Residual current monitoring circuit and earth leakage protection device

Abstract

Embodiments of the present disclosure provide a residual current monitoring circuit and an electric leakage protection device. A fluxgate circuit of the residual current monitoring circuit comprises an excitation circuit, a first resistor and a first current transformer. One end of the first resistor is electrically connected to the excitation circuit. The other end of the first resistor is electrically connected to a ground pole. The first current transformer has a first terminal and a second terminal. The first terminal of the first current transformer is electrically connected to the excitation circuit. The second terminal of the first current transformer is electrically connected to a node between the first resistor and the excitation circuit. A second current transformer has a third terminal and a fourth terminal. The second current transformer and the first current transformer encircle the same to-be-detected conductor. The winding direction of the second current transformer is the same as that of the first current transformer. The third terminal of the second current transformer is electrically connected to the second terminal of the first current transformer. A sampling circuit is electrically connected to the fourth terminal of the second current transformer.

Description

Technical Field

[0001] The embodiments disclosed herein relate generally to the field of electrical equipment, and more particularly to a residual current monitoring circuit and a leakage current protection device. Background Technology

[0002] When electrical systems experience faults such as leakage current or short circuits, they can pose serious threats to personal safety and equipment. Therefore, electrical safety is paramount in daily life and production. In conventional electrical systems, appropriate residual current monitoring devices can be selected based on the system type (e.g., AC or DC) to enhance safety. AC systems can use traditional residual current devices (RCDs) to detect fault current, while DC systems require high-precision sensors (such as fluxgate magnetometers) to monitor DC leakage current. Utility Model Content

[0003] In a first aspect of this disclosure, a residual current monitoring circuit is provided. The residual current monitoring circuit includes: a fluxgate circuit, the fluxgate circuit including: an excitation circuit; a first resistor, one end of which is electrically connected to the excitation circuit and the other end of which is electrically connected to a ground electrode; and a first current transformer having a first terminal and a second terminal, the first terminal being electrically connected to the excitation circuit and the second terminal being electrically connected to a node between the first resistor and the excitation circuit; a second current transformer having a third terminal and a fourth terminal, the second current transformer being adapted to wrap around the same conductor as the first current transformer, and the winding direction of the second current transformer being the same as that of the first current transformer, the third terminal of the second current transformer being electrically connected to the second terminal of the first current transformer; and a sampling circuit electrically connected to the fourth terminal of the second current transformer.

[0004] In some embodiments, the second current transformer is coaxially arranged with the first current transformer.

[0005] In some embodiments, the sampling circuit includes: a second resistor, one end of which is electrically connected to the fourth terminal of the second current transformer and the other end of which is electrically connected to the ground electrode; and a first filter circuit, which is electrically connected to the fourth terminal of the second current transformer and the ground electrode.

[0006] In some embodiments, the first filter circuit includes: a signal amplifier, the first input of which is electrically connected to a ground electrode; a third resistor, one end of which is electrically connected to a fourth terminal of a second current transformer and the other end of which is electrically connected to a second input of the signal amplifier; a fourth resistor, one end of which is electrically connected to the second input of the signal amplifier and the other end of which is electrically connected to an output of the signal amplifier; and a first capacitor, one end of which is electrically connected to the second input of the signal amplifier and the other end of which is electrically connected to an output of the signal amplifier.

[0007] In some embodiments, the residual current monitoring circuit further includes a second filter circuit electrically connected to the first filter circuit and the ground electrode, and adapted to be electrically connected to the analog-to-digital converter to prevent spectral aliasing.

[0008] In some embodiments, the second filter circuit includes: a fifth resistor, one end of which is electrically connected to the output of a signal amplifier; and a second capacitor, one end of which is electrically connected to the other end of the fifth resistor, the other end of which is electrically connected to ground, and the node between the second capacitor and the fifth resistor is adapted to be electrically connected to an analog-to-digital converter.

[0009] In some embodiments, the excitation circuit includes: a voltage divider circuit electrically connected to a ground electrode and adapted to be electrically connected to a drive power supply; a comparator having a first input terminal electrically connected to a second terminal of a first current transformer and a second input terminal electrically connected to the voltage divider circuit; a first semiconductor switch having a first electrode adapted to be electrically connected to the positive terminal of the power supply, a second electrode electrically connected to the first terminal of the first current transformer, a control terminal electrically connected to the output terminal of the comparator, and the control terminal of the first semiconductor switch being turned on when a high-level signal is received; and a second semiconductor switch having a first electrode electrically connected to the second electrode of the first semiconductor switch, a second electrode electrically connected to the negative terminal of the power supply, a control terminal electrically connected to the output terminal of the comparator, and the control terminal of the second semiconductor switch being turned on when a low-level signal is received.

[0010] In some embodiments, the voltage divider circuit includes: a sixth resistor, one end of which is electrically connected to a ground electrode and the other end of which is electrically connected to a second input terminal of a comparator; and a seventh resistor, one end of which is electrically connected to the second input terminal of a comparator and the other end of which is adapted to be electrically connected to a drive power supply.

[0011] In some embodiments, the residual current monitoring circuit further includes an inductor electrically connected between the excitation circuit and a first terminal of the first current transformer.

[0012] According to a second aspect of this disclosure, a leakage current protection device is provided. The leakage current protection device includes: a residual current monitoring circuit according to a first aspect of this disclosure; and an execution unit connected to both the residual current monitoring circuit and the conductor under test. When the residual current monitoring circuit detects residual current, the execution unit disconnects the conductor under test.

[0013] In embodiments of this disclosure, the residual current monitoring circuit includes a fluxgate circuit, a first current transformer, and a sampling circuit. The fluxgate circuit includes an excitation circuit, a first resistor, and a first current transformer. One end of the first resistor is electrically connected to the excitation circuit. The other end of the first resistor is electrically connected to a ground electrode. The first current transformer has a first terminal and a second terminal. The first terminal of the first current transformer is electrically connected to the excitation circuit. The second terminal of the first current transformer is electrically connected to the node between the first resistor and the excitation circuit. The second current transformer has a third terminal and a fourth terminal. The second current transformer and the first current transformer are wound around the same conductor under test. The winding direction of the second current transformer is the same as that of the first current transformer. The third terminal of the second current transformer is electrically connected to the second terminal of the first current transformer. The sampling circuit is electrically connected to the fourth terminal of the second current transformer. Using this arrangement, under DC current conditions, the first current transformer can detect changes in the DC current in the conductor under test, and the second current transformer can be used as an inductor to form a low-pass filter, thereby enabling the detection of DC or low-frequency components. When a high-frequency current exists in the circuit, the induced electromotive force at the node between the second terminal of the first current transformer and the third terminal of the second current transformer cancels each other out. Under these conditions, the second current transformer and the sampling circuit can continue to detect changes in the high-frequency current. Therefore, the residual current monitoring circuit can detect not only smoothed DC current, power frequency current, and power frequency pulsating DC current, but also high-frequency current and composite current, thus meeting the needs for residual current monitoring under various operating conditions.

[0014] It should be understood that the content described in this section is not intended to limit the key or essential features of the embodiments of this disclosure, nor is it intended to restrict the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0015] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. In the drawings, the same or similar reference numerals denote the same or similar elements, wherein: Figure 1 A circuit block diagram of a residual current monitoring circuit according to some embodiments of the present disclosure is shown.

[0016] Explanation of reference numerals in the attached figures: 501. Drive power supply; 502. Power supply; 503. Test lead; 100. Residual current monitoring circuit; 10. Fluxgate circuit; 11. First current transformer; 111. First terminal; 112. Second terminal; 12. Excitation circuit; 121. Voltage divider circuit; 1211. Sixth resistor; 1212. Seventh resistor; 122. Comparator; 123. First semiconductor switch; 124. Second semiconductor switch; 13. First resistor; 21. Second current transformer; 211. Third terminal; 212. Fourth terminal; 30. Sampling circuit; 31. Second resistor; 32. First filter circuit; 321. Signal amplifier; 322. Third resistor; 323. Fourth resistor; 324. First capacitor; 33. Second filter circuit; 331. Fifth resistor; 332. Second capacitor; 40. Inductance. Detailed Implementation

[0017] Embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0018] The term "comprising" and its variations as used herein signify open inclusion, i.e., "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "at least partially based on". The terms "one example embodiment" and "one embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc., may refer to different or the same objects.

[0019] As mentioned above, in some conventional electrical systems, appropriate residual current monitoring devices can be selected based on the type of electrical system (AC or DC) to improve electrical safety. For example, in AC systems, traditional residual current devices (RCDs) can be used to detect fault current. In DC systems, devices such as fluxgate magnets can be used to monitor DC leakage current. However, when electrical systems experience complex operating conditions such as DC current, high-frequency current, or AC / DC composite current, traditional residual current monitoring devices often struggle to simultaneously handle the detection needs of multiple current types, thus failing to meet the performance requirements of diverse application scenarios.

[0020] Embodiments of this disclosure provide a residual current monitoring circuit and a leakage current protection device. The residual current monitoring circuit includes a fluxgate magnetometer, a first current transformer, and a sampling circuit. The fluxgate magnetometer includes an excitation circuit, a first resistor, and a first current transformer. One end of the first resistor is electrically connected to the excitation circuit. The other end of the first resistor is electrically connected to a ground electrode. The first current transformer has a first terminal and a second terminal. The first terminal of the first current transformer is electrically connected to the excitation circuit. The second terminal of the first current transformer is electrically connected to the node between the first resistor and the excitation circuit. The second current transformer has a third terminal and a fourth terminal. The second current transformer and the first current transformer are wound around the same conductor under test. The winding direction of the second current transformer is the same as that of the first current transformer. The third terminal of the second current transformer is electrically connected to the second terminal of the first current transformer. The sampling circuit is electrically connected to the fourth terminal of the second current transformer. Using this arrangement, under DC current conditions, the first current transformer can detect changes in the DC current in the conductor under test, while the second current transformer can be used as an inductor to form a low-pass filter, thereby enabling the detection of DC or low-frequency components. When a high-frequency current exists in the circuit, the induced electromotive force at the node between the second terminal of the first current transformer and the third terminal of the second current transformer cancels each other out. In this case, the second current transformer and the sampling circuit can continue to detect changes in the high-frequency current. Therefore, the residual current monitoring circuit can detect not only smoothed DC current, power frequency current, and power frequency pulsating DC current, but also high-frequency current and composite current, thus meeting the needs of residual current monitoring under various operating conditions. The following will combine... Figure 1 The principles of this disclosure will be described in detail below.

[0021] like Figure 1 As shown, the residual current monitoring circuit 100 can be applied to various electrical devices for safety monitoring of the operating status of electrical systems. For example, in household electricity use, the residual current monitoring circuit 100 can detect potential leakage current, ensuring electrical safety. In industrial distribution cabinets, the residual current monitoring circuit 100 can be used to detect abnormal currents during equipment operation, preventing malfunctions caused by insulation damage or short circuits.

[0022] like Figure 1 As shown, the residual current monitoring circuit 100 may include a fluxgate circuit 10, a second current transformer 21, and a sampling circuit 30. The fluxgate circuit 10 may include an excitation circuit 12, a first resistor 13, and a first current transformer 11. One end of the first resistor 13 is electrically connected to the excitation circuit 12. The other end of the first resistor 13 is electrically connected to the ground terminal GND. In this way, the first resistor 13 can form a reference loop.

[0023] like Figure 1As shown, the first current transformer 11 has a first terminal 111 and a second terminal 112. The first terminal 111 of the first current transformer 11 is electrically connected to the excitation circuit 12. The second terminal 112 of the first current transformer 11 is electrically connected to the node between the first resistor 13 and the excitation circuit 12. The first current transformer 11 can detect the DC current or low-frequency component in the conductor 503 under test.

[0024] like Figure 1 As shown, the second current transformer 21 has a third terminal 211 and a fourth terminal 212. The second current transformer 21 has the same specifications and model as the first current transformer 11 and is wound around the same conductor 503 under test. For example, the winding direction of the second current transformer 21 is the same as that of the first current transformer 11. The number of turns in the second current transformer 21 is the same as that in the first current transformer 11.

[0025] In this way, when sensing the current change in the conductor 503 under test, the induced electromotive force of the first current transformer 11 and the induced electromotive force of the second current transformer 21 are in the same direction. The third terminal 211 of the second current transformer 21 is electrically connected to the second terminal 112 of the first current transformer 11. The sampling circuit 30 is electrically connected to the fourth terminal 212 of the second current transformer 21. By adding the second current transformer 21 and the sampling circuit 30 to the fluxgate circuit 10, not only is the function of the fluxgate circuit 10 in detecting DC signals retained, but the second current transformer 21 also functions as an inductor and a signal detector.

[0026] like Figure 1 As shown, when the residual current monitoring circuit 100 is working, the fluxgate circuit 10 functions when there is a DC current or low-frequency current in the conductor 503 under test. The first current transformer 11 can sense and output a signal related to the current change. At this time, the second current transformer 21 can be used as an inductive element to form a low-pass filter circuit, thereby reflecting the changes in the DC current or low-frequency component.

[0027] When a high-frequency current appears in the conductor 503 under test, the first current transformer 11 and the second current transformer 21 will simultaneously generate induced electromotive forces (EMFs), and the magnitudes and directions of these induced EMFs will be the same. For example, when a high-frequency current appears in the conductor 503 under test, the induced current of the first current transformer 11 flows sequentially through the second terminal 112, the connection node between the second terminal 112 and the third terminal 211, and the first resistor 13. The induced current of the second current transformer 21 flows sequentially through the first resistor 13, the connection node between the second terminal 112 and the third terminal 211, and the third terminal 211. Therefore, the induced EMFs of the first current transformer 11 and the second current transformer 21 at their connection nodes will cancel each other out. At this time, the second current transformer 21 and the sampling circuit 30 can detect the high-frequency current.

[0028] Using this arrangement, under DC current conditions, the first current transformer 11 can detect changes in the DC current in the conductor 503 under test, and the second current transformer 21 can be used as an inductor 40 to form a low-pass filter, thereby enabling the detection of DC or low-frequency components. Under high-frequency current conditions, the induced electromotive force at the node between the second terminal 112 of the first current transformer 11 and the third terminal 211 of the second current transformer 21 cancels each other out, and the fluxgate circuit 10 does not operate. The second current transformer 21 and the sampling circuit 30 can detect changes in the high-frequency current in the conductor 503 under test. Therefore, the residual current monitoring circuit 100 can simultaneously cover the monitoring of smooth DC current, power frequency current, power frequency pulsating DC current, high-frequency current, and composite current, thereby meeting the residual current detection requirements under different operating conditions.

[0029] In some embodiments, such as Figure 1 As shown, the first current transformer 11 and the second current transformer 21 are coaxially arranged. This arrangement ensures that the high-frequency current changes sensed by the first current transformer 11 and the second current transformer 21 are as consistent as possible. Under high-frequency current conditions, interference from the signal generated by the fluxgate circuit 10 to the detection of the second current transformer 21 can be avoided.

[0030] As an example, to increase structural stability, a housing can be provided outside the first current transformer 11 and the second current transformer 21. The housing not only fixes the position of both but also simplifies the installation process of the conductor 503 under test.

[0031] In some embodiments, such as Figure 1As shown, the sampling circuit 30 may include a second resistor 31 and a first filter circuit 32. One end of the second resistor 31 is electrically connected to the fourth terminal 212 of the second current transformer 21. The other end of the second resistor 31 is electrically connected to the ground terminal GND. The first filter circuit 32 is electrically connected to the fourth terminal 212 of the second current transformer 21 and the ground terminal GND. With this arrangement, the second resistor 31 can act as a sampling resistor in the residual current monitoring circuit 100 to acquire the current signal and convert it into a voltage change. Through the voltage change, the circuit can detect the current characteristics flowing through the circuit. The first filter circuit 32, as a low-pass filter circuit, can filter out high-frequency noise and interference in the current signal, thereby increasing the stability and reliability of the signal.

[0032] In some embodiments, such as Figure 1 As shown, the first filter circuit 32 may include a signal amplifier 321, a third resistor 322, a fourth resistor 323, and a first capacitor 324. The first input terminal of the signal amplifier 321 is electrically connected to ground (GND). One end of the third resistor 322 is electrically connected to the fourth terminal 212 of the second current transformer 21. The other end of the third resistor 322 is electrically connected to the second input terminal of the signal amplifier 321. One end of the fourth resistor 323 is electrically connected to the second input terminal of the signal amplifier 321. The other end of the fourth resistor 323 is electrically connected to the output terminal of the signal amplifier 321. One end of the first capacitor 324 is electrically connected to the second input terminal of the signal amplifier 321. The other end of the first capacitor 324 is electrically connected to the output terminal of the signal amplifier 321. With this arrangement, the current signal passes through the third resistor 322 and then enters the second input terminal of the signal amplifier 321. The signal amplifier 321 amplifies the current signal passing through the third resistor 322. The fourth resistor 323 inputs the signal to the output terminal of the signal amplifier 321, while the first capacitor 324 smooths the signal and filters out high-frequency components. The first capacitor 324 acts as a low-pass filter. The filtered signal is output from the output terminal of the signal amplifier 321, thus providing a stable and clear current signal for subsequent processing.

[0033] In some embodiments, such as Figure 1 As shown, the residual current monitoring circuit 100 may further include a second filter circuit 33. The second filter circuit 33 is electrically connected to the first filter circuit 32 and the ground terminal GND, and may also be electrically connected to the analog-to-digital converter. The second filter circuit 33 is an anti-aliasing filter circuit, which can prevent high-frequency components in the signal spectrum from overlapping with low-frequency signals, thereby avoiding aliasing.

[0034] In some embodiments, such as Figure 1As shown, the second filter circuit 33 includes a fifth resistor 331 and a second capacitor 332. One end of the fifth resistor 331 is electrically connected to the output of the signal amplifier 321. One end of the second capacitor 332 is electrically connected to the other end of the fifth resistor 331. The other end of the second capacitor 332 is electrically connected to ground (GND). With this arrangement, the other end of the second capacitor 332 is grounded, which can filter out high-frequency noise. The fifth resistor 331 can limit the signal current, thereby ensuring appropriate signal amplitude and frequency characteristics. The node between the second capacitor 332 and the fifth resistor 331 can be electrically connected to an analog-to-digital converter, thereby providing a filtered low-frequency signal and helping to prevent spectral aliasing.

[0035] In some embodiments, such as Figure 1 As shown, the excitation circuit 12 includes a voltage divider circuit 121, a comparator 122, a first semiconductor switch 123, and a second semiconductor switch 124. The voltage divider circuit 121 is electrically connected to ground (GND) and can be electrically connected to the drive power supply 501. The voltage divider circuit 121 can provide a reference voltage to the input terminal of the comparator 122. The first input terminal of the comparator 122 is electrically connected to the second terminal 112 of the first current transformer 11. The second input terminal of the comparator 122 is electrically connected to the voltage divider circuit 121. The first electrode of the first semiconductor switch 123 can be electrically connected to the positive terminal of the power supply 502. The second electrode of the first semiconductor switch 123 is electrically connected to the first terminal 111 of the first current transformer 11. The control terminal of the first semiconductor switch 123 is electrically connected to the output terminal of the comparator 122, and the control terminal of the first semiconductor switch 123 conducts when it receives a high-level signal. The first electrode of the second semiconductor switch 124 is electrically connected to the second electrode of the first semiconductor switch 123. The second electrode of the second semiconductor switch 124 is electrically connected to the negative terminal (VSS) of the power supply 502. The control terminal of the second semiconductor switch 124 is electrically connected to the output terminal of the comparator 122, and the control terminal of the second semiconductor switch 124 is turned on when a low-level signal is received.

[0036] In this way, the voltage divider circuit 121 can provide a reference voltage for the comparator 122, allowing the input of the comparator 122 to be compared with the signal to be measured. When the first current transformer 11 senses a DC current, the first input of the comparator 122 is connected to the second terminal 112 of the first current transformer 11, and the second input of the comparator 122 receives the reference voltage from the voltage divider circuit 121. By comparing the voltage difference between the two inputs, the comparator 122 can output a high-level or low-level signal.

[0037] When comparator 122 outputs a high-level signal, the first semiconductor switch 123 is turned on, and current flows in from the power supply 502, through the first semiconductor switch 123, the first current transformer 11, and the first resistor 13, before flowing to the ground terminal GND, forming a complete current path. The first current transformer 11 senses the current change and transmits the information. When comparator 122 outputs a low-level signal, the second semiconductor switch 124 is turned on, and current flows from the ground terminal GND to the first resistor 13, the first current transformer 11, and then to the second semiconductor switch 124. When the DC signal flips, comparator 122 can output a control signal according to the current change to trigger the switch switching.

[0038] In some embodiments, the first semiconductor switch 123 and the second semiconductor switch 124 may be MOS switches. For example, the first semiconductor switch 123 may be an N-channel MOSFET to be turned on under high-level control, and the second semiconductor switch 124 may be a P-channel MOSFET to be turned on under low-level control.

[0039] In other embodiments, the first semiconductor switch 123 and the second semiconductor switch 124 may also be other types of semiconductor switches, such as bipolar transistors (BJTs), insulated gate bipolar transistors (IGBTs), etc. Those skilled in the art can choose as needed, and this disclosure is not intended to limit the specific type of semiconductor switch.

[0040] In some embodiments, such as Figure 1 As shown, the voltage divider circuit 121 includes a sixth resistor 1211 and a seventh resistor 1212. One end of the sixth resistor 1211 is electrically connected to ground (GND). The other end of the sixth resistor 1211 is electrically connected to the second input terminal of comparator 122. One end of the seventh resistor 1212 is electrically connected to the second input terminal of comparator 122. The other end of the seventh resistor 1212 is adapted to be electrically connected to the drive power supply 501. With this arrangement, the sixth resistor 1211 and the seventh resistor 1212 can form a reference voltage at the connection node. When comparator 122 receives and compares the input signal, it outputs a high-level or low-level signal according to the set value of the reference voltage, thereby switching the conduction state of the first semiconductor switch 123 and the second semiconductor switch 124.

[0041] In some embodiments, such as Figure 1As shown, the residual current monitoring circuit 100 may further include an inductor 40. The inductor 40 is electrically connected between the excitation circuit 12 and the first terminal 111 of the first current transformer 11. In this way, since the inductor 40 itself does not saturate, a high-frequency oscillation signal can be generated by the inductor 40, thereby distinguishing large DC currents. For example, when the residual current of the conductor 503 under test reaches 5A or more, the first current transformer 11 saturates, causing the magnetic core to be unable to sense larger current changes, and the fluxgate circuit 10 cannot provide feedback on the magnitude of the residual current. At this time, the high-frequency oscillation signal of the inductor 40 can be used as a substitute signal, indirectly reflecting the magnitude of the residual current through the oscillation frequency in the circuit. For example, the fluxgate circuit 10 can operate at a frequency of 1kHz when the residual current is less than or equal to 5A. When the residual current exceeds 5A, the oscillation frequency can rise to 5kHz. In this way, the monitoring range of the residual current monitoring circuit 100 can be extended to cover the monitoring needs of larger currents.

[0042] In some embodiments, the inductance of inductor 40 may be 100 microhenries (μH). In other embodiments, the inductance of inductor 40 may be in the range of 10 microhenries (μH) to 500 microhenries (μH).

[0043] It should be noted that the figures, values, etc., mentioned above and elsewhere in this disclosure are exemplary and are not intended to limit the scope of this disclosure in any way. Any other suitable figures or values ​​are possible.

[0044] In some embodiments, a detection line can be provided at the connection node between the first semiconductor switch 123 and the inductor 40, and the magnitude of the residual current can be fed back by detecting the signal oscillation frequency at the node.

[0045] According to a second aspect of this disclosure, a leakage current protection device is provided. The leakage current protection device includes a residual current monitoring circuit 100 and an execution unit, as described above. The execution unit is connected to the residual current monitoring circuit 100 and the test lead 503, respectively. When the residual current monitoring circuit 100 detects residual current, the execution unit disconnects the test lead 503. As an example, the execution unit may include a tripping assembly and a four-bar linkage tripping mechanism. The tripping assembly may be at least one of a magnetic tripping assembly or a thermal tripping assembly. When the residual current monitoring circuit 100 detects residual current, the tripping assembly can unlock the four-bar linkage tripping mechanism, thereby disconnecting the test lead 503.

[0046] In the residual current protection device, under DC current conditions, the first current transformer 11 can detect changes in the DC current in the conductor 503 under test, and the second current transformer 21 can be used as an inductor to form a low-pass filter, thereby realizing the detection of DC or low-frequency components. Under high-frequency current conditions, the induced electromotive force at the node between the second terminal 112 of the first current transformer 11 and the third terminal 211 of the second current transformer 21 cancels each other out. The second current transformer 21 and the sampling circuit 30 can detect changes in the high-frequency current in the conductor 503 under test. Therefore, the residual current monitoring circuit 100 can simultaneously cover the monitoring of smooth DC current, power frequency current, power frequency pulsating DC current, high-frequency current, and composite current, thereby meeting the residual current detection requirements under different operating conditions.

[0047] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, and are not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A residual current monitoring circuit (100), characterized in that, include: Fluxgate circuit (10), the fluxgate circuit (10) includes: Excitation circuit (12); A first resistor (13), one end of which is electrically connected to the excitation circuit (12), and the other end of which is electrically connected to the ground electrode; and The first current transformer (11) has a first terminal (111) and a second terminal (112), the first terminal (111) being electrically connected to the excitation circuit (12), and the second terminal (112) being electrically connected to the node between the first resistor (13) and the excitation circuit (12); A second current transformer (21) has a third terminal (211) and a fourth terminal (212). The second current transformer (21) is adapted to be wound around the same conductor (503) as the first current transformer (11), and the winding direction of the second current transformer (21) is the same as that of the first current transformer (11). The third terminal (211) of the second current transformer (21) is electrically connected to the second terminal (112) of the first current transformer (11). The sampling circuit (30) is electrically connected to the fourth terminal (212) of the second current transformer (21).

2. The residual current monitoring circuit (100) according to claim 1, characterized in that, The second current transformer (21) is coaxially arranged with the first current transformer (11).

3. The residual current monitoring circuit (100) according to claim 1, characterized in that, The sampling circuit (30) includes: The second resistor (31) has one end electrically connected to the fourth terminal (212) of the second current transformer (21), and the other end electrically connected to the ground electrode; and The first filter circuit (32) is electrically connected to the fourth terminal (212) of the second current transformer (21) and the grounding electrode.

4. The residual current monitoring circuit (100) according to claim 3, characterized in that, The first filter circuit (32) includes: A signal amplifier (321) has its first input terminal electrically connected to the ground electrode; The third resistor (322) has one end electrically connected to the fourth terminal (212) of the second current transformer (21) and the other end electrically connected to the second input terminal of the signal amplifier (321); A fourth resistor (323), one end of which is electrically connected to the second input terminal of the signal amplifier (321), and the other end of which is electrically connected to the output terminal of the signal amplifier (321); and The first capacitor (324) has one end electrically connected to the second input terminal of the signal amplifier (321) and the other end electrically connected to the output terminal of the signal amplifier (321).

5. The residual current monitoring circuit (100) according to claim 4, characterized in that, Also includes: The second filter circuit (33) is electrically connected to the first filter circuit (32) and the ground electrode, and is adapted to be electrically connected to the analog-to-digital converter to prevent spectral aliasing.

6. The residual current monitoring circuit (100) according to claim 5, characterized in that, The second filter circuit (33) includes: The fifth resistor (331), one end of which is electrically connected to the output of the signal amplifier (321); and The second capacitor (332) has one end electrically connected to the other end of the fifth resistor (331) and the other end electrically connected to the ground electrode, and the node between the second capacitor (332) and the fifth resistor (331) is adapted to be electrically connected to the analog-to-digital converter.

7. The residual current monitoring circuit (100) according to any one of claims 1 to 4, characterized in that, The excitation circuit (12) includes: The voltage divider circuit (121) is electrically connected to the ground electrode and is adapted to be electrically connected to the drive power supply (501). The comparator (122) has its first input terminal electrically connected to the second terminal (112) of the first current transformer (11), and its second input terminal electrically connected to the voltage divider circuit (121). A first semiconductor switch (123) has a first electrode adapted to be electrically connected to the positive terminal of a power supply (502), a second electrode electrically connected to the first terminal (111) of the first current transformer (11), and a control terminal electrically connected to the output terminal of the comparator (122). The control terminal of the first semiconductor switch (123) is turned on when a high-level signal is received. The second semiconductor switch (124) has its first electrode electrically connected to the second electrode of the first semiconductor switch (123), its second electrode electrically connected to the negative terminal of the power supply (502), its control terminal electrically connected to the output terminal of the comparator (122), and the control terminal of the second semiconductor switch (124) is turned on when a low-level signal is received.

8. The residual current monitoring circuit (100) according to claim 7, characterized in that, The voltage divider circuit (121) includes: The sixth resistor (1211) has one end electrically connected to the ground electrode and the other end electrically connected to the second input terminal of the comparator (122); and The seventh resistor (1212) has one end electrically connected to the second input terminal of the comparator (122) and the other end adapted to be electrically connected to the drive power supply (501).

9. The residual current monitoring circuit (100) according to any one of claims 1 to 4, characterized in that, Also includes: An inductor (40) is electrically connected between the excitation circuit (12) and the first terminal (111) of the first current transformer (11).

10. A leakage current protection device, characterized in that, include: The residual current monitoring circuit (100) according to any one of claims 1 to 9. as well as An execution unit is connected to the residual current monitoring circuit (100) and the wire to be tested (503) respectively. When the residual current monitoring circuit (100) detects residual current, the execution unit disconnects the wire to be tested (503).

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