Power frequency-intermediate frequency equivalent experiment method based on withstand voltage and aging characteristics of insulating material

Abstract

The invention provides a power frequency-intermediate frequency equivalent experiment method based on voltage withstanding and aging characteristics of an insulating material, and the method comprises the steps: obtaining the breakdown time data of the insulating material under a power frequency voltage and an intermediate frequency voltage, and determining a first experiment result, which comprises a voltage suggestion value of a voltage withstanding test of an intermediate frequency transformer under the power frequency voltage; determining the partial discharge characteristics of the insulating material under the power frequency voltage and the intermediate frequency voltage, and determining a second experiment result, including the partial discharge voltage proportionality coefficient of the insulating material under the power frequency voltage and the intermediate frequency voltage; determining a parameter change curve of each aging characteristic of the insulating material under the power frequency voltage and the intermediate frequency voltage, and determining a third experiment result including an aging characteristic parameter change rate of the insulating material under the intermediate frequency voltage; and generating a power frequency-intermediate frequency equivalent experiment report according to the first experiment result, the second experiment result and the third experiment result. A theoretical basis is provided for insulation performance evaluation and design of the intermediate-frequency electrical equipment, and an acceleration mechanism and frequency dependence of the aging process are determined.

Description

Technical Field

[0001] This application relates to the technical field of research on the operation reliability of power equipment, and particularly to a power frequency - intermediate frequency equivalent experimental method based on the withstand voltage and aging characteristics of insulating materials. Background Art

[0002] Intermediate frequency transformers have a wide range of applications in modern power electronics and energy transmission fields. Especially in intermediate frequency induction heating, electric vehicles, and long - distance offshore energy transmission, as key power equipment, intermediate frequency transformers undertake frequent and efficient energy transmission tasks. In these application scenarios, the operating frequency is usually higher than the traditional power frequency range, typically between dozens of hertz and hundreds of hertz. This intermediate frequency environment poses unique challenges to the insulating materials inside the transformer. The intermediate frequency voltage induces significant electro - thermal effects, resulting in large dielectric losses on the surface and inside of the insulating materials. At the same time, the intermediate frequency electric field also accelerates the accumulation and migration of charges, causing the electrolyte in the oil - paper insulating material and the solid medium to gradually decompose under high temperature and high electric field, generating more acid value and moisture, and accelerating the generation of aging products such as furfural, shortening the service life of the equipment. Therefore, studying the insulation aging characteristics and reliability evaluation methods suitable for intermediate frequency conditions and establishing an equivalence model between power frequency and intermediate frequency environments have important engineering significance for improving the operation stability and reliability of intermediate frequency transformers.

[0003] In practical applications, it is difficult to generate complex intermediate frequency voltage waveforms. In engineering, power frequency voltage is commonly used to test the insulation performance of intermediate frequency equipment. For the factory inspection of intermediate frequency power transformer manufacturers, the short - time power frequency withstand voltage test standards for the high - and low - voltage windings to the ground are unclear, and the basis for partial discharge measurement is insufficient. Usually, the test standards of power frequency power transformers or instrument transformers are borrowed, and the insulation test effect is not good. Therefore, studying the correlation between power frequency and intermediate frequency voltage tests and developing equivalent standards for power frequency - intermediate frequency insulation performance tests have good practical application value. Currently, there is no research on power frequency - intermediate frequency insulation equivalence experiments, and due to the differences in material aging performance under power frequency and intermediate frequency, there is an urgent need for a power frequency - intermediate frequency insulation performance equivalence experimental method based on multi - parameter characterization. Summary of the Invention

[0004] The purpose of this application aims to solve at least one of the above - mentioned technical defects, especially the technical defect that there is no research on power frequency - intermediate frequency insulation equivalence experiments in the prior art, and due to the differences in material aging performance under power frequency and intermediate frequency, there is an urgent need for a power frequency - intermediate frequency insulation performance equivalence experimental method based on multi - parameter characterization.

[0005] In the first aspect, this application provides a power frequency - intermediate frequency equivalent experimental method based on the withstand voltage and aging characteristics of insulating materials. The method includes:

[0006] Obtain the breakdown time data of the insulating material under power frequency voltage and medium frequency voltage, and determine the first experimental result according to the breakdown time data. The first experimental result includes the recommended value of the withstand voltage test voltage of the medium frequency transformer under power frequency voltage;

[0007] Determine the partial discharge characteristics of the insulating material under power frequency voltage and medium frequency voltage, and determine the second experimental result according to the partial discharge characteristics. The second experimental result includes the partial discharge voltage proportionality coefficient of the insulating material under power frequency voltage and medium frequency voltage;

[0008] Determine the parametric change curves of each aging characteristic of the insulating material under power frequency voltage and medium frequency voltage, and determine the third experimental result according to each parametric change curve. The third experimental result includes the aging characteristic parametric change rate of the insulating material under medium frequency voltage;

[0009] Generate a power frequency - medium frequency equivalent experimental report according to the first experimental result, the second experimental result and the third experimental result.

[0010] In one embodiment, the step of obtaining the breakdown time data of the insulating material under power frequency voltage and medium frequency voltage includes:

[0011] In the pre - built power frequency - medium frequency withstand voltage test platform, adopt the standard electrical strength test method of insulating materials to obtain the breakdown time data of the insulating material under power frequency voltage and medium frequency voltage.

[0012] In one embodiment, the expression of the recommended value of the withstand voltage test voltage of the medium frequency transformer under power frequency voltage is:

[0013]

[0014] Where, is the recommended value of the test voltage of the withstand voltage test of the medium frequency transformer under power frequency voltage, is the medium frequency / power frequency conversion coefficient, is the 1 - minute withstand voltage test voltage value of the medium frequency transformer under medium frequency voltage.

[0015] In one embodiment, the step of determining the partial discharge characteristics of the insulating material under power frequency voltage and medium frequency voltage includes:

[0016] Under the pre - determined maximum voltage reference value and partial discharge voltage, obtain the partial discharge parameters of the insulating material under power frequency voltage and medium frequency voltage. The partial discharge parameters include kurtosis, skewness and phase concentration;

[0017] Determine the partial discharge characteristics according to the change trend of the partial discharge parameters with the voltage frequency.

[0018] In one embodiment, the expression for the proportionality coefficient of the partial discharge voltage of the insulating material under power frequency voltage and intermediate frequency voltage is:

[0019]

[0020] Wherein, is the proportionality coefficient of the partial discharge voltage, , are the withstand voltage values corresponding to the expected service life of the insulating material under power frequency voltage and intermediate frequency voltage, respectively.

[0021] In one embodiment, the steps for determining the parametric change curves of each aging characteristic of the insulating material under power frequency voltage and intermediate frequency voltage include:

[0022] Obtain the parameters of each aging characteristic of the insulating material under power frequency voltage, intermediate frequency voltage, and different aging times. The aging characteristics include acid value, micro water content, dissolved gas content, and furfural content;

[0023] Fit the parameters of each aging characteristic according to the parametric change law of each aging characteristic to obtain each parametric change curve.

[0024] In one embodiment, for the acid value and furfural content, the expression of the corresponding parametric change curve is:

[0025]

[0026] Wherein, is the change rate of the aging characteristic parameter, is the first aging rate constant, is the initial value of the aging characteristic quantity, is the saturation point.

[0027] In one embodiment, for the micro water content and dissolved gas content, the expression of the corresponding parametric change curve is:

[0028]

[0029] Wherein, is the change rate of the aging characteristic parameter, is the initial value of the aging characteristic quantity, is the second aging rate constant, is the power exponent.

[0030] In one embodiment, the expression for the change rate of the aging characteristic parameter of the insulating material under intermediate frequency voltage is:

[0031]

[0032] Wherein, is the change rate of aging characteristic parameters under medium-frequency conditions, is the frequency effect factor, is the change rate of aging characteristic parameters under power-frequency conditions.

[0033] In one embodiment, the expression of the frequency effect factor is:

[0034]

[0035] Wherein, is the frequency effect factor, is the frequency response coefficient, reflecting the sensitivity of medium frequency to the change of specific parameters, 、 are the test frequency and the reference 50Hz power frequency.

[0036] From the above technical solutions, it can be seen that the embodiments of the present application have the following advantages:

[0037] In the power-frequency - medium-frequency equivalent experimental method based on the withstand voltage and aging characteristics of insulating materials provided by the present application, the method determines the recommended value of the withstand voltage test voltage of the medium-frequency transformer under power-frequency voltage by obtaining the breakdown time data of the insulating material under power-frequency voltage and medium-frequency voltage, solves the problems of difficult generation of complex medium-frequency voltage waveforms and unclear power-frequency withstand voltage test standards in practical applications, provides a clear reference basis for the withstand voltage test of medium-frequency transformers, and improves the accuracy of insulation testing; by determining the partial discharge characteristics of the insulating material under power-frequency voltage and medium-frequency voltage, the partial discharge voltage proportionality coefficient is obtained, solves the problem of insufficient basis for partial discharge measurement, and makes the partial discharge test more targeted and effective; by determining the parametric change curves of each aging characteristic of the insulating material under the two voltages, the change rate of aging characteristic parameters under medium-frequency voltage is obtained, which helps to study the insulation aging characteristics suitable for medium-frequency conditions and provides data support for reliability assessment; the finally generated power-frequency - medium-frequency equivalent experimental report synthesizes the experimental results of breakdown time, partial discharge characteristics, parametric changes of aging characteristics, etc., establishes an equivalence model between power-frequency and medium-frequency environments, fills the blank of the current power-frequency - medium-frequency insulation equivalence experimental research, meets the requirements of the equivalent standard in practical applications, improves the operation stability and reliability of medium-frequency transformers, and has important engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0039] Figure 1 Schematic diagram of the power frequency - intermediate frequency equivalent experimental method based on the withstand voltage and aging characteristics of insulating materials provided by the embodiments of the present application;

[0040] Figure 2 Schematic diagram of the power frequency - intermediate frequency withstand voltage experimental platform provided by the embodiments of the present application;

[0041] Figure 3 V - t characteristic curve of insulating paper under different voltage frequencies provided by the embodiments of the present application;

[0042] Figure 4 Example diagram of the variation law of the acid value of the specimen with the voltage frequency provided by the embodiments of the present application;

[0043] Figure 5 Example diagram of the variation law of the acid value of the specimen with the voltage frequency provided by the embodiments of the present application;

[0044] Figure 6 Example diagram of the variation law of the furfural content of the specimen with the voltage frequency provided by the embodiments of the present application;

[0045] Figure 7 Example diagram of the variation law of CO2 / CO of the specimen with the voltage frequency provided by the embodiments of the present application;

[0046] Figure 8 Example diagram of the variation law of the micro - water content of the specimen with the voltage frequency provided by the embodiments of the present application. Detailed implementation manners

[0047] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without making creative efforts shall fall within the protection scope of the present application.

[0048] As Figure 1 shown, the present application provides a power frequency - intermediate frequency equivalent experimental method based on the withstand voltage and aging characteristics of insulating materials, and the method includes:

[0049] S101: Obtain the breakdown time data of the insulating material under power frequency voltage and intermediate frequency voltage, and determine the first experimental result according to the breakdown time data. The first experimental result includes the recommended value of the withstand voltage test voltage of the intermediate frequency transformer under power frequency voltage.

[0050] Among them, the insulating material refers to the material used to isolate the conduction of electric energy and prevent current leakage or short - circuit, such as the oil - paper insulating material in transformers. The power - frequency voltage refers to the alternating voltage with a frequency of 50Hz or 60Hz. The intermediate - frequency voltage refers to the alternating voltage with a frequency higher than the power - frequency range, usually between dozens of hertz and hundreds of hertz. The breakdown time refers to the time required for the insulating material to lose its insulating performance and break down under a specific voltage. The first experimental result refers to the general term of a series of data and conclusions obtained through experimental analysis on the voltage - withstand performance and breakdown characteristics of insulating materials under power - frequency and intermediate - frequency voltages. The recommended value of the voltage - withstand test voltage refers to the reasonable voltage value recommended for the voltage - withstand test of intermediate - frequency transformers based on experimental data and analysis results, which is used to guide the actual test and evaluation.

[0051] The first experimental result mainly focuses on the breakdown - time data of insulating materials under power - frequency voltage and intermediate - frequency voltage. It can include the recommended value of the voltage - withstand test voltage of intermediate - frequency transformers under power - frequency conditions, which is derived from the breakdown - time data through statistical analysis and engineering experience and is used to guide the reasonable voltage value of the voltage - withstand test of intermediate - frequency transformers under power - frequency conditions; statistical analysis of the breakdown - time data of insulating materials under power - frequency and intermediate - frequency voltages to obtain the breakdown - time distribution law, such as Weibull distribution parameters, etc., reflecting the consistency of the voltage - withstand performance of insulating materials at different frequencies; directly comparing the average breakdown time, the shortest breakdown time, the longest breakdown time, etc. of insulating materials under power - frequency and intermediate - frequency voltages to intuitively present the influence of frequency change on the breakdown characteristics of insulating materials.

[0052] In this step, a high - precision and high - stability AC voltage source can be selected, which can output power - frequency and intermediate - frequency voltages respectively, and is equipped with an accurate timing device and a safe and reliable breakdown detection system. According to the actual use situation of the insulating material in the intermediate - frequency transformer, insulating material specimens with consistent shapes, sizes and properties are prepared, such as cylindrical specimens of oil - paper insulating materials, to ensure the uniformity and representativeness of the specimens. The experiment is carried out in a laboratory environment with constant temperature and humidity to avoid the influence of changes in environmental temperature and humidity on the experimental results. For example, the experimental temperature is controlled at 20℃±2℃, and the relative humidity is controlled at 50%±5%. The prepared insulating material specimens are respectively placed in the test circuits of power - frequency and intermediate - frequency voltages, and a gradually increasing voltage is applied, and the time when each specimen breaks down is recorded. The experiment is repeated multiple times to obtain a sufficient number of breakdown - time data for subsequent statistical analysis.

[0053] Systematically organize the obtained breakdown time data, establish data sets separately for power frequency and intermediate frequency, and use statistical analysis methods such as the Weibull distribution model to fit and analyze the breakdown time data to obtain the breakdown time distribution law and characteristic parameters of the insulating material at different frequencies. According to the breakdown time distribution law and characteristic parameters, combined with the actual operation requirements and safety margins of the intermediate frequency transformer, through mathematical models and engineering experience, deduce a reasonable voltage recommendation value for the withstand voltage test of the intermediate frequency transformer under power frequency voltage. This recommendation value should not only ensure the insulation safety of the transformer during intermediate frequency operation but also effectively avoid unnecessary damage to the insulating material caused by excessive test voltage.

[0054] It can be understood that obtaining the breakdown time data of the insulating material under power frequency voltage and intermediate frequency voltage and determining the first experimental result are to solve the problems of difficult generation of complex intermediate frequency voltage waveforms and unclear power frequency withstand voltage test standards in practical applications. By accurately obtaining the breakdown time data at different frequencies, the withstand voltage performance and breakdown characteristics of the insulating material under different frequency electric fields can be deeply understood, providing a scientific basis for formulating reasonable withstand voltage test standards. Determining the voltage recommendation value for the withstand voltage test in the first experimental result can provide a clear reference for the factory inspection and operation and maintenance of the intermediate frequency transformer, ensuring the insulation safety and reliability of the transformer during actual operation. At the same time, this process helps to optimize the experimental process, improve the test efficiency, reduce unnecessary experimental costs and resource waste, and has important engineering application value.

[0055] S102: Determine the partial discharge characteristics of the insulating material under power frequency voltage and intermediate frequency voltage, and determine the second experimental result according to the partial discharge characteristics. The second experimental result includes the partial discharge voltage ratio coefficient of the insulating material under power frequency voltage and intermediate frequency voltage.

[0056] Among them, the partial discharge characteristic refers to the characteristics of the discharge phenomenon that occurs in the local area inside or on the surface of the insulating medium due to the existence of weaknesses or defects inside the insulation under the action of an electric field, including apparent discharge amount, discharge repetition rate, average discharge current, discharge power, partial discharge inception voltage, extinction voltage, etc. The partial discharge voltage ratio coefficient refers to the voltage ratio corresponding to the same apparent discharge amount or discharge repetition rate and other partial discharge characteristics of the insulating material under power frequency voltage and intermediate frequency voltage.

[0057] The second experimental result focuses on the partial discharge characteristics of insulating materials under power frequency voltage and medium frequency voltage, which can include the partial discharge voltage ratio coefficient, representing the ratio of the partial discharge inception voltage or extinction voltage of the insulating material under power frequency voltage and medium frequency voltage, and is used to quantitatively characterize the differences in partial discharge characteristics at different frequencies; the voltage values when partial discharge starts and disappears in the insulating material under power frequency and medium frequency voltages, which are used to evaluate the partial discharge performance of the insulating material; the magnitude and change trend of the discharge quantity of partial discharge in the insulating material at different frequencies, reflecting the influence of frequency on the discharge intensity; and the distribution of partial discharge at different phase angles, which is of great significance for understanding the location and nature of internal defects in the insulating material.

[0058] In this step, representative insulating material samples can be selected from actual medium frequency transformers to ensure the uniformity and consistency of the samples, so as to guarantee the reliability of the experimental results. Build a professional electrical test platform, including high-precision voltage application equipment, accurate timing devices, and reliable insulation test fixtures, etc., to ensure the stability and safety of the test environment. Determine the specific test values of power frequency voltage and medium frequency voltage according to the actual application scenario, as well as the number of test samples under each voltage, so as to meet the requirements of statistical analysis.

[0059] After that, apply power frequency voltage and medium frequency voltage to each insulating material sample in turn, starting from a low voltage and gradually increasing it. At the same time, closely observe the state of the sample, and parameters such as the apparent discharge quantity, discharge repetition rate, average discharge current, discharge power, partial discharge inception voltage, and extinction voltage of each partial discharge can be recorded. This process is repeated multiple times to obtain enough data points to ensure the integrity and accuracy of the data. Organize and statistically analyze the recorded partial discharge characteristic data, and statistical parameters such as the average value and standard deviation can be calculated, and the relationship curve between partial discharge characteristics and voltage can be plotted to analyze its distribution law. Statistical models such as Weibull distribution can be used to fit the data to more accurately describe the partial discharge characteristics of the insulating material. According to the analysis results of the partial discharge characteristic data, the ratio of power frequency voltage to medium frequency voltage can be calculated under the same apparent discharge quantity or discharge repetition rate to obtain the partial discharge voltage ratio coefficient.

[0060] Furthermore, the determined partial discharge voltage ratio coefficient can be applied to the factory inspection of actual medium frequency transformers, and compared and verified with the traditional power frequency partial discharge test standard to observe whether the number and type of insulating defects detected under the new standard are more in line with the actual operation situation, so as to verify the rationality and effectiveness of the ratio coefficient. It is also possible to conduct long-term operation tracking on medium frequency transformers that pass the partial discharge test according to the new ratio coefficient, record their insulation performance changes and fault conditions during actual operation, and further verify the guarantee effect of the partial discharge voltage ratio coefficient on the long-term stable operation of the transformer.

[0061] It can be understood that by determining the partial discharge characteristics, the partial discharge behavior and laws of insulating materials under different frequency voltages can be deeply understood, thereby providing a scientific basis for the insulation design and operation and maintenance of medium-frequency transformers. Determining the partial discharge voltage proportionality coefficients under power frequency voltage and medium-frequency voltage can provide accurate reference standards for factory inspection and on-site testing, effectively improving the operation stability and reliability of medium-frequency transformers and avoiding equipment failures and operation risks caused by insufficient insulation performance.

[0062] S103: Determine the parametric change curves of each aging characteristic of the insulating material under power frequency voltage and medium-frequency voltage, and based on each parametric change curve, determine the third experimental result. The third experimental result includes the aging characteristic parametric change rate of the insulating material under medium-frequency voltage.

[0063] Among them, the aging characteristic parameter refers to the physical or chemical parameter used to characterize the aging degree of the insulating material. The aging characteristic parametric change curve refers to the curve of the aging characteristic parameter of the insulating material changing with time under power frequency voltage and medium-frequency voltage as the aging time increases, reflecting the aging trend and laws of the insulating material under different frequency voltages. The aging characteristic parametric change rate refers to the degree of change of each aging characteristic parameter of the insulating material with time under medium-frequency voltage, which can be expressed by the change amount of the parameter per unit time, reflecting the aging speed of the insulating material in the medium-frequency environment.

[0064] The third experimental result involves the parametric change curves and their change rates of each aging characteristic of the insulating material under power frequency voltage and medium-frequency voltage, and can include the aging characteristic parametric change rate, indicating the degree of change of each aging characteristic parameter of the insulating material with time under medium-frequency voltage, usually expressed by the change amount of the parameter per unit time; drawing the aging characteristic parametric change curves of the insulating material under power frequency and medium-frequency voltages in the same coordinate system, the comparison result of the power frequency and medium-frequency aging characteristic parametric change curves obtained can visually present the trends and differences of parametric changes at different frequencies; dividing the aging stages of the insulating material according to the characteristics of the parametric change curves and summarizing the characteristics of parametric changes in each stage helps to deeply understand the aging mechanism of the insulating material; based on the parametric change curves and change rates, establishing the parameters required for the life prediction model of the insulating material, such as characteristic parameter thresholds, aging rate constants, etc., provides a basis for the reliability assessment and life management of the equipment.

[0065] In this step, equipment such as a high-precision dielectric spectrometer and an insulation resistance tester can be used to accurately measure the aging characteristic parameters of insulating materials at different frequencies. The prepared insulating material specimens are respectively placed in the test circuits of power frequency and intermediate frequency voltages, voltages are applied according to relevant standards, and aging characteristic parameters such as insulation resistance, polarization index, absorption ratio, dielectric loss factor, and permittivity are regularly measured and recorded, and curves of the parameters changing with time are plotted. The obtained curves of the aging characteristic parameter changes are systematically sorted out, data sets are established respectively according to power frequency and intermediate frequency, and mathematical models and statistical analysis methods are used to fit and analyze the curves to obtain the rates and trends of the parameter changes. According to the slope of the parameter change curve or through calculation by a mathematical model, the aging characteristic parameter change rate of the insulating material under intermediate frequency voltage is obtained. This rate can quantitatively characterize the aging speed of the insulating material in the intermediate frequency environment and provide a basis for subsequent insulation performance evaluation and life prediction.

[0066] It can be understood that determining the parameter change curves of each aging characteristic of the insulating material under power frequency voltage and intermediate frequency voltage and determining the third experimental result based on each parameter change curve are for studying the insulation aging characteristics applicable to intermediate frequency conditions and solving the insulation material aging problem caused by intermediate frequency voltage. By accurately measuring and analyzing the parameter change curves of the aging characteristics of the insulating material at different frequencies, the aging trends and laws of the insulating material under electric fields of different frequencies can be deeply understood. Determining the aging characteristic parameter change rate can quantitatively characterize the aging speed of the insulating material in the intermediate frequency environment, provide a scientific basis for the reliability evaluation and life prediction of intermediate frequency transformers, help optimize the operation and maintenance strategies of equipment, improve the operation stability and reliability of equipment, reduce equipment failures and economic losses, and has important engineering application value.

[0067] S104: Generate a power frequency - intermediate frequency equivalent experimental report according to the first experimental result, the second experimental result, and the third experimental result.

[0068] Among them, the power frequency - intermediate frequency equivalent experimental report refers to a detailed document on the equivalence of insulation performance under power frequency and intermediate frequency voltages obtained through comprehensive analysis based on experimental results such as the breakdown time, partial discharge characteristics, and aging characteristic parameter changes of the insulating material under power frequency and intermediate frequency voltages. Its purpose is to provide a scientific basis for the insulation test, evaluation, and operation of intermediate frequency transformers to ensure the safety and reliability of the equipment at different frequencies.

[0069] It is understandable that generating a power frequency - intermediate frequency equivalent experimental report based on the first experimental result, the second experimental result, and the third experimental result is to systematically integrate and analyze the performance data of insulating materials at different frequencies, and to solve the problem of the lack of a unified standard for the insulation test and evaluation of intermediate frequency transformers. By comprehensively collecting and organizing experimental data, the integrity and accuracy of the report content can be ensured; building a reasonable report structure helps to clearly present the complex experimental process and results, facilitating readers' understanding and application; through detailed analysis and discussion of the experimental results, the performance differences and equivalent relationships of insulating materials under power frequency and intermediate frequency voltages can be deeply revealed, providing a scientific basis for the insulation design, test, and operation of intermediate frequency transformers. The finally generated experimental report can not only provide a reference for intermediate frequency transformer manufacturers to formulate reasonable factory inspection standards, but also guide the operation and maintenance personnel of the power system to conduct effective equipment management and fault prevention, thereby improving the overall operation stability and reliability of intermediate frequency transformers, reducing equipment failures and economic losses, and having significant engineering application value and economic benefits.

[0070] In the above - mentioned embodiment, the method obtains the breakdown time data of insulating materials under power frequency voltage and intermediate frequency voltage, determines the recommended value of the withstand voltage test voltage of the intermediate frequency transformer under power frequency voltage, solves the problems of difficult generation of complex intermediate frequency voltage waveforms and unclear power frequency withstand voltage test standards in practical applications, provides a clear reference basis for the withstand voltage test of intermediate frequency transformers, and improves the accuracy of insulation testing; by determining the partial discharge characteristics of insulating materials under power frequency voltage and intermediate frequency voltage, the partial discharge voltage ratio coefficient is obtained, solving the problem of insufficient basis for partial discharge measurement, making the partial discharge test more targeted and effective; by determining the parametric change curves of each aging characteristic of insulating materials under the two voltages, the aging characteristic parametric change rate under intermediate frequency voltage is obtained, which helps to study the insulation aging characteristics applicable to intermediate frequency conditions and provides data support for reliability assessment; the finally generated power frequency - intermediate frequency equivalent experimental report synthesizes the experimental results in multiple aspects such as breakdown time, partial discharge characteristics, and parametric changes of aging characteristics, establishes an equivalence model between power frequency and intermediate frequency environments, fills the blank of the current power frequency - intermediate frequency insulation equivalence experimental research, meets the requirements of equivalent standards in practical applications, improves the operation stability and reliability of intermediate frequency transformers, and has important engineering application value.

[0071] In one embodiment, the step of obtaining the breakdown time data of insulating materials under power frequency voltage and intermediate frequency voltage includes:

[0072] In a pre - built power frequency - intermediate frequency withstand voltage test platform, using the standard electrical strength test method for insulating materials, the breakdown time data of insulating materials under power frequency voltage and intermediate frequency voltage are obtained.

[0073] Among them, the power frequency - intermediate frequency withstand voltage test platform refers to special equipment and supporting facilities that can generate power frequency and intermediate frequency voltages and conduct withstand voltage tests on insulating materials, including high-precision voltage sources, transformers, voltage measuring instruments, breakdown detection devices, and safety protection devices, etc., which are used to simulate the actual operating conditions of insulating materials under voltages of different frequencies. The standard electrical strength test method for insulating materials refers to the electrical strength test methods for insulating materials specified in international, national, or industrial standards, including specific requirements such as specimen preparation, electrode design, voltage rise rate, withstand voltage time, breakdown judgment criteria, etc., to ensure the accuracy and comparability of test results.

[0074] Specifically, high-precision and high-stability power frequency and intermediate frequency voltage sources can be selected, equipped with appropriate transformers and voltage regulating devices to ensure that power frequency and intermediate frequency voltages within the required range can be output. At the same time, voltage measuring instruments and breakdown detection devices with relatively high accuracy levels are selected to ensure the reliability of data. Necessary safety protection devices, such as overcurrent protection, short-circuit protection, and grounding protection, are installed on the test platform to ensure the safety of operators and equipment during the test process. According to the requirements of the standard electrical strength test method for insulating materials, insulating material specimens with consistent shapes, sizes, and properties are prepared, such as circular or square thin sheet specimens, to ensure that the specimen surfaces are flat, defect-free, and have uniform thickness. The prepared specimens are installed between the electrodes of the test platform to ensure good contact between the specimens and the electrodes and avoid test result deviations caused by poor contact.

[0075] Gradually increase the power frequency voltage applied to the specimen at the voltage rise rate specified by the standard, and at the same time start the timing device to record the time. Closely monitor the breakdown situation of the specimen. Once the specimen breaks down, immediately stop increasing the voltage and record the breakdown time. Switch the voltage source of the test platform to the intermediate frequency mode, select an appropriate intermediate frequency, and repeat the steps of the power frequency voltage test to obtain the breakdown time data of the insulating material under the intermediate frequency voltage. Keep detailed records of the breakdown time data for each test, including information such as test date, time, environmental conditions, voltage frequency, voltage rise rate, breakdown time, etc. Organize the data in the form of a table or a database for subsequent statistical analysis.

[0076] In this embodiment, in the pre-built power frequency - intermediate frequency withstand voltage test platform, the breakdown time data of the insulating material under power frequency voltage and intermediate frequency voltage are obtained by using the standard electrical strength test method of insulating materials, in order to accurately evaluate the electrical strength of the insulating material under different frequency voltages and solve the problems of difficult generation of complex intermediate frequency voltage waveforms and unclear power frequency withstand voltage test standards in practical applications. By conducting experiments on a dedicated test platform according to the standard test method, the standardization and consistency of the test conditions can be ensured, and the accuracy and reliability of the breakdown time data can be improved. The obtained breakdown time data can provide a basis for determining the recommended value of the withstand voltage test voltage of the intermediate frequency transformer under power frequency voltage in the follow-up, help to formulate reasonable test standards, avoid errors in the evaluation of insulation performance caused by non-standard test methods or inaccurate data, thereby improving the operation stability and reliability of the intermediate frequency transformer, reducing equipment failures and economic losses, and having important engineering application value.

[0077] In one example, the relationship between the breakdown voltage and the withstand voltage time has the function of predicting the long-term operating insulation life of the insulation system under a given voltage, and the V-t characteristic of the solid insulating material can be represented by an inverse power function model:

[0078]

[0079] In the formula, is the breakdown voltage; is the withstand voltage time; is the aging life index; is the electrical strength constant.

[0080] According to the standard IEC 60243-1:2013 Electrical strength test methods for insulating materials - Part 1: Tests at power frequency, between the sphere - plate electrodes is a slightly non-uniform electric field, with both normal and tangential electric field components, used to simulate the actual electric field distribution received by the insulating paper in the intermediate frequency transformer. Therefore, a sphere - plate electrode is used to study the withstand voltage level and partial discharge parameters of the insulating material. The partial discharge parameters include the average discharge amplitude, the number of discharges per cycle, and the total discharge amplitude per cycle. The partial discharge characteristic parameters include kurtosis K, skewness S, and phase concentration F, and the calculation formulas are:

[0081]

[0082]

[0083]

[0084] In the formula, is the average value of the partial discharge amplitude; is the number of partial discharges; is the number of discharges in the i-th interval.

[0085] Kurtosis describes the distribution pattern of PD signals, obtaining the characteristics of the tail thickness and peak sharpness of the distribution; skewness describes the symmetry of the discharge signal, and the positive or negative of skewness represents the phase deviation of the discharge amplitude distribution; phase concentration describes the shape and phase distribution characteristics of the discharge signal, and is often used to judge different discharge types. The three are important statistical indicators for analyzing partial discharge signals and are used as characteristic parameters for evaluating the correlation between power frequency - intermediate frequency PD signals.

[0086] Build a power frequency and intermediate frequency withstand voltage test platform as Figure 2 shown. The spherical - plate electrode and the insulating paper are immersed in insulating oil to reduce the interference of factors such as air partial discharge. The insulating oil is No. 25 transformer oil from Karamay. The diameter of the spherical electrode is 20 mm, the thickness of the plate electrode is 10 mm, and the diameter is 75 mm. The electrode support is composed of transparent insulating plates, which is convenient for observing the changes of the specimen during the experiment. The power frequency power supply consists of a voltage regulating console and an experimental transformer, and the intermediate frequency source consists of an intermediate frequency high - voltage power supply, with a large - power current - limiting resistor in series.

[0087] Use an ETS - 93686 type high - frequency pulse current sensor with a bandwidth of 10 kHz - 100 MHz to collect partial discharge signals; the oscilloscope is used to display and record PD signals. The thickness of the insulating paper is 0.5 mm. Before the experiment, it is wiped with absolute alcohol and placed in a vacuum drying oven at 70 °C for 24 h to remove surface moisture. The improved VMD algorithm is used to decompose the PD signal, the Equilibrium Optimizer (EO) algorithm is used to optimize the decomposition number K and the penalty factor α, and the kurtosis criterion is used to determine the effective components. The wavelet threshold denoising is used for the reconstructed signal to further remove the residual white noise.

[0088] According to the national standard GB / T1408.1 - 2016 Electrical strength test method for insulating materials, during the withstand voltage test, the ambient temperature is maintained at room temperature of 25 °C, the ambient relative humidity is 20%. The short - time breakdown voltage Us of the insulating paper is measured by the uniform voltage - rising method, the voltage - rising rate is set at 0.5 kV / s, and 70%Us - 95%Us is selected as the applied voltage value. The breakdown time data of the insulating paper material at power frequency (50 Hz) and intermediate frequency (100 - 200 Hz) are obtained through constant - voltage experiments, and the V - t curve of breakdown voltage and withstand voltage time is drawn as Figure 3 shown.

[0089] In one embodiment, the expression for the recommended value of the withstand voltage test voltage of the intermediate - frequency transformer under power - frequency voltage is:

[0090]

[0091] where, is the recommended value of the withstand voltage test voltage of the intermediate - frequency transformer under power - frequency voltage, is the intermediate - frequency / power - frequency conversion coefficient, It is the voltage value of the 1-minute withstand voltage test of the intermediate-frequency transformer under the intermediate-frequency voltage.

[0092] In this embodiment, this formula is used to calculate the recommended voltage value of the withstand voltage test of the intermediate-frequency transformer under the power-frequency voltage. , where p is the intermediate-frequency / power-frequency conversion coefficient. represents the voltage value of the 1-minute withstand voltage test of the intermediate-frequency transformer under the intermediate-frequency voltage. By multiplying the withstand voltage test value under the intermediate-frequency voltage by the conversion coefficient, this formula obtains the recommended value of the withstand voltage test applicable to the power-frequency voltage, which helps to formulate reasonable test standards, ensure the accurate and reliable evaluation of the insulation performance of the intermediate-frequency transformer at different frequencies, and thus improve its operation stability and safety.

[0093] In one example, from Figure 3 it can be seen that as the frequency of the applied voltage increases, the breakdown voltage of the insulating paper film decreases, and the breakdown voltages are 5.65 kV, 5.30 kV, 4.89 kV, and 4.21 kV respectively. The V-t expressions of the insulating paper under power frequency and intermediate frequency are shown in the following table:

[0094]

[0095] Among them, V0 better corresponds to the experimentally measured breakdown voltage, and the aging life index n reflects the rate of change of the withstand voltage performance with time. It can be seen from the table that the aging life index increases as the voltage frequency increases, indicating that the rate of decrease of the breakdown voltage with time is faster, and the aging process of the insulating paper film is more significant as the voltage frequency increases. According to the national standard GB / T 1094.3-2017 Power Transformers - Part 3: Insulation Levels, Insulation Tests and External Clearances in Air, the applied voltage withstand test is to verify the AC voltage withstand strength of the winding insulation. During the test, all terminals of the other windings are grounded, the waveform of the withstand voltage test is a single-phase AC voltage as close as possible to a sine wave, and the pressurization time is 1 minute.

[0096] Therefore, based on the V-t characteristics of the insulating material under sinusoidal power frequency and intermediate frequency voltages under the spherical-plate electrode model, the 1-minute withstand voltage levels of the insulating material under power frequency and intermediate frequency are obtained, the experimental voltage power-frequency-intermediate frequency equivalent coefficient p is proposed, and the recommended value of the short-time withstand voltage test of the power-frequency insulation test of the intermediate-frequency transformer is obtained.

[0097]

[0098]

[0099]

[0100] In the formula, is the 1-minute withstand voltage value of the insulating material under the intermediate-frequency voltage; is the 1-minute withstand voltage value of the material at power frequency; p is the conversion coefficient between intermediate frequency and power frequency, is the withstand voltage value corresponding to the expected service life; is the highest voltage of the intermediate frequency transformer equipment; is the 1-minute withstand voltage test voltage value of the intermediate frequency transformer under intermediate frequency conditions; is the recommended test voltage value of the withstand voltage test of the intermediate frequency transformer under power frequency conditions; k is the standard coefficient of the withstand voltage test of the power frequency transformer, which mainly depends on the insulation level and design standard of the equipment, and the value is usually between 1.5 and 2.5.

[0101] Use the ratio of the 1-minute withstand voltage value of the insulating material to the withstand voltage corresponding to the expected service life of 20 years as the standard coefficient k of the intermediate frequency transformer under intermediate frequency. The range of k is between 1.48 and 1.80 in the range of 100Hz - 200Hz, and it increases with the increase of the frequency of the applied voltage. The increase of the voltage frequency shortens the insulation life of the insulating material, so a greater requirement for the insulation margin is needed, and the withstand voltage ability under intermediate frequency is much less than that under power frequency. Therefore, the standard coefficient k under intermediate frequency conditions is less than that under power frequency conditions. The intermediate frequency / power frequency conversion coefficient p shows an upward trend with the increase of frequency. At this time, for the recommended value of the withstand voltage test of the intermediate frequency transformer under power frequency conditions, at 100Hz, 150Hz, and 200Hz are 1.10, 1.17, and 1.41 times the highest operating voltage respectively.

[0102] In one embodiment, the steps to determine the partial discharge characteristics of the insulating material under power frequency voltage and intermediate frequency voltage include:

[0103] Under the pre-determined highest voltage reference value and partial discharge voltage, obtain the partial discharge parameters of the insulating material under power frequency voltage and intermediate frequency voltage. The partial discharge parameters include kurtosis, skewness, and phase concentration;

[0104] Determine the partial discharge characteristics according to the change trend of the partial discharge parameters with the voltage frequency.

[0105] Among them, the partial discharge parameters are parameters used to describe and characterize the partial discharge characteristics, including kurtosis, skewness, and phase concentration, etc. These parameters can reflect information such as the intensity, stability, and location of internal discharge in the insulating material. Kurtosis is used to describe the sharpness of the partial discharge pulse amplitude distribution. The larger the kurtosis value, the more abnormal high-amplitude pulses exist in the discharge pulse. Skewness reflects the symmetry of the partial discharge pulse amplitude distribution. Positive skewness indicates the existence of more large positive pulses, and negative skewness is the opposite. Phase concentration measures the concentration degree of partial discharge pulses appearing in a specific phase interval within the voltage cycle. The higher the concentration, the more likely the discharge is to occur at a specific phase.

[0106] Specifically, on a pre-built power frequency - intermediate frequency withstand voltage test platform, ensure the normal operation of equipment such as voltage sources and partial discharge detectors, calibrate the equipment parameters, and set appropriate ranges and precisions. Install the insulating material specimen to be tested on the test fixture, ensure good contact between the specimen and the electrode, and avoid affecting the test results due to poor contact. Conduct the experiment in a laboratory environment with constant temperature and humidity to reduce the influence of environmental factors on the experimental results. For example, control the temperature at 25°C ± 2°C and the relative humidity at 50% ± 5%.

[0107] Under the pre-determined maximum voltage reference value and partial discharge voltage, apply a power frequency voltage to the insulating material, use a partial discharge detector to collect partial discharge parameters, including kurtosis, skewness, and phase concentration, and record the data. Switch the voltage source of the test platform to the intermediate frequency mode, select an appropriate intermediate frequency, such as 100 Hz, 200 Hz, etc., apply an intermediate frequency voltage to the insulating material under the same maximum voltage reference value and partial discharge voltage, and collect and record the partial discharge parameters. Store the collected partial discharge parameter data in a computer or storage device for subsequent data processing and analysis.

[0108] Conduct statistical analysis and curve fitting on the collected partial discharge parameter data, plot the trend curve of the parameters changing with the voltage frequency, and analyze the characteristics and variation laws of the curve. According to the parameter variation trend curve, evaluate the partial discharge characteristics of the insulating material under power frequency and intermediate frequency voltages, judge the discharge behavior and insulation performance differences of the insulating material at different frequencies, and provide a basis for subsequent insulation performance evaluation and equipment design.

[0109] In this embodiment, by obtaining parameters under standardized experimental conditions, the characteristic information of internal discharge of the insulating material can be accurately captured, providing a quantitative basis for the evaluation of insulation performance. Analyzing the variation trend of the parameters with frequency can reveal the discharge laws of the insulating material under power frequency and intermediate frequency, which helps to optimize the insulation design of intermediate frequency transformers, formulate reasonable test standards and operation and maintenance strategies, improve the operation stability and reliability of equipment, reduce economic losses and safety accidents caused by insulation failures, and has significant engineering application value and economic benefits.

[0110] In one example, according to the standard GB1094.3 - 2017 "Power Transformers - Part 3: Insulation Levels, Insulation Tests and External Clearances in Air", for the measurement of PD levels, select a voltage for partial discharge measurement, and the measurement time is 300 s. According to the test results of the V - t characteristics of the insulating material, use the withstand voltage value corresponding to the expected service life of 20 years as the reference U m , and conduct partial discharge measurement under. As Figure 4The figure shows the variation trends of partial discharge parameters at different frequencies corresponding to the withstand voltage values. As shown in the figure, with the increase of the voltage frequency, the kurtosis, skewness, and phase concentration all increase, showing the centralization and sharpening of discharges caused by the increase in frequency.

[0111] In one embodiment, the expression for the partial discharge voltage proportionality coefficient of the insulating material under power frequency voltage and intermediate frequency voltage is:

[0112]

[0113] where is the partial discharge voltage proportionality coefficient, , are the withstand voltage values corresponding to the expected service life of the insulating material under power frequency voltage and intermediate frequency voltage respectively.

[0114] In this embodiment, this formula is used to calculate the partial discharge voltage proportionality coefficient of the insulating material under power frequency voltage and intermediate frequency voltage , where is the withstand voltage value corresponding to the expected service life of the insulating material under power frequency voltage, is the withstand voltage value corresponding to the expected service life of the insulating material under intermediate frequency voltage. By dividing the withstand voltage value under intermediate frequency voltage by the withstand voltage value under power frequency voltage, the obtained proportionality coefficient can quantitatively characterize the difference in partial discharge characteristics of the insulating material at two frequencies, provide a basis for the insulation test and evaluation of intermediate frequency transformers, and help formulate reasonable test standards and operation and maintenance strategies to ensure the operation stability and reliability of the equipment.

[0115] In an example, according to the test results of the V-t characteristics of the insulating material, the withstand voltage value corresponding to the expected service life of 20 years is used as the reference U m , and partial discharge measurements are carried out under to obtain the power frequency - intermediate frequency partial discharge test voltage proportionality coefficient :

[0116]

[0117]

[0118] In the formula, is the recommended value of the partial discharge test voltage of the intermediate frequency transformer under power frequency conditions; , are the withstand voltage values corresponding to the expected service life of the material under power frequency and intermediate frequency respectively.

[0119] In one embodiment, the steps to determine the parametric change curves of each aging characteristic of the insulating material under power frequency voltage and intermediate frequency voltage include:

[0120] Obtain the parameters of each aging characteristic of the insulating material under power frequency voltage and medium frequency voltage, as well as different aging times. The aging characteristics include acid value, micro water content, dissolved gas content, and furfural content;

[0121] According to the variation law of the parameters of each aging characteristic, fit the parameters of each aging characteristic to obtain the parameter variation curve of each.

[0122] Among them, the aging characteristics include acid value, micro water content, dissolved gas content, and furfural content, etc.

[0123] Specifically, under power frequency voltage, the insulating material is subjected to different aging time treatments, and its acid value, micro water content, dissolved gas content, and furfural content are measured respectively. Switch the voltage source of the test platform to the medium frequency mode, select a suitable medium frequency, apply the same aging time treatment to the insulating material, and measure the above aging characteristic parameters. Record in detail the data of the aging characteristic parameters obtained each time, including information such as experimental conditions, time, and voltage frequency. Organize the obtained data of the aging characteristic parameters in chronological order, respectively for the data under power frequency and medium frequency voltages. Use mathematical models and fitting algorithms to fit the data of each aging characteristic parameter to obtain the curve of the parameter changing with time. Commonly used fitting methods include linear regression, polynomial fitting, exponential fitting, etc., and select a suitable fitting model according to the characteristics of the data. Analyze the obtained parameter variation curve, observe the characteristics of the curve shape, slope, etc., to understand the aging law of the insulating material under different voltage frequencies.

[0124] In this embodiment, by accurately measuring and analyzing the aging characteristic parameters, the aging degree of the insulating material can be quantitatively characterized, providing a scientific basis for the reliability assessment and life prediction of the medium frequency transformer. This process helps to optimize the operation and maintenance strategies of the equipment, detect potential insulation faults in advance, reduce equipment failures and economic losses, and improve the overall operation stability and safety of the medium frequency transformer, having significant engineering application value and economic benefits.

[0125] In an example, the acid value of the sample refers to the mass of potassium hydroxide (KOH) required to neutralize the acidic components per gram of oil, and it is determined according to the standard of GB 7599-1987 "Method for Determining Acid Value of Transformer Oil and Turbine Oil in Operation". The determination of the micro water content is carried out according to GB / T 7600-2014 "Method for Determining Water Content in Transformer Oil and Turbine Oil in Operation". The determination of the dissolved gas content is completed by gas chromatography equipment, which can measure the content of characteristic gases such as dissolved in the oil. The experiment measures the gas components and content according to DL / T 722-2000 "Guide for Analysis and Judgment of Dissolved Gases in Transformers" and calculates to obtain The numerical change. In addition, the furfural content in the oil was detected using a Waters 1525 liquid chromatograph.

[0126] In one embodiment, for the acid value and the furfural content, the expression of the corresponding parameter change curve is:

[0127]

[0128] Where, is the change rate of the aging characteristic parameter, is the first aging rate constant, is the initial value of the aging characteristic quantity, is the saturation point.

[0129] In this embodiment, as Figure 5 and Figure 6 shown, the change curves of the sample acid value and furfural content at different frequencies fit the exponential function model. Therefore, the acid value and furfural content are curve-fitted to obtain their corresponding change curve parameters, indicating that the aging characteristic parameter shows a trend of first fast and then slow with the increase of time, and finally approaches the saturation point . By experimentally measuring the values of the aging characteristic parameters at different time points, this curve can be fitted, and then the parameters , and in the formula can be determined, so as to quantitatively describe the aging process of the insulating material and provide a basis for evaluating the material life and formulating maintenance strategies. Among them, the first aging rate constant is related to temperature, the initial state of oil-paper, etc.

[0130] In one embodiment, for the micro water content and the dissolved gas content, the expression of the corresponding parameter change curve is:

[0131]

[0132] Where, is the change rate of the aging characteristic parameter, is the initial value of the aging characteristic quantity, is the second aging rate constant, is the power exponent.

[0133] In this embodiment, as Figure 7 and Figure 8 shown, the sample and the micro water content are more suitable for the power function model. Therefore, and the micro water content are curve-fitted to obtain their corresponding change curve parameters, indicating that the change of the aging characteristic parameter with time may show linear or non-linear characteristics, specifically depending on the power exponent Values. By experimentally measuring the values of the aging characteristic parameters at different time points, this curve can be fitted, and then the parameters in the formula can be determined. , and , so as to quantitatively describe the aging process of the insulating material and provide a basis for evaluating the material life and formulating maintenance strategies. Among them, the second aging rate constant is related to temperature, the initial state of oil-paper, etc.

[0134] In one embodiment, the expression for the change rate of the aging characteristic parameters of the insulating material under medium-frequency voltage is:

[0135]

[0136] where is the change rate of the aging characteristic parameters under medium-frequency conditions, is the frequency effect factor, is the change rate of the aging characteristic parameters under power-frequency conditions.

[0137] In this embodiment, this formula indicates that under medium-frequency voltage, the change rate of the aging characteristic parameters of the insulating material is the product of the change rate under power-frequency conditions and the frequency effect factor. Through this formula, the influence of frequency change on the aging process of the insulating material can be quantitatively evaluated, providing an important basis for the insulation design, life prediction, and maintenance strategy formulation of medium-frequency transformers.

[0138] In one embodiment, the expression for the frequency effect factor is:

[0139]

[0140] where is the frequency effect factor, is the frequency response coefficient, reflecting the sensitivity of medium frequency to the change of specific parameters, , are the test frequency and the reference 50Hz power frequency.

[0141] In this embodiment, different insulating materials and aging characteristic parameters may have different values. By experimental determination, that is, aging the insulating material at different frequencies, measuring the change rate of its aging characteristic parameters, and then determining by methods such as curve fitting. By calculating the frequency effect factor , the change rate of the aging characteristic parameters under power-frequency conditions can be converted into the change rate under medium-frequency conditions, so as to more accurately evaluate the insulation performance and life of medium-frequency transformers.

[0142] Through the tests on the breakdown voltage and withstand voltage time characteristics of the insulating paper material at different frequencies, the V-t characteristic curve was analyzed. The results show that as the voltage frequency increases, the breakdown voltage of the insulating material decreases, and the aging life index increases with the increase of frequency, and the withstand voltage ability decreases significantly. Based on the experimental data, the equivalent coefficient of the withstand voltage test under power frequency and medium frequency conditions was proposed, providing standard suggestions for the withstand voltage test of medium frequency transformers. Regarding the partial discharge characteristics, the withstand voltage values corresponding to the expected service life under power frequency and medium frequency were used to determine the proportional coefficient of the partial discharge test voltage, and the influence law of the frequency increase on the partial discharge parameters (such as kurtosis, skewness, phase concentration) was studied. The results show that the discharge behavior is more centralized and sharp under high frequency conditions; in the study of aging characteristics, the main aging parameters of oil-paper insulation (acid value, micro water content, dissolved gas content and furfural content) were tested. Through curve fitting, it was clear that the changes of acid value and furfural content with time are suitable for the exponential model, while the ratio and micro water content are more suitable for the power function model. Further introducing the frequency effect factor, the accelerating effect of the electric field frequency on the change of aging characteristics was revealed, and a rate model applicable to the change of aging characteristics under medium frequency conditions was established. These research results provide an important theoretical basis for the insulation performance evaluation and design of medium frequency electrical equipment, and at the same time clarify the acceleration mechanism of the aging process and its frequency dependence.

[0143] Finally, it should also be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the element. In this article, "a", "an", "the", "this" and "its" may also include the plural form, unless the context clearly indicates otherwise. More than one means at least two cases, such as 2, 3, 5 or 8, etc. "And / or" includes any and all combinations of the related listed items.

[0144] The various embodiments in this specification are described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0145] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A power frequency-medium frequency equivalent test method based on the withstand voltage and aging characteristics of insulating materials, characterized in that: The method comprises: Obtaining breakdown time data of the insulating material under power frequency voltage and medium frequency voltage, and determining a first experimental result based on the breakdown time data, wherein the first experimental result includes a recommended value of a withstand voltage test voltage of a medium frequency transformer under power frequency voltage; Determine the partial discharge characteristics of the insulating material under power frequency voltage and medium frequency voltage, and determine a second experimental result based on the partial discharge characteristics, wherein the second experimental result includes a partial discharge voltage proportional coefficient of the insulating material under power frequency voltage and medium frequency voltage; Determine a parameter change curve of each aging characteristic of the insulating material under power frequency voltage and medium frequency voltage, and determine a third experimental result according to each parameter change curve, wherein the third experimental result includes a parameter change rate of the aging characteristic of the insulating material under medium frequency voltage; A power frequency-medium frequency equivalent experiment report is generated according to the first experiment result, the second experiment result and the third experiment result.

2. The power frequency-medium frequency equivalent test method based on the withstand voltage and aging characteristics of insulating materials according to claim 1 is characterized in that: The step of obtaining the breakdown time data of the insulating material under power frequency voltage and medium frequency voltage comprises: In a pre-built power frequency-medium frequency withstand voltage test platform, a standard insulating material electrical strength test method is used to obtain the breakdown time data of the insulating material under power frequency voltage and medium frequency voltage.

3. The power frequency-medium frequency equivalent test method based on the withstand voltage and aging characteristics of insulating materials according to claim 1 is characterized in that: The expression for the recommended value of the withstand voltage test voltage of the medium frequency transformer under power frequency voltage is: in, It is the recommended value of the test voltage for the medium frequency transformer withstand voltage test under power frequency voltage. is the medium frequency / power frequency conversion factor, It is the 1-minute withstand voltage test voltage value of the medium frequency transformer under medium frequency voltage.

4. The power frequency-medium frequency equivalent test method based on the withstand voltage and aging characteristics of insulating materials according to claim 1 is characterized in that: The step of determining the partial discharge characteristics of the insulating material under power frequency voltage and medium frequency voltage comprises: Under a predetermined maximum voltage reference value and a partial discharge voltage, obtaining partial discharge parameters of the insulating material under power frequency voltage and medium frequency voltage, wherein the partial discharge parameters include kurtosis, skewness and phase concentration; The partial discharge characteristic is determined according to the variation trend of the partial discharge parameter with the voltage frequency.

5. The power frequency-medium frequency equivalent test method based on the withstand voltage and aging characteristics of insulating materials according to claim 1 is characterized in that: The expression of the partial discharge voltage proportional coefficient of the insulating material under power frequency voltage and medium frequency voltage is: in, is the partial discharge voltage proportionality coefficient, , They are the withstand voltage values ​​corresponding to the expected service life of the insulation materials under power frequency voltage and medium frequency voltage respectively.

6. The power frequency-medium frequency equivalent test method based on the withstand voltage and aging characteristics of insulating materials according to claim 1 is characterized in that: The step of determining the parameter variation curve of each aging characteristic of the insulating material under power frequency voltage and medium frequency voltage comprises: Obtaining parameters of each aging characteristic of the insulating material under power frequency voltage and medium frequency voltage and different aging times, wherein the aging characteristics include acid value, trace water content, dissolved gas content and furfural content; According to the parameter variation law of each aging characteristic, the parameter of each aging characteristic is fitted to obtain each parameter variation curve.

7. The power frequency-medium frequency equivalent test method based on the withstand voltage and aging characteristics of insulating materials according to claim 6 is characterized in that: For the acid value and the furfural content, the corresponding parameter change curve expression is: in, is the change rate of the aging characteristic parameter, is the first aging rate constant, is the initial value of the aging characteristic, is the saturation point.

8. The power frequency-medium frequency equivalent test method based on the withstand voltage and aging characteristics of insulating materials according to claim 6 is characterized in that: For the trace water content and the dissolved gas content, the corresponding parameter change curve expression is: in, is the change rate of the aging characteristic parameter, is the initial value of the aging characteristic, is the second aging rate constant, is the power index.

9. The power frequency-medium frequency equivalent test method based on the withstand voltage and aging characteristics of insulating materials according to claim 1 is characterized in that: The expression of the change rate of the aging characteristic parameter of the insulating material under medium frequency voltage is: in, is the changing rate of the aging characteristic parameters under medium frequency conditions, is the frequency effect factor, is the rate of change of the aging characteristic parameters under power frequency conditions.

10. The power frequency-medium frequency equivalent test method based on the withstand voltage and aging characteristics of insulating materials according to claim 9 is characterized in that: The expression of the frequency effect factor is: in, is the frequency effect factor, is the frequency response coefficient, which reflects the sensitivity of the intermediate frequency to changes in specific parameters. , The test frequency is the same as the reference 50Hz power frequency.

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