Harmonic transmission characteristic test system and method of mutual inductor based on wide frequency transformer

Abstract

The present application belongs to the field of high-voltage measurement technology and power quality analysis, and relates to a system and method for testing the harmonic transmission characteristics of a mutual inductor based on a wide-frequency transformer, the system comprising: a power frequency power supply module for generating a power frequency fundamental wave voltage; a wide-frequency harmonic power supply module for generating a wide-frequency harmonic voltage; a power frequency transformer for boosting the power frequency fundamental wave voltage to the primary side rated voltage of a tested voltage mutual inductor; a wide-frequency transformer for generating a composite high-voltage test signal; a resistance-capacitance voltage divider for dividing the composite high-voltage test signal into a low-voltage measurement signal; a control and data acquisition unit for synchronously collecting the standard voltage signal and the secondary output voltage signal of the tested voltage mutual inductor. The system has the test capabilities of high voltage, wide frequency band and high synchronism, the harmonic amplitude adjustment and simulation capabilities of high precision, and the continuous sweep frequency test capability of high efficiency, and provides key evaluation data for a new power system.

Description

Technical Field

[0001] This invention relates to the fields of high voltage measurement technology and power quality analysis technology, and in particular to a test system and method for the harmonic transmission characteristics of instrument transformers based on broadband transformers. Background Technology

[0002] As a core component for power system measurement, control, metering, and protection, the accuracy of voltage transformers directly determines the scientific validity of power grid dispatch decisions and the reliability of protection device operation. Theoretically, voltage transformers are primarily optimized for power frequency (50Hz) signals. However, as the frequency increases, the effects of the transformer's internal core nonlinear excitation characteristics, winding distributed capacitance, and stray inductance become drastically aggravated. These parasitic parameters lead to significant distortion in the secondary output voltage waveform, with amplitude attenuation and phase shift errors exceeding permissible ranges (e.g., ratio error exceeding ±10%, phase angle error exceeding ±1°). This prevents the transformer from providing accurate voltage data support for advanced applications such as broadband oscillation analysis, fault diagnosis, and harmonic source location.

[0003] Therefore, accurate testing and evaluation of the harmonic transmission characteristics of voltage transformers over a wide frequency range has become an urgent need to promote the development of broadband measurement technology for new power systems. Currently, existing test methods and related test equipment for the harmonic transmission characteristics of voltage transformers have many technical defects and application limitations: First, the voltage level coverage of existing harmonic test power supplies is insufficient. Most test schemes use low-voltage (such as 380V) harmonic sources for direct injection, which cannot directly conduct full-condition tests of power frequency superimposed harmonics on voltage transformers with power frequency voltage levels of up to 35kV or even higher.

[0004] Secondly, the harmonic frequency adjustment range of existing experimental methods is limited. Many schemes can only generate a limited number of harmonics (such as the 2nd, 3rd, and 5th), and cannot achieve continuous harmonic output across a wide frequency band of 25Hz to 3000Hz. At the same time, the ratio of harmonic amplitude to power frequency amplitude cannot be precisely and continuously adjusted within the range of 1% to 10%, and cannot simulate the complex real-world operating conditions of different harmonic contents and frequencies in the power grid.

[0005] Third, traditional testing methods often use discrete power frequency power supplies and harmonic sources to superimpose signals. The synchronization between the two is poor, resulting in a high distortion rate of the superimposed test voltage waveform, which easily introduces additional testing errors and leads to unreliable test results.

[0006] Fourth, existing methods for testing harmonic transmission characteristics are inefficient. Some test schemes require multiple single-frequency harmonics to be applied step by step to complete the test, which is cumbersome, time-consuming, and cannot achieve continuous frequency sweep testing of wide-band harmonics, making it difficult to obtain continuous frequency response characteristic curves. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a test system for the harmonic transmission characteristics of a current transformer based on a broadband transformer, employing the following technical solution: The power frequency power supply module is used to generate the power frequency fundamental voltage; Wideband harmonic power supply module, used to generate wideband harmonic voltage with a frequency range of 25Hz to 3000Hz and an amplitude adjustable between 1% and 10% of the fundamental voltage amplitude; A power frequency transformer, the low voltage winding of which is connected to the output terminal of the power frequency power module, is used to boost the power frequency fundamental voltage to the rated voltage of the primary side of the voltage transformer under test. A broadband transformer includes a low-voltage winding and a high-voltage winding independently wound on the same toroidal core. The low-voltage winding is connected to the output terminal of the broadband harmonic power supply module, and the high-voltage winding is connected in series with the high-voltage winding of the power frequency transformer. It is used to superimpose the broadband harmonic voltage onto the power frequency fundamental voltage without distortion to generate a composite high-voltage test signal. A resistive-capacitive voltage divider, the high-voltage arm of which is connected in parallel with the composite high-voltage test signal, is used to divide the composite high-voltage test signal into a low-voltage measurement signal as a standard voltage signal; The control and data acquisition unit is electrically connected to the output terminals of the power frequency power supply module, the broadband harmonic power supply module, the RC voltage divider, and the secondary output terminal of the voltage transformer under test, respectively. It is used to synchronously acquire the standard voltage signal and the secondary output voltage signal of the voltage transformer under test, and to analyze and process the acquired signals to calculate the ratio difference and angle difference of the voltage transformer under test at each harmonic frequency.

[0008] Preferably, the design parameters of the broadband transformer are optimized and determined through the following steps: Calculate core parameters: Using a toroidal silicon steel sheet core, its magnetizing inductance... satisfy ,in The permeability of free space, The relative permeability of the iron core. The number of turns in the winding. The cross-sectional area of ​​the iron core is... The average magnetic circuit length of the iron core; the no-load current at the lowest operating frequency. Less than 5% of the rated current, of which Rated voltage, For frequency; leakage inductance referred to the low-voltage side Controlled at 0.25mH, where leakage inductance , For leakage flux, For current; Stray capacitance calculation and control: Calculation of inter-turn stray capacitance ,in The vacuum permittivity, The relative permittivity of the insulating medium, The center distance of the conductor. Let the radius be the conductor. Given the average length of a single turn; calculate the interlayer stray capacitance. ,in This represents the overlap area of ​​the two winding layers. Given the interlayer insulation thickness; calculate the primary and secondary side stray capacitances. ,in This is the axial length of the winding. The outer radius of the primary winding is... The inner radius of the secondary winding; By increasing the thickness of interlayer insulation, adopting segmented winding or honeycomb winding to reduce the overlapping area, using low dielectric constant insulation materials, and optimizing the winding structure, the transformer achieves a total iron loss of ≤0.5% in the 25-3000Hz frequency band and has no resonant point.

[0009] Preferably, the resistor-capacitor voltage divider includes a high-voltage arm and a low-voltage arm connected in series, wherein the high-voltage arm is composed of a first resistor. Second resistor With the first capacitor Second capacitor The low-voltage arm is composed of a parallel-series combination, and the low-voltage arm is composed of a third resistor. With the third capacitor The circuit is configured in parallel; its design satisfies the matching condition that the voltage division ratio of the resistor is equal to that of the voltage division ratio of the capacitor. Ideal partial pressure ratio By selecting non-inductive resistors, a compact symmetrical structure, and a shielding ring design, the amplitude fluctuation is less than ±0.5% and the phase shift is minimized in the DC-3kHz frequency range.

[0010] Preferably, the control and data acquisition unit includes: A multi-channel synchronous data acquisition card with a sampling rate of at least 10 times the highest harmonic frequency (3000Hz), i.e., 30kS / s, and a resolution of no less than 24 bits; A digital signal processor or field-programmable gate array with a built-in fast Fourier transform algorithm module is used to perform real-time spectrum analysis on the acquired digital signal. The digital signal processor or field-programmable gate array is used to calculate the amplitude and phase of each harmonic. The human-machine interface is used to configure the output parameters of the power frequency and harmonic power supply, display the voltage waveform and spectrum in real time, and provide test reports on the output ratio difference and angle difference.

[0011] To address the aforementioned technical problems, this invention also provides a method for testing the harmonic transmission characteristics of a voltage transformer applied to the above-mentioned test system, employing the technical solution described below, including the following steps: S1, Optimized design of wideband transformer: By calculating core parameters and stray capacitance, a wideband transformer that can achieve low loss, linear transmission and precise superposition with power frequency voltage in a wide frequency range of 25-3000Hz is designed and manufactured. S2, Design of RC voltage divider: By calculating the ideal voltage division ratio and modeling the distributed parameters, an RC voltage divider with flat frequency response and small phase offset is designed as a standard voltage measurement device. S3, Set up the test system and configure parameters: Connect the high-voltage winding of the power frequency transformer and the high-voltage winding of the broadband transformer in series, and connect the resistive-capacitive voltage divider in parallel across the series branch; configure the power frequency power supply output to be the rated primary voltage of the voltage transformer under test through the control and data acquisition unit, and configure the broadband harmonic power supply to output the 2nd to 50th harmonics in sequence, with the content of each harmonic set to 2%, 3%, and 5% of the fundamental amplitude, respectively; S4, Synchronous Data Acquisition: Using the control and data acquisition unit, the standard voltage signal output by the resistive-capacitive voltage divider and the measured voltage signal output by the secondary side of the voltage transformer under test are acquired synchronously. S5, perform signal processing and characteristic calculation: perform fast Fourier transform analysis on the two acquired voltage signals, decompose the amplitude and phase of each harmonic, and calculate the ratio difference and angle difference at each harmonic frequency. S6. Analyze the transmission characteristics: Plot the frequency response curve with harmonic frequency as the abscissa and ratio difference and angle difference as the ordinate, and analyze the amplitude attenuation law and phase shift law of the tested voltage transformer in the entire wide frequency band.

[0012] Preferably, step S1, optimizing the design of the broadband transformer, specifically includes the following steps: S11, Calculate core parameters: Based on the transformer capacity requirements, use the magnetic flux density formula... Determine the cross-sectional area of ​​the iron core and number of turns ,in For voltage, For frequency; using the formula Calculate the magnetizing inductance And through the formula Check the no-load current Ensure that it is less than 5% of the rated current; S12, leakage inductance control: The primary and secondary windings of the toroidal core are concentrically wound and tightly wound, and the closed magnetic circuit of the core is used to control the leakage inductance referred to the low-voltage side. Controlled at 0.25mH; S13, Perform stray capacitance calculation and suppression: Calculate the inter-turn stray capacitance separately. Interlayer stray capacitance and primary and secondary side stray capacitance Furthermore, stray capacitances are suppressed by increasing the interlayer insulation thickness, using segmented winding or honeycomb winding, using low dielectric constant insulation materials, and using zigzag winding methods.

[0013] Preferably, step S2, designing the resistive-capacitive voltage divider, specifically includes the following steps: S21, Calculate the ideal partial pressure ratio: according to the formula Determine the theoretical partial pressure ratio, where For the high-voltage arm impedance, The impedance is low for the voltage arm and meets the matching conditions. This makes the transfer function Simplify to a constant ; S22, Perform distributed parameter modeling and compensation: Establish a model including stray capacitance to ground. Lead inductance and internal coupling capacitor The equivalent circuit model is obtained, and the actual frequency response is solved by the nodal admittance matrix. Compensation capacitors or RC networks are added to the low-voltage arm to match the actual time constant and ensure that the amplitude fluctuation is less than ±0.5% within DC-3kHz.

[0014] Preferably, step S5, which involves signal processing and characteristic calculation, specifically includes the following steps: S51, perform signal preprocessing: process the acquired standard voltage signal. and secondary side measured voltage signal Apply a window function to suppress spectral leakage and the picket fence effect; S52, Perform FFT transform and harmonic decomposition: Perform Fast Fourier Transform on the two preprocessed time-domain signals to obtain the frequency-domain signal. and It also decomposes the amplitudes of the fundamental wave and the 2nd to 50th harmonic components. With phase angle ; S53, Calculate the ratio difference: for each harmonic frequency According to the formula Calculate the ratio difference, where The rated transformation ratio of the voltage transformer under test. Standard voltage amplitude, The voltage amplitude is measured on the secondary side. S54, Calculate the angle difference: for each harmonic frequency According to the formula Calculate the angle difference.

[0015] Preferably, the frequency response curves plotted in step S6, which analyzes the transfer characteristics, specifically include the ratio difference-frequency curve and the angle difference-frequency curve; By analyzing the variation trend of the ratio difference-frequency curve in the 25Hz-3000Hz frequency band, the frequency points where the amplitude attenuation exceeds the allowable range can be identified. By analyzing the changing trend of the angle difference-frequency curve within the same frequency band, frequency points where the phase lag exceeds the allowable range can be identified.

[0016] To address the aforementioned technical problems, the present invention also provides a computer-readable storage medium, which employs the technical solution described below. The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the aforementioned test method for the harmonic transmission characteristics of a voltage transformer.

[0017] Compared with the prior art, the present invention has the following main advantages: (1) High-voltage, wide-bandwidth, and high-synchronization testing capabilities: By innovatively connecting the power frequency transformer in series with the high-voltage winding of a transformer specifically designed for wideband, it is possible to achieve integrated and highly synchronized superposition output of wideband harmonic signals of 25Hz-3000Hz and power frequency fundamental signals at voltage levels of up to 35kV and above. This solves the fundamental problems of insufficient voltage levels, narrow frequency range, and poor signal synchronization in existing technologies.

[0018] (2) It has high-precision harmonic amplitude adjustment and simulation capabilities: the wideband harmonic power supply can accurately control the harmonic amplitude to 1%-10% of the fundamental amplitude, with a step size as small as 0.1%, which can realistically simulate the complex working conditions of harmonics with different permeability in the power grid, providing a powerful tool for studying the saturation and nonlinear characteristics of voltage transformers under different harmonic contents.

[0019] (3) High-fidelity signal transmission and measurement: Through detailed modeling, calculation and suppression design of the core material, structure (ring), leakage inductance (controlled at 0.25mH) and various stray capacitances of the broadband transformer, the transmission of broadband harmonic signals with low loss (total iron loss ≤0.5%) and low distortion during the boosting and superposition process is ensured. At the same time, through the design of a resistor-capacitor voltage divider that meets the matching conditions, an ideal voltage division with amplitude fluctuation <±0.5% is achieved from DC to 3kHz frequency range, ensuring the ultra-high accuracy of the standard voltage signal.

[0020] (4) High-efficiency continuous frequency sweep testing capability: Full automation is achieved. The operator only needs to set the frequency sweep range (e.g., 2nd-50th harmonics) and amplitude step (e.g., 1%) in the control unit, and the system can automatically execute all test points and calculate and plot the continuous ratio difference-frequency and angle difference-frequency characteristic curves in real time. Compared with the traditional point-by-point testing method, the efficiency is improved by several times or even tens of times.

[0021] (5) Provides key evaluation data for new power systems: By obtaining the wideband transfer characteristic curve of the voltage transformer, its effective operating frequency band can be clearly defined, and its measurement error in different frequency bands can be quantified. This provides indispensable core data support for the selection of wideband measurement equipment, accurate assessment of power quality, and formulation of early warning and protection strategies for wideband oscillations in new power systems, and has important engineering application value. Attached Figure Description

[0022] To more clearly illustrate the solutions in this invention, the accompanying drawings used in the description of the embodiments of this invention will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a flowchart of an embodiment of the current transformer harmonic transmission characteristic test method based on broadband transformer of the present invention; Figure 2 This is a schematic diagram of the winding of the core coil of the broadband transformer used in the test method for harmonic transmission characteristics of the current transformer based on the broadband transformer of the present invention. Figure 3 This is a schematic diagram of the leakage flux of the core of the broadband transformer used in the test method for harmonic transmission characteristics of the current transformer based on the broadband transformer of the present invention. Figure 4 The equivalent circuit diagram of the distributed parameters of the resistor-capacitor voltage divider used in the test method for harmonic transmission characteristics of mutual inductors based on broadband transformers of the present invention is shown below. Figure 5 This is a schematic diagram of the test system used in the test method for harmonic transmission characteristics of current transformers based on broadband transformers of the present invention. Figures 6(a)-6(c) are typical voltage waveforms collected during the test in the method for testing the harmonic transmission characteristics of the current transformer based on the broadband transformer of the present invention. Figures 7(a) and 7(b) are harmonic transmission characteristic curves of a voltage transformer sample calculated by the method of the present invention. Detailed Implementation

[0024] 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 invention pertains; the terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings are used to distinguish different objects and not to describe a particular order.

[0025] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0026] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0027] Example 1 This embodiment illustrates a test system for the harmonic transmission characteristics of a current transformer based on a broadband transformer, including: a power frequency power supply module for generating a power frequency fundamental voltage; Wideband harmonic power supply module, used to generate wideband harmonic voltage with a frequency range of 25Hz to 3000Hz and an amplitude adjustable between 1% and 10% of the fundamental voltage amplitude; The power frequency transformer has its low-voltage winding connected to the output terminal of the power frequency power module, which is used to boost the power frequency fundamental voltage to the rated voltage of the primary side of the voltage transformer under test. A broadband transformer consists of a low-voltage winding and a high-voltage winding independently wound on the same toroidal core. The low-voltage winding is connected to the output terminal of the broadband harmonic power supply module, and the high-voltage winding is connected in series with the high-voltage winding of the power frequency transformer. It is used to superimpose the broadband harmonic voltage onto the power frequency fundamental voltage without distortion to generate a composite high-voltage test signal. A resistive-capacitive voltage divider, whose high-voltage arm is connected in parallel with the composite high-voltage test signal, is used to divide the composite high-voltage test signal into a low-voltage measurement signal as a standard voltage signal; The control and data acquisition unit is electrically connected to the output terminals of the power frequency power supply module, the broadband harmonic power supply module, the RC voltage divider, and the secondary output terminal of the voltage transformer under test, respectively. It is used to synchronously acquire the standard voltage signal and the secondary output voltage signal of the voltage transformer under test, and to analyze and process the acquired signals to calculate the ratio difference and angle difference of the voltage transformer under test at each harmonic frequency.

[0028] The broadband transformer is one of the core components of this embodiment. It consists of a low-voltage winding (primary side) and a high-voltage winding (secondary side) independently wound on the same toroidal core. The low-voltage winding is connected to the output terminal of the broadband harmonic power supply module. The high-voltage winding is connected in series with the high-voltage winding of the power frequency transformer. This unique topology is used to superimpose the broadband harmonic voltage onto the power frequency fundamental voltage without distortion and with high synchronization to generate a high-voltage composite test signal.

[0029] The design parameters of a broadband transformer are determined through the following optimization steps: Calculate core parameters: Using a toroidal silicon steel sheet core, its magnetizing inductance... satisfy ,in The permeability of free space, The relative permeability of the iron core. The number of turns in the winding. The cross-sectional area of ​​the iron core is... The average magnetic circuit length of the iron core; the no-load current at the lowest operating frequency. Less than 5% of the rated current, of which Rated voltage, For frequency; leakage inductance referred to the low-voltage side Controlled at 0.25mH, where leakage inductance , For leakage flux, For current; Stray capacitance calculation and control: Calculation of inter-turn stray capacitance ,in The vacuum permittivity, The relative permittivity of the insulating medium, The center distance of the conductor. Let the radius be the conductor. Given the average length of a single turn; calculate the interlayer stray capacitance. ,in This represents the overlap area of ​​the two winding layers. Given the interlayer insulation thickness; calculate the primary and secondary side stray capacitances. ,in This is the axial length of the winding. The outer radius of the primary winding is... The inner radius of the secondary winding; By increasing the thickness of interlayer insulation, adopting segmented winding or honeycomb winding to reduce the overlapping area, using low dielectric constant insulation materials, and optimizing the winding structure, the transformer achieves a total iron loss of ≤0.5% in the 25-3000Hz frequency band and has no resonant point.

[0030] A resistor-capacitor voltage divider consists of a high-voltage arm and a low-voltage arm connected in series. The high-voltage arm is formed by a first resistor. Second resistor With the first capacitor Second capacitor It consists of a parallel-series combination, with the low-voltage arm composed of a third resistor. With the third capacitor The circuit is configured in parallel; its design satisfies the matching condition that the voltage division ratio of the resistor is equal to that of the voltage division ratio of the capacitor. Ideal partial pressure ratio By selecting non-inductive resistors, a compact symmetrical structure, and a shielding ring design, the amplitude fluctuation is less than ±0.5% and the phase shift is minimized in the DC-3kHz frequency range.

[0031] The RC voltage divider is another core measurement component in this embodiment. Its high-voltage arm is connected in parallel with the composite high-voltage test signal to divide the composite high-voltage test signal into a measurement signal at a low voltage level according to a precise ratio, serving as a standard voltage signal. Its design ensures a flat amplitude-frequency response and a linear phase-frequency response from DC to 3kHz.

[0032] The control and data acquisition unit includes: A multi-channel synchronous data acquisition card with a sampling rate of at least 10 times the highest harmonic frequency (3000Hz), i.e., 30kS / s, and a resolution of no less than 24 bits, is used to capture the time-domain waveform of a wideband voltage signal completely and with high fidelity. A digital signal processor or field-programmable gate array with a built-in fast Fourier transform algorithm module is used to perform real-time spectrum analysis on the acquired digital signals. The digital signal processor or field-programmable gate array is used to calculate the amplitude and phase of each harmonic. The human-machine interface is used to configure the output parameters of the power frequency and harmonic power supply, display the voltage waveform and spectrum in real time, and provide test reports on the output ratio difference and angle difference. The purpose of this interface is to realize the automated control of the test process and the visualization of the test results.

[0033] The control and data acquisition unit is electrically connected to the output terminals of the power frequency power supply module, the broadband harmonic power supply module, the RC divider, and the secondary output terminal of the voltage transformer under test. The control and data acquisition unit performs three main tasks: first, to automatically configure the power frequency and harmonic power supply outputs; second, to synchronously and accurately acquire the standard voltage signal and the secondary output voltage signal of the voltage transformer under test; and third, to perform digital signal processing (including FFT analysis) on the acquired signals to automatically calculate the ratio difference and phase angle difference of the voltage transformer under test at various harmonic frequencies and output a test report.

[0034] Example 2 Please refer to Figure 1 A test method for the harmonic transmission characteristics of a voltage transformer applied to the test system of Embodiment 1 adopts the following technical solution, including the following steps: S1, Optimized Design of Wideband Transformer: By calculating core parameters and stray capacitance, a wideband transformer is designed and manufactured that can achieve low loss, linear transmission, and precise superposition with power frequency voltage in a wide frequency range of 25-3000Hz.

[0035] Step S1, optimizing the design of the broadband transformer, specifically includes the following steps: S11, Calculate core parameters: Based on the transformer capacity requirements, use the magnetic flux density formula... Determine the cross-sectional area of ​​the iron core and number of winding turns This refers to the number of turns in the coil of the winding. The voltage across the winding refers to the effective value of the voltage applied to the transformer winding. Frequency refers to the frequency of the voltage signal; it is expressed using the formula... Calculate the magnetizing inductance And through the formula Check the no-load current When the secondary side of the transformer is open-circuited, the current flowing through the primary side must be less than 5% of the rated current. Specifically: For a sinusoidal signal, the waveform coefficients are... . Vacuum permeability, a constant . : Relative permeability of iron core (dimensionless), which represents the magnetic permeability of iron core material relative to vacuum. Average magnetic path length of the iron core (unit: m): the average path length of the magnetic flux around the iron core. Rated voltage (unit: V): The effective value of the rated voltage applied to the winding.

[0036] The goal of this step is to determine the core size and number of winding turns of the broadband transformer through theoretical calculations, ensuring sufficient magnetizing inductance even at the lowest operating frequency of 25Hz, thereby reducing the impact of no-load current on measurement accuracy.

[0037] According to the law of electromagnetic induction Given the voltage, frequency, and preset magnetic flux density (e.g., 1.2T), the cross-sectional area of ​​the iron core is calculated iteratively. and number of winding turns Then, using the excitation inductance formula... Calculate the inductance value, where The permeability of free space, The relative permeability of the iron core. This is the average magnetic circuit length. (Using the no-load current formula...) Check the percentage of no-load current, which should be less than 5% of the rated current.

[0038] If the excitation inductance is insufficient, the no-load current will shun the harmonic signal, causing the harmonic amplitude superimposed on the high-voltage side to be lower than the set value, introducing system errors. By optimizing the core material (such as using high-permeability 1J85 alloy) and the number of turns design, the excitation impedance can be ensured to be high enough over a wide frequency range, ensuring efficient transmission of harmonic signals to the high-voltage side.

[0039] The purpose of step S1 is to ensure that the transformer has sufficient excitation impedance over a wide frequency range, thereby reducing the impact of no-load current on measurement accuracy.

[0040] Figure 2 This is a schematic diagram of the winding of the core coil of the broadband transformer used in the test method for harmonic transmission characteristics of the current transformer based on the broadband transformer of the present invention. Figure 2 This demonstrates the tightly wound, concentric arrangement of the primary and secondary windings on a toroidal core. Its purpose is to visually illustrate how structural design can reduce the leakage flux cross-sectional area, thereby controlling leakage inductance.

[0041] Figure 3 This is a schematic diagram of the leakage flux of the core of the broadband transformer used in the test method for harmonic transmission characteristics of the current transformer based on the broadband transformer of the present invention. Figure 3 This indicates the main magnetic flux. and leakage flux The path. Its function is to help explain the generation mechanism of leakage inductance, and the principle of suppressing leakage inductance by increasing the length of the leakage magnetic path through closed magnetic circuit design.

[0042] S12, leakage inductance control: The primary and secondary windings of the toroidal core are concentrically wound and tightly wound, and the closed magnetic circuit of the core is used to control the leakage inductance referred to the low-voltage side. Control it at 0.25mH.

[0043] The goal of this step is to control the leakage inductance of the broadband transformer referred to the low-voltage side to within 0.25mH, so as to reduce the impedance of leakage reactance to high-frequency signals, avoid resonance between leakage inductance and stray capacitance, and ensure the flatness of signal transmission over a wide frequency band.

[0044] Leakage inductance originates from the failure to simultaneously link the primary and secondary windings with magnetic flux. To suppress leakage inductance, this design employs a toroidal core structure, with the primary and secondary windings wound concentrically and tightly, maximizing their coupling. Because the toroidal core's magnetic circuit is closed, leakage flux requires a longer air path to close, thus naturally suppressing leakage inductance. Furthermore, through finite element simulation verification, the winding layout and turns distribution were optimized, ultimately controlling the leakage inductance to 0.25 mH.

[0045] At the highest operating frequency of 3000Hz, the inductive reactance corresponding to this leakage inductance is only about 4.71Ω, which is much smaller than the load impedance and will not cause a significant voltage drop on the harmonic signal. At the same time, the resonant frequency formed by this leakage inductance value and stray capacitance is much higher than 3000Hz, effectively avoiding resonance peaks in the test frequency band and ensuring distortion-free superposition of harmonic voltages.

[0046] The purpose of step S12 is to reduce leakage reactance, prevent it from resonating with stray capacitance, and ensure the flatness of signal transmission over a wide frequency band.

[0047] S13, Perform stray capacitance calculation and suppression: Calculate the inter-turn stray capacitance separately. Interlayer stray capacitance and primary and secondary side stray capacitance Furthermore, stray capacitances are suppressed by increasing the interlayer insulation thickness, using segmented winding or honeycomb winding, using low dielectric constant insulation materials, and using zigzag winding methods.

[0048] The goal of this step is to reduce the bypass effect and coupling interference of distributed capacitance on high-frequency signals by calculating and suppressing stray capacitance between turns, layers, and between primary and secondary sides, thereby preventing local resonance and ensuring low-distortion transmission of high-frequency harmonics.

[0049] Inter-turn stray capacitance Interlayer stray capacitance and primary and secondary side stray capacitances These capacitors can create low-impedance bypasses at high frequencies, leading to harmonic signal attenuation or distortion.

[0050] in: Vacuum permittivity . The relative permittivity (dimensionless) of an insulating medium represents the dielectric properties of an insulating material. Center-to-center distance of conductors (unit: m): The distance between the centers of two adjacent turns of conductors. : Conductor radius (unit: m). Average length of a single turn (unit: m), the average circumference of a single turn of conductor. Overlapping area of ​​two winding layers (unit: m²) 2 ), the area of ​​the upper and lower coils facing each other. Interlayer insulation thickness (unit: m): The thickness of the insulation layer between two windings. : Axial length of winding (unit: m), the length of the coil along the axis of the iron core. : Inner radius of the secondary winding (unit: m). : Outer radius of the primary winding (unit: m).

[0051] To suppress stray capacitance, several measures were taken: increasing the interlayer insulation thickness to reduce interlayer capacitance; using segmented winding or honeycomb winding to reduce overlapping area; selecting low dielectric constant insulating materials (such as Nomex paper); using a zigzag winding method to reduce inter-turn potential difference; and adding an electrostatic shielding layer between the primary and secondary sides and grounding it to effectively block capacitive coupling. Through these designs, the transformer's total iron loss is ensured to be ≤0.5% in the 25-3000Hz frequency band, with no resonant point.

[0052] The purpose of step S13 is to reduce the bypass effect and coupling interference of distributed capacitance on high-frequency signals, prevent local resonance, and ensure low-distortion transmission of high-frequency harmonics.

[0053] The purpose of step S1 is to serve as the basis for ensuring the signal source quality of the entire test system.

[0054] S2, Design of RC voltage divider: By calculating the ideal voltage division ratio and modeling the distributed parameters, an RC voltage divider with flat frequency response and small phase offset is designed as a standard voltage measurement device.

[0055] Step S2, designing the resistive-capacitive voltage divider, specifically includes the following steps: S21, Calculate the ideal partial pressure ratio: according to the formula Determine the theoretical partial pressure ratio, where For the high-voltage arm impedance, The impedance is low for the voltage arm and meets the matching conditions. This makes the transfer function Simplify to a constant .

[0056] The goal of this step is to determine the resistance and capacitance parameters of the RC voltage divider through theoretical calculations, so that the voltage division ratio remains constant across the entire frequency band, thereby achieving an ideal voltage division independent of frequency and ensuring the amplitude accuracy of broadband signal measurements.

[0057] A resistor-capacitor voltage divider consists of a high-voltage arm (high-voltage arm resistor) With high voltage arm capacitor (parallel or series-parallel combination) and low-voltage arm (resistor) With capacitor It is composed of parallel connections. Its transfer function is... When the matching conditions are met. When the transfer function is reduced to a constant, the transfer function is reduced to a constant. That is, the voltage division ratio is independent of the frequency.

[0058] in, Complex frequency (unit: rad / s) ,in .

[0059] First select the low-voltage arm resistor. and low-voltage arm capacitor Then, based on the matching conditions, the high-voltage arm is deduced. and For example, select Then it requires Then, combined with the required partial pressure ratio (e.g., 20000:1), determine... This design ensures a constant voltage division ratio from DC to 3kHz.

[0060] The purpose of step S21 is to achieve an ideal voltage divider that is theoretically independent of frequency, thus ensuring the accuracy of the amplitude measurement of broadband signals.

[0061] S22, Perform distributed parameter modeling and compensation: Establish a model including stray capacitance to ground. Lead inductance and internal coupling capacitor The equivalent circuit model is obtained, and the actual frequency response is solved by the nodal admittance matrix. Compensation capacitors or RC networks are added to the low-voltage arm to match the actual time constant and ensure that the amplitude fluctuation is less than ±0.5% within DC-3kHz.

[0062] The goal of this step is to analyze the impact of non-ideal components (lead inductance, stray capacitance to ground, etc.) on frequency response by establishing a distributed parameter equivalent circuit model, and to take compensation measures to ensure that the amplitude fluctuation of the resistor-capacitor voltage divider is less than ±0.5% and the phase offset is minimized within DC-3kHz.

[0063] In actual circuits, lead inductance Stray capacitance to ground Parasitic parameters such as internal coupling capacitance of components can cause the actual voltage division ratio at high frequencies to deviate from the ideal value. This step first establishes, for example... Figure 4 The equivalent circuit model shown is used to solve for the actual frequency response using the nodal admittance method, and the parasitic parameters with the greatest impact are identified.

[0064] To address these parameters, the following compensation measures are taken: non-inductive resistors (such as metal oxide film resistors) are selected to control the lead inductance below 0.1μH; a coaxial or compact tower structure is used to reduce stray capacitance to ground; the voltage divider is placed inside a shielded cylinder to reduce external interference; and a trimmer capacitor is connected in parallel on the low-voltage arm. (5-50pF). During actual calibration, apply a standard square wave signal and adjust... This ensures that the output waveform is free from overshoot and distortion, thereby achieving a flat amplitude-frequency response and a linear phase-frequency response.

[0065] The purpose of step S22 is to eliminate measurement errors caused by the non-ideality of actual components and distributed parameters, and to ensure the accuracy of broadband phase measurement.

[0066] The purpose of step S2 is to ensure the accuracy of the measurement results.

[0067] Figure 4 This is an equivalent circuit diagram of the distributed parameters of the resistive-capacitive voltage divider used in the transformer harmonic transmission characteristic test method based on a broadband transformer of the present invention. This diagram adds stray capacitance to ground to the ideal voltage divider circuit. Lead inductance and internal coupling capacitor Its function is to reveal the parasitic parameters that affect high-frequency performance in actual circuits, and to provide a theoretical model for compensation design.

[0068] S3, Set up the test system and configure parameters: Connect the high-voltage winding of the power frequency transformer and the high-voltage winding of the broadband transformer in series, and connect the RC voltage divider in parallel across the series branch; configure the power frequency power supply output to the rated primary voltage of the voltage transformer under test through the control and data acquisition unit, and configure the broadband harmonic power supply to output the 2nd to 50th harmonics in sequence, and set the content of each harmonic to 2%, 3%, and 5% of the fundamental amplitude, respectively.

[0069] The core of step S3 is to build a test platform that can stably, synchronously, and controllably output composite high-voltage signals of power frequency fundamental wave and broadband harmonics, and to precisely configure the test parameters.

[0070] The test system adopts a modular and layered structure, mainly including a power frequency power supply module, a broadband harmonic power supply module, a power frequency transformer, a broadband transformer, a resistor-capacitor (RC) divider, a control and data acquisition unit, and a voltage transformer under test. The key electrical connections are as follows: the high-voltage windings of the power frequency transformer and the broadband transformer are directly connected in series to form a composite high-voltage output branch; the high-voltage arm of the RC divider is connected in parallel across this series branch; the primary side of the voltage transformer under test is also connected in parallel across this branch; the low-voltage winding of the broadband transformer is connected to the broadband harmonic power supply; and the low-voltage winding of the power frequency transformer is connected to the power frequency power supply.

[0071] The advantages of this topology are as follows: the power frequency transformer undertakes the main voltage boosting task, ensuring that the primary side of the voltage transformer under test receives the rated power frequency voltage; the broadband transformer is only responsible for "injecting" broadband harmonic voltage into the power frequency high-voltage circuit, and does not need to bear the entire power frequency voltage itself, thus avoiding nonlinear distortion caused by core saturation in the broadband transformer. The series connection ensures the natural superposition of power frequency and harmonic voltages, eliminating the need for additional coupling circuits and improving signal synchronization and waveform purity.

[0072] The parameter configuration of the test system is uniformly completed by the control and data acquisition unit, which integrates an embedded controller (such as a DSP or FPGA) and communication interfaces (such as RS485 or Ethernet). This unit communicates with the mains frequency power supply module and the broadband harmonic power supply module via Modbus or TCP / IP protocols respectively, to realize the remote setting of output parameters.

[0073] The specific configuration details include: Power frequency power supply configuration: Set the output voltage to the rated primary voltage of the voltage transformer under test (e.g., 10kV, 35kV), the frequency to 50Hz, and start closed-loop control to ensure stable output.

[0074] Wideband harmonic power supply configuration: The operating mode is set to "automatic frequency sweep mode," covering the 2nd to 50th harmonics (corresponding to 100Hz~2500Hz; if designed to reach 3000Hz, it corresponds to the 60th harmonic). The frequency step is adjustable (e.g., 1Hz or step by harmonic order). At each harmonic frequency point, the harmonic amplitude can be further set to 2%, 3%, and 5% of the fundamental amplitude, and can automatically switch according to a preset sequence. The control unit also supports setting the duration and sampling trigger conditions for each test point, realizing a fully automatic, unattended testing process.

[0075] The purpose of step S3 is to ensure the repeatability, accuracy, and flexibility of the experimental parameters, and to provide stable excitation conditions for subsequent data collection.

[0076] Figure 5 This is a schematic diagram of the test system used in the test method for harmonic transmission characteristics of instrument transformers based on broadband transformers according to the present invention. The diagram fully illustrates the electrical connections between the power frequency power supply, broadband harmonic power supply, power frequency transformer, broadband transformer, resistive-capacitive voltage divider, control and data acquisition unit, and the voltage transformer under test. Its function is to serve as a direct blueprint for building the physical test platform.

[0077] S4, Synchronous Data Acquisition: Using the control and data acquisition unit, the standard voltage signal output by the RC divider and the measured voltage signal output by the secondary side of the voltage transformer under test are acquired synchronously.

[0078] The goal of step S4 is to acquire the standard voltage signal and the secondary output voltage signal of the voltage transformer under test with high precision and high synchronization during the test, so as to provide reliable data for subsequent amplitude and phase analysis.

[0079] A multi-channel synchronous data acquisition card is used as the core hardware. This acquisition card has the following key technical specifications: Synchronous sampling capability: All input channels share the same ADC clock source, and the sampling delay between channels is less than 1ns, ensuring that the phase relationship between the two signals is recorded truthfully and without distortion.

[0080] Sampling rate: Set to more than 10 times the highest harmonic frequency (3000Hz), with a typical configuration of 30kS / s ~ 1MS / s, to satisfy the Nyquist sampling theorem and avoid spectral aliasing.

[0081] Resolution: No less than 24 bits to capture voltage signals over a wide dynamic range, including weak harmonic components (possibly only 1% of the fundamental frequency).

[0082] Input range: Adapts to low-voltage signals (e.g., 0~10V) output from RC dividers and secondary output signals from current transformers (e.g., 0~100V), and features a programmable gain amplifier (PGA) to optimize the signal-to-noise ratio.

[0083] Before initiating a test, the control and data acquisition unit simultaneously sends a start signal to both the broadband harmonic power supply and the acquisition card via a hardware trigger line. The acquisition card employs an external rising edge trigger mode to ensure strict alignment between each data acquisition and the start time of the harmonic power supply output. At a single test frequency (e.g., 100Hz, 2% content), the acquisition card continuously acquires multiple power frequency cycles (e.g., 10 cycles, or 200ms of data) to guarantee the frequency resolution and statistical stability of the FFT analysis.

[0084] The two acquired analog signals are converted into digital quantities by an ADC and then transmitted in real time to the control unit's memory via a high-speed bus (such as PCIe, USB 3.0, or PXI). The software within the control unit (developed using LabVIEW or C++) caches the data, tags it (labeling the corresponding frequency and amplitude settings), and stores it on a solid-state drive in binary or TDMS format to prevent data loss. Simultaneously, the software supports real-time waveform display, facilitating operator monitoring of the experiment's status.

[0085] Through the above methods, step S4 achieves sub-microsecond channel synchronization, meets the sampling rate and resolution requirements for broadband signal acquisition, and fully automated data stream management, laying a solid data foundation for subsequent high-precision harmonic analysis.

[0086] Figures 6(a)-6(c) show typical voltage waveforms collected during the experiment in the test method for harmonic transmission characteristics of current transformers based on broadband transformers of this invention. Figure 6(a) shows the waveform with a superimposed 500Hz harmonic, Figure 6(b) shows the waveform with a superimposed 1500Hz harmonic, and Figure 6(c) shows the waveform with a superimposed 2500Hz harmonic. A direct verification of the waveform distortion: From Figures 6(a) to 6(c), it can be seen that as the superimposed harmonic frequency increases from 500Hz to 2500Hz, the density of "glitch" or "high-frequency ripple" in the composite voltage waveform increases significantly, and the waveform distortion characteristics become more pronounced. This directly proves that the experimental system can successfully generate a composite high-voltage signal with power frequency superimposed broadband harmonics, and that the higher the harmonic frequency, the stronger the modulation effect on the original power frequency sine wave.

[0087] Comparing the primary and secondary waveforms in each sub-figure reveals that when a 500Hz harmonic is superimposed, the secondary waveform effectively reproduces the distortion characteristics of the primary side, indicating that the transformer still exhibits good transmission performance at this frequency. However, when a 1500Hz harmonic is superimposed, the secondary waveform begins to show amplitude attenuation and waveform smoothing compared to the primary waveform, indicating that the transformer's transmission characteristics begin to deteriorate at this frequency. When a 2500Hz harmonic is superimposed, the distortion of the secondary waveform is significantly less than that of the primary waveform, and the high-frequency harmonic components are noticeably attenuated, directly reflecting the severe amplitude attenuation and phase lag problems of the voltage transformer in the high-frequency range.

[0088] These raw waveforms are the direct outputs of the data acquisition stage of this test system, demonstrating the effectiveness and completeness of the measurement from the broadband transformer output to the RC divider. Subsequent FFT analysis of these waveforms can accurately quantify the ratio difference and phase difference, providing a data foundation for broadband performance evaluation of the voltage transformer.

[0089] S5, perform signal processing and characteristic calculation: perform fast Fourier transform analysis on the two acquired voltage signals, decompose the amplitude and phase of each harmonic, and calculate the ratio difference and angle difference at each harmonic frequency.

[0090] Step S5, signal processing and characteristic calculation, specifically includes the following steps: S51, perform signal preprocessing: process the acquired standard voltage signal. and secondary side measured voltage signal Apply a window function to suppress spectral leakage and the fence effect.

[0091] The goal of this step is to apply a window function to the acquired time-domain voltage signal to suppress spectral leakage and picket fence effects, thereby improving the frequency resolution and amplitude accuracy of subsequent FFT analysis.

[0092] In actual data acquisition, due to the limited sampling time, it is impossible to guarantee that every harmonic frequency can be truncated to an integer period. Non-integer period truncation will cause spectral leakage in the frequency domain, that is, the energy of one frequency component spreads to adjacent frequency points, thereby reducing the accuracy of amplitude and phase measurements. In addition, discrete sampling itself can also introduce the picket fence effect, that is, only the spectral lines at discrete frequency points can be observed, which may miss important frequency components.

[0093] To suppress these errors, this step involves processing the standard voltage signal. and secondary side measurement signals Apply either a Hanning window or a Blackman window. The Hanning window is a cosine window with good sidelobe attenuation characteristics (sidelobe peak value approximately -32dB), achieving a good balance between suppressing spectral leakage and maintaining the main lobe width. The Blackman window offers even better sidelobe attenuation (approximately -58dB) and is suitable for applications requiring a higher dynamic range. Windowing is equivalent to smoothing the transition between the two ends of the signal, effectively reducing discontinuities at the truncation point, thereby significantly improving the accuracy of FFT analysis.

[0094] The purpose of step S51 is to improve the frequency resolution and amplitude accuracy of subsequent FFT analysis.

[0095] S52, Perform FFT transform and harmonic decomposition: Perform Fast Fourier Transform on the two preprocessed time-domain signals to obtain the frequency-domain signal. and It also decomposes the amplitudes of the fundamental wave and the 2nd to 50th harmonic components. With phase angle .

[0096] The goal of this step is to perform a fast Fourier transform on the preprocessed time-domain signal, decomposing the superimposed composite signal into the amplitude and phase of each harmonic, providing basic data for the calculation of ratio difference and angle difference.

[0097] FFT is an efficient discrete Fourier transform algorithm that can transform time-domain signals. Transform into frequency domain signal This allows us to obtain the amplitude and phase spectra of the signal at different frequencies. This sub-step applies the windowed signal... and Perform FFT separately, typically using 2048-point or 4096-point FFT to meet frequency resolution requirements (such as 1Hz or finer).

[0098] The frequency domain signal obtained after transformation and In the spectrum, the fundamental frequency component (50Hz) and all harmonic components (100Hz, 150Hz... up to 3000Hz) are presented as spectral lines. The amplitude at each harmonic frequency point is extracted. and phase angle This allows us to obtain the correspondence between the standard signal and the measured signal at various frequencies. The key to this step is to ensure that the frequency resolution of the FFT is sufficient to distinguish adjacent harmonics (such as 100Hz and 101Hz), while also ensuring the accuracy of the phase calculation. This requires that the sampling frequency and the number of sampling points satisfy the Nyquist theorem and the integer period requirement of the FFT.

[0099] The purpose of step S52 is to separate the time-domain superimposed signal into independent frequency components, providing basic data for error calculation.

[0100] S53, Calculate the ratio difference: for each harmonic frequency According to the formula Calculate the ratio difference, where The rated transformation ratio of the voltage transformer under test. Standard voltage amplitude, The voltage amplitude is measured on the secondary side.

[0101] The goal of this step is to quantitatively calculate the ratio difference at each harmonic frequency based on the standard voltage amplitude and the measured voltage amplitude on the secondary side of the tested transformer, in order to evaluate the amplitude measurement error of the transformer at different frequencies.

[0102] The ratio error is defined as the relative error between the voltage referred from the secondary side to the primary side of the transformer and the actual voltage on the primary side. The calculation formula is as follows: ,in It is the ratio of the primary side rated voltage to the secondary side rated voltage. For frequency The amplitude of the first harmonic measured by the lower resistive-capacitive voltage divider. For frequency The harmonic amplitude of the secondary output of the lower mutual inductor.

[0103] The sign of the ratio difference indicates the direction of the error: a positive value indicates that the transformer output is too high (amplification), and a negative value indicates that the output is too low (attenuation). For an ideal transformer, the ratio difference should be 0. In practice, as the frequency increases, factors such as increased iron loss and current shunting by distributed capacitance will cause the secondary side output to decrease, and the ratio difference will increase in the negative direction.

[0104] By calculating the ratio difference at each frequency point, the amplitude-frequency response characteristic curve of the current transformer can be quantitatively depicted. When the ratio difference exceeds the allowable range (e.g., ±10%), it indicates that the current transformer can no longer meet the measurement accuracy requirements at that frequency, providing a clear frequency band boundary for engineering applications.

[0105] The purpose of step S53 is to quantitatively assess the amplitude measurement error of the current transformer at different frequencies.

[0106] S54, Calculate the angle difference: for each harmonic frequency According to the formula Calculate the angle difference.

[0107] The goal of this step is to quantitatively calculate the phase difference at each harmonic frequency based on the difference between the standard voltage phase and the measured voltage phase on the secondary side of the tested transformer, in order to evaluate the phase measurement error of the transformer at different frequencies.

[0108] The phase difference is defined as the difference between the phase of the primary voltage and the phase of the secondary output voltage, and the calculation formula is as follows: ,in: Angular difference (unit: ° or ′), frequency The phase error below. Standard voltage phase angle (unit: °), the phase of the first harmonic measured by the RC divider. Secondary side measured voltage phase angle (unit: °), harmonic phase of the secondary output of the transformer.

[0109] The sign of the phase difference indicates the phase relationship: a positive value indicates that the transformer output phase lags behind the primary signal (a common occurrence), while a negative value indicates that it leads. The main cause of the phase difference is the phase shift caused by the excitation current and distributed capacitance inside the transformer. As the frequency increases, the effects of leakage inductance and stray capacitance intensify, and the phase difference usually increases significantly.

[0110] The unit of phase difference is usually degrees (°) or minutes (′), where 1° = 60′. For current transformers used for protection, phase difference requirements are usually quite strict (e.g., within ±1°). By calculating the phase difference at each frequency point and plotting the phase difference-frequency curve, the phase response characteristics of the current transformer at different frequencies can be visually evaluated, providing key parameters for applications such as broadband measurement and differential protection.

[0111] The purpose of step S54 is to quantitatively assess the phase measurement error of the current transformer at different frequencies.

[0112] S6. Analyze the transmission characteristics: Plot the frequency response curve with harmonic frequency as the abscissa and ratio difference and angle difference as the ordinate, and analyze the amplitude attenuation law and phase shift law of the tested voltage transformer in the entire wide frequency band.

[0113] The frequency response curves plotted in step S6, which analyzes the transfer characteristics, specifically include the ratio difference-frequency curve and the angle difference-frequency curve; By analyzing the variation trend of the ratio difference-frequency curve in the 25Hz-3000Hz frequency band, the frequency points where the amplitude attenuation exceeds the allowable range can be identified. By analyzing the changing trend of the angle difference-frequency curve within the same frequency band, frequency points where the phase lag exceeds the allowable range can be identified.

[0114] Figures 7(a) and 7(b) are harmonic transfer characteristic curves of a voltage transformer sample calculated using the method of this invention. Figure 7(a) is the ratio difference-frequency curve, and Figure 7(b) is the angle difference-frequency curve. These curves illustrate the following key issues: The amplitude-frequency response curve quantitatively reveals the variation of the voltage transformer's ratio error with harmonic frequency. As shown in the figure, in the lower frequency range (50Hz-500Hz), the absolute value of the ratio error is small and changes gradually, indicating that the transformer has high amplitude measurement accuracy in the power frequency and nearby frequency ranges. With increasing frequency, the absolute value of the ratio error increases significantly, typically showing a negative growth trend, indicating that the harmonic voltage amplitude output from the secondary side of the transformer is severely attenuated relative to the true value.

[0115] The phase-frequency response curve reveals the relationship between the phase angle difference of the voltage transformer and the harmonic frequency. As can be seen from the figure, in the low-frequency range (50Hz-500Hz), the absolute value of the phase angle difference is small and the linearity is good. As the frequency increases, the absolute value of the phase angle difference increases rapidly, typically exhibiting a hysteretic growth, indicating that high-frequency harmonic signals produce a significant phase delay after passing through the transformer.

[0116] This testing system enables efficient and continuous acquisition of such curves, achieving standardized evaluation of the wide-band performance of voltage transformers from different models and manufacturers. This addresses the shortcomings of traditional methods, such as the inability to obtain continuous wide-band characteristics and low testing efficiency. It provides core data support for the selection of wide-band measurement equipment, power quality assessment, and relay protection strategy formulation in new power systems.

[0117] This invention can be used in a wide variety of general-purpose or special-purpose computer system environments or configurations. Examples include: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, and distributed computing environments including any of the above systems or devices. This invention can be described in the general context of computer-executable instructions, such as program modules, that are executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform specific tasks or implement specific abstract data types. This invention can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0118] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by instructing related hardware through computer-readable instructions. These computer-readable instructions can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above methods. The aforementioned storage medium can be a non-volatile storage medium such as a magnetic disk, optical disk, or read-only memory (ROM), or random access memory (RAM).

[0119] It should be understood that although the steps in the flowcharts of the accompanying figures are shown sequentially as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the accompanying figures may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0120] Example 3: Design Case of Key Components of the Test System This example uses a voltage transformer with a rated voltage of 10kV as the test object to illustrate in detail the specific design process of the broadband transformer and the RC voltage divider in the test system of this invention.

[0121] S1, design a wideband transformer.

[0122] Objective: Design a wideband transformer with a rated low voltage of 415V and a rated high voltage of 5kV to boost harmonic voltages of 25-3000Hz and superimpose them onto the power frequency high voltage.

[0123] S11, Core parameter calculation: The core is made of high-permeability, low-loss toroidal silicon steel strip, model 1J85, with an initial relative permeability of [missing information]. The permeability is greater than 80,000, and the fluctuation of permeability is controlled within 5% in the 25-3000Hz frequency band.

[0124] According to the law of electromagnetic induction At the lowest frequency At that time, to ensure that the magnetic flux density B does not saturate (take B = 1.2T), and considering the low-voltage side voltage... Preliminary calculation of the number of turns and core cross-sectional area The product of the two. After iterative optimization, the final determination was: inner diameter of the iron core 100mm, outer diameter 180mm, height 80mm, and the cross-sectional area of ​​the iron core was calculated. m 2 Average magnetic circuit length Number of turns in the low-voltage winding Turns.

[0125] Then the magnetizing inductor The calculation is as follows: .

[0126] At 25Hz, no-load current for: .

[0127] Low voltage side rated current Approximately (Assuming capacity) = 0.83A, the no-load current accounts for approximately 19.3%, which is slightly high. The calculation was performed by increasing the number of turns to 200. , This accounts for approximately 10.8%. Further, by selecting higher... By using better materials or increasing the cross-sectional area of ​​the core, the no-load current ratio can be optimized to less than 5%. This calculation ensures that the transformer still has sufficiently high excitation impedance in the lowest frequency band, preventing harmonic signals from being shunted.

[0128] S12, perform leakage inductance control: The primary and secondary windings are concentrically wound and tightly coupled. The number of turns in the secondary winding (high-voltage side) is... Turns. Through tight winding, the leakage flux cross-sectional area It is limited to a very small range. According to the formula Finite element simulation verification shows that the final design will incorporate leakage inductance on the low-voltage side. The leakage inductance is controlled at 0.25mH. At 3000Hz, the leakage inductance is... Compared to the capacitive reactance of stray capacitors, it will not produce resonance, thus ensuring the smooth flow of high-frequency signals.

[0129] S13, perform stray capacitance calculation and suppression: The conductor is 2mm diameter copper wire, covered with a 0.5mm thick polyesterimide insulation layer. Calculate the inter-turn capacitance: conductor radius... center distance Relative permittivity Average length of a single turn .but: .

[0130] For interlayer capacitance, a 0.2mm thick Nomex paper is added between the layers ( (and adopt segmented winding to reduce the interlayer overlap area) Reduced by 50%. Interlayer capacitance before optimization. It could be as high as several thousand pF, but after optimization it can be reduced to several hundred pF.

[0131] primary and secondary side stray capacitance By increasing the insulation distance between the primary and secondary sides (thickening the insulation cylinder to 3mm) and adding an electrostatic shielding layer for grounding, the capacitance is reduced to below 50pF. These calculation and design measures aim to weaken the bypass path of high-frequency signals through the capacitor, avoid the formation of LC resonance peaks, and ensure a flat amplitude-frequency response within the 25-3000Hz frequency band.

[0132] Finally, the main structural parameters of the broadband transformer designed above are shown in Table 1. This transformer is the core component for achieving efficient and low-distortion broadband harmonic transmission.

[0133] Table 1 Structural parameters of power frequency transformers and broadband transformers

[0134] S2, design a resistive-capacitive voltage divider.

[0135] Objective: To design a resistive-capacitive voltage divider with a voltage division ratio of 20000:1 and a measurement error of less than ±0.5% in the DC-3kHz range.

[0136] S21, Calculation of ideal partial pressure ratio: A two-stage resistor-capacitor series high-voltage arm is used. (Selection) Then the total resistance of the high-voltage arm Select Then the total capacitance of the high-voltage arm .

[0137] Select low-voltage arm resistor ,capacitance .

[0138] Validate matching conditions: , .

[0139] The two are not equal and need adjustment. (Take...) Therefore, the high-voltage arm capacitor was redesigned: the total capacitance could be achieved by connecting 100 100pF capacitors in series and parallel. Alternatively, adjust the resistance value.

[0140] The high-voltage arm was finally selected: , Low-pressure arm: , .at this time , The matching condition is met.

[0141] Ideal partial pressure ratio This means that when the input is 20,000V, the output is approximately 1V.

[0142] transfer function .because ,so This is a constant, independent of frequency. The purpose of this step is to ensure, in principle, that the voltage division ratio remains constant across the entire frequency band.

[0143] S22, Perform distributed parameter modeling and compensation: In practical circuits, distributed parameters exist. For example... Figure 4 The equivalent circuit is shown. This is to reduce lead inductance. Non-inductive resistors (such as metal oxide film resistors) are selected, and a coaxial structure design is adopted to ensure that the inductance is less than 0.1μH. This is to reduce stray capacitance to ground. The voltage divider is placed inside a shielded cylinder and employs a compact tower-shaped structure. To compensate for the effects of residual parasitic parameters, a fine-tuning capacitor is connected in parallel on the low-voltage arm. (e.g., 5-50pF) In actual calibration, a standard square wave signal is applied to adjust... This ensures that the output waveform is free from overshoot and distortion, thereby achieving the best frequency response.

[0144] The above design ensures that the amplitude fluctuation of the RC voltage divider is less than ±0.5% and the phase offset is less than ±0.1° within 3kHz. The signal output by this voltage divider can be used as the "true value" or "standard value" for measuring the error of the current transformer.

[0145] Example 4: Test Case of Harmonic Transmission Characteristics of Voltage Transformer Step 1: Set up the experimental system.

[0146] according to Figure 5 The schematic diagram shown illustrates the setup for the test system. Connect the primary terminals A and N of the 10kV voltage transformer under test to the high-voltage output of the series connection between the power frequency transformer and the broadband transformer. Connect the high-voltage terminal of the RC divider in parallel at this point. Connect the low-voltage output of the RC divider and the secondary output of the transformer under test to the two synchronization channels of the data acquisition card, respectively.

[0147] Step 2: Configure the test parameters.

[0148] Configure the following settings through the human-machine interface of the control and data acquisition unit: Power frequency power supply: The output voltage is set to 10kV and the frequency is 50Hz.

[0149] Harmonic power supply: Set the frequency sweep mode, starting frequency 100Hz (2nd harmonic), ending frequency 2500Hz (50th harmonic), frequency step 100Hz. At each frequency point, set the harmonic content to 2%, 3%, and 5% respectively (relative to the 10kV fundamental frequency, i.e., harmonic amplitudes of 200V, 300V, and 500V respectively).

[0150] Step 3: Perform tests and collect data.

[0151] The automatic test program is initiated. The system automatically controls the harmonic power supply to output a 100Hz harmonic with an amplitude of 200V. This harmonic is stepped up by a broadband transformer and then superimposed in series with the 10kV power frequency voltage, forming a peak value of approximately [value missing]. The composite voltage is kV. The data acquisition card synchronously acquires the standard voltage signal within one power frequency cycle (20ms) at a sampling rate of 1ms / s and a resolution of 24 bits. and the secondary output signal of the tested transformer After the acquisition is completed, the harmonic power supply automatically jumps to the next frequency or amplitude point and repeats the acquisition process. Typical time-domain waveforms acquired in this experiment are shown in Figures 6(a)-(c). As can be seen in Figure 6(a), the 500Hz harmonic superimposed on the 50Hz fundamental wave forms a waveform with "ripple," and the primary and secondary waveforms are highly consistent. As can be seen in Figure 6(c), when the 2500Hz harmonic is superimposed, the high-frequency ripple of the secondary waveform is significantly smaller than that of the primary waveform, directly demonstrating high-frequency attenuation.

[0152] Step four: Perform signal processing and characteristic calculations.

[0153] After data collection is complete, proceed to step five: Signal preprocessing: processing the acquired signals... and Apply a Hanning window to reduce spectral leakage caused by non-integer period truncation.

[0154] FFT Transform: Perform a 2048-point FFT on the two windowed signals to obtain the spectrum. and The amplitude and phase of the fundamental frequency (50Hz) and each harmonic (100Hz, 200Hz, …, 2500Hz) are extracted from the spectrum.

[0155] Difference Calculation: Taking a test point at 2500Hz with a harmonic content of 3% as an example. Assume the standard voltage amplitude is obtained through FFT analysis. (Harmonic components) The voltage amplitude at the corresponding frequency measured on the secondary side of the tested transformer (rated secondary voltage 100V, turns ratio k=100). The difference is: .

[0156] A negative value indicates that the current transformer output is too low, i.e., the amplitude is attenuated.

[0157] Angle difference calculation: Taking the same test point as an example. Assume that the standard voltage phase is obtained from the FFT analysis. Phase of secondary voltage of current transformer Then the angle difference is:

[0158] A positive value indicates that the output phase of the current transformer is lagging.

[0159] Repeat the above calculations for all frequency points and amplitude points.

[0160] Step 5: Perform transfer characteristic analysis.

[0161] All the calculated ratio and angle difference data were plotted as curves with frequency as the abscissa, as shown in Figure 7(a) and Figure 7(b).

[0162] Analyzing the ratio error-frequency curve in Figure 7(a): In the 50Hz-500Hz range, the ratio error is within -0.2%, indicating high accuracy. In the 500Hz-1500Hz range, the ratio error increases negatively to -2%. In the 1500Hz-2500Hz range, the ratio error drops sharply to over -10%. This indicates that the effective operating frequency of this type of voltage transformer should not exceed 1500Hz; otherwise, the amplitude measurement error will be unacceptable.

[0163] Analyzing the phase difference-frequency curve in Figure 7(b): the phase difference is less than 0.5° in the 50Hz-500Hz range. At 2500Hz, the phase difference reaches 5°, indicating severe phase lag. This could lead to malfunctions in protection devices that require precise phase information (such as differential protection).

[0164] This experimental system and method, using only a single automatic frequency sweep test, completely and quantitatively obtained the full transmission characteristics of the voltage transformer over a wide frequency range. The experimental results show that this invention effectively solves the problems of low efficiency, narrow bandwidth, and poor accuracy in existing technologies, providing a technical means for the adaptability evaluation of voltage transformers in new power systems.

[0165] Example 5 The present invention also provides another embodiment, namely, a computer-readable storage medium storing computer-readable instructions that can be executed by at least one processor to cause the at least one processor to perform the steps of the above-described method for testing the harmonic transmission characteristics of a current transformer based on a broadband transformer.

[0166] The beneficial effects of implementing the above embodiments are as follows: (1) High-voltage, wide-bandwidth, and high-synchronization testing capabilities: By innovatively connecting the power frequency transformer in series with the high-voltage winding of a transformer specifically designed for wideband, it is possible to achieve integrated and highly synchronized superposition output of wideband harmonic signals of 25Hz-3000Hz and power frequency fundamental signals at voltage levels of up to 35kV and above. This solves the fundamental problems of insufficient voltage levels, narrow frequency range, and poor signal synchronization in existing technologies.

[0167] (2) It has high-precision harmonic amplitude adjustment and simulation capabilities: the wideband harmonic power supply can accurately control the harmonic amplitude to 1%-10% of the fundamental amplitude, with a step size as small as 0.1%, which can realistically simulate the complex working conditions of harmonics with different permeability in the power grid, providing a powerful tool for studying the saturation and nonlinear characteristics of voltage transformers under different harmonic contents.

[0168] (3) High-fidelity signal transmission and measurement: Through detailed modeling, calculation and suppression design of the core material, structure (ring), leakage inductance (controlled at 0.25mH) and various stray capacitances of the broadband transformer, the transmission of broadband harmonic signals with low loss (total iron loss ≤0.5%) and low distortion during the boosting and superposition process is ensured. At the same time, through the design of a resistor-capacitor voltage divider that meets the matching conditions, an ideal voltage division with amplitude fluctuation <±0.5% is achieved from DC to 3kHz frequency range, ensuring the ultra-high accuracy of the standard voltage signal.

[0169] (4) High-efficiency continuous frequency sweep testing capability: Full automation is achieved. The operator only needs to set the frequency sweep range (e.g., 2nd-50th harmonics) and amplitude step (e.g., 1%) in the control unit, and the system can automatically execute all test points and calculate and plot the continuous ratio difference-frequency and angle difference-frequency characteristic curves in real time. Compared with the traditional point-by-point testing method, the efficiency is improved by several times or even tens of times.

[0170] (5) Provides key evaluation data for new power systems: By obtaining the wideband transfer characteristic curve of the voltage transformer, its effective operating frequency band can be clearly defined, and its measurement error in different frequency bands can be quantified. This provides indispensable core data support for the selection of wideband measurement equipment, accurate assessment of power quality, and formulation of early warning and protection strategies for wideband oscillations in new power systems, and has important engineering application value.

[0171] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal device (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0172] Obviously, the embodiments described above are merely some embodiments of the present invention, not all embodiments. The accompanying drawings show preferred embodiments of the present invention, but do not limit the patent scope of the present invention. The present invention can be implemented in many different forms; rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of this invention.

Claims

1. A test system for harmonic transmission characteristics of a current transformer based on a broadband transformer, characterized in that, include: The power frequency power supply module is used to generate the power frequency fundamental voltage; Wideband harmonic power supply module, used to generate wideband harmonic voltage with a frequency range of 25Hz to 3000Hz and an amplitude adjustable between 1% and 10% of the fundamental voltage amplitude; A power frequency transformer, the low voltage winding of which is connected to the output terminal of the power frequency power module, is used to boost the power frequency fundamental voltage to the rated voltage of the primary side of the voltage transformer under test. A broadband transformer includes a low-voltage winding and a high-voltage winding independently wound on the same toroidal core. The low-voltage winding is connected to the output terminal of the broadband harmonic power supply module, and the high-voltage winding is connected in series with the high-voltage winding of the power frequency transformer. It is used to superimpose the broadband harmonic voltage onto the power frequency fundamental voltage without distortion to generate a composite high-voltage test signal. A resistive-capacitive voltage divider, the high-voltage arm of which is connected in parallel with the composite high-voltage test signal, is used to divide the composite high-voltage test signal into a low-voltage measurement signal as a standard voltage signal; The control and data acquisition unit is electrically connected to the output terminals of the power frequency power supply module, the broadband harmonic power supply module, the RC voltage divider, and the secondary output terminal of the voltage transformer under test, respectively. It is used to synchronously acquire the standard voltage signal and the secondary output voltage signal of the voltage transformer under test, and to analyze and process the acquired signals to calculate the ratio difference and angle difference of the voltage transformer under test at each harmonic frequency.

2. The instrument transformer harmonic transmission characteristic testing system based on a broadband transformer according to claim 1, characterized in that, The design parameters of the broadband transformer are determined through the following optimization steps: Calculate core parameters: Using a toroidal silicon steel sheet core, its magnetizing inductance... satisfy ,in The permeability of free space, The relative permeability of the iron core. The number of turns in the winding. The cross-sectional area of ​​the iron core is... The average magnetic circuit length of the iron core; the no-load current at the lowest operating frequency. Less than 5% of the rated current, of which Rated voltage, For frequency; leakage inductance referred to the low-voltage side Controlled at 0.25mH, where leakage inductance , For leakage flux, For current; Stray capacitance calculation and control: Calculation of inter-turn stray capacitance ,in The vacuum permittivity, The relative permittivity of the insulating medium, The center distance of the conductors, Let the radius be the conductor. Given the average length of a single turn; calculate the interlayer stray capacitance. ,in This represents the overlap area of ​​the two winding layers. Given the interlayer insulation thickness; calculate the primary and secondary side stray capacitances. ,in This is the axial length of the winding. The outer radius of the primary winding is... The inner radius of the secondary winding; By increasing the thickness of interlayer insulation, adopting segmented winding or honeycomb winding to reduce the overlapping area, using low dielectric constant insulation materials, and optimizing the winding structure, the transformer achieves a total iron loss of ≤0.5% in the 25-3000Hz frequency band and has no resonant point.

3. The instrument transformer harmonic transmission characteristic testing system based on a broadband transformer according to claim 1, characterized in that, The resistor-capacitor voltage divider includes a high-voltage arm and a low-voltage arm connected in series, the high-voltage arm being composed of a first resistor. Second resistor With the first capacitor Second capacitor The low-voltage arm is composed of a parallel-series combination, and the low-voltage arm is composed of a third resistor. With the third capacitor The circuit is configured in parallel; its design satisfies the matching condition that the voltage division ratio of the resistor is equal to that of the voltage division ratio of the capacitor. Ideal partial pressure ratio ; By selecting non-inductive resistors, a compact symmetrical structure, and a shielding ring design, the amplitude fluctuation is less than ±0.5% and the phase shift is minimized in the DC-3kHz frequency range.

4. The instrument transformer harmonic transmission characteristic testing system based on a broadband transformer according to claim 1, characterized in that, The control and data acquisition unit includes: A multi-channel synchronous data acquisition card with a sampling rate of at least 10 times the highest harmonic frequency (3000Hz), i.e., 30kS / s, and a resolution of no less than 24 bits; A digital signal processor or field-programmable gate array with a built-in fast Fourier transform algorithm module is used to perform real-time spectrum analysis on the acquired digital signal. The digital signal processor or field-programmable gate array is used to calculate the amplitude and phase of each harmonic. The human-machine interface is used to configure the output parameters of the power frequency and harmonic power supply, display the voltage waveform and spectrum in real time, and provide test reports on the output ratio difference and angle difference.

5. A method for testing the harmonic transmission characteristics of a voltage transformer applied to the test system described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1, Optimized design of wideband transformer: By calculating core parameters and stray capacitance, a wideband transformer that can achieve low loss, linear transmission and precise superposition with power frequency voltage in a wide frequency range of 25-3000Hz is designed and manufactured. S2, Design of RC voltage divider: By calculating the ideal voltage division ratio and modeling the distributed parameters, an RC voltage divider with flat frequency response and small phase offset is designed as a standard voltage measurement device. S3, Set up the test system and configure parameters: Connect the high-voltage winding of the power frequency transformer and the high-voltage winding of the broadband transformer in series, and connect the resistive-capacitive voltage divider in parallel across the series branch; configure the power frequency power supply output to be the rated primary voltage of the voltage transformer under test through the control and data acquisition unit, and configure the broadband harmonic power supply to output the 2nd to 50th harmonics in sequence, with the content of each harmonic set to 2%, 3%, and 5% of the fundamental amplitude, respectively; S4, Synchronous Data Acquisition: Using the control and data acquisition unit, the standard voltage signal output by the resistive-capacitive voltage divider and the measured voltage signal output by the secondary side of the voltage transformer under test are acquired synchronously. S5, perform signal processing and characteristic calculation: perform fast Fourier transform analysis on the two acquired voltage signals, decompose the amplitude and phase of each harmonic, and calculate the ratio difference and angle difference at each harmonic frequency. S6. Analyze the transmission characteristics: Plot the frequency response curve with harmonic frequency as the abscissa and ratio difference and angle difference as the ordinate, and analyze the amplitude attenuation law and phase shift law of the tested voltage transformer in the entire wide frequency band.

6. The test method according to claim 5, characterized in that, The step S1, optimizing the design of the broadband transformer, specifically includes the following steps: S11, Calculate core parameters: Based on the transformer capacity requirements, use the magnetic flux density formula... Determine the cross-sectional area of ​​the iron core and number of turns ,in For voltage, For frequency; using the formula Calculate the magnetizing inductance And through the formula Check the no-load current Ensure that it is less than 5% of the rated current; S12, leakage inductance control: The primary and secondary windings of the toroidal core are concentrically wound and tightly wound, and the closed magnetic circuit of the core is used to control the leakage inductance referred to the low-voltage side. Controlled at 0.25mH; S13, Perform stray capacitance calculation and suppression: Calculate the inter-turn stray capacitance separately. Interlayer stray capacitance and primary and secondary side stray capacitance Furthermore, stray capacitances are suppressed by increasing the interlayer insulation thickness, using segmented winding or honeycomb winding, using low dielectric constant insulation materials, and using zigzag winding methods.

7. The test method according to claim 5, characterized in that, Step S2, designing the resistive-capacitive voltage divider, specifically includes the following steps: S21, Calculate the ideal partial pressure ratio: according to the formula Determine the theoretical partial pressure ratio, where For the high-voltage arm impedance, The impedance is low for the voltage arm and meets the matching conditions. This makes the transfer function Simplify to a constant ; S22, Perform distributed parameter modeling and compensation: Establish a model including stray capacitance to ground. Lead inductance and internal coupling capacitors The equivalent circuit model is obtained, and the actual frequency response is solved by the nodal admittance matrix. Compensation capacitors or RC networks are added to the low-voltage arm to match the actual time constant and ensure that the amplitude fluctuation is less than ±0.5% within DC-3kHz.

8. The test method according to claim 5, characterized in that, Step S5, which involves signal processing and characteristic calculation, specifically includes the following steps: S51, perform signal preprocessing: process the acquired standard voltage signal. and secondary side measured voltage signal Apply a window function to suppress spectral leakage and the picket fence effect; S52, Perform FFT transform and harmonic decomposition: Perform Fast Fourier Transform on the two preprocessed time-domain signals to obtain the frequency-domain signal. and It also decomposes the amplitudes of the fundamental wave and the 2nd to 50th harmonic components. With phase angle ; S53, Calculate the ratio difference: for each harmonic frequency According to the formula Calculate the ratio difference, where The rated transformation ratio of the voltage transformer under test. Standard voltage amplitude, The voltage amplitude is measured on the secondary side. S54, Calculate the angle difference: for each harmonic frequency According to the formula Calculate the angle difference.

9. The test method according to claim 5, characterized in that, The frequency response curves plotted in step S6, which analyzes the transmission characteristics, specifically include the ratio difference-frequency curve and the angle difference-frequency curve. By analyzing the variation trend of the ratio difference-frequency curve in the 25Hz-3000Hz frequency band, the frequency points where the amplitude attenuation exceeds the allowable range can be identified. By analyzing the trend of the phase difference-frequency curve within the same frequency band, frequency points where the phase lag exceeds the allowable range can be identified.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps of the test method for the harmonic transmission characteristics of a voltage transformer as described in any one of claims 5 to 9.

Images