A double-ring electromagnetic magneto-optical hybrid current transformer

Abstract

The application belongs to the technical field of current measurement, and discloses a double-loop electromagnetic and magneto-optical hybrid current transformer, which comprises an electromagnetic current transformer and an optoelectronic transformer unit, the optoelectronic transformer unit comprises a first optoelectronic current transformer and a second optoelectronic current transformer; a test cable passes through the center of a ring-shaped iron core of the electromagnetic current transformer, two probes corresponding to the two optoelectronic current transformers are both installed on the ring-shaped iron core and are symmetrically arranged on the two sides of the test cable in parallel; the electromagnetic current transformer is used for measuring and obtaining steady-state current information of the test cable, and the optoelectronic transformer unit is used for measuring and obtaining transient current information of the test cable. The application can accurately measure the steady-state current and the transient current.

Description

Technical Field

[0001] This invention belongs to the field of current measurement technology, and more specifically, relates to a dual-ring electromagnetic-magnetic-optical hybrid current transformer. Background Technology

[0002] Current transformers are crucial components for measuring current in AC power systems, commonly used in online monitoring and relay protection of electrical equipment. Taking AC transmission lines as an example, steady-state currents are in the hundreds of amperes range, while single-phase ground fault currents are in the tens of thousands of amperes range. Currently, electromagnetic or electronic single-loop current transformers are commonly used for measuring power frequency steady-state current, while Rogowski coils are commonly used for transient current measurement. However, electromagnetic current transformers cannot accurately measure transient currents due to magnetic saturation in the iron core. Existing current measurement equipment cannot accurately measure both steady-state and transient currents. Summary of the Invention

[0003] This invention provides a dual-ring electromagnetic-magnetic-optical hybrid current transformer, which solves the problem that existing current measurement devices cannot accurately measure both steady-state and transient currents.

[0004] The present invention provides a dual-ring electromagnetic magneto-optical hybrid current transformer, comprising: an electromagnetic current transformer and a photoelectric current transformer unit, wherein the photoelectric current transformer unit comprises a first photoelectric current transformer and a second photoelectric current transformer.

[0005] The electromagnetic current transformer has a toroidal iron core, and the first and second terminals of the electromagnetic current transformer are both used to connect to an ammeter.

[0006] The first photoelectric current transformer includes a first probe, a first input optical fiber and a first output optical fiber respectively connected to the two ends of the first probe, and a first photodetector connected to the first output optical fiber; the first input optical fiber is used to connect to a first laser.

[0007] The second photoelectric current transformer includes a second probe, a second input optical fiber and a second output optical fiber respectively connected to the two ends of the second probe, and a second photodetector connected to the second output optical fiber; the second input optical fiber is used to connect to a second laser.

[0008] The test cable passes through the center of the toroidal core; the first probe and the second probe are both mounted on the toroidal core and arranged symmetrically on both sides of the test cable; the light transmission direction of the first probe and the second probe is perpendicular to the current direction of the test cable.

[0009] The electromagnetic current transformer is used to measure and obtain the steady-state current information of the test cable, and the photoelectric current transformer is used to measure and obtain the transient current information of the test cable.

[0010] Preferably, the light transmission directions of the first probe and the second probe are the same, and the magnetic field directions of the measured current in the first probe and the second probe are opposite, while the magnetic field strengths are the same.

[0011] Preferably, the first probe and the second probe have the same structure, and each probe includes an input collimator, a polarizer, a magneto-optical material, an analyzer, and an output collimator connected in sequence.

[0012] Preferably, the included angle between the polarizer and the analyzer is 45°.

[0013] Preferably, the input light intensity M1 and the output light intensity M2 of the probe satisfy the following relationship:

[0014]

[0015] In the formula, α is the angle between the polarizer and the analyzer, which is 45°; θ is the deflection angle.

[0016] Preferably, the primary current of the test cable passes through the center of the toroidal core of the electromagnetic current transformer, and the secondary current is output from the first and second terminals of the electromagnetic current transformer and measured by the ammeter.

[0017] Preferably, the primary side current is calculated using the following formula:

[0018] N1i1=N2i2

[0019] In the formula, i1 is the primary current, i2 is the secondary current, N1 is the number of turns in the primary winding, and N2 is the number of turns in the secondary winding.

[0020] Preferably, measuring and obtaining transient current information of the test cable includes the following steps:

[0021] The output voltages of the first photodetector and the second photodetector are obtained respectively.

[0022] Based on the output voltage of the first photodetector and the output voltage of the second photodetector, the output voltage information after removing common-mode interference is obtained;

[0023] The transient current information is calculated based on the output voltage information after removing common-mode interference.

[0024] Preferably, the relationship between the output voltage of either the first photodetector or the second photodetector and the magnetic field strength is as follows:

[0025]

[0026] In the formula, U is the output voltage of the photodetector, η is the proportionality coefficient, M1 is the input light intensity of the corresponding probe, V is the Wilder coefficient of the magneto-optical material, L is the length of the magneto-optical material, and H is the magnetic field strength on the magneto-optical material.

[0027] Since the output voltage U is linearly related to the magnetic field strength H on the magneto-optical material, the above equation simplifies to:

[0028] U = mH + n

[0029] In the formula, m and n are constants.

[0030] Preferably, the output voltage of the first photodetector is expressed as: U a =m(H+H′)+n; The output voltage of the second photodetector is expressed as: U b = m(-H+H′)+n; The output voltage information after removing common-mode interference is:

[0031] In the formula, U a U is the output voltage of the first photodetector, H is the magnetic field strength generated by the measured current, H' is the magnetic field strength generated by electromagnetic interference, and U is the magnetic field strength generated by electromagnetic interference. b U is the output voltage of the second photodetector. r This is the output voltage information after removing common-mode interference.

[0032] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0033] The dual-ring electromagnetic-magnetic-optical hybrid current transformer provided by this invention includes an electromagnetic current transformer and a photoelectric current transformer unit. The photoelectric current transformer unit includes a first photoelectric current transformer and a second photoelectric current transformer. The test cable passes through the center of the toroidal core of the electromagnetic current transformer. The two probes corresponding to the two photoelectric current transformers are mounted on the toroidal core and arranged symmetrically on both sides of the test cable. The electromagnetic current transformer is used to measure and obtain the steady-state current information of the test cable, and the photoelectric current transformer unit is used to measure and obtain the transient current information of the test cable. This invention addresses the limitations of existing current transformers in terms of measurement range and accuracy by proposing a dual-ring electromagnetic-magnetic-optical hybrid current transformer, suitable for field measurement of both transient and steady-state currents. It can meet the engineering requirement of using a single current measuring device to measure both steady-state current and transient short-circuit current. This invention not only combines electromagnetic and photoelectric current transformers but also suppresses their mutual interference, thereby enabling accurate measurement of both steady-state current and transient short-circuit current. Attached Figure Description

[0034] Figure 1This is a schematic diagram of the structure of a dual-ring electromagnetic-magnetic-optical hybrid current transformer provided in an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the structure of the probe of the photoelectric current transformer in a dual-ring electromagnetic-magnetic hybrid current transformer provided in an embodiment of the present invention;

[0036] Figure 3 An equivalent circuit diagram of the electromagnetic current transformer in a dual-ring electromagnetic-magnetic-optical hybrid current transformer provided in this embodiment of the invention;

[0037] Figure 4 A schematic diagram of the layout of the first and second probes in a dual-ring electromagnetic-magnetic-optical hybrid current transformer provided in an embodiment of the present invention;

[0038] Figure 5 This is a schematic diagram illustrating the application of a dual-ring electromagnetic-magnetic-optical hybrid current transformer, provided as an embodiment of the present invention.

[0039] Among them, 1-ring core, 2-first probe, 3-first input fiber, 4-second input fiber, 5-first terminal, 6-second probe, 7-second terminal, 8-second output fiber, 9-second photodetector, 10-first photodetector, 11-first output fiber;

[0040] 12-Output collimator, 13-Analyzer, 14-Magneto-optical material, 15-Polarizer, 16-Input collimator;

[0041] 17-First laser, 18-Second laser, 19-Ammeter, 20-Test cable. Detailed Implementation

[0042] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0043] This embodiment provides a dual-ring electromagnetic-magnetic hybrid current transformer. (See also...) Figure 1 , Figure 5 It includes: an electromagnetic current transformer and a photoelectric current transformer unit, wherein the photoelectric current transformer unit includes a first photoelectric current transformer and a second photoelectric current transformer.

[0044] The electromagnetic current transformer has a toroidal core 1, and the first terminal 5 and the second terminal 7 of the electromagnetic current transformer are both used to connect to the ammeter 19.

[0045] The first photoelectric current transformer includes a first probe 2, a first input optical fiber 3 and a first output optical fiber 11 connected to the two ends of the first probe 2 respectively, and a first photodetector 10 connected to the first output optical fiber 11; the first input optical fiber 3 is used to connect to the first laser 17.

[0046] The second photoelectric current transformer includes a second probe 6, a second input optical fiber 4 and a second output optical fiber 8 connected to the two ends of the second probe 6 respectively, and a second photodetector 9 connected to the second output optical fiber 8; the second input optical fiber 4 is used to connect to the second laser 18.

[0047] The test cable 20 passes through the center of the toroidal core 1; the first probe 2 and the second probe 6 are both mounted on the toroidal core 1 and are arranged symmetrically on both sides of the test cable 20; the light transmission direction of the first probe 2 and the second probe 6 is perpendicular to the current direction of the test cable 20.

[0048] The electromagnetic current transformer is used to measure and obtain the steady-state current information of the test cable 20, and the photoelectric current transformer is used to measure and obtain the transient current information of the test cable 20.

[0049] The first probe 2 and the second probe 6 have the same light transmission direction, and the magnetic field direction of the measured current in the first probe 2 and the second probe 6 is opposite, but the magnetic field strength is the same.

[0050] The first probe 2 and the second probe 6 have the same structure, such as Figure 2 As shown, each probe includes an input collimator 16, a polarizer 15, a magneto-optical material 14, an analyzer 13, and an output collimator 12 connected in sequence.

[0051] In a preferred embodiment, the included angle between the polarizer 15 and the analyzer 13 is 45°. The input light intensity M1 and output light intensity M2 of the probe satisfy the following relationship:

[0052]

[0053] In the formula, α is the angle between the polarizer and the analyzer, which is 45°; θ is the deflection angle.

[0054] The primary current of the test cable 20 passes through the center of the toroidal core 1 of the electromagnetic current transformer, and the secondary current is output from the first terminal 5 and the second terminal 7 of the electromagnetic current transformer and measured by the ammeter 19.

[0055] The primary current is calculated using the following formula:

[0056] N1i1=N2i2

[0057] In the formula, i1 is the primary current, i2 is the secondary current, N1 is the number of turns in the primary winding, and N2 is the number of turns in the secondary winding.

[0058] The process of measuring and obtaining transient current information of the test cable includes the following steps:

[0059] The output voltages of the first photodetector 10 and the second photodetector 9 are obtained respectively.

[0060] The output voltage information after removing common-mode interference is obtained based on the output voltage of the first photodetector 10 and the output voltage of the second photodetector 9.

[0061] The transient current information is calculated based on the output voltage information after removing common-mode interference.

[0062] Specifically, the relationship between the output voltage of either the first photodetector 10 or the second photodetector 9 and the magnetic field strength is as follows:

[0063]

[0064] In the formula, U is the output voltage of the photodetector, η is the proportionality coefficient, M1 is the input light intensity of the corresponding probe, V is the Wilder coefficient of the magneto-optical material, L is the length of the magneto-optical material, and H is the magnetic field strength on the magneto-optical material.

[0065] Since the output voltage U is linearly related to the magnetic field strength H on the magneto-optical material, the above equation simplifies to:

[0066] U = mH + n

[0067] In the formula, m and n are constants.

[0068] The output voltage of the first photodetector 10 is expressed as: U a =m(H+H′)+n; The output voltage of the second photodetector 9 is expressed as: U b = m(-H+H′)+n; The output voltage information after removing common-mode interference is:

[0069] In the formula, U a U is the output voltage of the first photodetector, H is the magnetic field strength generated by the measured current, H' is the magnetic field strength generated by electromagnetic interference, and U is the magnetic field strength generated by electromagnetic interference. b U is the output voltage of the second photodetector. r This is the output voltage information after removing common-mode interference.

[0070] The present invention will be further described below from four aspects.

[0071] 1) Steady-state current measurement model:

[0072] The equivalent circuit of an electromagnetic current transformer is as follows: Figure 3 As shown, i1 is the primary side current, i2 is the secondary side current, Z0 is the magnetizing impedance, R2 is the secondary side impedance, L2 is the sum of the secondary side leakage inductance and the load inductance, and i0 is the magnetizing current.

[0073] Considering the influence of the excitation current, according to the ideal transformer equation, we have:

[0074] N1(i1-i0)=N2i2

[0075]

[0076] Where N1 is the number of turns in the primary winding and N2 is the number of turns in the secondary winding. This refers to the magnetic flux passing through the iron core. Due to limitations in the material and size of the iron core, there is an upper limit to the magnetic flux.

[0077] When operating on a normal cable, the excitation current is relatively small, and:

[0078] N1i1=N2i2 (2)

[0079] Under normal circumstances, the iron core in an electromagnetic current transformer operates in a non-saturated state, at which point the excitation current is relatively small. The current transformer can normally feed back the secondary current, and the primary current can be obtained from equation (2), thus achieving the purpose of measuring the steady-state current of the cable. When a cable fault occurs, the current becomes a transient current tens of times greater than the steady-state current, causing magnetic saturation of the iron core and a sharp increase in the excitation current, making it impossible to accurately feed back the secondary current. Therefore, this invention uses the method described below to measure the transient current.

[0080] 2) Transient current measurement model:

[0081] According to the magneto-optical effect, linearly polarized light will be deflected in its polarization direction under the influence of a magnetic field, with a deflection angle θ:

[0082]

[0083] Where V is the Wilder coefficient of the magneto-optical material, in rad / (T·m), H is the amplitude of the magnetic field strength on the magneto-optical material, in T, and L is the optical path length of the polarized light, which here is the length of the magneto-optical material, in m.

[0084] By Ampère's circuital law, we have:

[0085]

[0086] Where r is the distance between the axis of the cable under test and the center of the magneto-optical material, and I is the current flowing through the cable, then the deflection angle is:

[0087]

[0088] Wilder coefficients satisfy:

[0089]

[0090] Where e and m are the charge and mass of an electron, c is the speed of light, λ is the wavelength of polarized light, and k is the dispersion of the magneto-optical material, which is affected by temperature changes.

[0091] After installation, r, V, and L are fixed, and the deflection angle is only related to the current in the conductor. The sensitivity of the output light intensity is greatest when the angle between the polarizer and the analyzer is 45° or 135°.

[0092] See Figure 2 , Figure 5 In use, for any photoelectric current transformer, the input fiber is connected to a laser. A polarized laser with an intensity of M1 is input to a probe containing an input collimator 16, a polarizer 15 (e.g., a polarizer), a magneto-optical material 14 (e.g., magneto-optical glass), an analyzer 13, and an output collimator 12. The laser light is converted into parallel light by the input collimator 16, then polarized by the polarizer 15, deflected by the magneto-optical material 14, detected by the analyzer 13, and transmitted to the output fiber via the output collimator 12. Finally, the photodetector collects the laser light intensity M2 transmitted from the output fiber.

[0093] According to Malus's law:

[0094]

[0095] The included angle α between the polarizer and the analyzer is 45°.

[0096] The output voltage of the photodetector is proportional to the light intensity, with a proportionality coefficient of η, as follows:

[0097]

[0098] In general, the deflection angle θ is very small. Approximating sin2θ as 2θ, we have:

[0099]

[0100] Due to the characteristics of magneto-optical materials, the current has a suitable deflection angle only at the kiloampere level. Therefore, the transient current in the cable can be obtained through equation (9).

[0101] 3) Differential method to remove common-mode interference

[0102] Because the photoelectric current transformer used in this invention adopts a direct optical path, it has advantages in long-term use compared to a current probe with a closed optical path. However, it is more susceptible to interference from external magnetic fields. Therefore, this invention uses a differential magnetic suppression method to eliminate common-mode interference from external magnetic fields. The principle is as follows:

[0103] From equations (4) and (9), the relationship between the output voltage U and the magnetic field strength H in the photodetector is as follows:

[0104]

[0105] The output voltage U is linearly related to the magnetic field strength H on the magneto-optical material, and the simplified equation (10) is:

[0106] U=mH+n (11)

[0107] Where m and n are constants.

[0108] In this invention, the first probe 2 and the second probe 6 are placed parallel to each other, and the test cable 20 passes through the center of the annular iron core 1, that is, the current to be measured (corresponding to the current to be measured in the test cable 20) passes through the central axis of the two probes. Figure 4 As shown.

[0109] See Figure 4 The signal input directions of the two probes (the first probe 2 and the second probe 6) are the same, and the magnetic field directions of the current to be measured in the two probes are opposite. However, when the external electromagnetic interference is far away, the magnetic field strength of the two probes is the same, thus forming common-mode interference.

[0110] The output voltages of the first photodetector 10 (which can be referred to as photodetector a) and the second photodetector 9 (which can be referred to as photodetector b) are:

[0111] U a =m(H+H′)+n (12)

[0112] U b =m(-H+H′)+n (13)

[0113] Where H is the magnetic field strength generated by the current to be measured, and H' is the magnetic field strength generated by electromagnetic interference.

[0114] Subtracting the output signals from the two optical paths can eliminate common-mode interference. The output voltage after interference elimination is:

[0115]

[0116] Among them, U r This is the output voltage after interference is eliminated.

[0117] 4) How to use:

[0118] See Figure 1 , Figure 5 The primary current in the cable under test 20 passes through the center of the toroidal core 1 of the electromagnetic current transformer. The secondary current, representing the steady-state current, is output from the first terminal 5 and the second terminal 7, and is measured by the ammeter 19. The first input optical fiber 3 and the second input optical fiber 4 are connected to the first laser 17 and the second laser 18, respectively, and the emitted laser light passes through the first probe 2 and the second probe 6, respectively. Finally, the output voltages obtained from the first photodetector 10 and the second photodetector 9 are processed using the above calculation method to obtain the transient current.

[0119] The dual-ring electromagnetic-magnetic hybrid current transformer provided by this invention has at least the following technical advantages:

[0120] This invention, combining the magneto-optical effect, proposes a hybrid current transformer capable of measuring both transient and steady-state currents, and provides corresponding calculation methods for steady-state and transient currents. This invention overcomes the limitation of electromagnetic current transformers, which cannot measure transient currents due to magnetic saturation, and facilitates the detection of currents in various wires and cables.

[0121] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A dual-ring electromagnetic-magnetic-optical hybrid current transformer, characterized in that, include: Electromagnetic current transformer and photoelectric current transformer unit, wherein the photoelectric current transformer unit includes a first photoelectric current transformer and a second photoelectric current transformer. The electromagnetic current transformer has a toroidal iron core, and the first and second terminals of the electromagnetic current transformer are both used to connect to an ammeter. The first photoelectric current transformer includes a first probe, a first input optical fiber and a first output optical fiber respectively connected to the two ends of the first probe, and a first photodetector connected to the first output optical fiber. The first input optical fiber is used to connect to the first laser; The second photoelectric current transformer includes a second probe, a second input optical fiber and a second output optical fiber respectively connected to the two ends of the second probe, and a second photodetector connected to the second output optical fiber; The second input optical fiber is used to connect to the second laser; The test cable passes through the center of the toroidal core; the first probe and the second probe are both mounted on the toroidal core and arranged symmetrically on both sides of the test cable; the light transmission direction of the first probe and the second probe is perpendicular to the current direction of the test cable. The electromagnetic current transformer is used to measure and obtain the steady-state current information of the test cable, and the photoelectric current transformer is used to measure and obtain the transient current information of the test cable.

2. The dual-ring electromagnetic-magnetic-optical hybrid current transformer according to claim 1, characterized in that, The first probe and the second probe have the same light transmission direction, and the magnetic field direction of the measured current in the first probe and the second probe are opposite, but the magnetic field strength is the same.

3. The dual-ring electromagnetic-magnetic-optical hybrid current transformer according to claim 1, characterized in that, The first probe and the second probe have the same structure. Each probe includes an input collimator, a polarizer, a magneto-optical material, an analyzer, and an output collimator connected in sequence.

4. The dual-ring electromagnetic-magnetic-optical hybrid current transformer according to claim 3, characterized in that, The included angle between the polarizer and the analyzer is 45°.

5. The dual-ring electromagnetic-magnetic-optical hybrid current transformer according to claim 4, characterized in that, The input light intensity M1 and the output light intensity M2 of the probe satisfy the following relationship: In the formula, α is the angle between the polarizer and the analyzer, which is 45°; θ is the deflection angle.

6. The dual-ring electromagnetic-magnetic-optical hybrid current transformer according to claim 1, characterized in that, The primary current of the test cable passes through the center of the toroidal core of the electromagnetic current transformer, and the secondary current is output from the first and second terminals of the electromagnetic current transformer and measured by the ammeter.

7. The dual-ring electromagnetic-magnetic-optical hybrid current transformer according to claim 6, characterized in that, The primary current is calculated using the following formula: N1i1=N2i2 In the formula, i1 is the primary current, i2 is the secondary current, N1 is the number of turns in the primary winding, and N2 is the number of turns in the secondary winding.

8. The dual-ring electromagnetic-magnetic-optical hybrid current transformer according to claim 1, characterized in that, Measuring and obtaining transient current information of the test cable includes the following steps: The output voltages of the first photodetector and the second photodetector are obtained respectively. Based on the output voltage of the first photodetector and the output voltage of the second photodetector, the output voltage information after removing common-mode interference is obtained; The transient current information is calculated based on the output voltage information after removing common-mode interference.

9. The dual-ring electromagnetic-magnetic-optical hybrid current transformer according to claim 8, characterized in that, The relationship between the output voltage and the magnetic field strength of either the first photodetector or the second photodetector is as follows: In the formula, U is the output voltage of the photodetector, η is the proportionality coefficient, M1 is the input light intensity of the corresponding probe, V is the Wilder coefficient of the magneto-optical material, L is the length of the magneto-optical material, and H is the magnetic field strength on the magneto-optical material. Since the output voltage U is linearly related to the magnetic field strength H on the magneto-optical material, the above equation simplifies to: U = mH + n In the formula, m and n are constants.

10. The dual-ring electromagnetic-magnetic-optical hybrid current transformer according to claim 9, characterized in that, The output voltage of the first photodetector is expressed as: U a =m(H+H′)+n; The output voltage of the second photodetector is expressed as: U b = m(-H+H′)+n; The output voltage information after removing common-mode interference is: In the formula, U a U is the output voltage of the first photodetector, H is the magnetic field strength generated by the measured current, H' is the magnetic field strength generated by electromagnetic interference, and U is the magnetic field strength generated by electromagnetic interference. b U is the output voltage of the second photodetector. r This is the output voltage information after removing common-mode interference.

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