Alternating current detection unit, current sampling device and voltage transformer in transformer substation

Abstract

The invention relates to an alternating current detection unit, a current sampling device and a voltage transformer in a transformer substation. The alternating current detection unit comprises a first annular iron core, a second annular iron core, a first winding, a second winding, a third winding and a compensation circuit, the first annular iron core and the second annular iron core are coaxially arranged and mutually overlapped, and a current-carrying wire serving as a primary winding of the alternating current detection unit penetrates through the first annular iron core and the second annular iron core. The current-carrying wire is used for being connected to a to-be-detected line The first winding is wound on the first annular iron core, the second winding is wound on the second annular iron core, and the third winding is simultaneously wound on the first annular iron core and the second annular iron core; the second winding is serially connected with the compensation circuit to form an electromotive force compensation loop; the first end of the first winding is connected with the first end of the third winding, and the second end of the first winding and the second end of the third winding jointly form a detection signal output end of the alternating current detection unit. The precision of alternating current detection can be improved.

Description

Technical Field

[0001] The present application relates to the field of monitoring technologies, and particularly to an alternating current detection unit, a current sampling device, and a voltage transformer in a substation. Background Art

[0002] In the field of on-line monitoring of the operation device and metering performance of capacitive voltage transformers, accurately measuring the primary capacitive current is crucial. The change of the primary capacitive current of the voltage transformer capacitor element under normal operation and fault conditions is extremely complex. Under normal operating conditions, the primary capacitive current exhibits specific amplitude and frequency characteristics. However, once a fault occurs in the capacitor element, such as capacitor breakdown, partial discharge, or capacitance value drift, the primary capacitive current will change significantly. This change may be manifested as a sharp increase or decrease in the current amplitude, a change in the frequency characteristics, and a phase shift, etc. Moreover, the current change characteristics caused by different fault types and fault degrees are different, which poses extremely high requirements for the accuracy and dynamic range of current measurement.

[0003] Traditional current measurement devices often have difficulty in simultaneously meeting the requirements of high accuracy, wide frequency band, and stable measurement. Some measurement devices have limitations in terms of accuracy and cannot reach the accuracy level required for on-line monitoring of the metering performance of capacitive voltage transformers. For example, they cannot accurately track and measure during the current change process. Summary of the Invention

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

[0005] An alternating current 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 core and the second toroidal core are coaxially arranged and overlap each other. A current-carrying wire serving as the primary winding of the alternating current detection unit passes through the first toroidal core and the second toroidal core, and the current-carrying wire is used to access the line to be detected;

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

[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 end of the alternating current detection unit.

[0009] In one embodiment, an air gap is provided in the magnetic circuit formed by the first toroidal core and the second toroidal core.

[0010] In one embodiment, the magnetomotive force of the first toroidal core is equal to that of the second toroidal core.

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

[0012] In one embodiment, the resistance value of the compensation circuit is determined based on the magnetomotive force of the first toroidal core and that of the second toroidal core.

[0013] In one embodiment, the wire diameters and number of turns corresponding to the first winding and the second winding are determined based on the core cross-sectional areas of the first toroidal core and the second toroidal core, the core materials of the first toroidal core and the second toroidal core, and the rated primary current value; the wire diameter and 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 embodiment, the first toroidal core and the second toroidal core are made of magnetic materials.

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

[0016] The above AC detection unit operates based on the principle of electromagnetic induction. When the current-carrying wire of the above AC detection unit is connected to the AC line to be detected, the alternating current in the current-carrying wire will generate a changing magnetic field in the first toroidal core and the second toroidal core. The corresponding secondary winding will induce an electromotive force and generate a corresponding secondary current. The first end of the first winding is connected to the first end of the above third winding, and the second end of the first winding and the second end of the above third winding together form the detection signal output end of the above AC detection unit. The second toroidal core generates a compensation electromotive force through the compensation circuit to cancel the electromotive force of the first toroidal core through the second winding, so as to achieve the zero-flux effect of the AC detection unit, thereby improving the accuracy of AC detection.

[0017] A current sampling device includes the above AC detection unit. Wherein, the current sampling device further includes a sampling circuit, and the sampling circuit is connected to the detection signal output end of the AC detection unit.

[0018] The above 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 other processes of the signal, and provides a basis for the accurate sampling of alternating current.

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

[0020] For the above voltage transformer in the substation, due to the setting of the current sampling device, a voltage transformer in the substation with an integrated wide dynamic range measurement ability is realized. When the capacitive voltage transformer breaks down, the current sampling device can quickly respond and sample the alternating current at a high frequency during the breakdown. In addition, the current-carrying wire of the current sampling device is connected to the primary 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 operating together with the capacitive voltage transformer, ensuring the safe and stable operation of the power grid. Brief Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

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

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

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

[0025] To facilitate the understanding of the present application, the following will describe the present application more comprehensively with reference to the relevant drawings. Embodiments of the present application are shown in the drawings. However, the present application can be implemented 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 those of ordinary skill in the technical field to which the present application belongs. The terms used in the description of the present application in this specification are only for the purpose of describing specific embodiments and are not intended to limit the present application.

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

[0028] It can be understood that for "connection" in the following embodiments, if there is transmission of electrical signals or data between the connected circuits, modules, units, etc., it should be understood as "electrical connection", "communication connection", etc.

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

[0030] As used herein, the singular forms "a", "an", and "the" may also include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprise / include" or "have" etc. specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. At the same time, the term "and / or" used in this specification includes any and all combinations of the related listed items.

[0031] In the field of on-line monitoring of the operation device and metering performance of capacitive voltage transformers, accurately measuring the primary capacitive current is of crucial importance. The change of the primary capacitive current of the capacitive element of the voltage transformer under normal operation and fault conditions is extremely complex. Under normal operating conditions, the primary capacitive current exhibits specific amplitude and frequency characteristics. However, once a fault occurs in the capacitive element, such as capacitor breakdown, partial discharge, or capacitance value drift, the primary capacitive current will change significantly. This change may be manifested as a sharp increase or decrease in the current amplitude, a change in the frequency characteristics, and a phase shift, etc. Moreover, the current change characteristics caused by different fault types and fault degrees are different, which poses extremely high requirements for the accuracy and dynamic range of current measurement. At the same time, the complexity of the on-site operating conditions also makes measurement difficult. The primary current range of CVT (Capacitor Voltage Transformer) varies significantly due to the grid voltage level, system load, and its own parameter settings, from normal small current to large current impact during capacitor breakdown, requiring the measurement device to have the ability to measure with a wide dynamic range; when the capacitor breaks down, the current changes instantaneously, and the measurement device needs to have fast response ability and high sampling frequency; in addition, the operating environment of the power system is complex and changeable, factors such as large temperature fluctuations, electromagnetic interference, humidity, and dust will not only directly interfere with the normal operation of the measurement device and increase errors, but also affect its long-term stability and reliability, causing measurement data to drift or deviate.

[0032] However, traditional current measurement methods and devices often struggle to meet the requirements of high accuracy, wide frequency range, and stable measurement simultaneously. Some measurement devices have limitations in terms of accuracy and cannot reach the accuracy level required for on-line monitoring of the metering performance of capacitive voltage transformers. For example, the error is large when measuring small currents, or it cannot accurately track the measurement during the current change process. Some devices have poor frequency characteristics and cannot comprehensively and accurately measure the current signals from low frequency to high frequency that may be involved during the operation of CVT, resulting in misjudgment or missed judgment of the fault characteristics of the capacitive element. Additionally, in terms of stability, the existing technologies are easily interfered by environmental factors, and it is difficult to guarantee the reliability of the measurement data during long-term operation, unable to provide continuous, stable, and accurate primary capacitive current data support for the on-line monitoring of the metering performance of capacitive voltage transformers, thus restricting the effective monitoring and maintenance of the operating status of capacitive voltage transformers in the power system.

[0033] Therefore, in order to achieve accurate measurement of the primary capacitive current in the on-line monitoring of the metering performance of capacitive voltage transformers, the inventors of this application conducted research on the change characteristics of the primary capacitive current before and after the fault of the capacitive element of the voltage transformer, determined the current measurement principle and factors affecting accuracy by analyzing the on-site operating conditions, and then clarified the performance index requirements of the high-accuracy wide-frequency capacitive current sensing module and proposed a hardware design scheme. In an exemplary embodiment, as Figure 1 - Figure 2As shown in the figure, the present application provides an AC detection unit, which includes a first toroidal core 100, a second toroidal core 200, a first winding 300, a second winding 400, a third winding 500, and a compensation circuit. The first toroidal core 100 and the second toroidal core 200 are coaxially arranged and overlap each other. A current-carrying wire 600, which serves as the primary winding of the AC detection unit, passes through the first toroidal core 100 and the second toroidal core 200. The current-carrying wire is used to connect to the line to be detected. The first winding 300 is wound around the first toroidal core 100, the second winding 400 is wound around the second toroidal core 200, and the third winding 500 is wound around both the first toroidal core 100 and the second toroidal core 200. The second winding 400 and the compensation circuit are connected in series to form an electromotive force compensation loop. The first end of the first winding 300 is connected to the first end of the third winding 500, and 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 AC detection unit. As Figure 2 In the schematic diagram shown, T1 refers to the first toroidal core, T2 refers to the second toroidal 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, and a compensation electromotive force is formed on the compensation circuit, and the ratio compensation of the loop included in the first toroidal core is negative. The magnitude of the magnetic shunt compensation value can be adjusted by increasing or decreasing the magnetic shunt cross-section. In this way, as long as appropriate compensation turns and the cross-section of the magnetic shunt are selected, the error of the transformer after magnetic shunt compensation can be significantly reduced, and the performance of the transformer can be greatly improved. The magnetic shunt compensation is positive for the ratio difference compensation, and the potential compensation is negative for the ratio difference compensation. In order to offset the negative compensation of the potential compensation for the ratio, in the magnetic shunt potential compensation, the weak magnetic shunt compensation should be strengthened. For this purpose, the number of magnetic shunt sheets can be increased, and the compensation turns can be appropriately increased.

[0035] The above AC 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 generated in electromagnetic induction to the equipment can be reduced. The above AC detection unit works based on the principle of electromagnetic induction. The current-carrying wire 600 of the above AC detection unit is connected to the AC line to be detected. The alternating current in the current-carrying wire 600 will generate a changing magnetic field in the first toroidal core 100 and the second toroidal 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, and 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 above AC detection unit. The second toroidal core 200 generates a compensation electromotive force through the compensation circuit and cancels the electromotive force of the first toroidal core 100, so as to achieve the zero-flux effect of the AC detection unit, and further improve the accuracy of AC detection.

[0036] In an exemplary embodiment, as Figure 1 shown, in the above AC detection unit, an air gap is provided in the magnetic circuit formed by the first toroidal core and the second toroidal core. Among them, the air gap can refer to a section of gap between the first toroidal core and the second toroidal core in the magnetic circuit. In practical applications, the first toroidal core and the second toroidal core need to be close to each other. After the first toroidal core and the second toroidal core are close to each other, a preset distance needs to be maintained between the first toroidal core and the second toroidal core. The preset distance is equivalent to providing a corresponding air gap in the magnetic circuit formed by the first toroidal core and the second toroidal core. The size and shape of the above air gap are precisely designed to fine-tune the magnetic resistance of the magnetic circuit, so as to further optimize the magnetic flux balance in the zero-flux state and improve the response accuracy and stability of the device to different current magnitudes and frequencies. In an exemplary embodiment, the preset distance is not greater than 2 mm, that is, the corresponding air gap is not greater than 2 mm.

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

[0038] Among them, 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 magnetic circuit strength. Among them, the number of ampere-turns of the first toroidal core is equal to the number of ampere-turns of the second toroidal core, that is, the magnetomotive forces generated by the first toroidal core and the second toroidal core are the same. By designing the number of ampere-turns of the first toroidal core to be equal to the number of ampere-turns of the second toroidal core, the purpose of making the magnetic field intensities of the first toroidal core and the second toroidal core consistent is achieved, thereby realizing the balance of the two cores.

[0039] In an exemplary embodiment, the compensation circuit is an LRC circuit or a compensating resistor with adjustable resistance. Among them, by adjusting the resistance value of the compensation circuit, the magnitude of the compensating electromotive force generated by the second toroidal core and the second winding can be precisely controlled to adapt to different application scenarios and the characteristics of the current to be measured, thereby ensuring that the compensating electromotive force generated by the second toroidal core through the compensation circuit and the second winding can cancel out the electromotive force of the first toroidal core to achieve a zero magnetic flux state and guarantee the high precision of AC detection. The compensation circuit can be a resistor with adjustable resistance 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; among them, the LRC circuit, also known as the RLC circuit, is a circuit composed of three basic elements: a resistor (R), an inductor (L), and a capacitor (C).

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

[0041] Among them, the resistance value of the compensation circuit can be the impedance of the LRC circuit or the resistance value of the compensating resistor.

[0042] Among them, in the actual application of the AC detection unit, the second end of the first winding and the second end of the third winding jointly form the detection signal output end of the AC detection unit, and the detection signal output end will be connected to a load to realize the output of the detection signal. In this embodiment, taking the connection of the detection signal output end to the sampling circuit as an example for illustration, the process of determining the resistance value of the compensation circuit based on the ampere-turns of the first toroidal core and the ampere-turns of the second toroidal core may include: First, determine the current in the loop included in the second toroidal core according to the ampere-turns of the first toroidal core and the ampere-turns of the second toroidal core, for example, determined by the following formula:

[0043]

[0044] Among them, represents the number of turns of the first winding; represents the secondary current corresponding to the preset rated primary current in the loop included in the first toroidal core. The loop included in the first toroidal core can refer to the closed loop formed by the first winding, the third winding on the first toroidal core, and the connected sampling circuit; represents the number of turns of the third winding; represents the current in the loop included in the second toroidal core. The loop included in the second toroidal core can refer to the electromotive force compensation loop formed by the series connection of the second winding on the second toroidal core and the compensation circuit; represents the number of turns of the second winding.

[0045] After determining the current of the loop included in the second toroidal core through 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 included in the first toroidal core. The loop included in the first toroidal core may refer to the closed loop formed by the first winding, the third winding on the first toroidal core and the connected sampling circuit; 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 included in the second toroidal core. The loop included in the second toroidal core may refer to the electromotive force compensation loop formed by the second winding on the second toroidal core and the compensation circuit in series; 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 through the above formula. When aiming at different ranges of alternating current to be detected, that is, for different preset rated primary currents, different resistance values of the compensation circuit can be obtained through the above process, so as to ensure that the compensation electromotive force generated by the second toroidal core through the compensation circuit and the second winding can cancel the electromotive force of the first toroidal core, so as to reach the zero magnetic flux state and ensure the high precision of AC detection. In addition, in practical applications, due to limitations such as core materials, processes, wire processes, and winding processes, there will eventually be certain deviations in the design of the same AC detection unit. Therefore, the resistance values of the compensation circuits are also different and need to be dynamically adjusted according to the calibration data. After the error of the compensation circuit is calibrated by a calibration device, it can be adjusted according to the error data.

[0049] In an exemplary embodiment, the wire diameters and turns of the above-mentioned first winding and the above-mentioned second winding are determined based on the core cross-sectional areas of the above-mentioned first toroidal core and the above-mentioned second toroidal core, the core materials of the above-mentioned first toroidal core and the above-mentioned second toroidal core, and the rated value of the primary current; the wire diameter and turns of the above-mentioned third winding are determined based on the target detection current range and the target detection accuracy.

[0050] Among them, the basis for determining the wire diameter and number of turns corresponding to the first winding and the second winding includes: the larger the cross-sectional area of the iron core, the greater the magnetic flux that can generally be carried and transmitted. According to the principle of electromagnetic induction, under a certain magnetic field change, a larger cross-sectional area of the iron core allows more magnetic lines of force to pass through, thereby inducing a larger electromotive force in the winding. In order to make full use of the magnetic conductivity of the iron core and enable the winding to effectively convert magnetic field energy into electrical energy, it is necessary to determine the number of turns and wire diameter of the winding according to the cross-sectional area of the iron core. When the cross-sectional area of the iron core is large, the number of turns of the winding can be appropriately increased to increase the induced electromotive force. At the same time, in order to carry a larger induced current, the wire diameter also needs to be increased accordingly. Different iron core materials have different magnetic properties such as magnetic permeability. Materials with high magnetic permeability, such as permalloy, can conduct the magnetic field more effectively, making the magnetic field distribution in the iron core more uniform and the loss smaller. For iron 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 iron core materials with high magnetic permeability, the number of turns of the winding may be relatively less to achieve the required induction effect; while for materials with lower magnetic permeability, it may be necessary to increase the number of turns to make up for the deficiency of magnetic properties. At the same time, different iron core materials may have different saturation characteristics under different magnetic field strengths, which will also affect the design of the winding to avoid the deterioration of the induction effect caused by iron core saturation. In addition, the rated value of the primary current determines the magnitude 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 magnitude 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 change of the primary current and ensure that when the primary current reaches the rated value, the winding will not be damaged by overheating due to excessive current or suffer from magnetic saturation and other problems, it is necessary to reasonably select the wire diameter and number of turns of the winding according to the rated value of the primary current. Generally speaking, the larger the rated value of the primary current, the thicker the wire diameter of the winding needs to be to carry a larger current. At the same time, the number of turns also needs to be adjusted according to the specific electromagnetic relationship to ensure the accuracy and stability of induction.

[0051] Among them, the determination basis for the wire diameter and number of turns of the third winding includes: The third winding is mainly used for current detection, and different application scenarios have different requirements for the range of detected current. If the target detected current range is relatively wide, in order to accurately detect the current signal throughout the entire range, it is necessary to reasonably design the number of turns and wire diameter of the third winding. For example, in the case of detecting small currents, in order to improve the detection sensitivity, it may be necessary to increase the number of turns of the winding so that a sufficient large electromotive force can be induced under the weak magnetic field generated by the small current; while for the case of detecting large currents, on the one hand, it is necessary to consider that the winding can withstand the large current without being damaged, and a thicker wire diameter needs to be selected. On the other hand, in order to avoid core saturation under large currents resulting in detection distortion, the number of turns cannot be too many. Under the premise of ensuring the detection accuracy, the winding should still be able to work normally under large currents. In addition, the detection accuracy is an important indicator to measure the detection performance. In order to achieve a high detection accuracy, it is necessary to precisely control the number of turns and wire diameter of the third winding. The number of turns directly affects the magnitude of the induced electromotive force, and thus affects the resolution and accuracy of current detection. If the number of turns is inaccurate or unreasonable, it may lead to a large error in the detection result. The selection of the wire diameter also affects the detection accuracy. If the wire diameter is too thin, it may generate a large resistance, resulting in signal attenuation and distortion during transmission, affecting the detection accuracy; if the wire diameter is too thick, it may increase the cost and volume, and in some cases, it may introduce additional electromagnetic interference and other problems. Therefore, according to the requirements of the target detection accuracy, various factors need to be comprehensively considered to accurately determine the wire diameter and number of turns of the third winding to ensure that the current 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 above-mentioned first toroidal core and the above-mentioned second toroidal core are made of magnetic materials. Among them, the materials used for the first toroidal core and the second toroidal core are magnetic materials. Magnetic materials have the characteristics of being magnetizable and having magnetic conductivity. In electromagnetic devices, using magnetic materials to make toroidal cores can better gather and conduct magnetic fields, enabling electromagnetic induction and other phenomena to occur more effectively, thereby realizing the specific functions of the device. For example, in an AC detection unit, a toroidal core made of magnetic materials can guide and enhance the magnetic field, enabling the winding to more efficiently induce an electromotive force and realizing functions such as measuring and transforming parameters such as current and voltage. In an application example, the first toroidal core and the above-mentioned second toroidal core are made of magnetic materials with high magnetic permeability and low hysteresis loss characteristics to improve the stability and reliability of the zero-flux effect.

[0053] In an exemplary embodiment, the above magnetic material is a composite material made of permalloy and nanocrystalline alloy. Among them, permalloy is an alloy mainly composed of iron and nickel, which has excellent magnetic properties such as high magnetic permeability and low coercivity. Permalloy can be easily magnetized, and when the magnetic field changes, it can respond quickly and accurately with relatively small losses. Nanocrystalline alloy is a new type of magnetic material prepared by a special process and has a nanoscale crystal structure; nanocrystalline alloy has a variety of excellent properties such as high magnetic permeability, high saturation magnetic induction intensity, and low loss. Its nanoscale crystal structure enables it to have more uniform magnetic properties at the microscopic level and can more precisely control the distribution and change of the magnetic field; therefore, using the composite of permalloy and nanocrystalline alloy as the magnetic material of the iron core can further optimize the magnetic permeability of the material; compared with traditional magnetic materials, nanocrystalline alloy shows better stability at high temperatures, which means that when working in a high-temperature environment, the iron core made of the composite material of permalloy and nanocrystalline alloy can maintain more stable performance and reduce performance fluctuations caused by temperature changes; in application scenarios that need to process large currents or high-frequency signals, this composite material can also effectively reduce hysteresis loss and eddy current loss, reduce operating costs, and improve energy efficiency.

[0054] In an exemplary embodiment, the present application also provides a current sampling device, including the above-mentioned AC detection unit. Among them, the current sampling device further includes a sampling circuit (such as Figure 2 the shown resistor R2), and the above sampling circuit is connected to the detection signal output end of the above AC detection unit. Among them, the current signal is converted into a voltage signal for acquisition during collection and then obtained through data processing. The principle of this current sampling device is similar to that of a current transformer. The large current signal on the primary side is converted into a small signal for collection through the current sampling device. Its current ratio is inversely proportional to the turns ratio of the winding. After the signal is obtained through the sampling circuit, it is converted according to the ratio to obtain the primary capacitive current signal.

[0055] The above current sampling device is designed based on the zero-flux principle and is composed of an AC detection unit and a sampling circuit that act as a high-precision micro current transformer. It can quickly and accurately measure the current change amount and change process caused by capacitor breakdown, effectively meet the accurate measurement requirements of the capacitive current of the capacitive voltage transformer, and provide key technical support for the online monitoring of its metering performance.

[0056] In some embodiments, the above current sampling device can also be equipped with a housing, and the AC detection unit and related circuit components are encapsulated with electromagnetic interference shielding materials to reduce external interference and ensure accurate measurement.

[0057] Compared with the prior art, the beneficial effects of the above current sampling device include: 1. High accuracy: The above current sampling device is designed based on the zero-flux principle, with a high accuracy of 0.01 level, and can accurately measure the primary capacitive current of the capacitive voltage transformer. 2. Good stability: Supported by material characteristics and by reducing the influence of external factors on the internal magnetic field distribution through structural design, unstable factors such as electromagnetic coupling are reduced, and a compensation circuit is added to ensure the stability of the output signal. It is ensured that in a complex field environment, the device can maintain the stability of measurement data and provide reliable data support for the on-line monitoring of the metering performance of the CVT. 3. Good frequency characteristics: First, the iron core material has high cut-off frequency and low loss characteristics, and the number of turns and wire diameter of the winding are reasonably planned through structural design to reduce distributed capacitance and inductance, reduce the loss and distortion of high-frequency signal transmission, and have a shell with good shielding effect to prevent external high-frequency interference signals and the electromagnetic interference of itself to surrounding equipment, realizing good frequency response characteristics, having a smooth processing ability within 400 Hz, and being able to accurately measure capacitive current at different frequencies. 4. Wide temperature range: Through the characteristics of the iron core material, it can adapt to a relatively wide temperature range (-25°C to +55°C) and still maintain good performance at different ambient temperatures.

[0058] In an exemplary embodiment, as Figure 3 shown, the present application also provides a voltage transformer in a substation, including the current sampling device 10 described above, and a capacitive voltage transformer 20. The current-carrying wire of the above current sampling device is multiplexed and connected in series to the primary high-voltage tail of the above capacitive voltage transformer. Among them, when the current sampling device is connected to the primary high-voltage tail of the capacitive voltage transformer, it can use its own configured current-carrying wire; it can also be directly connected to the primary high-voltage tail of the capacitive voltage transformer, and the line of the primary high-voltage tail is used as the current-carrying wire to connect. The above current sampling device has a high accuracy of 0.01 level, good stability, frequency characteristics, and a wide temperature characteristic suitable for the temperature range of the substation. Therefore, it does not affect the safe and stable operation of the power grid during operation. With the synergistic effect of each part inside the current sampling device, it can accurately and quickly measure the current change amount and process caused by capacitor breakdown, effectively meeting the accurate measurement requirement of the capacitive current of the capacitive voltage transformer and laying a technical support foundation for its on-line monitoring of metering performance.

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

[0060] In the description of this specification, the descriptions referring to terms such as "some embodiments", "other embodiments", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0061] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0062] The above-described embodiments only represent several implementation manners of the present application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to 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 AC detection unit, characterized in that: The AC detection unit includes a first annular iron core, a second annular iron core, a first winding, a second winding, a third winding and a compensation circuit, wherein: The first annular iron core and the second annular iron core are coaxially arranged and overlap each other, and a current-carrying wire as a primary winding of an AC detection unit passes through the first annular iron core and the second annular iron core, and the current-carrying wire is used to connect to a circuit 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 both the first annular core and the second annular core; the second winding is connected in series with the compensation circuit to form an electromotive force compensation loop; 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 a detection signal output end of the AC detection unit.

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

3. The AC detection unit according to claim 1, characterized in that: The ampere-turns of the first annular core are equal to the ampere-turns of the second annular core.

4. The AC detection unit according to claim 1, characterized in that: The compensation circuit is an LRC circuit or a compensation resistor with adjustable resistance.

5. The AC detection unit according to claim 4, characterized in that: The resistance of the compensation circuit is determined based on the ampere-turns of the first annular core and the ampere-turns of the second annular core.

6. The AC detection unit according to claim 1, characterized in that: The wire diameter and 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 primary current rating; the wire diameter and number of turns corresponding to the third winding are determined based on the target detection current range and target detection accuracy.

7. The AC detection unit according to claim 1, characterized in that: The first annular iron core and the second annular iron core are made of magnetic material.

8. The AC detection unit according to claim 7, characterized in that: The magnetic material is a composite material made of Permalloy and nanocrystalline alloy.

9. A current sampling device, characterized in that: The AC detection unit comprises the AC detection unit according to any one of claims 1 to 8, wherein the current sampling device further comprises a sampling circuit, and the sampling circuit is connected to the detection signal output terminal of the AC detection unit.

10. A voltage transformer in a substation, characterized in that: It comprises the current sampling device as claimed in claim 9, and a capacitive voltage transformer, wherein the current-carrying conductor of the current sampling device is multiplexed and connected in series to the primary high-voltage tail of the capacitive voltage transformer.

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