Current detection device

Abstract

The current detection device (1) includes an analog circuit (40), an AD converter (50), and a calculation unit (60). The analog circuit (40) has a differential input circuit (41) connected to the two output terminals (11, 12) of the Rogowski coil (10). The AD converter (50) converts the analog signal output from the analog circuit (40) into a digital signal. The calculation unit (60) calculates the value of the current flowing through the conductor (2) based on the digital signal output from the AD converter (50). The Rogowski coil (10) has a neutral point (13) located at a position that will divide the voltage generated between the two output terminals (11, 12) into two equal parts. The analog ground (3) of the differential input circuit (41) is connected to the neutral point (13) of the Rogowski coil (10).

Description

Technical Field

[0001] This invention relates to a current detection device for detecting the current flowing through a conductor. Background Technology

[0002] Currently, current detection devices that use Rogowski coils are known as current detection devices for detecting the current flowing through a conductor. For example, Patent Document 1 discloses a current detection device that includes a Rogowski coil, an analog circuit, an AD (Analogue to Digital) converter, and a CPU (Central Processing Unit).

[0003] In the current detection device described in Patent Document 1, the output of a Rogowski coil with a conductor inserted is input to an analog circuit. The analog signal output from the analog circuit is converted into a digital signal by an AD converter. The CPU calculates the value of the current flowing through the conductor based on the output of the AD converter.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2001-343401

[0005] However, the analog circuit of the current detection device described in Patent Document 1 does not use a differential input circuit structure based on analog ground. When the analog circuit of a current detection device using a Rogowski coil uses a differential input circuit, if a common-mode voltage is generated between the analog ground and the earth, a leakage current is generated. Due to the common-mode noise generated by this leakage current, the current detection accuracy in the current detection device may deteriorate. Summary of the Invention

[0006] The present invention is proposed in view of the above circumstances, and its object is to provide a current detection device that can detect the current with high accuracy even when a common-mode voltage is generated between the simulated ground and the earth in a current detection device that combines a Rogowski coil and a differential input circuit.

[0007] To address the aforementioned issues and achieve the objective, the current detection device of the present invention includes a Rogowski coil, an analog circuit, an analog-to-digital converter (ADC), and a calculation unit. The Rogowski coil is positioned to surround a conductor. The analog circuit has a differential input circuit connected to the two output terminals of the Rogowski coil. The ADC converts an analog signal output from the analog circuit into a digital signal. The calculation unit calculates the value of the current flowing through the conductor based on the digital signal output from the ADC. The Rogowski coil has a neutral point positioned to bisec the voltage generated between the two output terminals. The analog ground of the differential input circuit is connected to the neutral point of the Rogowski coil.

[0008] The effects of the invention

[0009] According to the present invention, the current detection device, which combines a Rogowski coil and a differential input circuit, can detect the current with high accuracy even when a common-mode voltage is generated between the simulated ground and the earth. Attached Figure Description

[0010] Figure 1 This is a diagram illustrating an example of the structure of the current detection device according to Embodiment 1.

[0011] Figure 2 This is a diagram illustrating an example of the structure of a current sensing device using a Rogowski coil without a neutral point.

[0012] Figure 3 It is used for in Figure 2 The diagram illustrates the path of leakage current flowing to the ground in the current detection device shown.

[0013] Figure 4 This is a diagram used to illustrate the path of leakage current to the ground in the current detection device according to Embodiment 1.

[0014] Figure 5 This is a diagram used to illustrate the path of leakage current flowing to the ground via the stray capacitance of the cable in the current detection device according to Embodiment 1.

[0015] Figure 6 This is a diagram illustrating an example of the structure of the Rogowski coil according to Embodiment 1.

[0016] Figure 7 This is a diagram illustrating another example of the structure of the Rogowski coil according to Embodiment 1. Detailed Implementation

[0017] Hereinafter, the current detection device according to the embodiments will be described in detail based on the accompanying drawings.

[0018] Implementation method 1.

[0019] Figure 1 This is a diagram illustrating an example of the structure of the current detection device according to Embodiment 1. (See diagram for example.) Figure 1 As shown, the current detection device 1 according to Embodiment 1 includes a Rogowski coil 10, a circuit board 20, and a cable 30.

[0020] The Rogowski coil 10 is formed in a circular ring shape. The Rogowski coil 10 is positioned to surround the primary conductor, i.e., conductor 2. The Rogowski coil 10 has output terminals 11 and 12 and a neutral point 13. The output terminals 11 and 12 output voltages proportional to changes in the primary current flowing through conductor 2, and the neutral point 13 is positioned to equally divide the voltages generated at the output terminals 11 and 12.

[0021] The circuit board 20 has input terminals 21, 22, and 23, analog circuitry 40, an AD converter 50, and a computing unit 60. Input terminals 21, 22, and 23 are connected to output terminals 11 and 12 and a neutral point 13 via cables 30. Cable 30 has conductors connecting output terminal 11 to input terminal 21, conductors connecting output terminal 12 to input terminal 22, and conductors connecting neutral point 13 to input terminal 23.

[0022] Analog circuit 40 includes a differential input circuit 41 and integrating circuits 42 and 43. The differential input circuit 41 has input resistors 44 and 45, and is connected to output terminals 11 and 12 via input terminals 21 and 22. One end of input resistor 44 is connected to input terminal 21, and the other end is connected to analog ground 3. Similarly, one end of input resistor 45 is connected to input terminal 22, and the other end is connected to analog ground 3. The circuit including differential input circuit 41 and integrating circuits 42 and 43 is a differential circuit symmetrical with reference to analog ground 3.

[0023] Input resistors 44 and 45 are resistors with the same resistance value. Through these input resistors 44 and 45, the output voltage e of the Rogowski coil 10 is divided into two equal parts with reference to analog ground 3. Thus, the voltage at one end of one of the input resistors 44 and 45 is +e / 2, and the voltage at one end of the other is -e / 2.

[0024] The output voltage e of the Rogowski coil 10 is input to integrator circuits 42 and 43 as the differential voltage. A voltage of +e / 2 is input to one of integrator circuits 42 and 43, and a voltage of -e / 2 is input to the other. The waveform of the output voltage e of the Rogowski coil 10 is the differential waveform of the primary current. Therefore, integrator circuits 42 and 43 restore the similar waveform of the primary current based on the waveform of the output voltage e of the Rogowski coil 10 by integrating the input voltage.

[0025] The AD converter 50 is a ΔΣ type AD converter that converts the differential voltage output from the integrator circuits 42 and 43 as an analog signal into a digital signal. By using a ΔΣ type AD converter as AD converter 50, advantages such as oversampling or independent inter-channel synchronous detection are achieved. The calculation unit 60 calculates the instantaneous value and RMS value of the primary current flowing through conductor 2 based on the digital signal output from the AD converter 50. The calculation unit 60 may be, for example, a microcomputer, but may also be an arithmetic circuit other than a microcomputer.

[0026] In the current detection device 1 according to Embodiment 1, a neutral point 13 is provided in the Rogowski coil 10, and the neutral point 13 is connected to the simulated ground 3. Therefore, even if a common-mode voltage is generated between the simulated ground 3 and the ground (not shown), the current detection device 1 can detect the current flowing through the conductor 2 with high accuracy. The reasons for this will be explained in detail below.

[0027] First, the output voltage e of the Rogowski coil 10 will be explained. If a current that varies with time flows through the conductor 2, a voltage E corresponding to the current flowing through the conductor 2 will be generated in the Rogowski coil 10 due to the Rogowski coil 10. The voltage E generated in the Rogowski coil 10 is the voltage of the waveform after differentiating the waveform of the current flowing through the conductor 2, and the current I flowing through the Rogowski coil 10 is represented by the following equation (1).

[0028] I=E / (r+R)···(1)

[0029] In equation (1) above, "r" is the internal impedance of the Rogowski coil 10, and "R" is the input impedance of the analog circuit 40. Hereinafter, the internal impedance of the Rogowski coil 10 will sometimes be referred to as the internal resistance r, and the input impedance of the analog circuit 40 will sometimes be referred to as the input resistance R. The voltage output from the output terminals 11 and 12 of the Rogowski coil 10, i.e., the output voltage e, is represented by the following equation (2).

[0030] e=E×R / (r+R)···(2)

[0031] The internal resistance r of the Rogowski coil 10 varies depending on the number of turns and winding temperature. That is, the internal resistance r depends on the rated current of the Rogowski coil 10 and the ambient temperature. To reduce the impact of these factors on the output voltage e of the Rogowski coil 10, the input resistance R of the analog circuit 40 can be set to a sufficiently large value compared to the internal resistance r. As can be seen from equation (2) above, this is because increasing the input resistance R reduces the influence of the internal resistance r on the output voltage e of the Rogowski coil 10.

[0032] Next, refer to Figure 2 Specifically, this explains the mechanism by which leakage current is generated when a common-mode voltage is generated between simulated ground 3 and the earth, and common-mode noise is generated through the aforementioned leakage current. Figure 2 This diagram illustrates an example of the structure of a current sensing device using a Rogowski coil without a neutral point. Figure 2 In the middle, for those with Figure 1 The structural elements with the same function as the current detection device 1 shown are labeled with the same numbers and their descriptions are omitted.

[0033] Figure 2The difference between the current detection device 1A shown and the current detection device 1 is that it has a Rogowski coil 10A, a circuit board 20A, and a cable 30A instead of the Rogowski coil 10, the circuit board 20, and the cable 30. The difference between the Rogowski coil 10A and the Rogowski coil 10 is that it does not have... Figure 1 Neutral point 13 is shown. The difference between circuit board 20A and circuit board 20 is that it does not have... Figure 1 The input terminal 23 is shown. Cable 30A differs from cable 30 in that it does not have the function of... Figure 1 The wire connecting the neutral point 13 to the input terminal 23 is shown.

[0034] exist Figure 2 In the current detection device 1A shown, when a common-mode voltage is generated between the simulated ground 3 and the earth (not shown), a leakage current is generated on the circuit board 20A. This leakage current flows to the ground via the inter-winding capacitance of the Rogowski coil 10A and the stray capacitance of the cable 30A. The stray capacitance of the cable 30A is the stray capacitance between the cable 30A and the earth, also known as parasitic capacitance. The inter-winding capacitance of the Rogowski coil 10A is the electrostatic capacitance between the Rogowski coil 10A and the primary conductor, i.e., conductor 2.

[0035] Figure 3 It is used for in Figure 2 The diagram illustrates the path of leakage current to ground in the current detection device shown. Figure 3 As shown, when a common-mode voltage Vcom is generated between analog ground 3 and earth 4, the leakage current branches from analog ground 3 into the first path and the second path. The first path is the path that flows from input terminal 21 to output terminal 11 through input resistor 44, and the second path is the path that flows from input terminal 22 to output terminal 12 through input resistor 45.

[0036] The leakage current flowing through paths 1 and 2 flows to ground 4 via the stray capacitance of cable 30A and the inter-winding capacitance of Rogowski coil 10A. Input resistances 44 and 45 are necessarily present in the path of the leakage current to ground 4. Therefore, the common-mode noise V generated between the input resistances 44 and 45 and the analog ground 3 due to the leakage current... CM It is represented by the following equation (3). In the following equation (3), "Ra" represents the resistance value of the input resistors 44 and 45, and "I" represents the resistance value of the input resistors 44 and 45. reaq "Indicates the magnitude of the leakage current.

[0037] V CM =I reaq ×Ra···(3)

[0038] When the current flowing through conductor 2 is a commercial frequency AC current, the impedance generated by the inter-winding capacitance and stray capacitance is sufficiently large compared to the impedance of the input resistors 44 and 45 in the commercial frequency band. Therefore, the leakage current I... reaq The value is determined by the inter-winding capacitance and the stray capacitance of the 30A cable.

[0039] Common-mode noise V CM The input is fed to the positive and negative terminals of the AD converter 50 through the integrating circuits 42 and 43. Therefore, due to the noise components not completely removed by the AD converter 50, the current detection accuracy of the current sensing device 1A deteriorates. Specifically, in the current sensing device 1A using the Rogowski coil 10A, as described above, it is necessary to increase the resistance values ​​of the input resistors 44 and 45, thus increasing the common-mode noise V, as expressed by equation (3) above. CM As the current increases, the decrease in current detection accuracy becomes significant. The same applies if the analog circuit 40 uses the current detection device of the differential input circuit 41, and if an AD converter other than a ΔΣ type AD converter is used as the AD converter 50.

[0040] Therefore, in Figure 1 In the current detection device 1 according to Embodiment 1 shown, as described above, a neutral point 13 is provided in the Rogowski coil 10, and the neutral point 13 is connected to the analog ground 3. In the current detection device 1, when a common-mode voltage Vcom is generated between the analog ground 3 and the earth 4, regarding the path of leakage current flowing to the earth 4, there are two paths: one flowing to the earth 4 via the inter-winding capacitance of the Rogowski coil 10 and the other flowing to the earth 4 via the stray capacitance of the cable 30. The inter-winding capacitance of the Rogowski coil 10 is the electrostatic capacitance between the Rogowski coil 10 and the primary conductor, i.e., conductor 2.

[0041] First, refer to Figure 4 The path of leakage current flowing to ground 4 through the inter-winding capacitance of Rogowski coil 10 is explained in the current detection device 1, where a common-mode voltage Vcom is generated between analog ground 3 and earth 4. Figure 4 This is a diagram used to illustrate the path of leakage current to ground in the current detection device according to Embodiment 1. Furthermore, in Figure 4 The calculation section 60 is omitted.

[0042] To keep the explanation simple, in Figure 4 In the process, virtual points 14a, 14b, and 14c, through which leakage current flows to ground 4 via inter-winding capacitance, are located inside the Rogowski coil 10. Virtual point 14a is a virtual point connected to output terminal 11, virtual point 14b is a virtual point connected to output terminal 12, and virtual point 14c is a virtual point connected to neutral point 13.

[0043] First, if we consider the path of leakage current flowing from virtual point 14a to ground 4 via inter-winding capacitance, then in the above path there exists in parallel the input resistance 44, the winding resistance of Rogowski coil 10 between neutral point 13 and output terminal 11.

[0044] In the current detection device 1 using the Rogowski coil 10, as described above, the input resistance is a sufficiently large value compared to the winding resistance. Therefore, in the path of leakage current flowing from the virtual point 14a to ground 4 via the inter-winding capacitance, almost all of the leakage current flows through the winding resistance between the neutral point 13 and the output terminal 11 to ground 4. Therefore, the leakage current flowing through the input resistance 44 is a very small value.

[0045] Similarly, considering the path of leakage current flowing from virtual point 14b through the inter-winding capacitance to ground 4, the input resistor 45 and the winding resistance of the Rogowski coil 10 between neutral point 13 and output terminal 12 are connected in parallel along this path. Therefore, the leakage current in this path also flows almost entirely through the winding resistance between neutral point 13 and output terminal 12 to ground 4. Thus, the leakage current flowing through input resistor 45 is a very small value.

[0046] Therefore, in the path of leakage current flowing to ground 4 through the inter-winding capacitance of Rogowski coil 10, common-mode noise V is generated across the input resistors 44 and 45 respectively. CM The magnitude is represented by the following formula (4). In the following formula (4), "Ra" represents the resistance value of the input resistors 44 and 45, "r" represents the value of the winding resistance from the neutral point 13 to each output terminal 11 and 12, and "I" represents the value of the winding resistance from the neutral point 13 to each output terminal 11 and 12. reaq "Indicates the magnitude of the leakage current.

[0047] V CM =I reaq ×(r×Ra) / (r+Ra)

[0048] =I reaq ×r / {(r / Ra)+1}···(4)

[0049] In the current detection device 1, the internal resistance *r* of the Rogowski coil 10 is, for example, a few ohms to several hundred ohms, while the resistances of the input resistors 44 and 45 are, for example, tens of kilohms to several megahms. In this case, the internal resistance *r* is at least 100 times smaller than the resistances of the input resistors 44 and 45. Therefore, the resistance of the parallel circuit between the internal resistance *r* and the input resistors 44 and 45 is approximately equal to the resistance of the internal resistance *r*. Therefore, the common-mode noise V... CM The size of can be considered as the following equation (5).

[0050] VCM =I reaq ×r···(5)

[0051] When the current flowing through conductor 2 is a commercial frequency alternating current, in the commercial frequency band, the impedance generated by the inter-winding capacitance of the Rogowski coil 10 and the stray capacitance of the cable 30 is sufficiently large compared to the impedance of the input resistances 44 and 45. Therefore, the leakage current I... reaq The value is determined by the inter-winding capacitance of the Rogowski coil 10 and the stray capacitance of the cable 30.

[0052] Here, we assume that Rogowski coil 10 and Rogowski coil 10A have the same number of turns, and that cable 30 and cable 30A have the same wiring length. In this case, the leakage current I... reaq The magnitude of is the same in both current sensing device 1 and current sensing device 1A. Furthermore, since r << Ra, the common-mode noise V, as expressed by equation (5) above, is... CM The common-mode noise V is significantly smaller than that expressed by equation (3) above. CM The value of . That is, the common-mode noise V generated in the current detection device 1. CM It is significantly smaller than the common-mode noise V generated in the current sensing device 1A. CM The value of .

[0053] Next, refer to Figure 5 The path of leakage current flowing to ground 4 via the stray capacitance of cable 30 is explained when a common-mode voltage Vcom is generated between simulated ground 3 and earth 4. Figure 5 This diagram illustrates the path of leakage current flowing to ground via stray capacitance of the cable in the current detection device according to Embodiment 1. Furthermore, in Figure 5 The calculation section 60 is omitted.

[0054] To keep the explanation simple, in Figure 5 In this cable 30, virtual points 15a, 15b, and 15c are set in each line of the cable 30 to direct the leakage current to the ground 4 via the stray capacitance of the cable 30. Virtual point 15a is a virtual point connected to the output terminal 11, virtual point 15b is a virtual point connected to the output terminal 12, and virtual point 15c is a virtual point connected to the neutral point 13.

[0055] First, if we consider the path of leakage current flowing from virtual point 15a through the stray capacitance of cable 30 to ground 4, then in the above path there exists in parallel the input resistance 44, the winding resistance of Rogowski coil 10 between neutral point 13 and output terminal 11.

[0056] In the current detection device 1 using the Rogowski coil 10, as described above, the input resistances 44 and 45 are sufficiently large compared to the winding resistance. Therefore, in the path of leakage current flowing from the virtual point 15a through the stray capacitance of the cable 30 to ground 4, approximately all of the leakage current flows to ground 4 through the winding resistance between the neutral point 13 and the output terminal 11. Therefore, the leakage current flowing through the input resistance 44 is a very small value.

[0057] Similarly, considering the path of leakage current flowing from virtual point 15b through the stray capacitance of cable 30 to ground 4, the input resistor 45 and the winding resistance of the Rogowski coil 10 between neutral point 13 and output terminal 12 exist in parallel along this path. Therefore, the leakage current in this path also flows almost entirely through the winding resistance between neutral point 13 and output terminal 12 to ground 4. Thus, the leakage current flowing through input resistor 45 is a very small value.

[0058] Therefore, in the path of leakage current flowing to ground 4 through the stray capacitance of cable 30, common-mode noise V is generated across each of the input resistors 44 and 45. CM The size of is represented by the following formula (6), which is the same as the above formula (4).

[0059] V CM =I reaq ×(r×Ra) / (r+Ra)···(6)

[0060] Therefore, in the path where the leakage current flows to ground 4 via the stray capacitance of cable 30, similar to the path where the leakage current flows to ground 4 via the inter-line capacitance of Rogowski coil 10, in the commercial frequency band, the impedance generated by the inter-winding capacitance and stray capacitance is a sufficiently large value compared to the impedance of the input resistances 44 and 45.

[0061] As described above, when a common-mode voltage Vcom is generated between the simulated ground 3 and the earth 4, the leakage current flowing through the input resistors 44 and 45 is bypassed to a path from the neutral point 13 through the inter-winding capacitance of the Rogowski coil 10 and the stray capacitance of the cable 30 to the earth 4. Therefore, in the current detection device 1, the common-mode noise generated at each end of the input resistors 44 and 45 can be reduced, and the current detection accuracy in noisy environments can be improved compared to the current detection device 1A.

[0062] Next, the structure of the Rogowski coil 10 will be explained. Figure 6 This is a diagram illustrating an example of the structure of the Rogowski coil according to Embodiment 1.

[0063] Figure 6The Rogowski coil 10 shown has a coil 18 and a ring-shaped spool 17. The coil 18 is spirally mounted on the outer periphery of the spool 17 and has a sheathing layer. The coil 18 includes a first coil portion 18a and a second coil portion 18b. One end of the first coil portion 18a is connected to the output terminal 11, and the other end is connected to the neutral point 13. One end of the second coil portion 18b is connected to the output terminal 12, and the other end is connected to the neutral point 13. To ensure that their respective output voltages are the same, the first coil portion 18a and the second coil portion 18b each have the same number of turns.

[0064] The first coil section 18a has the following structure, namely, starting from the neutral point 13, according to Figure 6 After winding counterclockwise along the outer circumference of the spool 17 for nearly half a circumference, it is then wound counterclockwise around the outer circumference of the spool 17 toward the output terminal 11. The second coil section 18b has the following structure: starting from the neutral point 13... Figure 6 After winding clockwise along the outer circumference of the spool 17 for approximately half a turn, the coil is then wound counterclockwise around the outer circumference of the spool 17 toward the output terminal 12. Alternatively, the first coil portion 18a may be wound clockwise around the outer circumference of the spool 17 toward the output terminal 11, and the second coil portion 18b may also be wound clockwise around the outer circumference of the spool 17 toward the output terminal 12.

[0065] Rogowski coil 10 is not limited to Figure 6 The shape shown can also be formed by combining two semi-circular Rogowski coils. Figure 7 This is a diagram illustrating another example of the structure of the Rogowski coil according to Embodiment 1.

[0066] Figure 7 The Rogowski coil 10 shown is composed of semi-circular Rogowski coils, namely half-Rogowski coils 10a and 10b. Half-Rogowski coils 10a and 10b are an example of a segmented Rogowski coil.

[0067] Each Rogowski coil 10a and 10b has a coil 18 and a semi-circular spool 17. The coil 18 is spirally mounted on the outer periphery of the spool 17 and has a covering layer. The spool 17 has a semi-circular spool body 17a, a first fitting portion 17b provided at one end of the spool body 17a, and a second fitting portion 17c provided at the other end of the spool body 17a. The first fitting portion 17b is convex, and the second fitting portion 17c is concave.

[0068] To ensure that their respective output voltages are the same, the number of turns of coil 18 of the half Rogowski coils 10a and 10b is the same. The starting point 18c of the winding of coil 18 is connected to the neutral point 13, and the ending point 18d of the winding of coil 18 is connected to either output terminal 11 or 12.

[0069] The half-Rogowski coil 10a has a structure in which, after the coil 18 is wound along the outer periphery of the bobbin 17 from the second engagement portion 17c toward the first engagement portion 17b, the coil 18 is then wound counterclockwise around the outer periphery of the bobbin 17 from the first engagement portion 17b toward the second engagement portion 17c. Alternatively, the half-Rogowski coil 10a may also have a structure in which the coil 18 is wound clockwise around the outer periphery of the bobbin 17 from the first engagement portion 17b toward the second engagement portion 17c.

[0070] The half-Rogowski coil 10b has a structure in which, after the coil 18 is wound along the outer periphery of the spool 17 from the first engagement portion 17b toward the second engagement portion 17c, the coil 18 is then wound counterclockwise around the outer periphery of the spool 17 from the second engagement portion 17c toward the first engagement portion 17b. Alternatively, the half-Rogowski coil 10b may also have a structure in which the coil 18 is wound clockwise around the outer periphery of the spool 17 from the second engagement portion 17c toward the first engagement portion 17b.

[0071] The half-Rogowski coil 10a and the half-Rogowski coil 10b are connected by connecting their respective first fitting portion 17b and second fitting portion 17c. Specifically, the first fitting portion 17b of the half-Rogowski coil 10a is fitted into the second fitting portion 17c of the half-Rogowski coil 10b, and the second fitting portion 17c of the half-Rogowski coil 10a is fitted into the first fitting portion 17b of the half-Rogowski coil 10b. Thus, the half-Rogowski coil 10a and the half-Rogowski coil 10b are connected.

[0072] Furthermore, the winding starting points 18c of the half-Rogowski coils 10a and 10b are connected to each other, and the connection point of the winding starting points 18c is the neutral point 13 of the Rogowski coil 10. In this way, by using the half-Rogowski coils 10a and 10b, a Rogowski coil 10 with a neutral point 13 can be manufactured with a simple structure.

[0073] Furthermore, the aforementioned current detection device 1 has an analog circuit 40 with integrating circuits 42 and 43, but the analog circuit 40 may also have a structure without integrating circuits 42 and 43. In this case, the calculation unit 60 has an integration processing unit that integrates the two digital signals output from the AD converter 50 and calculates the value of the current flowing through the conductor 2 based on the integration result of the integrating circuit.

[0074] Furthermore, in the current detection device 1 described above, the AD converter 50 is described as a ΔΣ type AD converter, but the AD converter 50 is not limited to a ΔΣ type AD converter. The current detection device 1 according to Embodiment 1 can be used in circuit breakers, and in particular, it is preferably used in low-voltage air circuit breakers.

[0075] As described above, the current detection device 1 according to Embodiment 1 includes a Rogowski coil 10, an analog circuit 40, an AD converter 50, and a calculation unit 60. The Rogowski coil 10 is positioned to surround the conductor 2. The analog circuit 40 has a differential input circuit 41 connected to the two output terminals 11 and 12 of the Rogowski coil 10. The AD converter 50 converts the analog signal output from the analog circuit 40 into a digital signal. The calculation unit 60 calculates the value of the current flowing through the conductor 2 based on the digital signal output from the AD converter 50. The Rogowski coil 10 has a neutral point 13 located at a position that equally divides the voltage 2 generated between the two output terminals 11 and 12. The analog ground 3 of the differential input circuit 41 is connected to the neutral point 13 of the Rogowski coil 10. Therefore, in the current detection device 1, when a common-mode voltage Vcom is generated by the simulated ground 3, the leakage current flowing through the input resistors 44 and 45 is bypassed to two paths: one through the neutral point 13, and the other through the inter-winding capacitance of the Rogowski coil 10, and the other through the stray capacitance of the cable 30 connecting the neutral point 13 and the simulated ground 3. Thus, the current detection device 1 can reduce the common-mode noise generated between the input resistors 44 and 45, and improve the accuracy of current detection in noisy environments.

[0076] Furthermore, the Rogowski coil 10 is composed of a combination of two half-Rogowski coils 10a and 10b. The half-Rogowski coils 10a and 10b are an example of a split Rogowski coil. The neutral point 13 is the connection point between the two half-Rogowski coils 10a and 10b. Thus, the Rogowski coil 10 can be manufactured with a simple structure.

[0077] In addition, the two half Rogowski coils 10a and 10b are each formed into a semi-circular ring. The Rogowski coil 10 can be made with a simple construction.

[0078] The structure shown in the above implementation is an example and can be combined with other known technologies. Without departing from the main idea, some parts of the structure can be omitted or changed.

[0079] Explanation of the label

[0080] 1. 1A current detection device, 2. Conductor, 3. Simulated ground, 4. Earth, 10. 10A Rogowski coil, 10a. 10b. Half Rogowski coil, 11. 12. Output terminals, 13. Neutral point, 14a. 14b. 14c. 15a. 15b. 15c. Virtual points, 17. Bore, 17a. Bore body, 17b. First fitting part, 17c. Second fitting part, 18. Coil, 18a. First coil part, 18b. Second coil part, 18c. Winding start point, 18d. Winding end point, 20. 20A circuit board, 21. 22. 23. Input terminals, 30. 30A cable, 40. Analog circuit, 41. Differential input circuit, 42. 43. Integrating circuit, 44. 45. Input resistor, 50. AD converter, 60. Calculation unit.

Claims

1. A current detection device, characterized in that, have: A Rogowski coil is positioned to surround a conductor. An analog circuit having a differential input circuit connected to two output terminals of the Rogowski coil; An AD converter converts an analog signal output from the analog circuit into a digital signal; and The computing unit calculates the value of the current flowing through the conductor based on the digital signal output from the AD converter. The Rogowski coil has a neutral point positioned at a location that will divide the voltage generated between the two output terminals into two equal parts. The analog ground of the differential input circuit is connected to the neutral point of the Rogowski coil.

2. The current detection device according to claim 1, characterized in that, The Rogowski coil is composed of a combination of two split Rogowski coils. The neutral point is the connection point between the two split Rogowski coils.

3. The current detection device according to claim 2, characterized in that, The two segmented Rogowski coils are each formed into a semi-circular ring.

Images