A current transformer and metering device

Abstract

The application relates to a current transformer and a metering device. The current transformer comprises an input winding, a proportional winding, a compensation winding, a first core and a second core; the input winding passes through the first core and the second core at the same time, the proportional winding is wound on the first core and the second core, the compensation winding is wound on the first core, and the proportional winding is electrically connected with the compensation winding; the physical characteristics of the first core are the same as those of the second core; the compensation winding is used for compensating corresponding excitation errors between the current provided by the input winding and the current actually output by the proportional winding; the first-order excitation error of the proportional winding is the same as the second-order excitation error of the compensation winding, and the error of the current transformer is the product between the first-order excitation error and the second-order excitation error. The metering device comprises the current transformer.

Description

Technical Field

[0001] This application relates to the field of electrical energy measurement technology, and in particular to a current transformer and metering device. Background Technology

[0002] As the global power system transitions to smart grids, high-precision electricity metering has become a key supporting technology for fair energy trading, grid stability, and efficient energy dispatch. Currently, the accuracy level of smart meters is advancing from the traditional 1.0 and 0.5S levels to higher levels such as 0.2S and even higher. The accuracy of high-end electricity meters (e.g., three-phase prepaid meters) largely depends on the performance of their core component—the current transformer (CT).

[0003] During the operation of a current transformer, a portion of the primary magnetomotive force must be consumed to maintain the magnetic field in the iron core and drive the metering instruments; this current is called the excitation current. The existence of the excitation current causes a vector difference between the actual output secondary current and the theoretical value, which directly leads to amplitude deviation (i.e., ratio difference) and phase deviation (i.e., angle difference). Although traditional error compensation techniques can suppress excitation errors to some extent, even minute excitation losses can still have a significant impact on calculation accuracy when current transformers require extremely high precision, such as 0.2S class. Summary of the Invention

[0004] Therefore, it is necessary to provide a current transformer and metering device with high metering accuracy.

[0005] In a first aspect, embodiments of this application provide a current transformer, including:

[0006] The system includes an input winding, a proportional winding, a compensating winding, a first iron core, and a second iron core. The input winding passes through both the first and second iron cores. The proportional winding is wound on both the first and second iron cores. The compensating winding is wound on the first iron core. The proportional winding and the compensating winding are electrically connected. The physical characteristics of the first iron core are the same as those of the second iron core.

[0007] The compensation winding is used to compensate for the excitation error between the current provided by the input winding and the actual output current of the proportional winding. The first-stage excitation error of the proportional winding is the same as the second-stage excitation error of the compensation winding. The error of the current transformer is the product of the first-stage excitation error and the second-stage excitation error.

[0008] In one exemplary embodiment, the number of turns in the proportional winding is the same as the number of turns in the compensating winding.

[0009] In an exemplary embodiment, there are a first sampling resistor and a second sampling resistor; the resistance value of the first sampling resistor and the resistance value of the second sampling resistor are the same.

[0010] The first sampling resistor is connected to the proportional winding, the compensation winding, and the second sampling resistor, respectively. The second sampling resistor is connected to the compensation winding.

[0011] In an exemplary embodiment, the proportional winding includes an inner partial winding and an outer partial winding, the inner partial winding being wound on a first iron core and a second iron core, and the outer partial winding being wound on the inner partial winding; the first sampling resistor includes a first sub-sampling resistor and a second sub-sampling resistor.

[0012] The first end of the outer winding is connected to the second end of the inner winding, the second end of the outer winding is connected to the first end of the first sub-sampling resistor, and the second end of the first sub-sampling resistor is connected to the first end of the second sub-sampling resistor; the first end of the inner winding is connected to the second end of the second sub-sampling resistor, the first end of the compensation winding, and the first end of the second sampling resistor, respectively; the second end of the compensation winding is connected to the second end of the second sampling resistor.

[0013] The inner winding and the outer winding form a differential sampling circuit structure.

[0014] In an exemplary embodiment, the ratio between the number of turns in the outer winding and the number of turns in the inner winding is determined by the sum of the number of turns in the outer winding and the inner winding, as well as the maximum number of turns in the outermost layer; the maximum number of turns in the outermost layer is the number of turns in the outermost layer of the outer winding that is furthest from the first core and the second core.

[0015] In an exemplary embodiment, the sum of the number of turns of the outer portion winding and the inner portion winding, and the maximum number of turns of the outermost layer, are determined by the dimensions of the first core and the second core, respectively; the dimensions of the first core and the second core are the same.

[0016] In an exemplary embodiment, the total leakage voltage of the current transformer is expressed by the following formula:

[0017]

[0018] Among them, U x n represents the total leakage voltage value. max Indicates the maximum number of turns in the outermost layer, ΔU n I2 represents the leakage voltage of the nth turn in the outermost layer of the outer winding, R represents the current flowing from the proportional winding to the compensating winding, n2 represents the inherent resistance of the proportional winding, and n3 represents the number of turns in the outer winding.

[0019] In one exemplary embodiment, the number of turns in the outer partial winding is 1660, where the sum of the number of turns in the outer partial winding and the inner partial winding is 3000, and the maximum number of turns in the outermost layer is 300.

[0020] In one exemplary embodiment, the current transformer has an accuracy class of 0.2S.

[0021] Secondly, embodiments of this application provide a metering device, including a metering instrument and a current transformer as described in any of the first aspects of this application, wherein the two ends of the current transformer are respectively connected to the circuit under test and the metering instrument.

[0022] Measuring instruments are used to collect the current of a circuit under test through a current transformer.

[0023] The aforementioned current transformer includes an input winding, a proportional winding, a compensation winding, a first core, and a second core. The input winding passes through both the first and second cores. The proportional winding is wound on both the first and second cores, and the compensation winding is wound on the first core. The physical characteristics of the first core and the second core are the same. Furthermore, the primary excitation error of the proportional winding is the same as the secondary excitation error of the compensation winding. Since both the primary and secondary excitation errors are much less than 1, the product of the primary and secondary excitation errors, i.e., the error of the current transformer, can be reduced to a minimum. Therefore, it can be seen that the current transformer with a segmented, dual-stage, dual-core coupled structure provided in this application embodiment can significantly reduce the error of the current transformer and achieve higher measurement accuracy. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of a current transformer provided in an embodiment of this application;

[0026] Figure 2 This is a schematic diagram of another current transformer provided in an embodiment of this application;

[0027] Figure 3 This is a schematic diagram of the structure of a multi-core smart meter testing system provided in an embodiment of this application;

[0028] Figure 4 This is a physical schematic diagram of a smart meter provided in an embodiment of this application. Detailed Implementation

[0029] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0030] 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 this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0031] It is 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 one element from another. For example, without departing from the scope of this application, a first iron core may be referred to as a second iron core, and similarly, a second iron core may be referred to as a first iron core. Both the first iron core and the second iron core are iron cores, but they are not the same iron core.

[0032] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0033] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

[0034] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” 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. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0035] like Figure 1 As shown, one embodiment of a current transformer includes:

[0036] The system comprises an input winding 10, a proportional winding 20, a compensating winding 30, a first iron core 40, and a second iron core 50. The input winding 10 passes through both the first iron core 40 and the second iron core 50. The proportional winding 20 is wound on both the first iron core 40 and the second iron core 50. The compensating winding 30 is wound on the first iron core 40. The proportional winding 20 and the compensating winding 30 are electrically connected. The physical characteristics of the first iron core 40 are the same as those of the second iron core 50.

[0037] The compensation winding 30 is used to compensate for the excitation error between the current provided by the input winding 10 and the actual output current of the proportional winding 20. The first-stage excitation error of the proportional winding 20 is the same as the second-stage excitation error of the compensation winding 30. The error of the current transformer is the product of the first-stage excitation error and the second-stage excitation error.

[0038] The input winding 10 is used to carry the current supplied by the circuit under test. The input winding 10 passes through both the first iron core 40 and the second iron core 50, so that the magnetic field of the current supplied by the circuit under test is simultaneously coupled to both the first iron core 40 and the second iron core 50. It can be understood that the input winding 10 is the input terminal of the current transformer. For the proportional winding 20 and the compensation winding 30, the current supplied by the circuit under test, i.e., the current supplied by the input winding 10, is the input current.

[0039] The proportional winding 20 refers to a winding that forms a specific current transformation relationship with the input winding 10, so as to output a current with a specific current transformation ratio between the current provided by the input winding 10 and the current provided by the input winding 10.

[0040] Since the current transformer provided in this application embodiment has two iron cores, a first iron core 40 and a second iron core 50, it can be understood that the current provided by the input winding 10 is the primary current, and the current actually output by the proportional winding 20 is the secondary current.

[0041] It should be noted that during the establishment of the magnetic field by the first iron core 40 and the second iron core 50, a portion of the current provided by the input winding 10 is needed to establish the magnetic field. This portion of the current is the excitation current. Therefore, the current provided by the input winding 10 and the converted current obtained after adjusting for the current ratio of the proportional winding 20 will have an excitation error due to the missing excitation current. Based on this, this embodiment of the application provides a compensation winding 30 in the current transformer to compensate for the excitation error corresponding to the difference between the current provided by the input winding 10 and the actual output current of the proportional winding 20.

[0042] The compensation winding 30 is used to sense the excitation current component from the first iron core 40 to generate a compensation current related to the excitation error corresponding to the excitation current, and inject the compensation current into the output current of the proportional winding 20, so as to compensate for the excitation error corresponding to the current provided by the input winding 10 and the actual output current of the proportional winding 20.

[0043] It should be noted that the excitation error between the current provided by the input winding 10 and the actual output current of the proportional winding 20 refers to the difference between the current provided by the input winding 10 and the calculated current obtained after the actual output current of the proportional winding 20 is converted according to the current ratio of the current transformer, that is, the excitation error corresponding to the excitation current.

[0044] Optionally, the proportional winding 20 and the compensation winding 30 can be electrically connected through a sampling resistor.

[0045] The physical characteristics of the first iron core 40 are the same as those of the second iron core 50, meaning that the first iron core 40 and the second iron core 50 are completely identical in terms of different physical characteristics such as size, material, magnetic properties, and manufacturing process.

[0046] Optionally, both the first iron core 40 and the second iron core 50 can be toroidal iron cores.

[0047] The first-level excitation error of the proportional winding 20 refers to the excitation error between the current supplied by the input winding 10 and the actual output current of the proportional winding 20 when the compensation winding 30 is not installed in the current transformer. Specifically, it corresponds to the excitation error caused by the excitation current consumed by the first core 40 and the second core 50 during the establishment of the magnetic field. The first-level excitation error reflects the excitation performance of the proportional winding 20.

[0048] It can also be understood that the first-level excitation error of the proportional winding 20 refers to the excitation error caused by the excitation current on the first iron core 40 and the second iron core 50 of the proportional winding 20 when no compensation winding 30 is provided in the current transformer.

[0049] The secondary excitation error of the compensation winding 30 refers to the excitation error caused by the excitation current on the first iron core 40 of the compensation winding 30 after the compensation winding 30 is introduced into the secondary side.

[0050] The error of a current transformer refers to the error between the current output of the current transformer (after the excitation error between the current supplied by the input winding 10 and the actual output current of the proportional winding 20 is compensated by the compensation winding 30) and the current supplied by the input winding 10, based on the two-stage, two-core structure of the current transformer.

[0051] It can also be understood that the error of the current transformer refers to the error between the converted value of the current output by the current transformer after the compensation effect of the compensation winding 30 and the current provided by the input winding 10.

[0052] Since the primary excitation error and the secondary excitation error are both much smaller than 1, the product of the primary excitation error and the secondary excitation error, i.e., the error of the current transformer, is also much smaller than the primary excitation error and the secondary excitation error, respectively. Therefore, it can be seen that after introducing a compensation winding 30 into the current transformer, the error of the current transformer can be reduced to a minimum.

[0053] Optionally, the current transformer provided in this embodiment can be encapsulated within an electricity meter. Optionally, the electricity meter can be a smart meter; for example, a smart meter can be a DTZM666C high-end three-phase meter with controlled charges.

[0054] Optionally, the input terminal of the input winding 10 can be connected to the circuit under test, such as the incoming live wire. When the circuit under test is the incoming live wire, the current provided by the input winding 10 is the current flowing into the incoming live wire. The output terminals of the proportional winding 20 and the compensation winding 30 can be connected to other operating modules within the energy meter. Exemplarily, these other operating modules within the energy meter can be, for example, the metering chip, analog-to-digital converter, processor, or other modules.

[0055] As can be seen, this embodiment uses a current transformer with a dual-stage dual-core structure to reduce the excitation error by a small margin. That is, the excitation error of the first stage is compensated in real time by the theoretical output current of the second stage. This achieves the reduction of the basic ratio error and phase error of the current transformer through multi-stage compensation, thereby improving the measurement accuracy of the current transformer.

[0056] The aforementioned current transformer includes an input winding 10, a proportional winding 20, a compensation winding 30, a first iron core 40, and a second iron core 50. The input winding 10 passes through both the first iron core 40 and the second iron core 50. The proportional winding 20 is wound on both the first iron core 40 and the second iron core 50. The compensation winding 30 is wound on the first iron core 40. The physical characteristics of the first iron core 40 are the same as those of the second iron core 50. Furthermore, the primary excitation error of the proportional winding 20 is the same as the secondary excitation error of the compensation winding 30. Since both the primary and secondary excitation errors are much less than 1, the product of the primary and secondary excitation errors—that is, the error of the current transformer—can be reduced to a minimum. Therefore, it can be seen that the current transformer with a segmented, dual-stage, dual-core coupled structure provided in this application embodiment can significantly reduce the error of the current transformer and achieve higher measurement accuracy.

[0057] In one exemplary embodiment, the number of turns of the proportional winding 20 is the same as the number of turns of the compensating winding 30.

[0058] The proportional winding 20 and the compensation winding 30 have the same number of turns. This is to ensure that, under the same magnetic flux change, the induced electromotive force of the proportional winding 20 and the compensation winding 30 is proportional to the rate of change of magnetic flux on their respective iron cores. In other words, it ensures that the theoretical output current on the secondary side of the current transformer can be induced in the compensation winding 30 at a 1:1 ratio, thus guaranteeing the compensation effect of the compensation winding 30. Based on this, by further using two sampling resistors with the same resistance value, the compensation current output by the compensation winding 30 can be made exactly equal to the excitation current missing between the proportional winding 20 and the input winding 10 due to the establishment of a magnetic field.

[0059] Optionally, the winding direction of the proportional winding 20 and the winding direction of the compensating winding 30 can be the same or opposite.

[0060] In one exemplary embodiment, such as Figure 1 As shown, the current transformer also includes:

[0061] The first sampling resistor R1 and the second sampling resistor R2; the resistance value of the first sampling resistor R1 is the same as the resistance value of the second sampling resistor R2;

[0062] The first sampling resistor R1 is connected to the proportional winding 20, the compensation winding 30 and the second sampling resistor R2 respectively, and the second sampling resistor R2 is connected to the compensation winding 30.

[0063] Based on the circuit connection, it can be understood that the first sampling resistor R1 corresponds to the proportional winding 20, and the second sampling resistor R2 corresponds to the compensation winding 30.

[0064] The first terminal of the first sampling resistor R1 is connected to the first terminal of the proportional winding 20. The second terminal of the first sampling resistor R1 is connected to the second terminal of the compensation winding 30 and the first terminal of the second sampling resistor R2. The second terminal of the second sampling resistor R2 is connected to the second terminal of the compensation winding 30. The two ends of the first sampling resistor R1 are the output terminals of the proportional winding 20, and the two ends of the second sampling resistor R2 are the output terminals of the compensation winding 30, which can be used to connect other working modules of the energy meter.

[0065] The first sampling resistor R1 has the same resistance value as the second sampling resistor R2. This is to ensure that the compensation voltage corresponding to the compensation current generated by the compensation winding 30 matches the excitation voltage corresponding to the missing excitation current in the proportional winding 20 in terms of voltage magnitude. Furthermore, the compensation voltage and the excitation voltage can cancel each other out through the principle of voltage inverse superposition. It can be seen that the same resistance value for the first sampling resistor R1 and the second sampling resistor R2 is to ensure that the error of the current transformer is the product of the first-stage excitation error and the second-stage excitation error. This ensures that the compensation winding 30 can accurately compensate for the excitation error corresponding to the difference between the current provided by the input winding 10 and the actual output current of the proportional winding 20.

[0066] For example, the error of a current transformer can be expressed by the following formula:

[0067] (1)

[0068] Where δ represents the error of the current transformer, U1 represents the actual output voltage of the secondary side of the current transformer, U represents the theoretical output voltage of the secondary side of the current transformer, R represents the resistance value of the sampling resistor, I2 represents the theoretical output current of the proportional winding 20, I2' represents the actual output current of the proportional winding 20, I3' represents the actual output current of the compensation winding 30, δ1 represents the first-stage excitation error, and δ2 represents the second-stage excitation error.

[0069] The theoretical output current of the proportional winding 20 can also be understood as the theoretical output current of the primary secondary side of the current transformer.

[0070] The actual output voltage of the secondary side of the current transformer refers to the actual output voltage of the secondary side of the current transformer after the excitation error corresponding to the current provided by the compensation winding 30 to the input winding 10 and the actual output current of the proportional winding 20 is compensated.

[0071] Since the resistance values ​​of the first sampling resistor R1 and the second sampling resistor R2 are the same, the resistance value of the sampling resistor in formula (1) can be substituted into the resistance value of the first sampling resistor R1 or the resistance value of the second sampling resistor R2. That is, the resistance values ​​of the first sampling resistor R1 and the second sampling resistor R2 are uniformly represented by R.

[0072] For example, the first-stage excitation error of the proportional winding 20 can be expressed by the following formula:

[0073] (2)

[0074] Where j represents a phase shift of +90°, ω represents the angular frequency of the current supplied by the input winding 10, and L2 represents the inductance of the proportional winding 20.

[0075] For example, after introducing the compensation winding 30 into the current transformer, the secondary excitation error of the compensation winding 30 can be expressed by the following formula:

[0076] (3)

[0077] Where I3 represents the theoretical output current of the compensation winding 30, I k2 I represents the secondary excitation current without considering the compensation winding 30. k L3 represents the theoretical output current on the secondary side of the current transformer, and L3 represents the inductance of the compensation winding 30. L3 = 2L2.

[0078] Optionally, the theoretical output current of the secondary side of the current transformer can be obtained by calculating the secondary side output current after the current provided by the input winding 10 is converted according to the current ratio of the current transformer.

[0079] As can be seen, since the proportional winding 20 is wound on the first iron core 40 and the second iron core 50, and the compensation winding 30 is wound on the first iron core 40, and the physical characteristics of the first iron core 40 are the same as those of the second iron core 50, the inductance of the proportional winding 20 is twice that of the compensation winding 30, that is, L3 = 2L2.

[0080] In an equipotential environment, the errors of current transformers include not only excitation errors caused by the excitation current, but also distributed capacitance coupling errors unique to equipotential environments. In the design of high-precision current transformers, distributed capacitances exist between winding conductors and between the winding and the core, determined by physical characteristics. In the equipotential testing environment of an automated production line, a constant potential difference of up to 220V exists between the sampling circuits on the primary and secondary sides of the current transformer (usually with the neutral line as a reference ground). This large constant potential difference generates a significant capacitive leakage current due to the stray coupling capacitance within the current transformer. Because the phase angle of this capacitive leakage current is close to 90°, its diagonal difference and reactive power error have a drastic impact, becoming the core cause of metering deviations in current transformers.

[0081] Therefore, existing current transformer designs still have limitations in dealing with equipotential interference in the automated production of high-end energy meters. Thus, in addition to effectively suppressing excitation error interference, to fully improve the metering accuracy of current transformers, it is also necessary to effectively suppress capacitive leakage current interference from the hardware structure to solve the metering accuracy problem of current transformers under small-signal operating conditions.

[0082] Based on this, in an exemplary embodiment, such as Figure 2As shown, the proportional winding 20 includes an inner winding 204 and an outer winding 202. The inner winding 204 is wound on the first iron core 40 and the second iron core 50, and the outer winding 202 is wound on the inner winding 204. The first sampling resistor R1 includes a first sub-sampling resistor R11 and a second sub-sampling resistor R12.

[0083] The first end of the outer winding 202 is connected to the second end of the inner winding 204. The second end of the outer winding 202 is connected to the first end of the first sub-sampling resistor R11. The second end of the first sub-sampling resistor R11 is connected to the first end of the second sub-sampling resistor R12. The first end of the inner winding 204 is connected to the second end of the second sub-sampling resistor R12, the first end of the compensation winding 30, and the first end of the second sampling resistor R2. The second end of the compensation winding 30 is connected to the second end of the second sampling resistor R2.

[0084] The inner winding 204 and the outer winding 202 form a differential sampling circuit structure.

[0085] Since the proportional winding 20 includes an inner winding 204 and an outer winding 202, the proportional winding 20 in this embodiment is a segmented winding.

[0086] The second end of the outer winding 202 and the first end of the first sub-sampling resistor R11, as well as the first end of the inner winding 204 and the second end of the second sub-sampling resistor R12, are all output terminals of the proportional winding 20, which can be used to connect other working modules of the energy meter.

[0087] The equivalent resistance between the first sub-sampling resistor R11 and the second sub-sampling resistor R12 is the same as the resistance of the first sampling resistor R1.

[0088] The winding direction of the inner winding 204 is opposite to that of the outer winding 202.

[0089] Based on the circuit connection relationship, it can be understood that the inner winding 204 and the outer winding 202 are connected in reverse parallel.

[0090] Furthermore, the winding direction of the inner winding 204 is opposite to that of the outer winding 202. Based on this, the induced voltage on the inner winding 204 and the induced voltage on the outer winding 202 have opposite polarities, thus forming a differential sampling circuit structure.

[0091] The inner winding 204 is wound on the first core 40 and the second core 50, meaning that the inner winding 204 is the earlier winding in the proportional winding 20. The inner winding 204 is wound directly and tightly against the surface of the first core 40 and the second core 50.

[0092] The outer winding 202 is wound on the inner winding 204, meaning that the outer winding 202 is the later winding in the proportional winding 20. The outer winding 202 is not in direct contact with either the first core 40 or the second core 50.

[0093] Optionally, a first insulating layer may be provided between the inner winding 204 and the first iron core 40 and the second iron core 50, respectively, and a second insulating layer may be provided between the inner winding 204 and the outer winding 202. Optionally, the first insulating layer and the second insulating layer may respectively include insulating varnish or insulating tape.

[0094] In this embodiment, the proportional winding 20 is a segmented winding, and the inner winding 204 and the outer winding 202 of the proportional winding 20 form a differential sampling circuit structure. Based on this, the capacitive error caused by the large capacitive leakage current generated by the stray coupling capacitor inside the current transformer can be reduced. Thus, by balancing the leakage voltage values ​​generated by the two winding segments 204 and 202, the total leakage voltage value can be minimized. Therefore, the error of the current transformer can be significantly reduced and the measurement accuracy can be improved.

[0095] In an exemplary embodiment, the ratio between the number of turns of the outer portion winding 202 and the number of turns of the inner portion winding 204 is determined by the sum of the number of turns of the outer portion winding 202 and the inner portion winding 204 and the maximum number of turns in the outermost layer; the maximum number of turns in the outermost layer is the number of turns of the outer portion winding 202 in the outermost layer away from the first iron core 40 and the second iron core 50.

[0096] This can be understood as the outer layer winding 202 being wound on the inner layer winding 204, forming a multi-layer structure. The outermost layer is the outermost layer in this multi-layer structure, that is, the layer exposed on the surface.

[0097] The sum of the number of turns of the outer winding 202 and the inner winding 204 is the total number of turns of the proportional winding 20.

[0098] In this embodiment, the number of turns in the outer winding 202 and the number of turns in the inner winding 204 satisfy a linear proportional relationship. Furthermore, the sum of the number of turns in the outer winding 202 and the inner winding 204, as well as the maximum number of turns in the outermost layer, are determined. Based on this, by precisely allocating the number of turns in the outer winding 202 and the inner winding 204, a segmented winding designed to address capacitive errors can be constructed. This reduces the interference voltage caused by the potential difference between the primary and secondary sides of the current transformer. It can be seen that the segmented winding provided in this embodiment can significantly reduce the error of the current transformer and achieve higher metering accuracy by suppressing capacitive errors.

[0099] In an exemplary embodiment, the sum of the number of turns of the outer portion winding 202 and the inner portion winding 204, and the maximum number of turns of the outermost layer, are determined by the dimensions of the first core 40 and the second core 50, respectively; the dimensions of the first core 40 and the second core 50 are the same.

[0100] In this context, it is easy to understand that the dimensions of the first core 40 and the second core 50 affect the winding process of the proportional winding 20. Therefore, the dimensions of the first core 40 and the second core 50 affect the sum of the number of turns in the outer winding 202 and the inner winding 204, as well as the maximum number of turns in the outermost layer. That is to say, the sum of the number of turns in the outer winding 202 and the inner winding 204, and the maximum number of turns in the outermost layer, are all determined by the dimensions of the first core 40 and the second core 50.

[0101] In an exemplary embodiment, the total leakage voltage of the current transformer is expressed by the following formula:

[0102] (4)

[0103] Among them, U x n represents the total leakage voltage value. max Indicates the maximum number of turns in the outermost layer, ΔU n I2 represents the leakage voltage value of the nth turn in the outermost layer of the outer winding 202, I2 represents the current shunted from the proportional winding 20 to the compensating winding 30, R represents the inherent resistance value of the proportional winding 20, n2 represents the number of turns in the outer winding 202, and n3 represents the number of turns in the inner winding 204.

[0104] It is easy to understand that the values ​​of n are: 1, 2, ..., n max-1 n max .

[0105] In this embodiment, a formula for the total leakage voltage of a current transformer is proposed. This formula can be understood as an optimal allocation model for segmented windings to address capacitive errors. It obtains the optimal value between the number of turns in the outer winding 202 and the inner winding 204, while minimizing the total leakage current of the current transformer. Therefore, based on the proportional winding 20 with the optimal turns allocation, the voltage offset generated by the segmented windings can offset the capacitive leakage voltage induced by the 220V potential difference. In other words, it can suppress capacitive errors under equipotential conditions, significantly reducing the error of the current transformer and achieving higher metering accuracy.

[0106] In an exemplary embodiment, the number of turns in the outer partial winding 202 is 1660 when the sum of the number of turns between the outer partial winding 202 and the inner partial winding 204 is 3000 and the maximum number of turns in the outermost layer is 300.

[0107] In the case that the sum of the number of turns of the outer winding 202 and the inner winding 204 is 3000 and the number of turns of the outer winding 202 is 1660, it is easy to understand that the number of turns of the inner winding 204 is 1340.

[0108] In one exemplary embodiment, the current transformer has an accuracy class of 0.2S.

[0109] Among them, the accuracy class of the current transformer is 0.2S, which means that within the range of 1% to 120% of the rated current of the current transformer, the ratio difference (i.e., ratio error) of the current transformer does not exceed ±0.2%, and the phase difference (i.e., phase error) does not exceed ±10 minutes (i.e., 0.167°).

[0110] Of course, this is not the only one; the accuracy of current transformers can also be 1.0 class or 0.5S class.

[0111] Optionally, with an accuracy class of 0.2S, the current transformer can meet the needs of power plants, substations, inter-regional transmission lines, or other power consumption scenarios that require high metering accuracy.

[0112] Optionally, the current transformer with the proportional winding 20 provided in this embodiment, including the inner winding 204 and the outer winding 202, can be compared with a conventional current transformer in an equipotential environment to evaluate whether the active power error and reactive power error of the segmented winding provided in this embodiment meet the accuracy level requirements of the current transformer, so as to determine whether the production quality of the current transformer provided in this embodiment is qualified.

[0113] For example, when the current transformer is encapsulated within a smart meter, it can be utilized as follows: Figure 3 The multi-core smart meter testing system shown tests a current transformer in an equipotential environment. It is easy to understand that the multi-core smart meter testing system can switch between equipotential and non-equipotential environments to facilitate the testing of the current transformer.

[0114] For example, such as Figure 4 As shown, a current transformer 400 with a two-stage, two-core structure is encapsulated within a smart meter.

[0115] As can be seen, the current transformer provided in this embodiment has the following advantages: First, because the proportional winding 20 is a segmented winding, the metering accuracy under equipotential conditions is significantly improved, enabling the error of the current transformer to meet industrial standard requirements; Second, it effectively solves the problem of batch pass rate in the automated production process of high-end energy meters; Third, it provides solid physical support for high-precision gate metering and laboratory standard current transformers.

[0116] It is understood that the current transformer described above can also take other forms, and is not limited to the forms already mentioned in the above embodiments, as long as it can achieve the function of high metering accuracy.

[0117] In one exemplary embodiment, a metering device is also provided, including a metering instrument and a current transformer as described in any of the above embodiments of the current transformer, wherein the two ends of the current transformer are respectively connected to the circuit under test and the metering instrument.

[0118] Measuring instruments are used to collect the current of a circuit under test through a current transformer.

[0119] Optionally, the measuring instrument may be an electricity meter.

[0120] In the description of this specification, references to terms such as "some embodiments," "other embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0121] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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, they should be considered to be within the scope of this specification.

[0122] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A current transformer, characterized in that, include: Input winding, proportional winding, compensating winding, first core, and second core; The input winding passes through both the first iron core and the second iron core, the proportional winding is wound on both the first iron core and the second iron core, the compensation winding is wound on the first iron core, and the proportional winding is electrically connected to the compensation winding. The physical properties of the first iron core are the same as those of the second iron core; The compensation winding is used to compensate for the excitation error corresponding to the current provided by the input winding and the actual output current of the proportional winding; the first-stage excitation error of the proportional winding is the same as the second-stage excitation error of the compensation winding, and the error of the current transformer is the product of the first-stage excitation error and the second-stage excitation error.

2. The current transformer according to claim 1, characterized in that, The number of turns of the proportional winding is the same as the number of turns of the compensating winding.

3. The current transformer according to claim 1, characterized in that, Also includes: A first sampling resistor and a second sampling resistor; the resistance values ​​of the first sampling resistor and the second sampling resistor are the same; The first sampling resistor is connected to the proportional winding, the compensation winding, and the second sampling resistor, respectively, and the second sampling resistor is connected to the compensation winding.

4. The current transformer according to claim 3, characterized in that, The proportional winding includes an inner winding and an outer winding. The inner winding is wound on the first iron core and the second iron core, and the outer winding is wound on the inner winding. The first sampling resistor includes a first sub-sampling resistor and a second sub-sampling resistor. The first end of the outer winding is connected to the second end of the inner winding; the second end of the outer winding is connected to the first end of the first sub-sampling resistor; the second end of the first sub-sampling resistor is connected to the first end of the second sub-sampling resistor; the first end of the inner winding is connected to the second end of the second sub-sampling resistor, the first end of the compensation winding, and the first end of the second sampling resistor; the second end of the compensation winding is connected to the second end of the second sampling resistor. The inner winding and the outer winding form a differential sampling circuit structure.

5. The current transformer according to claim 4, characterized in that, The ratio between the number of turns in the outer winding and the number of turns in the inner winding is determined by the sum of the number of turns in the outer winding and the inner winding, as well as the maximum number of turns in the outermost layer; the maximum number of turns in the outermost layer is the number of turns in the outermost layer of the outer winding that is furthest from the first iron core and the second iron core.

6. The current transformer according to claim 5, characterized in that, The sum of the number of turns of the outer layer winding and the inner layer winding, and the maximum number of turns of the outermost layer, are determined by the dimensions of the first iron core and the second iron core, respectively; the dimensions of the first iron core and the second iron core are the same.

7. The current transformer according to claim 5, characterized in that, The total leakage voltage of the current transformer is expressed by the following formula: Among them, U x n represents the total leakage voltage value. max Indicates the maximum number of turns in the outermost layer, ΔU n I2 represents the leakage voltage value of the nth turn in the outermost layer of the outer winding, R represents the current flowing from the proportional winding to the compensating winding, n2 represents the inherent resistance of the proportional winding, and n3 represents the number of turns in the outer winding.

8. The current transformer according to claim 7, characterized in that, When the sum of the number of turns of the outer winding and the inner winding is 3000, and the maximum number of turns of the outermost winding is 300, the number of turns of the outer winding is 1660.

9. The current transformer according to claim 1, characterized in that, The accuracy class of the current transformer is 0.2S.

10. A measuring device, characterized in that, The device includes a measuring instrument and a current transformer as described in any one of claims 1-9, wherein the two ends of the current transformer are respectively connected to the circuit under test and the measuring instrument. The measuring instrument is used to collect the current of the circuit under test through the current transformer.

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