Ac detection unit, current sampling device, and voltage transformer in a substation

Abstract

The application relates to an alternating current detection unit, a current sampling device and a voltage mutual inductor in a transformer substation. The alternating current detection unit comprises a first ring-shaped core, a second ring-shaped core, a first winding, a second winding, a third winding and a compensation circuit, wherein: the first ring-shaped core and the second ring-shaped core are coaxially arranged and overlap with each other, current-carrying wires serving as a primary winding of the alternating current detection unit pass through the first ring-shaped core and the second ring-shaped core, and the current-carrying wires are used for being connected to a line to be detected; the first winding is wound on the first ring-shaped core, the second winding is wound on the second ring-shaped core, and the third winding is wound on the first ring-shaped core and the second ring-shaped core at the same time; the second winding and the compensation circuit are connected in series to form an electromotive force compensation loop; a first end of the first winding is connected with a first end of the third winding, and a second end of the first winding and a second end of the third winding jointly form a detection signal output end of the alternating current detection unit. The application can improve the precision of alternating current detection.

Description

Technical Field

[0001] This application relates to the field of monitoring technology, and in particular to an AC detection unit, a current sampling device, and a voltage transformer in a substation. Background Technology

[0002] In the field of online monitoring of capacitive voltage transformer operation devices and metering performance, accurate measurement of primary capacitive current is crucial. The changes in primary capacitive current of the capacitor element in a voltage transformer under normal operation and fault conditions are extremely complex. Under normal operating conditions, the primary capacitive current exhibits specific amplitude and frequency characteristics. However, once a capacitor element fails, such as due to capacitor breakdown, partial discharge, or capacitance drift, the primary capacitive current will change significantly. This change may manifest as a sharp increase or decrease in current amplitude, alteration of frequency characteristics, and phase shift. Moreover, different fault types and degrees result in different current change characteristics, placing extremely high demands on the accuracy and dynamic range of current measurement.

[0003] Traditional current measurement devices often struggle to simultaneously meet the demands for high accuracy, wide bandwidth, and stable measurement. Some devices have limitations in accuracy, failing to achieve the precision levels required for online monitoring of capacitive voltage transformer metering performance; for example, they cannot accurately track and measure current changes. Summary of the Invention

[0004] Therefore, it is necessary to provide an AC detection unit, a current sampling device, and a voltage transformer in a substation that can accurately track and measure current.

[0005] An AC detection unit includes: a first toroidal core, a second toroidal core, a first winding, a second winding, a third winding, and a compensation circuit, wherein:

[0006] The first toroidal iron core and the second toroidal iron core are coaxially arranged and overlap each other. A current-carrying wire, which serves as the primary winding of the AC detection unit, passes through the first toroidal iron core and the second toroidal iron core. The current-carrying wire is used to connect to the circuit to be tested.

[0007] The first winding is wound around the first toroidal iron core, the second winding is wound around the second toroidal iron core, and the third winding is wound around both the first toroidal iron core and the second toroidal iron core; the second winding is connected in series with the compensation circuit to form an electromotive force compensation circuit;

[0008] The first end of the first winding is connected to the first end of the third winding, and the second end of the first winding and the second end of the third winding together form the detection signal output terminal of the AC detection unit.

[0009] In one of the embodiments, an air gap is arranged in the magnetic circuit formed by the first ring-shaped iron core and the second ring-shaped iron core.

[0010] In one of the embodiments, the number of ampere turns of the first ring-shaped iron core is equal to the number of ampere turns of the second ring-shaped iron core.

[0011] In one of the embodiments, the compensation circuit is an LRC circuit or a compensation resistor with adjustable resistance.

[0012] In one of the embodiments, the resistance of the compensation circuit is determined based on the number of ampere turns of the first ring-shaped iron core and the number of ampere turns of the second ring-shaped iron core.

[0013] In one of the embodiments, the wire diameter and the number of turns corresponding to the first winding and the second winding are determined based on the cross-sectional area of the iron core of the first ring-shaped iron core and the second ring-shaped iron core, the material of the iron core of the first ring-shaped iron core and the second ring-shaped iron core, and the primary current rating; and the wire diameter and the number of turns corresponding to the third winding are determined based on the target detection current range and the target detection accuracy.

[0014] In one of the embodiments, the first ring-shaped iron core and the second ring-shaped iron core are made of a magnetic material.

[0015] In one of the embodiments, the magnetic material is a composite material made of a permalloy and a nanocrystalline alloy.

[0016] The above AC detection unit works based on the principle of electromagnetic induction. The current-carrying wire of the AC detection unit is connected to the AC line to be detected. The alternating current in the current-carrying wire generates a changing magnetic field in the first ring-shaped iron core and the second ring-shaped iron core. The corresponding secondary winding induces an electromotive force and generates a corresponding secondary current. The first end of the first winding is connected to the first end of the third winding. The second end of the first winding and the second end of the third winding together form the detection signal output end of the AC detection unit. The second ring-shaped iron core generates a compensation electromotive force through the compensation circuit and the second winding to offset the electromotive force of the first ring-shaped iron core, thereby achieving the zero flux effect of the AC detection unit and improving the accuracy of AC detection.

[0017] A current sampling device includes an AC detection unit as described above, wherein the current sampling device further includes a sampling circuit connected to the detection signal output end of the AC detection unit.

[0018] The current sampling device, through the cooperation of the sampling circuit and the AC detection unit, can convert the current signal output by the AC detection unit into a voltage signal according to Ohm's law, which is convenient for subsequent circuits to measure, amplify, analyze, and process the signal, and provides a basis for accurate sampling of AC current.

[0019] The voltage transformer in a substation comprises the current sampling device as described above, and a capacitive voltage transformer, and the current-carrying wire of the current sampling device is connected in series to the high-voltage tail of the capacitive voltage transformer.

[0020] The voltage transformer in a substation described above, because of the current sampling device, realizes the voltage transformer in a substation with integrated wide dynamic range measurement capability, and when the capacitive voltage transformer is broken down, the current sampling device can quickly respond and sample the alternating current at high frequency; in addition, the current-carrying wire of the current sampling device is connected to the high-voltage tail of the capacitive voltage transformer, and the current sampling device does not affect the safe and stable operation of the power grid when it operates with the capacitive voltage transformer, thereby ensuring the safety and stability of the power grid. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 It is a structural schematic diagram of the AC detection unit in an embodiment;

[0023] Figure 2 It is a circuit schematic diagram of the current sampling device in an embodiment;

[0024] Figure 3 It is an application environment schematic diagram of the voltage transformer in a substation in an embodiment. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the related drawings. The drawings show embodiments of the present application. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments of the present application and are not intended to limit the present application.

[0027] It can be understood that the terms "first", "second" and the like used in the present application can be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from the second element. For example, without departing from the scope of the present application, the first resistor can be referred to as the second resistor, and similarly, the second resistor can be referred to as the first resistor. The first resistor and the second resistor are both resistors, but they are not the same resistor.

[0028] It can be understood that "connection" in the following embodiments, if the circuits, modules, units and the like connected to each other have the transmission of electrical signals or data, should be understood as "electrically connected", "communicatively connected" and the like.

[0029] It can be understood that "at least one" means one or more, and "multiple" means two or more. "At least part of the element" means part or all of the element.

[0030] As used herein, the singular forms "a", "an" and "the" can also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "comprise / comprising" or "have / having" or the like specifies the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but does not exclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof. At the same time, the term "and / or" used in the specification includes any and all combinations of the related listed items.

[0031] In the field of capacitor voltage transformer operation device and measurement performance online monitoring, accurate measurement of primary capacitive current is crucial. The primary capacitive current of voltage transformer capacitor element changes extremely complex in normal operation and fault state. In normal working condition, the primary capacitive current presents specific amplitude and frequency characteristics, however, once the capacitor element fails, for example, capacitor breakdown, partial discharge or capacitor value drift, the primary capacitive current will change significantly. This change may be manifested as a sharp increase or decrease in current amplitude, change in frequency characteristics, and phase shift, etc. Moreover, different fault types and fault degrees lead to different current change characteristics, which puts high requirements on the accuracy and dynamic range of current measurement. At the same time, the complexity of the field operation condition also has difficulty in measurement. The CVT (Capacitor Voltage Transformer) primary current range has obvious differences due to the grid voltage level, system load and its own parameter settings, from normal small current to capacitor breakdown large current impact, requiring the measuring device to have wide dynamic range measurement capability; the current instantaneously mutates when the capacitor breaks down, requiring the measuring device to have fast response capability and high sampling frequency; in addition, the power system operating environment is complex and changeable, with large temperature fluctuations, electromagnetic interference, humidity and dust, etc. Factors will not only directly interfere with the normal work of the measuring device and cause error increase, but also affect its long-term stability and reliability, causing measurement data drift or deviation.

[0032] However, the traditional current measurement method and device often cannot meet the requirements of high accuracy, wide frequency and stable measurement at the same time. Some measuring devices have limitations in accuracy and cannot achieve the required precision level for online monitoring of the measurement performance of capacitor voltage transformers, for example, the error is large when measuring small current, or it cannot accurately track the measurement during current change. The frequency characteristics of some devices are not good, and they cannot fully and accurately measure the current signal from low frequency to high frequency that may be involved in the CVT operation process, leading to misjudgment or missed judgment of the fault characteristics of the capacitor element. In addition, in terms of stability, the existing technology is easily disturbed by environmental factors, and the reliability of the measurement data in the long-term operation process is difficult to guarantee, which cannot provide continuous, stable and accurate primary capacitive current data support for the online monitoring of the measurement performance of capacitor voltage transformers, thereby restricting the effective monitoring and maintenance of the operation state of capacitor voltage transformers by the power system.

[0033] Therefore, the present inventors have conducted research on the change characteristics of primary capacitive current before and after the failure of voltage transformer capacitor element in order to realize accurate measurement of primary capacitive current in online monitoring of the measurement performance of capacitor voltage transformers. By analyzing the field operation condition, the current measurement principle and accuracy influencing factors are determined, and then the performance index requirements of high-accuracy wide-frequency capacitive current sensing module are determined and a hardware design scheme is proposed. In one exemplary embodiment, as shown in Figures 1-2As shown, the application provides an alternating current detection unit, which comprises a first ring-shaped core 100, a second ring-shaped core 200, a first winding 300, a second winding 400, a third winding 500 and a compensation circuit. The first ring-shaped core 100 and the second ring-shaped core 200 are coaxially arranged and overlap with each other, and the first ring-shaped core 100 and the second ring-shaped core 200 have a current-carrying wire 600 passing therethrough as a primary winding of the alternating current detection unit, and the current-carrying wire is used to access a line to be detected; the first winding 300 is wound on the first ring-shaped core 100, the second winding 400 is wound on the second ring-shaped core 200, and the third winding 500 is wound on the first ring-shaped core 100 and the second ring-shaped core 200 at the same time; the second winding 400 and the compensation circuit are connected in series to form an electromotive force compensation loop; a first end of the first winding 300 is connected to a first end of the third winding 500, and a second end of the first winding 300 and a second end of the third winding 500 together form a detection signal output end of the alternating current detection unit. As shown in the principle diagram, Figure 2 As shown in the principle diagram, T1 refers to the first ring-shaped core, T2 refers to the second ring-shaped core, L1 refers to the first winding, L2 refers to the second winding, L3 refers to the third winding, and R1 refers to the compensation circuit.

[0034] Specifically, in the electromotive force compensation loop, the second winding generates a secondary current, the secondary current passes through the compensation circuit, a compensation electromotive force is formed on the compensation circuit, and the ratio of the compensation electromotive force to the ratio of the loop containing the first ring-shaped core is negative. The size of the magnetic shunt compensation value can be adjusted by increasing or decreasing the magnetic shunt cross section. In this way, as long as the appropriate compensation turns and the cross section of the magnetic shunt are selected, the error of the mutual inductor after the magnetic shunt compensation can be significantly reduced, and the performance of the mutual inductor can be greatly improved. The magnetic shunt compensation is positive for the ratio difference compensation, and the electromotive force compensation is negative for the ratio difference compensation. In order to offset the negative compensation of the ratio value, the weak magnetic shunt compensation should be strengthened in the magnetic shunt electromotive force compensation. For this purpose, the number of magnetic shunt pieces can be increased, and the compensation turns can be appropriately increased.

[0035] The above alternating current detection unit is designed based on the magnetic shunt compensation principle and the electromotive force compensation principle. Through the above principles, the interference caused by the induced electromagnetic field in electromagnetic induction to the equipment can be reduced. The alternating current detection unit works based on the electromagnetic induction principle. The current-carrying wire 600 of the alternating current detection unit is connected to the alternating current line to be detected. The alternating current in the current-carrying wire 600 will generate a changing magnetic field in the first annular core 100 and the second annular core 200. The corresponding secondary winding will induce an electromotive force and generate a corresponding secondary current. The first end of the first winding 300 is connected to the first end of the third winding 500. The second end of the first winding 300 and the second end of the third winding 500 together form the detection signal output end of the alternating current detection unit. The second annular core 200 generates a compensation electromotive force with the second winding 400 through the compensation circuit to offset the electromotive force of the first annular core 100, so as to achieve the zero magnetic flux effect of the alternating current detection unit, and further improve the precision of alternating current detection.

[0036] In an exemplary embodiment, as shown in Figure 1 In the above alternating current detection unit, a gap is arranged in the magnetic circuit formed by the first annular core and the second annular core. The gap can refer to a gap between the first annular core and the second annular core in the magnetic circuit. In actual application, the first annular core and the second annular core need to be close. After the first annular core and the second annular core are close, a predetermined distance is maintained between the first annular core and the second annular core, which is equivalent to arranging a corresponding gap in the magnetic circuit formed by the first annular core and the second annular core. The size and shape of the above gap are accurately designed to fine-tune the magnetic resistance of the magnetic circuit, so as to further optimize the magnetic flux balance in the zero magnetic flux state and improve the response precision and stability of the device to different current sizes and frequencies. In an exemplary embodiment, the predetermined distance is not greater than 2 mm, that is, the corresponding gap is not greater than 2 mm.

[0037] In an exemplary embodiment, the number of ampere turns of the first annular core is equal to the number of ampere turns of the second annular core.

[0038] The number of ampere turns can refer to the product of the current in the coil and the number of turns of the coil, which is used to reflect the ability of the coil to generate a magnetic field and can determine the strength of the magnetic circuit. The number of ampere turns of the first annular core is equal to the number of ampere turns of the second annular core, that is, the magnetic motive force generated by the first annular core and the second annular core is the same. By designing the number of ampere turns of the first annular core to be equal to the number of ampere turns of the second annular core, the magnetic field strength of the first annular core and the second annular core is consistent, so as to realize the balance of the two cores.

[0039] In an exemplary embodiment, the compensation circuit is an LRC circuit or a resistance-adjustable compensation resistor. By adjusting the resistance of the compensation circuit, the size of the compensation electromotive force generated by the second annular core and the second winding can be accurately controlled to adapt to different application scenarios and the characteristics of the current to be measured, thereby ensuring that the compensation electromotive force generated by the second annular core through the compensation circuit and the second winding can offset the electromotive force of the first annular core to achieve a zero flux state, thereby ensuring high accuracy of AC detection. The compensation circuit can be a resistance-adjustable resistor or an LRC circuit. For example, the LRC circuit can adaptively match the LRC circuit according to the impedance parameters of the voltage transformer under test. The LRC circuit, also known as an RLC circuit, is a circuit composed of three basic elements: resistance (R), inductance (L), and capacitance (C).

[0040] In an exemplary embodiment, the resistance of the compensation circuit is determined based on the number of ampere turns of the first annular core and the number of ampere turns of the second annular core.

[0041] The resistance of the compensation circuit can be the impedance of the LRC circuit or the resistance of the compensation resistor.

[0042] In actual application of the AC detection unit, the second end of the first winding and the second end of the third winding together form a detection signal output end of the AC detection unit, which is connected to a load to output the detection signal. In this embodiment, a sampling circuit is connected to the detection signal output end as an example. The process of determining the resistance of the compensation circuit based on the number of ampere turns of the first annular core and the number of ampere turns of the second annular core can include: first, determining the current of the loop contained in the second annular core based on the number of ampere turns of the first annular core and the number of ampere turns of the second annular core, for example, by the following formula:

[0043]

[0044] wherein, N1 represents the number of turns of the first winding; I2 represents the secondary current corresponding to the preset rated primary current of the loop contained in the first annular core. The loop contained in the first annular core can refer to the closed loop formed by the first winding, the third winding, and the sampling circuit connected to the first annular core; N3 represents the number of turns of the third winding; I2 represents the current of the loop contained in the second annular core. The loop contained in the second annular core can refer to the electromotive force compensation loop formed by the second winding and the compensation circuit connected in series to the second annular core; N2 represents the number of turns of the second winding.

[0045] After the current of the loop contained by the second annular core is determined by the above formula, the resistance value of the compensation circuit can be determined according to the following formula, that is:

[0046]

[0047] wherein, represents the secondary current corresponding to the preset rated primary current of the loop contained by the first annular core, and the loop contained by the first annular core can refer to a closed loop formed by the first winding, the third winding and the sampling circuit connected on the first annular core; represents the resistance value of the first winding; represents the resistance value of the third winding; represents the resistance value of the sampling circuit; represents the current of the loop contained by the second annular core, and the loop contained by the second annular core can refer to an electromotive force compensation loop formed by the second winding and the compensation circuit in series on the second annular core; represents the resistance value of the second winding; represents the resistance value of the compensation circuit.

[0048] Therefore, the resistance value of the compensation circuit can be obtained by the above formula. For different ranges of alternating currents to be detected, that is, for different preset rated primary currents, different resistance values of the compensation circuit can be obtained by the above process, so as to ensure that the compensation electromotive force generated by the second annular core through the compensation circuit and the second winding can offset the electromotive force of the first annular core to achieve a zero flux state, thereby ensuring high accuracy of alternating current detection. In addition, in actual application, due to the limitations of core material, process, wire process and winding process, there will be certain deviations in the design of the same alternating current detection unit, so the resistance value of the compensation circuit is also different, which needs to be dynamically adjusted according to the calibration data. After error calibration by the calibration device, the error data can be adjusted.

[0049] In an exemplary embodiment, the wire diameter and the number of turns corresponding to the first winding and the second winding are determined based on the core cross-sectional area of the first annular core and the second annular core, the core material of the first annular core and the second annular core, and the rated primary current; and the wire diameter and the number of turns corresponding to the third winding are determined based on the target detection current range and the target detection accuracy.

[0050] The determination of the wire diameter and the number of turns corresponding to the first winding and the second winding is based on the following: the larger the cross-sectional area of the core, the larger the magnetic flux that can be generally borne and transmitted. According to the principle of electromagnetic induction, under a certain magnetic field change, a larger cross-sectional area of the core can allow more magnetic lines of force to pass through, thereby inducing a larger electromotive force in the winding. In order to fully utilize the magnetic conductivity of the core and enable the winding to effectively convert magnetic field energy into electrical energy, the number of turns and the wire diameter of the winding need to be determined according to the cross-sectional area of the core. A larger cross-sectional area of the core can appropriately increase the number of turns of the winding to increase the induced electromotive force, and at the same time, in order to bear a larger induced current, the wire diameter also needs to be increased accordingly. Different core materials have different magnetic properties such as magnetic permeability. Materials with high magnetic permeability, such as permalloy, can more effectively conduct the magnetic field, making the magnetic field more evenly distributed in the core and the loss smaller. For core materials with high magnetic permeability, under the same magnetic field excitation, a larger induced electromotive force can be generated in the winding. Therefore, when using core materials with high magnetic permeability, the number of turns of the winding can be relatively small to achieve the desired induction effect; for materials with lower magnetic permeability, the number of turns may need to be increased to compensate for the lack of magnetic properties. At the same time, different core materials may have different saturation characteristics under different magnetic field strengths, which will also affect the design of the winding to avoid saturation of the core leading to poor induction effect. In addition, the primary current rating determines the size of the current passing through the current-carrying wire. According to the law of electromagnetic induction, the magnetic field strength generated by the primary current is proportional to the size of the current, which in turn affects the electromotive force and current induced in the first winding and the second winding. In order to enable the first winding and the second winding to accurately reflect the changes in the primary current, and when the primary current reaches the rated value, the winding will not overheat and be damaged or have magnetic saturation problems due to excessive current, the wire diameter and the number of turns of the winding need to be reasonably selected according to the primary current rating. Generally speaking, the larger the primary current rating, the thicker the wire diameter of the winding needs to be to carry a larger current, and the number of turns also needs to be adjusted according to the specific electromagnetic relationship to ensure the accuracy and stability of the induction.

[0051] The third winding wire diameter and the number of turns are determined according to the following aspects: the third winding is mainly used for detecting current, and different application scenarios have different requirements for the range of detected current. If the target detection current range is wide, in order to accurately detect the current signal in the entire range, the number of turns and the wire diameter of the third winding need to be reasonably designed. For example, for the case of detecting small current, in order to improve the detection sensitivity, the number of turns of the winding may need to be increased so that a large electromotive force can be induced under the weak magnetic field generated by small current; for the case of detecting large current, on the one hand, the winding needs to be selected with a relatively thick wire diameter to withstand large current without damage, and on the other hand, in order to avoid core saturation under large current, which leads to detection distortion, the number of turns cannot be too many, and the winding needs to work normally under large current on the premise of ensuring detection accuracy. In addition, detection accuracy is an important indicator to measure detection performance. In order to achieve high detection accuracy, the number of turns and the wire diameter of the third winding need to be accurately controlled. The number of turns directly affects the size of the induced electromotive force, and further affects the resolution and accuracy of current detection. If the number of turns is inaccurate or unreasonable, it may cause large errors in the detection result. The selection of wire diameter also affects the detection accuracy. If the wire diameter is too thin, it may generate a large resistance, causing signal attenuation and distortion during transmission, affecting the accuracy of detection; if the wire diameter is too thick, it may increase the cost and volume, and in some cases may introduce additional electromagnetic interference and other problems. Therefore, according to the requirements of the target detection accuracy, various factors are considered to accurately determine the wire diameter and the number of turns of the third winding, so as to ensure that the transformer can accurately detect the true value of the current. In some other embodiments, the target detection accuracy can be 0.01 level.

[0052] In an exemplary embodiment, the first annular core and the second annular core are made of magnetic material. The material used for the first annular core and the second annular core is a material with magnetic properties. Magnetic materials have the characteristics of being magnetized and conducting magnetic fields, etc. In electromagnetic devices, annular cores made of magnetic materials can better concentrate and conduct magnetic fields, so that electromagnetic induction and other phenomena can occur more effectively, thereby realizing the specific functions of the device. For example, in an alternating current detection unit, the annular core made of magnetic material can guide and enhance the magnetic field, so that the winding can more efficiently induce an electromotive force to realize the functions of measuring, converting, etc. of current, voltage and other parameters. In an application example, the first annular core and the second annular core are made of magnetic material with high magnetic permeability and low magnetic hysteresis loss characteristics to improve the stability and reliability of the zero flux effect.

[0053] In one exemplary embodiment, the magnetic material is a composite material made of permalloy and nanocrystalline alloy. Permalloy is an alloy with iron and nickel as its main components, possessing excellent magnetic properties such as high permeability and low coercivity. Permalloy can be easily magnetized and can respond quickly and accurately to changes in the magnetic field, with relatively low losses. Nanocrystalline alloys are a novel type of magnetic material, prepared through a special process, and possess a nanoscale crystal structure. They exhibit a variety of superior properties, including high permeability, high saturation magnetic induction, and low loss. Their nanoscale crystal structure provides more uniform magnetic properties at the microscopic level, enabling more precise control over the distribution and variation of the magnetic field. Therefore, using a composite of permalloy and nanocrystalline alloys as the core material can further optimize the material's permeability. Compared to traditional magnetic materials, nanocrystalline alloys exhibit better stability at high temperatures. This means that cores made from permalloy and nanocrystalline alloy composites can maintain more stable performance and reduce performance fluctuations caused by temperature changes when operating in high-temperature environments. In applications requiring the processing of high currents or high-frequency signals, this composite material can also effectively reduce hysteresis and eddy current losses, lower operating costs, and improve energy efficiency.

[0054] In one exemplary embodiment, this application also provides a current sampling device, including the AC detection unit as described above, wherein the current sampling device further includes a sampling circuit (such as...). Figure 2 (R2 shown), the sampling circuit is connected to the detection signal output terminal of the AC detection unit. The current signal is converted into a voltage signal during acquisition, and then processed to obtain the voltage signal. The principle of this current sampling device is similar to that of a current transformer. It converts the large primary current signal into a small signal for acquisition. The current ratio is inversely proportional to the winding turns ratio. After the signal is acquired by the sampling circuit, it is converted according to the ratio to obtain the primary capacitive current signal.

[0055] The aforementioned current sampling device is designed based on the zero flux principle and consists of an AC detection unit and a sampling circuit, which are high-precision miniature current transformers. It can quickly and accurately measure the current change and process caused by capacitor breakdown, effectively meeting the requirements for accurate measurement of capacitive current in capacitive voltage transformers and providing key technical support for online monitoring of their metering performance.

[0056] In some embodiments, the aforementioned current sampling device may also be equipped with a housing, which encapsulates the AC detection unit and related circuit components using shielding electromagnetic interference materials to reduce external interference and ensure accurate measurement.

[0057] Compared with the prior art, the current sampling device has the following beneficial effects: 1. High accuracy: The current sampling device is designed based on the zero magnetic flux principle and has a high accuracy of 0.01 level, so that the precise measurement of the capacitive current of the capacitive voltage transformer can be realized. 2. Good stability: The influence of external factors on the internal magnetic field distribution is reduced through the material characteristics and structural design, and the output signal is stabilized by adding a compensation circuit, so that the device can maintain the stability of the measurement data in a complex field environment, and provide reliable data support for the online monitoring of the CVT measurement performance. 3. Good frequency characteristics: The device has high cutoff frequency and low loss characteristics on the core material, reasonable structural design of winding turns, wire diameter and other factors, reduced distributed capacitance and inductance, reduced loss and distortion of high-frequency signal transmission, and a shell with good shielding effect to prevent external high-frequency interference signals and self-electromagnetic interference to surrounding equipment, so that good frequency response characteristics are realized, and the device has a smoothing processing capability within 400Hz, and can accurately measure the capacitive current at different frequencies. 4. Wide temperature range: The device can adapt to a wide temperature range (-25℃ to +55℃) through the material characteristics of the core, and still maintain good performance at different environmental temperatures.

[0058] In one exemplary embodiment, as shown in Figure 3 The application also provides a voltage transformer in a transformer substation, which comprises the current sampling device 10 and a capacitive voltage transformer 20. The current-carrying wire of the current sampling device is connected in series to the high-voltage tail of the capacitive voltage transformer. When the current sampling device is connected to the high-voltage tail of the capacitive voltage transformer, the current-carrying wire of the current sampling device can be used, or the line of the high-voltage tail can be directly connected to the current sampling device as the current-carrying wire. The current sampling device has high accuracy of 0.01 level, good stability, frequency characteristics and wide temperature characteristics suitable for the temperature range of the transformer substation, so that it does not affect the safe and stable operation of the power grid during operation, and can accurately and quickly measure the current change and process caused by capacitive breakdown through the synergistic effect of the internal parts of the current sampling device, thereby meeting the precise measurement requirements of the capacitive current of the capacitive voltage transformer and providing a solid technical support foundation for the online monitoring of the measurement performance.

[0059] In another exemplary embodiment, as shown in Figure 3 The detection signal output end of the current sampling device is also connected to a data processing unit 30, and the data processing unit is used for data processing to obtain the alternating current on the current-carrying wire. In addition, a secondary voltage signal can be obtained from the voltage capacitor arm of the capacitive voltage transformer 20 and connected to the data processing unit 30.

[0060] In the description of the specification, the description of the terms "some embodiments", "other embodiments", etc. means that the particular feature, structure, material, or characteristic being described is included in at least one embodiment or example of the application. The illustrative descriptions in this specification are not necessarily to be construed as indicating that all embodiments or examples of the application include the described feature, structure, material or characteristic.

[0061] The technical features of the above-described embodiments can be combined in any manner, and for brevity, not all possible combinations of the technical features in the above-described embodiments are described, but it should be considered that any combination of the technical features is within the scope of the present application as long as the combination does not result in a contradiction.

[0062] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the present application. It should be noted that for those skilled in the art, some modifications and improvements can be made without departing from the concept of the present application, and these are within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. An alternating current detection unit, characterized by, The alternating current detection unit comprises a first annular core, a second annular core, a first winding, a second winding, a third winding and a compensation circuit. The first annular core and the second annular core are coaxially arranged and overlap with each other, and the first annular core and the second annular core are provided with a current-carrying wire as a primary winding of the alternating current detection unit, which is used to access a line to be detected. The first winding is wound on the first annular core, the second winding is wound on the second annular core, and the third winding is wound on the first annular core and the second annular core at the same time; the second winding and the compensation circuit are connected in series to form an electromotive force compensation loop. A first end of the first winding is connected to a first end of the third winding, and a second end of the first winding and a second end of the third winding together form a detection signal output end of the alternating current detection unit.

2. The AC detection unit according to claim 1, characterized in that An air gap is arranged in a magnetic circuit formed by the first annular core and the second annular core.

3. The AC detection unit of claim 1, wherein The number of ampere turns of the first annular core is equal to the number of ampere turns of the second annular core.

4. The AC detection unit of claim 1, wherein The compensation circuit is an LRC circuit or a compensation resistor with adjustable resistance.

5. The AC detection unit of claim 4, wherein The resistance of the compensation circuit is determined based on the number of ampere turns of the first annular core and the number of ampere turns of the second annular core.

6. The AC detection unit of claim 1, wherein The corresponding wire diameter and number of turns of the first winding and the second winding are determined based on the core cross-sectional area of the first annular core and the second annular core, the core material of the first annular core and the second annular core, and the primary current rating; and the corresponding wire diameter and number of turns of the third winding are determined based on the target detection current range and the target detection accuracy.

7. The AC detection unit of claim 1, wherein The first annular core and the second annular core are made of a magnetic material.

8. The AC detection unit of claim 7, wherein The magnetic material is a composite material made of permalloy and nanocrystalline alloy.

9. A current sampling device, characterized by The current sampling device comprises the alternating current detection unit according to any one of claims 1 to 8, wherein the current sampling device further comprises a sampling circuit connected to the detection signal output end of the alternating current detection unit.

10. A voltage transformer in a substation, characterized by The current sampling device comprises the alternating current detection unit according to any one of claims 1 to 8, wherein the current sampling device further comprises a sampling circuit connected to the detection signal output end of the alternating current detection unit. The current sampling device comprises the alternating current detection unit according to any one of claims 1 to 8, wherein the current sampling device further comprises a sampling circuit connected to the detection signal output end of the alternating current detection unit.

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