An open magnetic circuit voltage transformer device resistant to DC bias

Abstract

The present invention discloses an open magnetic circuit voltage transformer device that is resistant to direct current bias, and belongs to the technical field of high voltage equipment measurement. The device of the present invention comprises: a T-shaped core, wherein the core comprises a cylindrical core and a rectangular core, wherein the diameter length of the cylindrical core is consistent with the width length of the rectangular core, and the bottom surface of the cylindrical core is located at the center of the top surface of the rectangular core; a primary winding and a secondary winding, wherein the primary winding and the secondary winding are wound on the cylindrical core and arranged up and down; and an error compensation circuit, wherein the error compensation circuit compensates for the measurement error. The open magnetic circuit voltage transformer of the device of the present invention has the function of resisting direct current bias after compensation, and the error level meets the accuracy requirements of the transformer for on-site measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of high voltage equipment measurement, and more specifically, to an open magnetic circuit voltage transformer device resistant to direct current bias. Background Art

[0002] Power transformers are key equipment for power metering and power system protection. In key links such as power generation, transmission, transformation, distribution, and power consumption, a large number of power transformers are used for high-voltage and high-current measurement and safety protection. With the rapid development of the new generation of power systems characterized by a high proportion of clean energy and a high proportion of power electronic devices, coupled with the construction of ultra-high voltage direct current transmission, the impact of the DC component in the power grid is becoming increasingly prominent.

[0003] Under DC bias conditions, both the transient characteristics and steady-state transmission characteristics of the power transformer will undergo mutations. Exploring its mechanism of action and proposing further preventive measures and governance solutions are of great reference significance for ensuring the safe and stable operation of modern power systems and the fairness of electricity trade measurement. Summary of the invention

[0004] In view of the above problems, the present invention proposes an open magnetic circuit voltage transformer device resistant to DC bias, comprising:

[0005] A T-shaped core, wherein the core includes a cylindrical core and a rectangular core, the diameter of the cylindrical core is consistent with the width of the rectangular core, and the bottom surface of the cylindrical core is located at the center of the top surface of the rectangular core;

[0006] A primary winding and a secondary winding, wherein the primary winding and the secondary winding are wound on a cylindrical core and arranged up and down;

[0007] An error compensation circuit is used to compensate for the measurement error.

[0008] Optionally, the error compensation circuit includes an RC element and a small mutual inductor, and the error compensation circuit is connected to the secondary side of the device.

[0009] Optionally, the compensation amount of the measurement error includes: a ratio error compensation amount and a phase error compensation amount.

[0010] Optionally, the ratio error compensation amount is calculated as follows:

[0011]

[0012] Among them, Δε f is the ratio error compensation, ΔU f is the compensation amount of the ratio error of the small transformer K1, ΔU δis the phase error compensation of the small transformer K2, α is the phase shift angle of the phase shift circuit, N x and N y is the potential at two turns, N x For ratio error compensation, N y Used for phase error compensation, K1 and K2 are the transformation ratios of the ratio error compensation transformer and the phase error compensation transformer respectively, and N2 is the number of turns of the secondary winding.

[0013] Optionally, the calculation formula of the phase error compensation amount is as follows:

[0014]

[0015] Δε δ and β are the phase error compensation amounts.

[0016] Optionally, the T-shaped core forms an open magnetic circuit structure.

[0017] The open magnetic circuit voltage transformer of the device of the present invention has a DC bias resistance function after compensation, and the error level meets the accuracy requirement of the transformer for field measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 An equivalent circuit diagram of a voltage transformer of the device of the present invention;

[0019] Figure 2 The excitation curve diagram of the voltage transformer of the device of the present invention under different conditions;

[0020] Figure 3 is a structural diagram of the device of the present invention;

[0021] Figure 4 is a schematic diagram of the device of the present invention;

[0022] Figure 5 The error compensation principle diagram of the open magnetic circuit voltage transformer of the device of the present invention is shown in FIG.

[0023] Figure 6 It is the error compensation vector diagram of the device of the present invention;

[0024] Figure 7a-7e This is a voltage waveform diagram of the transformer under different DC bias voltages of the present invention. DETAILED DESCRIPTION

[0025] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0026] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0027] The present invention will be further described below in conjunction with embodiments and drawings:

[0028] The following first introduces the influence of DC bias magnetism on voltage transformer measurement error;

[0029] Voltage transformer schematic diagram and equivalent schematic diagram are as follows Figure 1 As shown, T is a 1:1 ideal transformer, Z1 is the DC resistance and leakage reactance of the primary winding of the transformer, Z2 is the DC resistance and leakage reactance of the secondary winding equivalent to the primary winding, and Z m is the excitation impedance of the transformer, I0 is the excitation current flowing through the excitation impedance, Z b is the load impedance equivalent to the primary side of the transformer;

[0030] According to the definition of voltage transformer error, the error consists of excitation error and load error, which can be expressed as:

[0031]

[0032] In the above formula, is the excitation error, is the load error.

[0033] Voltage transformers are generally used for measurement, and have high accuracy requirements. The focus is on examining their transmission characteristics. The excitation curves under different working conditions are as follows: Figure 2 shown.

[0034] Under the action of DC bias, DC current flows into the primary winding of the voltage transformer, generating DC magnetic flux Φ0 in the core of the voltage transformer. Under the action of Φ0, the curve of magnetic flux Φ will shift, so that the working point of the voltage transformer enters the saturation zone from the linear zone, the excitation current i increases, and distortion occurs. It can be seen that the distortion of the excitation current i when there is a DC component is caused by the nonlinearity of the end of the Φ-i curve of the voltage transformer. At this time, the transformer is in a saturated state. Therefore, the excitation current characteristics are not only related to the design parameters of the voltage transformer, but also closely related to the amplitude-frequency characteristics of the DC voltage.

[0035] In order to limit the influence of DC bias on the measurement accuracy of voltage transformer, the present invention proposes an open magnetic circuit voltage transformer device resistant to DC bias, such as Figure 3 As shown, the device of the present invention is an open magnetic circuit voltage transformer with a "T-shaped" iron core. The iron core consists of two parts, a cylinder and a cuboid. The bottom surface of the cylinder is located at the center of the top surface of the cuboid, and the diameter of the circular bottom surface is the same as the width of the cuboid. The primary and secondary windings are arranged up and down and are wound on the cylindrical iron core in sequence.

[0036] The function of the voltage transformer is to convert the primary voltage into the secondary voltage according to the turns ratio, and the accuracy of the voltage conversion mainly depends on the material and structural characteristics of the core, such as Figure 4 As shown in the figure, for the open magnetic circuit voltage transformer, due to its symmetrical structure, it is considered that there are two magnetic circuit branches in the iron core. Now we analyze one of them. Assume that the equivalent length of the magnetic circuit in the iron core is The equivalent length of the magnetic circuit in air is Without considering the edge effect of the interface between the core and the air, and ignoring the magnetic leakage of the core, the following formula is given for the core and air magnetic circuit:

[0037]

[0038] Where B is the magnetic induction intensity, is the average magnetic field strength in air, is the average magnetic field strength in the iron core, μ0 is the vacuum permeability, μ core is the relative magnetic permeability of the core.

[0039] According to Ampere's circuit theorem:

[0040]

[0041] Where, N is the number of turns of the primary winding, and I is the primary current;

[0042] make The primary current is:

[0043]

[0044] Therefore, under the same material parameters, the primary current of the open magnetic circuit voltage transformer with a "T-shaped" core increases by (1+αμ core ) times, that is, the DC bias resistance is improved. However, while the DC bias resistance is enhanced, the equivalent magnetic permeability of the magnetic circuit decreases, affecting the measurement accuracy of the transformer.

[0045] For the device of the present invention, error compensation design is performed. For example, although the open magnetic circuit voltage transformer has DC resistance, its measurement error has exceeded the measurement accuracy requirements of field applications, and error compensation is required. Design an error compensation method, the principle circuit diagram is as follows Figure 5 shown.

[0046] Take N on the core C1 x and N y The potential between the two turns, N x For ratio error compensation, N y Used for phase error compensation.

[0047] (1) Ratio error compensation

[0048] N x The secondary side voltage is low, usually a few volts, and a small transformer K1 (whose voltage transformation ratio is K1) is connected to the back end. The secondary side output of the small transformer K1 is ΔU f For ratio error compensation, it should be noted that: ΔU f The amplitude and phase can be adjusted according to the target value to be compensated. The transformer ratio K1 is adjusted by adjusting the number of turns of the small transformer K1 to achieve flexible adjustment of the ratio error compensation amount. In addition, the primary and secondary polarities of the small transformer K2 are changed, and the output phase of K2 is changed (flipped 180°) to achieve positive and negative changes in phase error compensation.

[0049] (2) Phase error compensation

[0050] The principle of phase error compensation is similar, except that y The RC series phase shift circuit is added to the back end, and then passes through the small transformer K2 (the ratio is K2), and the secondary side output ΔU δ Used for phase error compensation, same as year-over-year error compensation, ΔU δ The amplitude and phase of can be adjusted according to the compensation target value, and ΔU can be adjusted by adjusting the number of turns of K2. δ The amplitude of the compensation can be adjusted by changing the same-name end to adjust the phase of the compensation. In addition, the resistance value of the resistor R and the capacitance value of the capacitor C can also be modulated to adjust the compensation value ΔU δ amplitude and phase.

[0051] Based on the above analysis, the compensation circuit can perform error compensation on the secondary side of the open magnetic circuit voltage transformer. The vector diagram of the compensation principle is as follows: Figure 6 shown.

[0052] Figure 6 Middle,U 21 is the output voltage of the secondary proportional winding N2, which is used as the reference direction and its amplitude is assumed to be unity, ΔU f is the compensation amount of ratio error, ΔU δ is the compensation amount of the phase error, U2 after the three vector synthesis is the final output voltage, α is the phase shift angle of the phase shift circuit, and β is the final phase error compensation amount. According to the phase diagram relationship, we can get:

[0053]

[0054]

[0055] It can be seen from the vector diagram that ΔU δ When the quadrature component is compensated, the in-phase component error compensation will be introduced. Therefore, the ratio error compensation actually consists of two parts: the ratio error compensation itself and the in-phase component generated during the phase error compensation.

[0056] Final ratio error compensation Δε f :

[0057]

[0058] Final phase error compensation Δε δ :

[0059]

[0060] According to the error theory calculation results, the value of error compensation can be obtained to determine N x 、N y , R, C, α can be obtained by equation (5). Substituting into equations (8) and (9) we can get K1, K2.

[0061] Taking the 25kV and 0.5 error level transformer used in electric railways as an example, the parameters and error compensation design of open magnetic circuit transformer are carried out.

[0062] First, the parameters of the 25kV open magnetic circuit voltage transformer are designed, mainly including rated voltage, rated load, accuracy level, turn potential selection, and rated working magnetic flux density. Among them, the turn potential has a direct impact on the cost and error of the transformer. Considering that the excitation current of the open magnetic circuit voltage transformer is large, the turn potential in this design needs to be lower than that of the conventional transformer. The selected parameters are shown in Table 1.

[0063] Table 1

[0064]

[0065] By applying excitation to the primary winding of the voltage transformer, the excitation is the superposition of the power frequency sinusoidal voltage and the DC bias voltage, and the excitation voltage Uin is:

[0066]

[0067] Where U m is the rated sinusoidal power frequency voltage peak value of the open magnetic circuit voltage transformer, U dc is the DC bias component of the open magnetic circuit transformer. Since the DC resistance level of the 25kV voltage transformer is required to reach 2.5kV, U dc The value range is set to 0~4kA, the interval is 1kA, the transformer load is 5VA, and the power factor Connect a 2kΩ resistor to the secondary side.

[0068] Measure the primary and secondary voltage waveforms of the open-circuit voltage transformer under different DC bias voltages, such as Figure 7a -e as shown.

[0069] according to Figure 7a -e It can be seen that when the DC component is zero, the secondary waveform distortion caused by the nonlinearity of the core excitation branch is not obvious. As the DC component increases, the secondary voltage increases and the waveform distortion becomes serious, which causes the transmission characteristics of the core to deteriorate, resulting in deviations in electric energy metering and measurement, causing huge losses to the power company.

[0070] In order to analyze the influence of DC bias on the ratio error and angle error of the transformer, the three-parameter sinusoidal curve fitting algorithm is applied to the waveforms of the primary voltage and secondary voltage (converted to the primary side), and the coefficients A1 (cosine function amplitude), B1 (sine function amplitude) and A2, B2 can be obtained. Finally, the error of the transformer under different DC bias voltages can be calculated, as shown in Table 2.

[0071] Table 2

[0072]

[0073] As a voltage transformer for measurement, it has high requirements for accuracy, generally needing to reach level 0.5. Table 3 gives the error limits of level 0.5 voltage transformers.

[0074] Table 3

[0075]

[0076] It can be seen from Table 3 that although the open magnetic circuit voltage transformer has DC resistance, its measurement error has exceeded the error limit of 0.5 and needs to be compensated.

[0077] According to the error theoretical calculation results shown in Table 2, the values ​​that need error compensation can be obtained, which require a comparison error compensation of +0.89% and a phase error compensation of -29.91′. First, take N x =9,N y =2, R = 100Ω, C = 30μF, and α = π / 4 can be obtained by equation (8). Substituting into equations (11) and (12), we can get K1 = 5, K2 = 1, and finally the open magnetic circuit voltage transformer error is shown in Table 4, which meets the error limit requirements of the 0.5-level transformer.

[0078] Table 4

[0079]

[0080] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of complete hardware embodiments, complete software embodiments, or embodiments in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0081] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0082] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0083] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0084] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0085] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. An open magnetic circuit voltage transformer device resistant to DC bias, the device comprising: A T-shaped core, wherein the core includes a cylindrical core and a rectangular core, the diameter of the cylindrical core is consistent with the width of the rectangular core, and the bottom surface of the cylindrical core is located at the center of the top surface of the rectangular core; A primary winding and a secondary winding, wherein the primary winding and the secondary winding are wound on a cylindrical core and arranged up and down; an error compensation circuit, wherein the error compensation circuit compensates for the measurement error; The error compensation circuit includes an RC element and a small mutual inductor, and the error compensation circuit is connected to the secondary side of the device; The compensation amount of the measurement error includes: a ratio error compensation amount and a phase error compensation amount; The calculation formula of the ratio error compensation is as follows: Among them, Δε f is the ratio error compensation, ΔU f is the compensation amount of the ratio error of the small transformer K1, ΔU δ is the phase error compensation of the small transformer K2, α is the phase shift angle of the phase shift circuit, N x and N y is the potential at two turns, N x For ratio error compensation, N y Used for phase error compensation, K1 and K2 are the transformation ratios of the ratio error compensation transformer and the phase error compensation transformer respectively, and N2 is the number of turns of the secondary winding; The calculation formula of the phase error compensation amount is as follows: Δε δ and β are the phase error compensation amounts.

2. According to the device of claim 1, the T-shaped iron core forms an open magnetic circuit structure.

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