying the correction value by the output of the filter circuit 18.

[0042] As described above, the leakage current sensor 1a according to Embodiment 2 is a leakage current sensor 1a that detects leakage current in the measured current line 30, including: a magnetic core 11 through which the measured current line 30 passes; an excitation coil 12 wound on the magnetic core 11; a detection coil 13 wound on the magnetic core 11; a magnetic sensor 14 that detects the excitation magnetic field generated by the excitation coil 12; an oscillation circuit 17 that generates an excitation signal with the excitation frequency as the basic frequency; an imbalance determination circuit 15a that generates and outputs a control signal based on the output of the magnetic sensor 14 and the output of the oscillation circuit 17; an excitation circuit 16a that applies an excitation current to the excitation coil 12 based on the output of the oscillation circuit 17; and a detection coil 13 wound on the magnetic core 11. The output voltage of circuit 3 is extracted by a filter circuit 18 that extracts the component of twice the excitation frequency; and the output circuit 19a amplifies the output of the filter circuit. The imbalance judgment circuit 15a determines the asymmetry of the positive and negative excitation magnetic field when the balanced current flows through the measured current line 30 based on the excitation magnetic field and excitation signal obtained from the magnetic sensor 14. It generates a control signal, and the output circuit 19a corrects the output of the filter circuit 18 according to the control signal, calculates the corrected output, amplifies and outputs the corrected output. Therefore, when the excitation current requires a large current and high frequency, resulting in the asymmetry of the positive and negative excitation magnetic field, it can suppress the false detection of leakage current.

[0043] Figure 15 This is a schematic diagram illustrating an example of the hardware of the imbalance determination circuit 15 in Embodiment 1 and the imbalance determination circuit 15a in Embodiment 2. The imbalance determination circuits 15 and 15a are implemented by a processor 40, such as a CPU (Central Processing Unit), that executes programs stored in the memory 50. The memory 50 is also used as a temporary storage device for each process executed by the processor 40. Alternatively, multiple processing circuits may jointly execute the above functions. Furthermore, the above functions can also be implemented using dedicated hardware.

[0044] When the above functions are implemented using dedicated hardware, such dedicated hardware includes, for example, a single circuit, a composite circuit, a programmable processor, a parallel programmable processor, an ASIC (Application Specific Integrated Circuit), a FPGA (Field-Programmable Gate Array), or a combination thereof. When the above functions are implemented using processor 40 and memory 50, processor 40 is a CPU, such as a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, DSP (Digital Signal Processor), or a combination thereof. Memory 50 includes, for example, non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), magnetic disk, floppy disk, optical disk, or a combination thereof. Processor 40 and memory 50 are connected to each other via a bus.

[0045] This application describes various exemplary embodiments, but the various features, forms and functions described in one or more embodiments are not limited to the application of a specific embodiment, and can be applied to the embodiment alone or in various combinations. Therefore, it can be assumed that numerous variations not illustrated are also included within the scope of the technology disclosed in this application. For example, this includes cases involving modifications, additions, or omissions of at least one constituent element, as well as cases involving the extraction of at least one constituent element and its combination with constituent elements of other embodiments. Label Explanation

[0046] 1.1a Leakage sensor, 10 Leakage detection unit, 11 Magnetic core, 12 Excitation coil, 13 Detection coil, 14 Magnetic sensor, 15, 15a Imbalance judgment circuit, 16, 16a Excitation circuit, 17 Oscillation circuit, 18 Filtering circuit, 19, 19a Output circuit, 20 Relay unit, 21 Protection circuit, 30 Measured current line, 40 Processor, 50 Memory.

Claims

1. A leakage current sensor for detecting leakage current in a measured current line, characterized in that, include: The magnetic core through which the measured current line passes; An excitation coil wound on the magnetic core; A detection coil wound around the magnetic core; A magnetic sensor that detects the excitation magnetic field generated by the excitation coil; An oscillation circuit that generates an excitation signal with the excitation frequency as its fundamental frequency. An imbalance determination circuit generates and outputs a control signal based on the output of the magnetic sensor and the output of the oscillation circuit. An excitation circuit that applies excitation current to the excitation coil based on the output of the oscillation circuit and the output of the imbalance determination circuit; A filter circuit that extracts the component of twice the excitation frequency from the output voltage of the detection coil; as well as The output circuit that amplifies the output of the filter circuit. When the imbalance determination circuit detects leakage current, it does not determine the asymmetry of the positive and negative signs of the excitation magnetic field. Instead, it determines the asymmetry of the positive and negative signs of the excitation magnetic field based on the excitation magnetic field and the excitation signal obtained from the magnetic sensor when the balanced current flows through the measured current line, and generates the control signal. The control signal generated by the excitation circuit based on the determination of the asymmetry of the positive and negative signs of the excitation magnetic field when the balanced current flows through the measured current line makes the amplitude of either the positive or negative sign of the excitation current smaller than its original size, or adds a positive or negative offset current to the excitation current.

2. The leakage current sensor as described in claim 1, characterized in that, The magnetic sensor is disposed between the magnetic core and the excitation coil.

3. The leakage current sensor as described in claim 1, characterized in that, The magnetic sensor is disposed on the magnetic core and is not wound around the excitation coil, thus exposing the opening of the magnetic core.

4. The leakage current sensor as described in claim 1, characterized in that, The magnetic core has a notch. The magnetic sensor is located at the cut.

5. A circuit protection system, characterized in that, include: The leakage current sensor according to any one of claims 1 to 4; The presence or absence of a leakage relay unit is determined based on the output of the output circuit. as well as The protection circuit cuts off the measured current line when it is determined that leakage has occurred in the relay unit.

6. A leakage current sensor for detecting leakage current in a measured current line, characterized in that, include: The magnetic core through which the measured current line passes; An excitation coil wound on the magnetic core; A detection coil wound around the magnetic core; A magnetic sensor that detects the excitation magnetic field generated by the excitation coil; An oscillation circuit that generates an excitation signal with the excitation frequency as its fundamental frequency. An imbalance determination circuit that generates and outputs control signals based on the output of the magnetic sensor and the output of the oscillation circuit; An excitation circuit that applies excitation current to the excitation coil based on the output of the oscillation circuit; A filter circuit that extracts the component of twice the excitation frequency from the output voltage of the detection coil; as well as The output circuit that amplifies the output of the filter circuit. The imbalance determination circuit determines the asymmetry of the excitation magnetic field (positive or negative) based on the excitation magnetic field and excitation signal obtained from the magnetic sensor when the balanced current flows through the measured current line, and generates the control signal. The output circuit corrects the output of the filter circuit according to the control signal, calculates the corrected output, amplifies the corrected output, and outputs it.

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