High-voltage standard current transformer

Abstract

The invention relates to the technical field of current transformers, in particular to a high-voltage standard current transformer which comprises a complete machine, a primary high-precision current transformer, a primary copper rod, a secondary high-precision current transformer, an annular main iron core, an annular compensation iron core, a secondary iron core, a multi-strand copper core wire winding and a single-strand copper core tapped primary winding. The primary high-precision current transformer is used for high-precision transmission of high-voltage current to low-voltage current, the primary copper bar reduces the influence of interlayer and turn-to-turn leakage current of primary high voltage on the error of the primary high-precision current transformer, and the secondary high-precision current transformer changes the overall transformation ratio of the high-voltage standard current transformer. The primary iron core is used for winding a primary high-precision current transformer, the secondary iron core is used for winding a secondary high-precision current transformer, the single-strand copper core tapped primary winding is cascaded with the primary high-precision current transformer, the high-voltage standard current transformer reduces the influence of leakage current under high voltage on the error of the standard current transformer, and the accuracy of the standard current transformer is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of current transformers, and in particular to a high-voltage standard current transformer. Background Art

[0002] Based on ensuring the safe and stable operation of the power grid and the fairness of power trade settlement, the accuracy, safety, and reliability of high-voltage metering equipment are crucial. The accurate metering of medium- and high-voltage current transformers is even more important. However, the capacitive leakage of medium- and high-voltage current transformers under high voltage causes significant changes in the errors of current transformers, especially the influence of the errors of three-phase combined transformers is more obvious.

[0003] Three-phase combined transformers have the advantages of being able to measure phase voltages, being less likely to generate ferroresonance when a ground fault occurs, thus being less likely to cause equipment damage, and having good anti-stealing electricity capabilities. Therefore, both three-phase two-element combined transformers and three-phase three-element combined transformers have a large number of applications. Since three-phase combined transformers operate at high voltage, leakage current will be generated when the primary circuit of the current transformer is at high voltage. This leakage current is superimposed on the secondary circuit of the transformer, thereby generating additional errors and affecting the metering results. According to the requirements of "JJF1701.6-2019 Type Evaluation Outline for Measuring Transformers: Part 6: Three-Phase Combined Transformers", "Q / GDW 10572.4-2024 Technical Specification for Measuring Transformers Part 4: 10kV~35kV Three-Phase Combined Transformers", and "JJG1165-2019 Three-Phase Combined Transformers", verification and calibration work are carried out on three-phase combined transformers for metering purposes to improve the metering accuracy of three-phase combined transformers. Three-phase high-voltage standard current transformers and three-phase standard voltage transformers play an extremely important role in the verification and calibration work of three-phase combined transformers for power metering. Therefore, suppressing and eliminating the leakage current of high-voltage standard current transformers is a necessary means to ensure the effective verification of the accuracy of three-phase combined transformers.

[0004] Currently, the influence of leakage current on the errors of current transformers and the elimination measures, as well as how to ensure the accuracy of standard current transformers under high voltage, are not yet mature. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-voltage standard current transformer, aiming to reduce the influence of leakage current under high voltage on the errors of the standard current transformer.

[0006] To achieve the above object, the present invention provides a high-voltage standard current transformer, which includes a whole machine, a first-level high-precision current transformer, a primary copper bar, a second-level high-precision current transformer, a ring-shaped main iron core, a ring-shaped compensation iron core, a second iron core, a multi-strand copper core wire winding, and a single-strand copper core tap-type primary winding; the first-level high-precision current transformer is assembled on one side of the whole machine, the primary copper bar is assembled on one side of the whole machine, the second-level high-precision current transformer is arranged at the bottom of the whole machine, the ring-shaped main iron core is arranged on one side of the first-level high-precision current transformer, the ring-shaped compensation iron core is arranged on one side of the first-level high-precision current transformer, the multi-strand copper core wire winding is arranged on one side of the ring-shaped main iron core, and the single-strand copper core tap-type primary winding is arranged on one side of the second-level high-precision current transformer.

[0007] Among them, the whole machine includes a top surface insulating epoxy board, a side surface insulating epoxy board, an epoxy resin insulating sleeve, and a closed-loop copper foil. The top surface insulating epoxy board is assembled on both sides of the side surface insulating epoxy board. The epoxy resin insulating sleeve is arranged outside the primary copper bar. The closed-loop copper foil is arranged on the side of the epoxy resin insulating sleeve away from the primary copper bar.

[0008] Among them, the second-level high-precision current transformer and the first-level high-precision current transformer form a cascaded structure.

[0009] Among them, the ring-shaped main iron core and the ring-shaped compensation iron core maintain a certain distance.

[0010] Among them, the multi-strand copper core wire winding is evenly wound 10 turns on the ring-shaped main iron core and forms a ratio of 10:1 with the primary copper bar.

[0011] A high-voltage standard current transformer of the present invention. The primary high-precision current transformer serves as the core component of the high-voltage standard current transformer and is used for the high-precision transfer of converting high-voltage current into low-voltage current. By adopting measures such as isolation, low ampere-turns, and shielding, the influence of leakage current under high-voltage conditions on the error of the primary high-precision current transformer is effectively reduced. The primary copper bar allows a large primary high-voltage current to pass through. The primary copper bar is wound through one turn, effectively reducing the influence of inter-layer and inter-turn leakage current of the primary high voltage on the error of the primary high-precision current transformer. The secondary high-precision current transformer is cascaded with the primary high-precision current transformer to change the overall turns ratio of the high-voltage standard current transformer. The annular main iron core is made of silicon steel and is the main winding iron core of the primary high-precision current transformer. The ratio of the main winding is 10:1, and the rated capacity is 1000A×2V. The annular compensation iron core serves as the compensation iron core of the annular main iron core, compensating for the loss of the annular main iron core during excitation, enabling the annular main iron core to be in a zero magnetic flux state, and improving the accuracy of its ratio. The secondary iron core is made of ultra-microcrystalline material and is used for winding the secondary high-precision current transformer, ensuring low loss and high precision. It is cascaded with the primary high-precision current transformer to form the overall unit of the high-voltage standard current transformer. The single-strand copper-core tap-type primary winding is arranged on one side of the secondary high-precision current transformer to form a certain ratio and is cascaded with the primary high-precision current transformer at a ratio of 10:1 to form a high-precision multi-turns ratio current transformer. This high-voltage standard current transformer reduces the influence of leakage current under high voltage on the error of the standard current transformer and ensures the accuracy of the high-voltage standard current transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present invention 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 invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0013] Figure 1 It is a schematic diagram of the overall unit of a high-voltage standard current transformer provided by the present invention.

[0014] Figure 2 It is a cross-sectional view of a high-voltage standard current transformer provided by the present invention.

[0015] Figure 3 It is a front view of a high-voltage standard current transformer provided by the present invention.

[0016] Figure 4 It is a schematic diagram of the high-voltage leakage current principle.

[0017] In the figure: 1-whole machine, 2-primary high-precision current transformer, 3-primary copper bar, 4-secondary high-precision current transformer, 5-annular main iron core, 6-annular compensation iron core, 7-secondary iron core, 8-multi-strand copper core wire winding, 9-single-strand copper core tap primary winding, 10-top surface insulating epoxy board, 11-side surface insulating epoxy board, 12-epoxy resin insulating sleeve, 13-closed-loop copper foil. Detailed implementation mode

[0018] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0019] Please refer to Figures 1 to 4 , the present invention provides a high-voltage standard current transformer, including a whole machine 1, a primary high-precision current transformer 2, a primary copper bar 3, a primary-secondary high-precision current transformer 4, an annular main iron core 5, an annular compensation iron core 6, a secondary iron core 7, a multi-strand copper core wire winding 8 and a single-strand copper core tap primary winding 9; the primary high-precision current transformer 2 is assembled on one side of the whole machine 1, the primary copper bar 3 is assembled on one side of the whole machine 1, the primary-secondary high-precision current transformer 4 is arranged at the bottom of the whole machine 1, the annular main iron core 5 is arranged on one side of the primary high-precision current transformer 2, the annular compensation iron core 6 is arranged on one side of the primary high-precision current transformer 2, the multi-strand copper core wire winding 8 is arranged on one side of the annular main iron core 5, and the single-strand copper core tap primary winding 9 is arranged on one side of the primary-secondary high-precision current transformer 4.

[0020] In an embodiment of the present invention, the primary high-precision current transformer 2, as the core component of the high-voltage standard current transformer, is used for the high-precision transmission of converting high-voltage current into low-voltage current. By adopting measures such as isolation, low ampere-turns, and shielding, the influence of leakage current under high-voltage conditions on the error of the primary high-precision current transformer 2 is effectively reduced. The primary copper bar 3 allows the passage of a large primary high-voltage current. The primary copper bar 3 passes through the center of the primary high-precision current transformer 2 for one turn, effectively reducing the influence of inter-layer and inter-turn leakage current of the primary high-voltage on the error of the primary high-precision current transformer 2. The secondary high-precision current transformer 4 is cascaded with the primary high-precision current transformer 2 to change the turns ratio of the whole machine 1 of the high-voltage standard current transformer. The toroidal main iron core 5 is made of silicon steel and is the main winding iron core of the primary high-precision current transformer 2. The ratio of the main winding is 10:1, and the rated capacity is 1000A×2V. The toroidal compensation iron core 6, as the compensation iron core of the toroidal main iron core 5, compensates for the loss of the toroidal main iron core 5 during magnetization, so that the toroidal main iron core 5 is in a zero magnetic flux state, improving the accuracy of its ratio. The secondary iron core 7 is made of ultra-microcrystal and is used for winding the secondary high-precision current transformer 4 to ensure low loss and high precision. It is cascaded with the primary high-precision current transformer 2 to form the whole machine 1 of the high-voltage standard current transformer. The single-strand copper-core tapped primary winding 9 is arranged on one side of the secondary high-precision current transformer 4 to form a certain ratio, and is cascaded with the primary high-precision current transformer 2 at a ratio of 10:1 to form a high-precision multi-turns ratio current transformer. This high-voltage standard current transformer reduces the influence of leakage current under high voltage on the error of the standard current transformer and ensures the accuracy of the standard current transformer.

[0021] Further, the whole machine 1 includes a top surface insulating epoxy board 10, a side surface insulating epoxy board 11, an epoxy resin insulating sleeve 12, and a closed-loop copper foil 13. The top surface insulating epoxy board 10 is assembled on both sides of the side surface insulating epoxy board 11. The epoxy resin insulating sleeve 12 is arranged outside the primary copper bar 3. The closed-loop copper foil 13 is arranged on the side of the epoxy resin insulating sleeve 12 away from the primary copper bar 3.

[0022] In an embodiment of the present invention, the primary copper bar 3 passes through the center of the primary high-precision current transformer 2 for one turn. The two ends of the primary copper bar 3 pass through two rectangular holes (φ12mm) symmetrically opened on the top surface insulating epoxy board 10 and are fixed at both ends of the top surface insulating epoxy board 10 to form the primary side input end of the current transformer. The front surface of the top surface insulating epoxy board 10 is marked with "P1" and "P2". The epoxy resin insulating sleeve 12 is cast outside the primary copper bar 3. There is a layer of the closed-loop copper foil 13 outside the cast epoxy resin insulating sleeve 12, and a lead wire is led out from the outside of the closed-loop copper foil 13 and electrically connected to the grounding end. The toroidal main iron core 5 and the toroidal compensation iron core 6 are fixed outside the closed-loop copper foil 13.

[0023] Further, the primary secondary high-precision current transformer 4 and the primary high-precision current transformer 2 form a cascaded structure.

[0024] In the embodiment of the present invention, since the primary of the primary high-precision current transformer 2 adopts a single-turn through-core design, when the primary is in a large current state, secondly, the secondary output current is large, making measurement difficult. Only by converting the large current into a small current again can the measurement difficulty be reduced; secondly, the standard value of the secondary circuit of the current transformer is generally the rated current of 5A or 1A. For the convenience of differential measurement, the rated secondary current of the high-voltage standard current transformer can only be designed as 5A or 1A; thirdly, the ratio of the primary high-precision current transformer 2 is single. By cascading the secondary high-precision current transformer 4, the range of the high-voltage standard current transformer can be expanded to meet the requirements of the "Technical Specification for Measuring Transformers Part 4: 10kV - 35kV Three-Phase Combined Transformers" (Q / GDW 10572.4 - 2024) for the rated value of the current transformer.

[0025] Further, the annular main iron core 5 and the annular compensation iron core 6 maintain a certain distance.

[0026] In the embodiment of the present invention, the purpose of maintaining a certain distance between the annular main iron core 5 and the annular compensation iron core 6 is mainly to reduce the magnetic flux interference between the annular main iron core 5 and the annular compensation iron core 6, so as to accurately detect smaller error signals, including leakage current, and thus better control the output of the compensation current to achieve the best compensation effect, making the high-voltage standard current transformer accurate and stable.

[0027] Further, the multi-strand copper core wire winding 8 is evenly wound 10 turns around the annular main iron core 5 and forms a ratio of 10∶1 with the primary copper bar 3.

[0028] For a better understanding of this technical solution, the following embodiments are provided for further illustration: The core part of the high-voltage standard current transformer of the present invention is that the primary of the high-voltage current transformer adopts a single-turn through-core design with a copper bar having a diameter of 35 mm, passing through three main windings and the compensation winding coil. The secondary of the three main windings is wound with 10 turns of soft wire with a cross-sectional area of 40 square millimeters, with a ratio of 1∶10, a voltage class of 10 kV, and a current ratio reaching 1000A / 100A. It is cascaded with a secondary low-voltage current transformer (0.5~100)A / 5A to form a high-voltage standard current transformer of (5~1000)A / 5A; the secondary of the compensation winding is wound with 1200 turns of enameled wire with a diameter of 0.55 mm.

[0029] The high-voltage standard current transformer of the present invention is applied to the error verification and calibration of combined transformers and operates in a high-voltage environment of 10 kV. By analyzing the operating state of a single current transformer under high voltage, when the primary winding rises to a certain voltage, due to the relatively large cross-sectional area of the primary winding wire or copper bar, a group of capacitors will be formed between turns and layers, as described Figure 4 as shown

[0030] When a certain voltage is applied to the primary winding, due to the distributed capacitance existing between turns and layers of the primary winding of the current transformer, under primary AC conditions, the leakage currents Ico and Icx flow from the primary winding into the secondary side circuit and are superimposed on the secondary circuit current, bringing additional errors to the current transformer. According to the basic error formula (1) of the current transformer ratio error, the combined error expression is (2): (1); (2); In the formula, f is the ratio difference value of the current transformer, K1 is the rated current transformation ratio of the current transformer, I1 is the primary current of the current transformer in actual operation, I2 is the actual secondary current of the current transformer, I 2x is the coupled current on the secondary side of the transformer under test, I 20 is the coupled current on the secondary side of the standard transformer, I co is the leakage current flowing from the standard primary side into the secondary circuit, I cx is the leakage current flowing from the primary side of the transformer under test into the secondary circuit

[0031] It can be seen from the above formula that only when the distributed capacitance existing between turns and layers of the primary winding of the current transformer is very small can the additional error of the current transformer caused by the leakage current be eliminated. Therefore, the high-voltage standard current transformer of the present invention adopts a single turn through the primary, at this time I co is very small, close to 0, I20 » I co , formula (2) can be simplified to formula (3) (3); In the formula, f′ is the transformer error, Fi is the basic ratio difference of the transformer under test, and Δf is the additional ratio difference caused by high-voltage conditions

[0032] It can be seen from formula (3) that for the current transformer error under high voltage, in addition to the error caused by core excitation, there is also an additional error value Δf caused by high-voltage leakage current. Only when the error I cx brought by the leakage current of the standard current transformer tends to 0 can the additional error I cx. The magnitude of the primary high-voltage leakage current is closely related to the magnitude of the distributed capacitance of the primary winding. Only when the number of primary turns is the least and the number of layers is the least can the distributed capacitance be minimized. Therefore, the primary winding of the high-voltage standard current transformer of the present invention is made of one turn, and there is no distributed capacitance caused by inter-turn and inter-layer.

[0033] The output of the secondary winding of the first-stage high-voltage transformer of the high-voltage standard current transformer of the present invention passes through a secondary analog signal collector, and enters an analog signal processor together with the signal of the compensation detection winding for calculation and identification. According to the magnitude and direction of the detection quantity of the compensation detection winding, the secondary analog single signal is converted into four signals that are in phase with the secondary signal, opposite to the secondary signal, the phase of the secondary signal is -90°, and the phase of the secondary signal is +90°. The amplitudes of these four signals are the same, but the phases are different. Then, two signals are selected from the two in-phase groups respectively, and two signals with a phase shift of 90 degrees are selected from the two groups, and they are respectively converted into signals with adjustable arbitrary magnitudes using a DAC, input to an adder for addition, and power-amplified to drive the injection compensation winding. To obtain high-precision standards.

[0034] The above-disclosed is only a preferred embodiment of a high-voltage standard current transformer of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A high-voltage standard current transformer, It is characterized in that; It includes a whole machine, a first-level high-precision current transformer, a primary copper bar, a second-level high-precision current transformer, a ring-shaped main iron core, a ring-shaped compensation iron core, a second-level iron core, a multi-strand copper core wire winding and a single-strand copper core tap-type primary winding; The first-level high-precision current transformer is assembled on one side of the whole machine, the primary copper bar is assembled on one side of the whole machine, the second-level high-precision current transformer is arranged at the bottom of the whole machine, the ring-shaped main iron core is arranged on one side of the first-level high-precision current transformer, the ring-shaped compensation iron core is arranged on one side of the first-level high-precision current transformer, the multi-strand copper core wire winding is arranged on one side of the ring-shaped main iron core, and the single-strand copper core tap-type primary winding is arranged on one side of the second-level high-precision current transformer.

2. The high-voltage standard current transformer according to claim 1, characterized in that ； The whole machine includes a top surface insulating epoxy board, a side surface insulating epoxy board, an epoxy resin insulating sleeve and a closed-loop copper foil. The top surface insulating epoxy board is assembled on both sides of the side surface insulating epoxy board. The epoxy resin insulating sleeve is arranged outside the primary copper bar. The closed-loop copper foil is arranged on the side of the epoxy resin insulating sleeve away from the primary copper bar.

3. The high-voltage standard current transformer according to claim 1, characterized in that ； The second-level high-precision current transformer and the first-level high-precision current transformer form a cascaded structure.

4. The high-voltage standard current transformer according to claim 1, wherein ； There is a certain distance between the ring-shaped main iron core and the ring-shaped compensation iron core.

5. The high-voltage standard current transformer according to claim 1, characterized in that; The multi-strand copper core wire winding is evenly wound 10 turns on the ring-shaped main iron core and forms a ratio of 10:1 with the primary copper bar.

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