Current detection device, and earth leakage circuit breaker

Abstract

To provide a current detection device and earth leakage circuit breaker that detect a relatively large detected current.SOLUTION: A current detection device comprises: a magnetic core that surrounds a conductor through which a detected current flows; an excitation coil wound around the magnetic core; an excitation circuit that outputs a rectangular wave voltage to the excitation coil; a binarization circuit that is connected to other end of the excitation coil, outputs a binary value signal consisting of a low-level signal and a high-level signal, outputs the low-level signal when the voltage of the excitation coil exceeds a first reference voltage in response to the rectangular wave voltage, and outputs the high-level signal when the voltage of the excitation coil is under a second reference voltage smaller than the first reference voltage; and a detection circuit that detects the detected current flowing to the conductor on the basis of a first time from a first time-point when the excitation circuit outputs the rectangular wave voltage to the excitation coil until a second time-point when the binarization circuit outputs the high-level signal firstly after the first time-point.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a current detection device and a leakage circuit breaker.

Background Art

[0002] Patent Document 1 discloses a current detection device including an annular magnetic core having an inner diameter substantially matching the diameter of a detection target such as a gas pipe, an excitation coil and a detection coil wound around the magnetic core respectively, and a detector electrically connected to the detection coil. According to the current detection device disclosed in Patent Document 1, a DC detected current flowing through the detection target can be detected.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the current detection device disclosed in Patent Document 1, when a relatively large detected current that saturates the magnetic core flows through the detection target, the magnetic flux density passing through the magnetic core may not change constantly. As a result, it may be impossible to detect a relatively large detected current through the detection coil.

[0005] The present disclosure provides a current detection device and a leakage circuit breaker that can detect a relatively large detected current.

Means for Solving the Problems

[0006] In a first aspect, a magnetic core surrounding a conductor through which a detected current flows, an exciting coil wound around the magnetic core, an exciting circuit that outputs a rectangular wave voltage to the exciting coil, and a binarization circuit that is connected to the other end of the exciting coil and outputs a binary signal composed of a low-level signal and a high-level signal, wherein the binarization circuit outputs the low-level signal when the voltage of the exciting coil exceeds a first reference voltage according to the rectangular wave voltage, and outputs the high-level signal when the voltage of the exciting coil falls below a second reference voltage lower than the first reference voltage, and a detection circuit that detects the detected current flowing through the conductor based on a first time period from a first time point when the exciting circuit outputs the rectangular wave voltage to the exciting coil to a second time point when the binarization circuit first outputs the high-level signal after the first time point.

Advantages of the Invention

[0007] According to the technology of the present disclosure, it is possible to provide a current detection device and a leakage circuit breaker that detect a relatively large detected current.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the current detection device according to the embodiment will be described with reference to the drawings. Note that "connection" is not limited to physical connection and may include the meaning of electrical connection. For example, when object A is connected to object B, it is not limited to the case where object A is conductively (e.g., at the same potential) connected to object B, and may include the case where object A is conductively connected to object B via object C.

[0010] [First Embodiment] <Current Detection Device 1> Referring to FIGS. 1 and 2, an example of the configuration of the current detection device 1 according to the first embodiment is shown. FIG. 1 is a schematic block diagram showing an example of the overall configuration of the current detection device 1 according to the first embodiment. FIG. 2 is a circuit diagram showing a configuration example of the excitation circuit 30 and the binarization circuit 40 of the current detection device 1 according to the first embodiment.

[0011] As shown in FIG. 1, the current detection device 1 includes a magnetic core 10, an excitation coil 20, an excitation circuit 30, a binarization circuit 40, and a detection circuit 50. The current detection device 1 may be used, for example, as detection means for detecting a detected current such as a leakage current in a leakage circuit breaker 100 (see FIG. 8). Hereinafter, the current detection device 1 will be described as a current detection device applied to the leakage circuit breaker 100. Also, the detected currents such as leakage current are collectively referred to as "detected current" hereinafter. However, the use of the current detection device 1 is not limited to this. A configuration example of the leakage circuit breaker 100 will be described separately with reference to FIG. 8.

[0012] The conductor 2 is an electric circuit that conducts current from the power source 3 to the load 4. The power source 3 is, for example, a DC power source that transmits a DC current to the load 4, such as a solar cell or a fuel cell. However, the power source 3 may be an AC power source that transmits a single-phase or three-phase AC current to the load 4. The load 4 is various devices that are driven by being supplied with a current such as the DC current transmitted from the power source 3.

[0013] In the example shown in FIG. 1, as the conductor 2, two conductors 2a and 2b pass through the inside of the magnetic core 10. Each of the conductors 2a and 2b is connected between the power source 3 and the load 4. A DC current that reciprocates between the power source 3 and the load 4 flows through the conductors 2a and 2b. Specifically, a DC current Ia flowing from the power source 3 toward the load 4 flows through the conductor 2a. Also, a DC current Ib flowing from the load 4 toward the power source 3 flows through the conductor 2b.

[0014] Each of the conductors 2a and 2b extends substantially parallel to each other between the power source 3 and the load 4. The direction of the current Ia flowing through the conductor 2a and the direction of the current Ib flowing through the conductor 2b are opposite to each other. When there is no leakage or ground fault in the electric circuit including the conductors 2a and 2b, there is no difference between the current value of the current Ia and the current value of the current Ib.

[0015] On the other hand, when there is a leakage or a ground fault in the electric circuit including the conductors 2a and 2b, a difference occurs between the current value of the current Ia and the current value of the current Ib. When a difference occurs between the current value of the current Ia and the current value of the current Ib, the current detection device 1 detects the current to be detected based on the electrical signal output from the excitation coil 20. Hereinafter, each component included in the current detection device 1 will be described. When describing each component included in the current detection device 1, unless otherwise specified, it is assumed that no current to be detected is flowing through the conductors 2a and 2b. The state where no current to be detected is flowing through the conductors 2a and 2b is hereinafter referred to as the "steady state".

[0016] <Magnetic Core 10 and Excitation Coil 20> As shown in Fig. 1, the magnetic core 10 is an annular magnetic member that surrounds conductors 2a and 2b. As an example of the material constituting the magnetic core 10, a soft magnetic material such as an Fe-Ni based magnetic alloy can be mentioned. However, the material constituting the magnetic core 10 is not limited.

[0017] As the magnetic field acting on the magnetic core 10 increases, the magnetic flux density passing through the magnetic core 10 increases. Further, when the magnetic field acting on the magnetic core 10 becomes even larger and exceeds a predetermined value, the magnetic flux density passing through the magnetic core 10 stops changing. That is, the magnetic core 10 becomes magnetically saturated.

[0018] The exciting coil 20 is wound around the magnetic core 10. That is, the magnetic core 10 is inserted inside each winding portion constituting the exciting coil 20. When a direct current or an alternating current exciting current flows through the exciting coil 20, a magnetic field H1 is generated inside the exciting coil 20. If the magnetic core 10 is not magnetically saturated, the magnetic flux density passing through the magnetic core 10 changes in response to the change in the magnetic field H1 generated inside the exciting coil 20. Note that the number of turns, cross-sectional area, etc. of the exciting coil 20 are not limited.

[0019] <Excitation circuit 30> As shown in Figs. 1 and 2, the excitation circuit 30 is connected to one end 20a of the exciting coil 20. The excitation circuit 30 sequentially outputs a plurality of rectangular wave voltages Vp having a predetermined period to the exciting coil 20. Each time a plurality of rectangular wave voltages Vp are input to the exciting coil 20, an exciting current flows. Further, each time an exciting current flows through the exciting coil 20, a back electromotive force is generated.

[0020] The period of the rectangular wave voltage Vp output by the excitation circuit 30 is not limited. The amplitude and pulse width of the rectangular wave voltage Vp output by the excitation circuit 30 are preferably values equal to or greater than the magnitude at which the magnetic core 10 becomes magnetically saturated.

[0021] As shown in Fig. 2, the excitation circuit 30 according to the first embodiment is an oscillation circuit including a CR oscillation circuit 31 and a push-pull circuit 32 connected to the CR oscillation circuit 31. However, the configuration of the excitation circuit 30 is not limited to this.

[0022] <Binary conversion circuit 40> The binary conversion circuit 40 is connected to the other end 20b of the excitation coil 20. The voltage of the other end 20b of the excitation coil 20 (hereinafter referred to as "the voltage of the excitation coil 20" or "the output voltage of the excitation coil 20") is input to the binary conversion circuit 40. When the output voltage of the excitation coil 20 exceeds the first reference voltage V1 according to the rectangular wave voltage Vp, the binary conversion circuit 40 outputs a low-level signal LS (see FIG. 3). Further, when the output voltage of the excitation coil 20 falls below the second reference voltage V2, the binary conversion circuit 40 outputs a high-level signal HS (see FIG. 3). The second reference voltage V2 is smaller than the first reference voltage V1. The binary conversion circuit 40 alternately outputs the low-level signal LS and the high-level signal HS.

[0023] As shown in FIG. 2, the binary conversion circuit 40 according to the first embodiment is a circuit including a hysteresis comparator. Specifically, the binary conversion circuit 40 includes a current-voltage conversion element 41, a voltage converted by the current-voltage conversion element 41, a comparator 42 that compares the voltage with the first reference voltage V1 or the second reference voltage V2, and resistors 43 and 44 for setting the first reference voltage V1 and the second reference voltage V2. However, the configuration of the binary conversion circuit 40 is not limited to this.

[0024] The current-voltage conversion element 41 converts the current flowing through the excitation coil 20 and the current-voltage conversion element 41 into a voltage. The current-voltage conversion element 41 is, for example, a resistor. However, the current-voltage conversion element 41 is not limited to a resistor. One end of the current-voltage conversion element 41 is connected to the other end 20b of the excitation coil 20. Also, the other end of the current-voltage conversion element 41 is connected to the reference voltage unit 48.

[0025] The inverting input terminal 42a of the comparator 42 is connected to a connection point 45a between one end of the current-voltage conversion element 41 and the other end 20b of the excitation coil 20 through a wiring. The output voltage of the excitation coil 20 is input to the inverting input terminal 42a of the comparator 42.

[0026] The non-inverting input terminal 42b of the comparator 42 is connected to the connection point 45b between the resistor 43 and the resistor 44 through a wire. Also, the output terminal 42c of the comparator 42 is fed back to the non-inverting input terminal 42b through a wire passing through the resistor 44. The voltage output from the output terminal 42c of the comparator 42 and the voltage of the reference voltage unit 48 are divided by the resistors 43 and 44. Further, the voltage divided by the resistors 43 and 44 is input to the non-inverting input terminal 42b of the comparator 42 as the first reference voltage V1 or the second reference voltage V2.

[0027] When the output voltage of the excitation coil 20 exceeds the first reference voltage V1, the output terminal 42c outputs a low-level signal LS. At this time, the reference voltage input to the non-inverting input terminal 42b of the comparator 42 switches from the first reference voltage V1 to the second reference voltage V2. Thereafter, when the output voltage of the excitation coil 20 decreases and falls below the second reference voltage V2, the output terminal 42c outputs a high-level signal HS. Thereby, the binarization circuit 40 outputs a binary signal corresponding to the low-level signal LS and the high-level signal HS to the detection circuit 50. Also, the binarization circuit 40 outputs a binary signal to the detection circuit 50 according to the input voltage from the excitation coil 20. As an example of the binary signal, a rectangular wave signal can be mentioned.

[0028] <Detection circuit 50> The detection circuit 50 is connected to the binarization circuit 40. The detection circuit 50 detects the current to be detected based on the binary signal composed of the low-level signal LS and the high-level signal HS output from the binarization circuit 40.

[0029] The detection circuit 50 may be a digital circuit that processes the binary signal output from the binarization circuit 40. For example, the detection circuit 50 may be an electronic circuit incorporated in a processing device such as a microcomputer. The detection circuit 50 may include, for example, an arithmetic processing circuit composed of a CPU (Central Processing Unit) and a ROM (Read Only Memory) that stores a program executed by the CPU. Further, the detection circuit 50 may include a storage medium other than the ROM, such as an EEPROM (Electrically Erasable Programmable Read-Only Memory). Furthermore, the detection circuit 50 may sequentially output a control signal for outputting the rectangular wave voltage Vp at a predetermined period to the excitation circuit 30.

[0030] The detection circuit 50 detects a relatively large detected current that magnetically saturates the magnetic core 10 based on the time T12 from the first time point T1 when the excitation circuit 30 outputs the rectangular wave voltage Vp to the excitation coil 20 to the second time point T2 when the binarization circuit 40 first outputs the high-level signal HS after the first time point T1. In this specification, the "high-level signal HS first output after the first time point T1" does not include the high-level signal HS continuously output from the binarization circuit 40 before the first time point T1. The relatively large detected current that magnetically saturates the magnetic core 10 is hereinafter referred to as the "first current Id1". The detection operation of the first current Id1 in the current detection device 1 will be separately described with reference to FIG. 5. The time T12 is an example of the "first time". Note that, for example, the input point 321 (see FIG. 2) of the push-pull circuit 32 in the excitation circuit 30 may be connected to the detection circuit 50. That is, when the excitation circuit 30 outputs the rectangular wave voltage Vp, the detection circuit 50 can specify the first time point T1 by inputting the electrical signal input from the CR oscillation circuit 31 to the input point 321 of the push-pull circuit 32 to the detection circuit 50.

[0031] In contrast, the detection circuit 50 detects a detected current that does not cause the magnetic core 10 to reach magnetic saturation based on a time T31, which is the difference between the duration HT of the high-level signal HS and the duration LT of the low-level signal LS output from the binarization circuit 40. The time T31 is an example of the "third time". The detected current that does not cause the magnetic core 10 to reach magnetic saturation is hereinafter referred to as the "second current Id2". The detection operation of the second current Id2 in the current detection device 1 will be separately described with reference to FIG. 4.

[0032] Further, the detection circuit 50 may determine that a detected current (hereinafter referred to as the "third current Id3") flows through the conductors 2a and 2b when the detection circuit 50 does not acquire the first high-level signal HS after the first time point T1 even after a time Tf of one cycle of the rectangular wave voltage Vp has elapsed from the first time point T1 when the excitation circuit 30 outputs the rectangular wave voltage Vp to the excitation coil 20. Here, one cycle of the rectangular wave voltage Vp is the time (period) from when the rectangular wave voltage Vp is output until the next rectangular wave voltage Vp is output. However, the period for determining whether the third current Id3 flows in the detection circuit 50 is not limited to one cycle of the rectangular wave voltage Vp. In this specification, the "first high-level signal HS after the first time point T1" does not include the high-level signal HS continuously output from the binarization circuit 40 before the first time point T1. The third current Id3 is a current that does not cause the magnetic core 10 to reach magnetic saturation but magnetizes the magnetic core 10 to a state near magnetic saturation. The third current Id3 is a current that is larger than the second current Id2 and smaller than the first current Id1. The detection operation of the third current Id3 in the current detection device 1 will be separately described with reference to FIG. 6.

[0033] As shown in FIG. 1, the detection circuit 50 includes a first time measurement circuit 51, a first determination circuit 52, a second time measurement circuit 53, a second determination circuit 54, an integration circuit 55, and an OR processing circuit 56. In the first embodiment, the first current Id1 is detected by the first time measurement circuit 51 and the first determination circuit 52. Also, the second current Id2 is detected by the second time measurement circuit 53, the second determination circuit 54, and the integration circuit 55. However, the configuration of the detection circuit 50 is not limited to this.

[0034] The first time measurement circuit 51 measures the time T12 between the first time point T1 and the second time point T2. The first time measurement circuit 51 may be realized by, for example, a counter circuit. The first time measurement circuit 51 outputs a measurement signal indicating the measurement result to the first determination circuit 52.

[0035] The first determination circuit 52 determines that the first current Id1 has flowed through the conductors 2a and 2b when the time T12 measured by the first time measurement circuit 51 is less than the first threshold value Th1. Also, the first determination circuit 52 may calculate the difference between the time T12 measured by the first time measurement circuit 51 and the time T22 between the first time point T1 and the second time point T2 in the steady state. At this time, the first determination circuit 52 may determine that the first current Id1 has flowed through the conductors 2a and 2b when the calculated difference exceeds the second threshold value Th2. Further, the first determination circuit 52, for example, when the high-level signal HS first output after the first time point T1 is not acquired even once within the time Tf (see FIG. 6) of one cycle of the rectangular wave voltage Vp (that is, when the measurement signal from the first time measurement circuit 51 is not acquired after the first time point T1), may determine that the third current Id3 has flowed through the conductors 2a and 2b. By referring to the first threshold value Th1, the second threshold value Th2, and the time Tf of one cycle of the rectangular wave voltage Vp in the determination of the first determination circuit 52, false detection caused by another factor such as noise can be suppressed. Information regarding the first threshold value Th1, the second threshold value Th2, and the time Tf of one cycle of the rectangular wave voltage Vp is stored, for example, in the storage medium of the detection circuit 50. The first determination circuit 52 is realized by, for example, an arithmetic processing circuit such as a CPU. The time T22 is an example of the "second time".

[0036] The information of the time T22 in the steady state may be stored in advance in a storage medium such as the EEPROM of the detection circuit 50. The first determination circuit 52 may determine that the first current Id1 has flowed through the conductors 2a and 2b by referring to the information of the time T22 stored in a storage medium such as the EEPROM. The first determination circuit 52 outputs a first detection signal indicating that the first current Id1 has flowed through the conductors 2a and 2b to the logical sum processing circuit 56. Further, the first determination circuit 52 outputs a detection signal indicating that the third current Id3 has flowed through the conductors 2a and 2b to the logical sum processing circuit 56.

[0037] The second time measurement circuit 53 measures the duration HT of the high-level signal HS output from the binarization circuit 40 and the duration LT of the low-level signal LS immediately after the inversion of the high-level signal HS. The second time measurement circuit 53 may be realized by, for example, a counter circuit. The second time measurement circuit 53 outputs a measurement signal indicating the duration HT of the high-level signal HS and a measurement signal indicating the duration LT of the low-level signal LS to the second determination circuit 54.

[0038] Further, binary signals sequentially output from the binarization circuit 40 are sequentially input to the second time measurement circuit 53. The second time measurement circuit 53 sequentially measures the duration HT of each high-level signal HS and the duration LT of the low-level signal LS from the sequentially input high-level signal HS and low-level signal LS of the binary signal. Further, the second time measurement circuit 53 sequentially outputs a measurement signal indicating the measured duration HT of the high-level signal HS and a measurement signal indicating the duration LT of the low-level signal LS to the second determination circuit 54.

[0039] The second determination circuit 54 calculates a time T31, which is the difference between the duration HT of the high-level signal HS measured by the second time measurement circuit 53 and the duration of the low-level signal LS. Further, the second determination circuit 54 executes a determination process of determining whether or not the calculated time T31 exceeds a third threshold Th3. The second determination circuit 54 is realized by an arithmetic processing circuit such as a CPU, for example. When the second determination circuit 54 determines that the calculated time T31 exceeds the third threshold Th3, the second determination circuit 54 outputs a determination signal to the integration circuit 55.

[0040] Further, each time a plurality of binary signals sequentially output from the binarization circuit 40 are input to the second determination circuit 54, the second determination circuit 54 executes a determination process. That is, the second determination circuit 54 determines each time whether or not the time T31 exceeds the third threshold Th3 based on the difference between the duration HT of the high-level signal HS and the duration LT of the low-level signal LS included in each sequentially input binary signal. Also, each time the second determination circuit 54 determines in each determination process that the time T31 exceeds the third threshold Th3, the second determination circuit 54 sequentially outputs a determination signal to the integration circuit 55. Note that after the second determination circuit 54 outputs a determination signal once, the output of the determination signal is continued until the timing when it is determined that the time T31 does not exceed the third threshold Th3 next.

[0041] The integration circuit 55 is connected to the second determination circuit 54. When a plurality of determination signals sequentially output from the second determination circuit 54 are continuously input for a time equal to or longer than a fourth threshold Th4 as a result of the determination process, the integration circuit 55 outputs a detection signal indicating that a detected current has flowed through the conductors 2a and 2b to the logical sum processing circuit 56. When the sum value of the plurality of determination signals processed by the integration circuit 55 becomes equal to or greater than the fourth threshold Th4, a second detection signal is output from the integration circuit 55, thereby suppressing false detection caused by another factor such as noise.

[0042] The logical sum processing circuit 56 performs a logical sum process of determining whether any one of the first detection signal (including a detection signal indicating that a third current Id3 has flowed through the conductors 2a and 2b) from the first determination circuit 52 or the second detection signal from the integration circuit 55 is input. The logical sum processing circuit 56 is, for example, an OR gate. When any one of the first detection signal from the first determination circuit 52 or the second detection signal from the integration circuit 55 is input as a result of the logical sum process, the logical sum processing circuit 56 outputs a third detection signal indicating that a detected current has flowed through the conductors 2a and 2b. Further, the logical sum processing circuit 56 may output the third detection signal to the interruption means 200 (see FIG. 8) of the leakage breaker 100. The third detection signal is an example of a "detection signal".

[0043] <Operation> Next, with reference to FIGS. 3 to 6, the operation of the current detection device 1 will be described. FIG. 3 is a timing chart showing the operation of the current detection device 1 in a steady state. FIG. 4 is a timing chart showing the operation of the current detection device 1 when a second current Id2 flows through the conductors 2a and 2b. FIG. 5 is a timing chart showing the operation of the current detection device 1 when a first current Id1 flows through the conductors 2a and 2b. FIG. 6 is a timing chart showing the operation of the current detection device 1 when a third current Id3 flows through the conductors 2a and 2b. Also, the waveforms shown in the upper part of each of FIGS. 3 to 6 correspond to the waveform of the rectangular wave voltage Vp output from the excitation circuit 30. The waveforms shown in the middle part of each of FIGS. 3 to 6 correspond to the waveform of the output voltage of the excitation coil 20. The waveforms shown in the lower part of each of FIGS. 3 to 6 correspond to the waveform of the binary signal output from the binarization circuit 40. In FIGS. 4 to 6, the waveforms indicated by the broken lines correspond to the waveforms in the steady state shown in FIG. 3.

[0044] First, referring to FIG. 3, the operation of the current detection device 1 in the steady state will be described. A plurality of rectangular wave voltages Vp (Vp1, Vp2, ···) output from the excitation circuit 30 are sequentially input to the excitation coil 20. Each time a rectangular wave voltage Vp is input to the excitation coil 20, an excitation current flows through the excitation coil 20 accordingly. Further, according to the excitation current that flows through the excitation coil 20 each time, a magnetic field H1 is generated from the excitation coil 20, and the magnetic flux density in the magnetic core 10 increases. As a result, inductance is generated in the excitation coil 20, and the change in the voltage of the excitation coil 20 accompanying the rise of the rectangular wave voltage Vp is suppressed. Here, the BH curve of the magnetic core 10 showing the relationship between the magnetic field acting on the magnetic core 10 and the magnetic flux density is theoretically symmetric with respect to the origin. The direction of change of the magnetic flux density in the magnetic core 10 here corresponds to the direction in which the magnetic flux density goes toward the plus side of the BH curve.

[0045] Thereafter, when the magnetic field H1 from the excitation coil 20 exceeds a predetermined value, the magnetic core 10 becomes magnetically saturated. Therefore, the inductance of the excitation coil 20 becomes zero. As a result, the voltage of the excitation coil 20 that was suppressed increases and exceeds the first reference voltage V1. Accordingly, the high-level signal HS output from the binarization circuit 40 is switched to the low-level signal LS.

[0046] Subsequently, when the rectangular wave voltage Vp output from the excitation circuit 30 falls and changes to the low level, the excitation current of the excitation coil 20 also decreases. Accordingly, the magnetic field H1 from the excitation coil 20 and the magnetic flux density of the magnetic core 10 change so as to decrease respectively. As a result, inductance is generated in the excitation coil 20, and the change in the voltage of the excitation coil 20 accompanying the fall of the rectangular wave voltage Vp is suppressed. The direction of change of the magnetic flux density in the magnetic core 10 here corresponds to the direction in which the magnetic flux density goes toward the minus side of the BH curve.

[0047] Thereafter, when the magnetic field H1 from the excitation coil 20 further changes and the magnetic flux density of the magnetic core 10 greatly increases on the negative side of the BH curve and reaches a predetermined value, the magnetic core 10 becomes magnetically saturated again. Therefore, the inductance of the excitation coil 20 becomes zero. As a result, the voltage of the excitation coil 20 decreases and falls below the second reference voltage V2. Along with this, the low-level signal LS that has been output from the binarization circuit 40 switches to the high-level signal HS. Each time a rectangular-wave voltage is sequentially input from the excitation circuit 30 to the excitation coil 20, the voltage of the excitation coil 20 and the binary signal of the binarization circuit 40 repeat the same changes as described above. As shown in FIG. 3, in the steady state, the duration HT of the high-level signal HS and the duration LT of the low-level signal LS are substantially the same.

[0048] Next, with reference to FIG. 4, the operation of the current detection device 1 when a second current Id2 flows through the conductors 2a and 2b will be described. First, the magnetic flux density within the magnetic core 10 has a predetermined value corresponding to the magnitude and direction of the second current Id2 in the conductors 2a and 2b even before an excitation current flows through the excitation coil 20.

[0049] Subsequently, the excitation circuit 30 outputs a rectangular-wave voltage Vp to the excitation coil 20. In response, an excitation current flows through the excitation coil 20. However, since the magnetic flux density within the magnetic core 10 has a predetermined value in advance, the change in the voltage of the excitation coil 20 is different from the change in the voltage of the excitation coil 20 in the steady state. Specifically, the timing at which the voltage of the excitation coil 20 exceeds the first reference voltage V1 is different from that in the steady state. In the example shown in FIG. 4, the timing at which the voltage of the excitation coil 20 exceeds the first reference voltage V1 is later than that in the steady state. As a result, the duration HT of the high-level signal HS becomes longer than the duration HT in the steady state. On the other hand, the duration LT of the low-level signal LS becomes shorter than the duration LT in the steady state.

[0050] However, depending on the direction of the second current Id2, the timing at which the voltage of the exciting coil 20 exceeds the first reference voltage V1 may be earlier than in the steady state. As a result, the duration HT of the high-level signal HS is shorter than the duration HT in the steady state. On the other hand, the duration LT of the low-level signal LS is longer than the duration LT in the steady state.

[0051] When the second current Id2 flows through the conductors 2a and 2b, the time T31, which is the difference between the duration HT of the high-level signal HS and the duration LT of the low-level signal LS, increases compared to the time T31 in the steady state. The detection circuit 50 detects the change in the time T31 and detects that the second current Id2 flows through the conductors 2a and 2b. With this detection operation, the current detection device 1 can properly detect the second current Id2 even if the second current Id2 is very small.

[0052] Next, referring to Fig. 5, the operation of the current detection device 1 when the first current Id1 flows through the conductors 2a and 2b will be described. The excitation circuit 30 outputs a square wave voltage Vp to the excitation coil 20. In response to this, an excitation current flows through the excitation coil 20. Here, the magnetic core 10 is magnetically saturated by the first current Id1 flowing through the conductors 2a and 2b before the excitation current flows through the excitation coil 20. Therefore, even if the excitation current flows through the excitation coil 20, no inductance is generated in the excitation coil 20. As a result, the voltage of the excitation coil 20 changes in response to the change in the square wave voltage Vp.

[0053] Specifically, the voltage of the exciting coil 20 exceeds the first reference voltage V1 in synchronization with the rising edge of the square wave voltage Vp. As a result, the binary signal of the binarization circuit 40 switches from a high-level signal HS to a low-level signal LS. Also, in synchronization with the falling edge of the square wave voltage Vp, the voltage of the exciting coil 20 falls below the second reference voltage V2. As a result, the binary signal of the binarization circuit 40 switches from a low-level signal LS to a high-level signal HS.

[0054] The binarization circuit 40 outputs a low-level signal LS while the rectangular wave voltage Vp maintains a high level after rising. Also, the binarization circuit 40 outputs a high-level signal HS while maintaining a low level after the rectangular wave voltage Vp falls. The duty ratio of the rectangular wave voltage Vp is 1 / 2. Therefore, the duration HT of the high-level signal HS and the duration LT of the low-level signal LS output from the binarization circuit 40 are approximately the same. As a result, the time T31, which is the difference between the duration HT of the high-level signal HS and the duration LT of the low-level signal LS, does not change from the time T31 in the steady state. That is, when a first current Id1 flows through the conductors 2a and 2b, the time T31, which is the difference between the duration HT of the high-level signal HS and the duration LT of the low-level signal LS, is approximately zero. Therefore, it is difficult for the current detection device 1 to detect the first current Id1 by the detection operation described with reference to FIG. 4.

[0055] Incidentally, when a first current Id1 flows through the conductors 2a and 2b, as shown in FIG. 5, from the first time point T1 when the excitation circuit 30 outputs a rectangular wave voltage Vp to the excitation coil 20, the time T12 until the binarization circuit 40 first outputs a high-level signal HS after the first time point T1 is shorter than the time T22 from the first time point T1 to the second time point T2 in the steady state. The detection circuit 50 of the current detection device 1 detects the first current Id1 by detecting that the time T12 and the time T22 are different.

[0056] Next, with reference to FIG. 6, the operation of the current detection device 1 when a third current Id3 flows through the conductors 2a and 2b will be described. Also for the example shown in FIG. 6, similar to the example shown in FIG. 5, the excitation circuit 30 outputs a rectangular wave voltage Vp to the excitation coil 20. Accordingly, an excitation current flows through the excitation coil 20. At this time, the magnetic core 10 is also excited by the third current Id3. Here, when an excitation current due to the rectangular wave voltage Vp flows through the excitation coil 20, the output voltage of the excitation coil 20 increases. However, before the magnetic core 10 reaches magnetic saturation, the rectangular wave voltage Vp falls. Therefore, since the output voltage of the excitation coil 20 does not exceed the first reference voltage V1, the binary circuit 40 does not output a low-level signal LS. Accordingly, the first high-level signal HS after the first time point T1 is not output from the binary circuit 40.

[0057] Therefore, in the example shown in FIG. 6, the detection circuit 50 does not acquire the first high-level signal HS after the first time point T1 even once until, for example, the time Tf of one cycle of the rectangular wave voltage Vp elapses from the first time point T1. In this case, the detection circuit 50 determines that the third current Id3 has flowed through the conductors 2a and 2b.

[0058] <Advantages and effects> According to the present embodiment, even when a relatively large first current Id1 flows through the conductors 2a and 2b, the detection circuit 50 can detect the first current Id1 based on the time T12 from the first time point T1 when the excitation circuit 30 outputs the rectangular wave voltage Vp to the excitation coil 20 until the second time point T2 when the binary circuit 40 first outputs the high-level signal HS after the first time point T1. Thereby, even when it is difficult to detect the detected current from the difference between the duration HT of the high-level signal HS and the duration LT of the low-level signal LS of the binary signal due to magnetic saturation of the magnetic core 10, the relatively large first current Id1 can be detected.

[0059] Further, the current detection device 1 can detect a second current Id2 that does not cause the magnetic core 10 to reach magnetic saturation based on a time T31 that is the difference between the duration HT of the high-level signal HS and the duration LT of the low-level signal LS. Further, even when a third current Id3 that is smaller than the first current Id1 and larger than the second current Id2 flows through the conductors 2a and 2b as the current to be detected, the third current Id3 can be detected. Therefore, according to the first embodiment, a current detection device 1 with a wide detection range of the current to be detected can be provided.

[0060] [Second Embodiment] <Current Detection Device 1A> Next, with reference to FIG. 7, an example of the configuration of the current detection device 1A according to the second embodiment will be shown. FIG. 7 is a schematic block diagram showing an example of the overall configuration of the current detection device 1A according to the second embodiment. The current detection device 1A according to the second embodiment is different from the first embodiment in that it includes an excitation circuit 30A including a digital circuit section and a detection circuit 50, and further includes a first level shift circuit 61 and a second level shift circuit 65. Here, the "digital circuit section" refers to, for example, a circuit section that performs a desired operation by processing binary digital signals. In the second embodiment, components having substantially the same configuration as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted as appropriate. In FIG. 7, the magnetic core 10 is omitted, but the excitation coil 20 is wound around the magnetic core 10 as in the example shown in FIG. 1.

[0061] The digital circuit section of the detection circuit 50 includes the first time measurement circuit 51, the first determination circuit 52, the second time measurement circuit 53, the second determination circuit 54, the integration circuit 55, and the logical sum processing circuit 56, which were described with reference to FIG. 1. The detection circuit 50 and the excitation circuit 30A may be circuit components included in the same integrated circuit chip, or may be circuit components included in different integrated circuit chips.

[0062] The excitation circuit 30A outputs a pulse signal as a rectangular wave voltage Vp to the excitation coil 20. The excitation circuit 30A includes an oscillation circuit that oscillates the pulse signal as a digital circuit section. Further, the excitation circuit 30A may include an oscillation control section such as a processor that controls the operation of the oscillation circuit. However, the operation of the oscillation circuit of the excitation circuit 30A may be controlled by, for example, the CPU of the detection circuit 50.

[0063] As shown in FIG. 7, the first level shift circuit 61 is disposed between the excitation circuit 30A and the excitation coil 20. The first level shift circuit 61 boosts the voltage value (hereinafter simply referred to as "voltage value") corresponding to the amplitude of the rectangular wave voltage Vp input from the excitation circuit 30A. Thereby, the voltage value of the rectangular wave voltage Vp, which has been limited to or below the allowable voltage (for example, 5V) in the digital circuit section of the excitation circuit 30A, can be boosted. The configuration of the first level shift circuit 61 is arbitrary, and examples thereof include a logic IC (integrated circuit) such as a level shifter. However, the configuration of the first level shift circuit 61 is not limited thereto.

[0064] The rectangular wave voltage Vp boosted by the first level shift circuit 61 is supplied to one end 20a of the excitation coil 20. Further, as shown in FIG. 7, a push-pull circuit 71 may be disposed between the first level shift circuit 61 and one end 20a of the excitation coil 20. For example, when the rectangular wave voltage Vp from the first level shift circuit 61 is input to the first terminal 72 of the push-pull circuit 71, the first switch 73 turns on and the second switch 74 turns off. Thereby, the rectangular wave voltage Vp from the first level shift circuit 61 is supplied to the excitation coil 20 through the push-pull circuit 71. When the rectangular wave voltage Vp falls, the first switch 73 turns off and the second switch 74 turns on. Thereby, the second terminal 75 is conducted to the ground 76, and the supply of the rectangular wave voltage Vp stops. In FIG. 7, the push-pull circuit 71 is shown as a circuit separate from the first level shift circuit 61, but a circuit similar to the push-pull circuit 71 may be included in the first level shift circuit 61.

[0065] The second-level shift circuit 65 is disposed between the binarization circuit 40 and the detection circuit 50. The second-level shift circuit 65 steps down the voltage value (hereinafter simply referred to as "voltage value") corresponding to the amplitude of the binary signal input from the binarization circuit 40. For example, the second-level shift circuit 65 steps down the voltage value of the high-level signal HS input from the binarization circuit 40. Thereby, the voltage value of the binary signal from the binarization circuit 40 can be stepped down to be equal to or lower than the allowable voltage (for example, 5V) in the digital circuit section of the detection circuit 50. The configuration of the second-level shift circuit 65 is arbitrary, and examples thereof include a circuit including a voltage-dividing resistor. However, the configuration of the second-level shift circuit 65 is not limited thereto.

[0066] <Operational effects> According to the present embodiment, each of the excitation circuit 30A and the detection circuit 50 includes a digital circuit section. Thereby, miniaturization of the current detection device 1A can be achieved. Further, a first-level shift circuit 61 for stepping up the voltage value of the rectangular wave voltage Vp from the excitation circuit 30A is provided between the excitation circuit 30A and the excitation coil 20. Thereby, a rectangular wave voltage Vp having a relatively high voltage value can be input to the excitation coil 20, and the magnetic core 10 can be magnetically saturated in a short time. As a result, an increase in the period of the rectangular wave voltage Vp can be avoided. Further, a second-level shift circuit 65 for stepping down the voltage value of the binary signal from the binarization circuit 40 is provided between the binarization circuit 40 and the detection circuit 50. Thereby, damage to the detection circuit 50 can be prevented. Further, since an increase in the period of the rectangular wave voltage Vp is suppressed, an increase in the period of the binary signal of the binarization circuit 40 is also avoided. That is, an increase in the sampling period of the signal input to the detection circuit 50 can be suppressed. Therefore, a decrease in responsiveness when detecting the current to be detected can be suppressed. In addition, the current detection device 1A according to the second embodiment has the same effects as those of the first embodiment.

[0067] [Third Embodiment] <Leakage circuit breaker 100> Next, referring to FIG. 8, the leakage circuit breaker 100 according to the third embodiment will be described. FIG. 8 is a block diagram showing an example of the overall configuration of the leakage circuit breaker 100 according to the third embodiment.

[0068] As shown in FIG. 8, the leakage circuit breaker 100 includes a current detection device 1 or a current detection device 1A and a cutoff means 200. The cutoff means 200 cuts off the circuit connecting the power supply 3 and the load 4 based on the detection signal output from the detection circuit 50 of the current detection device 1.

[0069] The cutoff means 200 includes, for example, an actuator that is connected to the detection circuit 50 of the current detection devices 1 and 1A and operates to cut off the circuit according to the detection signal output from the detection circuit 50. Further, the cutoff means 200 may include an electromagnetic contactor or the like that opens and closes the circuit. Furthermore, the cutoff means 200 may be an electronic circuit including a semiconductor switching element or the like. However, the configuration of the cutoff means 200 is not limited thereto.

[0070] As described above, the embodiments have been explained. However, the above embodiments are presented as examples, and the present invention is not limited by the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0071] 1, 1A Current detection device 10 Magnetic core 20 Excitation coil 30 Excitation circuit 31 CR oscillation circuit 32 Push-pull circuit 40 Binarization circuit 41 Current-voltage conversion element 42 Comparator 50 Detection circuit 51 First time measurement circuit 52 First determination circuit 53 Second time measurement circuit 54 Second determination circuit 55 Integrating circuit 56 OR processing circuit 61 First level shift circuit 65 Second level shift circuit 100 Leakage breaker 200 Interrupting means

Claims

1. a magnetic core surrounding a conductor through which a current to be detected flows; an excitation coil wound around the magnetic core; an excitation circuit that outputs a rectangular wave voltage to the excitation coil; a binarization circuit connected to the other end of the excitation coil and outputting a binary signal composed of a low level signal and a high level signal, the binarization circuit outputting the low level signal when the voltage of the excitation coil exceeds a first reference voltage in response to the rectangular wave voltage, and outputting the high level signal when the voltage of the excitation coil falls below a second reference voltage lower than the first reference voltage; a detection circuit that detects the current to be detected that has flowed through the conductor based on a first time period between a first time point when the excitation circuit outputs the rectangular wave voltage to the excitation coil and a second time point when the binarization circuit outputs the high level signal for the first time after the first time point; A current detection device comprising:

2. the detection circuit determines that the current to be detected has flowed through the conductor when the detection circuit does not acquire the first high-level signal after the first time point until one period of the rectangular wave voltage has elapsed from the first time point. The current detection device according to claim 1 .

3. the detection circuit includes a first determination circuit, The first determination circuit is determining that the detected current has flowed through the conductor when the first time period is less than a first threshold value; Alternatively, when a difference between the first time and a second time between the first time point and the second time point when the current to be detected does not flow through the conductor exceeds a second threshold value, it is determined that the current to be detected has flowed through the conductor. The current detection device according to claim 1 or 2.

4. the detection circuit detects the current to be detected that has flowed through the conductor based on a third time that is a difference between the duration of the high-level signal and the duration of the low-level signal output from the binarization circuit. The current detection device according to claim 1 or 2.

5. The detection circuit includes: a second determination circuit that executes a determination process as to whether or not the third time period exceeds a third threshold value, and outputs a determination signal when the third time period exceeds the third threshold value; an integrating circuit connected to the second determination circuit; Further comprising: the second determination circuit executes the determination process based on a difference between the duration of the high-level signal and the duration of the low-level signal included in each of the binary signals, each time the second determination circuit receives the binary signals sequentially output from the binarization circuit; When the plurality of determination signals sequentially output from the second determination circuit are continuously input for a period of time equal to or longer than a fourth threshold as a result of the determination process, the integration circuit outputs a detection signal indicating that the current to be detected has flowed through the conductor. The current detection device according to claim 4.

6. The excitation circuit is connected to one end of the excitation coil. The current detection device according to claim 1 or 2.

7. The excitation circuit and the detection circuit include a digital circuit unit. The current detection device according to claim 1 or 2.

8. a first level shift circuit disposed between the excitation coil and the excitation circuit and configured to boost a voltage value of the rectangular wave voltage from the excitation circuit; a second level shift circuit disposed between the binarization circuit and the detection circuit, the second level shift circuit lowering a voltage value of the binary signal from the binarization circuit; The current sensing device of claim 7 further comprising:

9. A ground fault circuit interrupter comprising: a current detection device; and a breaker that breaks an electric path connecting a power source and a load based on a detection signal output from the current detection device, The current detection device is a magnetic core surrounding a conductor through which a current to be detected flows; an excitation coil wound around the magnetic core; an excitation circuit that outputs a rectangular wave voltage to the excitation coil; a binarization circuit connected to the other end of the excitation coil, which outputs a low level signal when the voltage of the excitation coil exceeds a first reference voltage in response to the rectangular wave voltage, and outputs a high level signal when the voltage of the excitation coil falls below a second reference voltage that is lower than the first reference voltage; a detection circuit that detects the current to be detected that has flowed through the conductor based on a first time period between a first time point when the excitation circuit outputs the rectangular wave voltage to the excitation coil and a second time point when the binarization circuit outputs the high level signal for the first time after the first time point; Equipped with the detection circuit outputs a detection signal to the interrupter when the detection circuit detects the current to be detected flowing through the conductor. Earth leakage circuit breaker.

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