An insulation sample superimposed harmonic electric heat aging test device, method and equipment

Abstract

This invention relates to the field of electrothermal aging life testing technology for insulating materials, and in particular to an electrothermal aging test device, method, and equipment for superimposed harmonics on insulating samples. It is applicable to insulating samples and includes an insulating oil tank filled with insulating oil for immersing the insulating sample in the oil; an oil bath heating device for adjusting the temperature of the insulating oil to keep the insulating sample operating within a preset test temperature range; a power frequency voltage source for applying a preset power frequency electrical stress to the insulating sample; a high frequency voltage source for applying a preset high frequency harmonic electrical stress to the insulating sample; and a protective capacitor for blocking the power frequency voltage source and the high frequency voltage source. Utilizing the higher breakdown field strength and arc-extinguishing capability of the insulating oil compared to air, it avoids corona discharge phenomena generated in air under AC high voltage and high frequency harmonic voltage. The combination of the power frequency voltage source and the high frequency voltage source reproduces the composite electrothermal stress characteristics and high-temperature operating environment experienced by insulating materials in actual power scenarios.

Description

Technical Field

[0001] This invention relates to the field of electrothermal aging life testing technology for insulating materials, and in particular to an electrothermal aging testing device, method and equipment for superimposed harmonics on insulating samples. Background Technology

[0002] Currently, electrical aging tests on insulation materials are generally conducted only under a 50 Hz power frequency voltage condition. However, with the continuous growth of grid-connected capacity of new energy sources such as wind and solar power, power electronic conversion devices with IGBTs as their core are widely used in the power grid. These devices achieve power conversion through high-frequency pulse width modulation. The high-speed switching action of IGBTs introduces abundant high-order harmonics into the system, with their main spectral components concentrated around 10 kHz. Therefore, AC cable insulation used in new energy grid connection not only withstands the fundamental power frequency voltage in actual operation but also endures the superposition effect of high-frequency harmonic voltages with a frequency of approximately 10 kHz for extended periods.

[0003] Numerous studies have shown that high-frequency harmonic voltages have a significant accelerating effect on the aging process of insulating materials. They can exacerbate partial discharge activity, increase dielectric loss heating, and promote the injection and accumulation of space charge, thus accelerating the aging of insulating materials under the long-term effects of electro-thermal stress and charge effects. Furthermore, in the enclosed spaces of distribution cabinets or cable trenches, the heat from insulating materials is difficult to dissipate. Ultimately, under the combined effects of poor environmental heat dissipation and high-frequency harmonic electro-thermal stress, localized high-temperature hotspots are formed, accelerating the aging of insulating materials under high temperature and high field strength conditions. Therefore, relying solely on power frequency electrical aging tests cannot accurately reproduce the composite electro-thermal stress characteristics and high-temperature conditions experienced by cable insulation under new energy grid connection conditions, and the test results are insufficient to effectively assess the insulation aging life under actual operating conditions.

[0004] Existing electrical aging tests for insulating materials are typically conducted in ambient air at room temperature. Under alternating current, the initial field strength of corona discharge in air is often less than 3 kV / mm. However, to perform electrical aging tests by superimposing high-frequency harmonic voltages, a higher voltage needs to be applied, resulting in a very high electric field strength in the electrode area. During the test, the sample will be quickly burned through by the arc induced by the corona discharge. Since the test voltage and temperature cannot reproduce the combined electro-thermal stress characteristics and high-temperature conditions experienced by the insulating material in actual scenarios, the sample will be damaged. Summary of the Invention

[0005] The present invention aims to provide an electrothermal aging test device, method and equipment for superimposed harmonics on insulating samples, in order to reproduce the composite electrothermal stress characteristics and high temperature conditions that insulating materials are subjected to in actual power scenarios, and to test the electrothermal aging life of insulating materials, so that the test process is closer to the working conditions of the new energy grid-connected scenario of insulating cables, thereby improving the effectiveness of the insulation material life test results.

[0006] To achieve the above objectives, a first aspect of the present invention provides an electrothermal aging test apparatus for insulating samples with superimposed harmonics, suitable for insulating samples, comprising: An insulating oil tank, the insulating oil tank being filled with insulating oil, is used to immerse the insulating sample in the insulating oil; An oil bath heating device is used to regulate the temperature of the insulating oil so that the insulating sample is within a preset test temperature range; A power frequency voltage source is used to apply a preset power frequency electrical stress to the insulating sample. A high-frequency voltage source is used to apply a preset high-frequency harmonic electrical stress to the insulating sample. A protective capacitor is used to block the power frequency voltage source and the high frequency voltage source; The host computer is used to determine the various test indicators, and then to conduct an electrothermal aging test on the insulation sample under the conditions of the test temperature range, the power frequency electric stress and the high frequency harmonic electric stress, so as to obtain the test data of the various test indicators.

[0007] The aforementioned electrothermal aging test apparatus for superimposed harmonics on insulating samples immerses the insulating sample in insulating oil within an insulated oil tank. Utilizing the higher breakdown field strength and arc-extinguishing capability of the insulating oil compared to air, it avoids the corona discharge phenomenon that occurs in air under AC high voltage and high-frequency harmonic voltages. This allows the sample to withstand the superimposed voltage of power frequency and high-frequency harmonics in an insulating oil environment without being directly burned through. Simultaneously, the oil bath heating device can regulate the temperature of the insulating oil, thus creating a preset high-temperature test environment for the insulating sample. To enable the power frequency voltage source and high-frequency voltage source to work collaboratively, preset power frequency electrical stress and high-frequency harmonic electrical stress are applied to the insulating material, respectively, simulating the composite electrical stress characteristics of the fundamental wave and higher harmonics superimposed on cable insulation under new energy grid connection scenarios. A protective capacitor is connected in series in the circuit to block mutual interference between the power frequency voltage source and the high-frequency voltage source, preventing high-frequency harmonic current from flowing back into the power frequency power supply or the power frequency current from affecting the high-frequency power supply output. Ultimately, through the coordinated operation of the aforementioned components, this invention can reproduce the composite electrothermal stress characteristics and high-temperature working environment experienced by insulating materials in actual power scenarios, preventing premature damage to the samples due to air corona discharge, making the test process closer to actual working conditions, and significantly improving the effectiveness and accuracy of the electrothermal aging life test results of insulating materials.

[0008] Furthermore, the oil bath heating device is equipped with an oil bath pot and an oil pump, and the oil bath heating device is connected to the insulated oil tank through several oil inlets and several oil outlets; wherein: The oil bath receives insulating oil flowing from the insulated oil tank through the oil inlet, and then adjusts the temperature of the insulating oil before pumping it back to the insulated oil tank from the oil outlet through the oil pump.

[0009] In this implementation, the oil bath heating device introduces insulating oil from the top of the insulated oil tank through the oil inlet. After being heated in the oil bath, the oil is pressurized by the oil pump and then returned to the insulated oil tank through multiple oil outlets located at the bottom. The evenly distributed layout of multiple oil outlets distributes the hot oil flow, reducing the flow velocity at individual outlets, preventing direct impact of the oil flow on the sample, avoiding sample drift and electrode slippage, and simultaneously ensuring a more uniform temperature distribution. This prevents excessively high local temperatures in the oil tank caused by a single outlet, improving the uniformity of oil temperature and heating efficiency within the tank.

[0010] Furthermore, the heat-insulating oil tank is equipped with a high-voltage electrode and a low-voltage electrode. The insulating sample is electrically connected to the power frequency voltage source and the high-frequency voltage source through the high-voltage electrode, and the insulating sample is grounded through the low-voltage electrode. The insulating sample is located above the low-voltage electrode, and the oil outlet is located below the low-voltage electrode so that the low-voltage electrode protects the insulating sample from the impact of hot oil flowing out of the oil outlet.

[0011] In this implementation, when heating the insulating oil for high-temperature electrical aging testing, an oil pump is needed to circulate the oil flow to maintain temperature uniformity within the tank. However, the circulating oil flow can easily cause mechanical disturbances, leading to mechanical drift of the sample, which in turn can cause distortion of the electric field between electrodes or even flashover, resulting in test failure. To mitigate the mechanical impact of the circulating oil bath on the sample, this invention places the oil outlet below the low-voltage electrode and uses a large-area low-voltage plate as a shielding and guiding structure. This allows the circulating high-temperature insulating oil to first impact the bottom surface of the low-voltage plate, and then rise smoothly after being buffered and guided by the plate. This reduces the direct scouring force of the oil on the sample, ensuring sample stability. Simultaneously, the low-voltage plate itself provides excellent flow guidance and equalization, creating a gentle laminar flow above the plate, preventing flashover and sample drift caused by oil flow disturbances, and improving test stability.

[0012] Furthermore, the oil bath heating device is equipped with a temperature measuring thermocouple, which is in contact with the low-pressure electrode to obtain the electrode temperature of the low-pressure electrode; the oil bath adjusts the temperature of the insulating oil based on the electrode temperature to maintain the electrode temperature within a preset test temperature range, thereby enabling the insulating sample to operate within the preset test temperature range.

[0013] In this implementation, the thermocouple is in direct contact with the low-voltage electrode, and the electrode temperature is detected in real time and used as a feedback signal for temperature control. Since the insulating sample is placed in close contact with the low-voltage electrode, the electrode temperature reflects the actual temperature the sample is subjected to. The oil bath adjusts the heating power according to the deviation between the electrode temperature and the preset temperature, so that the electrode temperature is stably maintained within the preset test temperature range. This ensures that the insulating sample is always in a controlled high-temperature environment throughout the test, improving the accuracy of the aging test results.

[0014] Furthermore, the insulating oil is silicone oil.

[0015] It should be noted that in long-term high-temperature electrothermal aging tests, if mineral insulating oil is used, the insulating sample easily absorbs a large amount of oil and swells, leading to significant changes in sample size and shape, thus distorting the test results. In this implementation method, silicone oil is selected as the insulating oil. Compared to traditional mineral insulating oil, low-viscosity silicone oil has excellent thermal conductivity, high chemical stability, and a lower oil absorption rate for commonly used cable insulation materials such as cross-linked polyethylene. Using silicone oil can effectively suppress the swelling and deformation of the sample at high temperatures, maintaining the stability of the sample's geometric dimensions and shape. Simultaneously, the low viscosity of silicone oil facilitates oil bath circulation, and combined with the aforementioned oil outlet layout, it can create a more uniform temperature field within the oil tank, reducing the mechanical interference of the oil flow on the sample, thereby ensuring the authenticity and validity of the electrothermal aging life test results for the insulating material.

[0016] Furthermore, the electrothermal aging test device for superimposed harmonics on an insulating sample is provided with a protective resistor, wherein: the insulating sample is electrically connected to the first end of the high-voltage electrode, the second end of the high-voltage electrode is electrically connected to the first end of the protective resistor, the second end of the protective resistor is electrically connected to the output end of the power frequency voltage source and the first end of the protective capacitor, and the second end of the protective capacitor is electrically connected to the output end of the high-frequency voltage source.

[0017] In this implementation, when the insulation sample breaks down or the test circuit experiences an unexpected short circuit during the test, the protective resistor can limit the amplitude of the discharge current, reduce the arc energy generated at the moment of the short circuit, prevent the generation of a large short circuit current that could impact the power frequency voltage source and the high frequency voltage source, avoid damage to the high voltage test power supply due to overcurrent, and ensure the safety of the electrothermal aging test process.

[0018] Furthermore, the aforementioned electrothermal aging test device for superimposed harmonics on insulating samples includes a plurality of insulating samples. The device further includes a plurality of high-voltage electrodes and protective inductors corresponding to the plurality of insulating samples, wherein: Each of the insulating samples is electrically connected to the first end of the corresponding high-voltage electrode, and the second end of each high-voltage electrode is electrically connected to the first end of the corresponding protective inductor; The second terminal of each of the protective inductors is connected in parallel to each other and then electrically connected to the first terminal of the protective resistor.

[0019] In this implementation, by connecting multiple insulating samples in series with protective inductors and then in parallel to the same high-voltage test circuit, the lifetime data of multiple sets of samples can be acquired simultaneously in one test cycle, significantly reducing the total time spent testing each sample individually and improving the efficiency of the electrothermal aging test. To address the issue that the transient short-circuit current generated by the initial breakdown of one sample during parallel testing may endanger other samples, this invention connects protective inductors in series in each branch to limit the rise rate of the breakdown transient current. When a sample breaks down and forms a short-circuit path, the protective inductor utilizes its characteristic of suppressing sudden current changes to limit the rise rate of the breakdown transient current, thereby suppressing the high amplitude and steepness of transient overvoltages induced in the common bus, leads, and power supply internal impedance due to rapidly changing current. Therefore, the transient overvoltage can be blocked from being transmitted to the ends of the remaining intact samples that have not yet broken down, thus preventing the intact samples from experiencing abnormal chain breakdowns due to transient overvoltages. This ensures that the breakdown events of each sample are statistically independent, guaranteeing the statistical independence of the breakdown events of each sample and ensuring the accuracy and validity of the results of multi-sample parallel tests.

[0020] Furthermore, the low-voltage electrode has a bulk conductor structure, wherein: Each of the insulating samples is electrically connected to the low-voltage electrode, which is grounded.

[0021] In this implementation, a block conductor is used as a low-voltage electrode, providing a low-impedance common grounding path for multiple parallel insulating samples. The block structure has a large cross-sectional area and low parasitic inductance, which can ensure that the potential of the grounding terminals of each sample remains consistent, eliminating potential fluctuations caused by differences in grounding impedance. This improves the stability of the multi-sample parallel circuit test conditions and ensures the reliability of the electrothermal aging life test results.

[0022] The second aspect of the present invention provides an electrothermal aging test method for superimposed harmonics on an insulating sample, applicable to an electrothermal aging test device for superimposed harmonics on an insulating sample, the electrothermal aging test device for superimposed harmonics on an insulating sample includes an insulating oil tank, an oil bath heating device, a power frequency voltage source, a high frequency voltage source, a protective capacitor and a host computer. The heat-insulating oil tank is filled with insulating oil and is used to immerse the insulating sample in the insulating oil; The oil bath heating device is used to adjust the temperature of the insulating oil so that the insulating sample is within a preset test temperature range. The power frequency voltage source is used to apply a preset power frequency electrical stress to the insulating sample; The high-frequency voltage source is used to apply a preset high-frequency harmonic electrical stress to the insulating sample. The protective capacitor is used to block the power frequency voltage source and the high frequency voltage source; This method is executed by the host computer and includes the following steps: Identify all the indicators to be measured; Under the conditions of preset test temperature range, preset power frequency electric stress and preset high frequency harmonic electric stress, the insulating sample is subjected to electrothermal aging test to obtain test data of each of the test indicators.

[0023] Furthermore, the oil bath heating device is equipped with an oil bath pot and an oil pump, and the oil bath heating device is connected to the insulated oil tank through several oil inlets and several oil outlets; wherein: The oil bath receives insulating oil flowing from the insulated oil tank through the oil inlet, and then adjusts the temperature of the insulating oil before pumping it back to the insulated oil tank from the oil outlet through the oil pump.

[0024] In this implementation, the oil bath heating device introduces insulating oil from the top of the insulated oil tank through the oil inlet. After being heated in the oil bath, the oil is pressurized by the oil pump and then returned to the insulated oil tank through multiple oil outlets located at the bottom. The evenly distributed layout of multiple oil outlets distributes the hot oil flow, reducing the flow velocity at individual outlets, preventing direct impact of the oil flow on the sample, avoiding sample drift and electrode slippage, and simultaneously ensuring a more uniform temperature distribution. This prevents excessively high local temperatures in the oil tank caused by a single outlet, improving the uniformity of oil temperature and heating efficiency within the tank.

[0025] Furthermore, the heat-insulating oil tank is equipped with a high-voltage electrode and a low-voltage electrode. The insulating sample is electrically connected to the power frequency voltage source and the high-frequency voltage source through the high-voltage electrode, and the insulating sample is grounded through the low-voltage electrode. The insulating sample is located above the low-voltage electrode, and the oil outlet is located below the low-voltage electrode so that the low-voltage electrode protects the insulating sample from the impact of hot oil flowing out of the oil outlet.

[0026] In this implementation, when heating the insulating oil for high-temperature electrical aging testing, an oil pump is needed to circulate the oil flow to maintain temperature uniformity within the tank. However, the circulating oil flow can easily cause mechanical disturbances, leading to mechanical drift of the sample, which in turn can cause distortion of the electric field between electrodes or even flashover, resulting in test failure. To mitigate the mechanical impact of the circulating oil bath on the sample, this invention places the oil outlet below the low-voltage electrode and uses a large-area low-voltage plate as a shielding and guiding structure. This allows the circulating high-temperature insulating oil to first impact the bottom surface of the low-voltage plate, and then rise smoothly after being buffered and guided by the plate. This reduces the direct scouring force of the oil on the sample, ensuring sample stability. Simultaneously, the low-voltage plate itself provides excellent flow guidance and equalization, creating a gentle laminar flow above the plate, preventing flashover and sample drift caused by oil flow disturbances, and improving test stability.

[0027] Furthermore, the oil bath heating device is equipped with a temperature measuring thermocouple, which is in contact with the low-pressure electrode to obtain the electrode temperature of the low-pressure electrode; the oil bath adjusts the temperature of the insulating oil based on the electrode temperature to maintain the electrode temperature within a preset test temperature range, thereby enabling the insulating sample to operate within the preset test temperature range.

[0028] In this implementation, the thermocouple is in direct contact with the low-voltage electrode, and the electrode temperature is detected in real time and used as a feedback signal for temperature control. Since the insulating sample is placed in close contact with the low-voltage electrode, the electrode temperature reflects the actual temperature the sample is subjected to. The oil bath adjusts the heating power according to the deviation between the electrode temperature and the preset temperature, so that the electrode temperature is stably maintained within the preset test temperature range. This ensures that the insulating sample is always in a controlled high-temperature environment throughout the test, improving the accuracy of the aging test results.

[0029] Furthermore, the insulating oil is silicone oil.

[0030] It should be noted that in long-term high-temperature electrothermal aging tests, if mineral insulating oil is used, the insulating sample easily absorbs a large amount of oil and swells, leading to significant changes in sample size and shape, thus distorting the test results. In this implementation method, silicone oil is selected as the insulating oil. Compared to traditional mineral insulating oil, low-viscosity silicone oil has excellent thermal conductivity, high chemical stability, and a lower oil absorption rate for commonly used cable insulation materials such as cross-linked polyethylene. Using silicone oil can effectively suppress the swelling and deformation of the sample at high temperatures, maintaining the stability of the sample's geometric dimensions and shape. Simultaneously, the low viscosity of silicone oil facilitates oil bath circulation, and combined with the aforementioned oil outlet layout, it can create a more uniform temperature field within the oil tank, reducing the mechanical interference of the oil flow on the sample, thereby ensuring the authenticity and validity of the electrothermal aging life test results for the insulating material.

[0031] Furthermore, the electrothermal aging test device for superimposed harmonics on an insulating sample is provided with a protective resistor, wherein: the insulating sample is electrically connected to the first end of the high-voltage electrode, the second end of the high-voltage electrode is electrically connected to the first end of the protective resistor, the second end of the protective resistor is electrically connected to the output end of the power frequency voltage source and the first end of the protective capacitor, and the second end of the protective capacitor is electrically connected to the output end of the high-frequency voltage source.

[0032] In this implementation, when the insulation sample breaks down or the test circuit experiences an unexpected short circuit during the test, the protective resistor can limit the amplitude of the discharge current, reduce the arc energy generated at the moment of the short circuit, prevent the generation of a large short circuit current that could impact the power frequency voltage source and the high frequency voltage source, avoid damage to the high voltage test power supply due to overcurrent, and ensure the safety of the electrothermal aging test process.

[0033] Furthermore, the aforementioned electrothermal aging test device for superimposed harmonics on insulating samples includes a plurality of insulating samples. The device further includes a plurality of high-voltage electrodes and protective inductors corresponding to the plurality of insulating samples, wherein: Each of the insulating samples is electrically connected to the first end of the corresponding high-voltage electrode, and the second end of each high-voltage electrode is electrically connected to the first end of the corresponding protective inductor; The second terminal of each of the protective inductors is connected in parallel to each other and then electrically connected to the first terminal of the protective resistor.

[0034] In this implementation, by connecting multiple insulating samples in series with protective inductors and then in parallel to the same high-voltage test circuit, the lifetime data of multiple sets of samples can be acquired simultaneously in one test cycle, significantly reducing the total time spent testing each sample individually and improving the efficiency of the electrothermal aging test. To address the issue that the transient short-circuit current generated by the initial breakdown of one sample during parallel testing may endanger other samples, this invention connects protective inductors in series in each branch to limit the rise rate of the breakdown transient current. When a sample breaks down and forms a short-circuit path, the protective inductor utilizes its characteristic of suppressing sudden current changes to limit the rise rate of the breakdown transient current, thereby suppressing the high amplitude and steepness of transient overvoltages induced in the common bus, leads, and power supply internal impedance due to rapidly changing current. Therefore, the transient overvoltage can be blocked from being transmitted to the ends of the remaining intact samples that have not yet broken down, thus preventing the intact samples from experiencing abnormal chain breakdowns due to transient overvoltages. This ensures that the breakdown events of each sample are statistically independent, guaranteeing the statistical independence of the breakdown events of each sample and ensuring the accuracy and validity of the results of multi-sample parallel tests.

[0035] Furthermore, the low-voltage electrode has a bulk conductor structure, wherein: Each of the insulating samples is electrically connected to the low-voltage electrode, which is grounded.

[0036] In this implementation, a block conductor is used as a low-voltage electrode, providing a low-impedance common grounding path for multiple parallel insulating samples. The block structure has a large cross-sectional area and low parasitic inductance, which can ensure that the potential of the grounding terminals of each sample remains consistent, eliminating potential fluctuations caused by differences in grounding impedance. This improves the stability of the multi-sample parallel circuit test conditions and ensures the reliability of the electrothermal aging life test results.

[0037] A third aspect of the present invention provides a computer device, comprising: a memory configured to store instructions; The processor is configured to execute the stored instructions, causing the computer device to perform operations to implement an electrothermal aging test method for superimposed harmonics on an insulating sample as described in the second aspect of the present invention. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of an electrothermal aging test device for superimposed harmonics on an insulating sample provided in an embodiment of the present invention; Figure 2 This is a schematic flowchart of an electrothermal aging test method for superimposed harmonics on an insulating sample provided in an embodiment of the present invention. Among them: 1. Insulated oil tank; 11. Insulating oil; 12. High voltage electrode; 13. Low voltage electrode; 2. Oil bath heating device; 21. Thermocouple; 3. Power frequency voltage source; 4. High frequency voltage source; C. Protective capacitor; 5. Oil inlet; 6. Oil outlet; R. Protective resistor; L. Protective inductor. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the following detailed descriptions are exemplary and intended to provide further detailed explanation of the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to limit the application; 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, not to describe a particular order.

[0040] 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.

[0041] Before describing this application in detail with reference to the accompanying drawings and embodiments, the technical background of this application will first be explained.

[0042] When designing the insulation structure of power equipment, it is essential to consider not only the short-term breakdown field strength of the insulating material but also its operational life and reliability under long-term operating electric fields. To scientifically evaluate the electrical withstand performance of insulating materials during their expected service life, electrical aging tests must be conducted to obtain their long-term withstand voltage capability and life characteristic parameters. Currently, the standardized test method widely used in the industry is the constant stress method, also known as the constant voltage accelerated aging test. This method first prepares a batch of insulating samples and randomly divides them into several groups. Then, several different levels of electric field strength, but always constant, are applied to each group of samples. These field strengths are typically significantly higher than the expected operating field strength to reasonably accelerate the aging process. During the test, the time elapsed for each sample from the initial pressure application until breakdown occurs is continuously monitored and accurately recorded; this is the withstand voltage life. To obtain statistically significant results, each group of samples needs to contain a sufficient number of subsamples to reflect the inherent life dispersion of the material itself. The measured life data generally follows extreme value statistical distributions such as the Weibull distribution, from which the characteristic life or median life at each stress level can be calculated. Based on the characteristic lifetime sequences obtained under different constant electric field intensities, an empirical model of the lifetime-electric field intensity relationship can be established. The most commonly used model in engineering is the inverse power model. t = kE −n Here, t represents the lifetime, E represents the applied electric field strength, and k and n are material constants obtained through regression fitting of experimental data. By performing regression analysis on multiple sets of data using the least squares method or the maximum likelihood method, the electrical aging lifetime curve of the insulating material can be plotted. Finally, by reasonably extrapolating the lifetime curve to a lower operating field strength, the expected lifetime of the material under the design operating field strength can be estimated, thus providing a basis for the design margin, operation and maintenance strategy, and reliability assessment of the insulation structure.

[0043] Currently, electrical aging tests on insulation materials are generally conducted only under a 50 Hz power frequency voltage condition. However, with the continuous growth of grid-connected capacity of new energy sources such as wind and solar power, power electronic conversion devices with IGBTs as their core are widely used in the power grid. These devices achieve power conversion through high-frequency pulse width modulation. The high-speed switching action of IGBTs introduces abundant high-order harmonics into the system, with their main spectral components concentrated around 10 kHz. Therefore, AC cable insulation used in new energy grid connection not only withstands the fundamental power frequency voltage in actual operation but also endures the superposition effect of high-frequency harmonic voltages with a frequency of approximately 10 kHz for extended periods.

[0044] Numerous studies have shown that high-frequency harmonic voltages have a significant accelerating effect on the aging process of insulating materials. They can exacerbate partial discharge activity, increase dielectric loss heating, and promote the injection and accumulation of space charge, thus accelerating the aging of insulating materials under the long-term effects of electro-thermal stress and charge effects. Furthermore, in the enclosed spaces of distribution cabinets or cable trenches, the heat from insulating materials is difficult to dissipate. Ultimately, under the combined effects of poor environmental heat dissipation and high-frequency harmonic electro-thermal stress, localized high-temperature hotspots are formed, accelerating the aging of insulating materials under high temperature and high field strength conditions. Therefore, relying solely on power frequency electrical aging tests cannot accurately reproduce the composite electro-thermal stress characteristics and high-temperature conditions experienced by cable insulation under new energy grid connection conditions, and the test results are insufficient to effectively assess the insulation aging life under actual operating conditions.

[0045] Existing electrical aging tests for insulating materials are typically conducted in ambient air at room temperature. Under alternating current, the initial field strength of corona discharge in air is often less than 3 kV / mm. However, to perform electrical aging tests by superimposing high-frequency harmonic voltages, a higher voltage needs to be applied, resulting in a very high electric field strength in the electrode area. During the test, the sample will be quickly burned through by the arc induced by the corona discharge. Since the test voltage and temperature cannot reproduce the combined electro-thermal stress characteristics and high-temperature conditions experienced by the insulating material in actual scenarios, the sample will be damaged.

[0046] Furthermore, when cables transmit current, conductor resistance losses significantly increase their temperature, keeping the insulation layer at a high operating temperature (typically up to 90°C) for extended periods. In this situation, evaluating the service life of insulation materials under actual high-temperature conditions solely based on performance parameters obtained from electrical aging tests conducted at room temperature will result in significant deviations. Simultaneously, when heating mineral insulating oil for high-temperature electrical aging tests, its poor thermal conductivity necessitates forced circulation using an oil pump; otherwise, localized high temperatures can easily occur near the heating point. However, the mechanical disturbances caused by oil circulation can lead to sample drift, resulting in flashover between electrodes and causing the thermal aging test to fail. Moreover, cross-linked polyethylene and other insulating materials have a high oil absorption rate for mineral insulating oil. During long-term high-temperature testing, the insulating material absorbs a large amount of mineral insulating oil and swells, causing significant changes in sample size and shape, thus distorting the test results.

[0047] The core idea of ​​this invention is to simultaneously apply power frequency voltage and high-frequency harmonic voltage to the insulating sample to achieve a more scientific life evaluation of the insulating material used in new power systems; at the same time, multiple insulating samples are connected in parallel in the same high-voltage test circuit to obtain multiple sets of life data in one test cycle, thereby significantly reducing the total time accumulated by testing each sample individually and significantly improving the efficiency and throughput of the electrical aging test; at the same time, the electrodes and samples are placed in an insulated oil tank 1 filled with low-viscosity silicone oil, and the oil bath heating device 2 is used to control the temperature of the oil tank to ensure that the electrodes and samples are at the preset test temperature.

[0048] Please refer to Figure 1 To achieve the above objectives, the first aspect of the present invention provides an electrothermal aging test apparatus for insulating samples with superimposed harmonics, suitable for insulating samples, comprising: Insulating oil tank 1, wherein the insulating oil tank 1 is filled with insulating oil 11, for immersing the insulating sample in the insulating oil 11; Oil bath heating device 2 is used to adjust the temperature of the insulating oil 11 so that the insulating sample is within a preset test temperature range; Power frequency voltage source 3 is used to apply a preset power frequency electrical stress to the insulating sample; High-frequency voltage source 4 is used to apply a preset high-frequency harmonic electrical stress on the insulating sample; A protective capacitor C is used to block the power frequency voltage source 3 and the high frequency voltage source 4; The host computer is used to determine the various test indicators, and then to conduct an electrothermal aging test on the insulation sample under the conditions of the test temperature range, the power frequency electric stress and the high frequency harmonic electric stress, so as to obtain the test data of the various test indicators.

[0049] The aforementioned electrothermal aging test apparatus for superimposed harmonics on insulating samples immerses the insulating sample in insulating oil 11 within an insulating oil tank 1. Utilizing the higher breakdown field strength and arc-extinguishing capability of the insulating oil 11 compared to air, it avoids the corona discharge phenomenon that occurs in air under AC high voltage and high-frequency harmonic voltages. This allows the sample to withstand the superimposed voltage of power frequency and high-frequency harmonics in the insulating oil 11 environment without being directly burned through. Simultaneously, the oil bath heating device 2 can regulate the temperature of the insulating oil 11, thereby creating a preset high-temperature test environment for the insulating sample. To enable the power frequency voltage source 3 and the high-frequency voltage source 4 to work collaboratively, preset power frequency electrical stress and high-frequency harmonic electrical stress are applied to the insulating material, respectively, simulating the composite electrical stress characteristics of the fundamental wave and higher-order harmonics superimposed on cable insulation under new energy grid connection scenarios. A protective capacitor C is connected in series in the circuit to block mutual interference between the power frequency voltage source 3 and the high-frequency voltage source 4, preventing high-frequency harmonic current from flowing back into the power frequency power supply or the power frequency current from affecting the high-frequency power supply output. Ultimately, through the coordinated operation of the aforementioned components, this invention can reproduce the composite electrothermal stress characteristics and high-temperature working environment experienced by insulating materials in actual power scenarios, preventing premature damage to the samples due to air corona discharge, making the test process closer to actual working conditions, and significantly improving the effectiveness and accuracy of the electrothermal aging life test results of insulating materials.

[0050] It should also be noted that the protective capacitor C exhibits high capacitive reactance to power frequency signals, which can effectively block power frequency high voltage and prevent it from flowing back to the output port of high frequency voltage source 4, thereby protecting high frequency voltage source 4 from power frequency voltage impact; at the same time, the capacitor exhibits low capacitive reactance to high frequency harmonic signals, ensuring that the high frequency voltage component can be transmitted to the sample end with extremely low attenuation, so that the high frequency voltage is effectively applied to the insulating sample, thereby achieving reliable superposition of power frequency and high frequency harmonic voltage.

[0051] In a preferred embodiment, the shell of the insulated oil tank 1 is provided with an insulation layer structure to reduce temperature fluctuations during the test and maintain stable oil temperature.

[0052] Furthermore, the oil bath heating device 2 is equipped with an oil bath pot and an oil pump, and the oil bath heating device 2 is connected to the insulated oil tank 1 through several oil inlets 5 and several oil outlets 6; wherein: The oil bath receives insulating oil 11 flowing from the insulated oil tank 1 through the oil inlet 5, and then adjusts the temperature of the insulating oil 11 before pumping the insulating oil 11 back to the insulated oil tank 1 from the oil outlet 6 through the oil pump.

[0053] In this implementation, the oil bath heating device 2 introduces insulating oil 11 from the top of the insulated oil tank 1 through the oil inlet 5. After being heated in the oil bath, the oil is pressurized by the oil pump and then sent back to the insulated oil tank 1 through multiple oil outlets 6 located at the bottom. The evenly distributed distribution of multiple oil outlets 6 distributes the hot oil flow, which can reduce the flow velocity of a single oil outlet 6, avoid the oil flow directly impacting the sample, prevent sample drift, and avoid flashover between electrodes. At the same time, it can make the temperature distribution more uniform, avoid excessive local temperature in the oil tank caused by a single oil outlet 6, and improve the uniformity of oil temperature and heating efficiency in the oil tank.

[0054] Furthermore, the heat-insulating oil tank 1 is provided with a high-voltage electrode 12 and a low-voltage electrode 13. The insulating sample is electrically connected to the power frequency voltage source 3 and the high-frequency voltage source 4 through the high-voltage electrode 12, and the insulating sample is grounded through the low-voltage electrode 13. The insulating sample is located above the low-voltage electrode 13, and the oil outlet 6 is located below the low-voltage electrode 13 so that the low-voltage electrode 13 protects the insulating sample from the impact of hot oil flowing out from the oil outlet 6.

[0055] In this implementation, when heating the insulating oil 11 to achieve a high-temperature electrical aging test, an oil pump is needed to circulate the oil flow to maintain temperature uniformity within the oil tank. However, the circulating oil flow is prone to mechanical disturbances, causing mechanical drift of the sample, which in turn leads to distortion of the electric field between electrodes or even flashover, resulting in test failure. To mitigate the mechanical impact of the circulating oil bath on the sample, this invention places the oil outlet 6 below the low-voltage electrode 13 and uses a large-area low-voltage plate as a shielding and guiding structure. This allows the circulating high-temperature insulating oil 11 to first impact the bottom surface of the low-voltage plate, and then rise smoothly after being buffered and guided by the plate, reducing the direct scouring force of the oil on the sample and ensuring sample stability. At the same time, the low-voltage plate itself plays a good role in guiding and equalizing the flow, forming a gentle laminar flow above the plate, preventing flashover and sample drift caused by oil flow disturbances, and improving test stability.

[0056] Furthermore, the oil bath heating device 2 is equipped with a temperature measuring thermocouple 21, which is in contact with the low-pressure electrode 13 to obtain the electrode temperature of the low-pressure electrode 13; the oil bath adjusts the temperature of the insulating oil 11 based on the electrode temperature to maintain the electrode temperature within the preset test temperature range, thereby enabling the insulating sample to work within the preset test temperature range.

[0057] In this implementation, the temperature-measuring thermocouple 21 is in direct contact with the low-voltage electrode 13, and the electrode temperature is detected in real time and used as a feedback signal for temperature control. Since the insulating sample is placed in close contact with the low-voltage electrode 13, the electrode temperature can reflect the actual temperature that the sample is subjected to. The oil bath adjusts the heating power according to the deviation between the electrode temperature and the preset temperature, so that the electrode temperature is stably maintained within the preset test temperature range, ensuring that the insulating sample is always in a controlled high-temperature environment throughout the test, thereby improving the accuracy of the aging test results.

[0058] Furthermore, the insulating oil 11 is silicone oil.

[0059] It should be noted that in long-term high-temperature electrothermal aging tests, if mineral insulating oil is used, the insulating sample easily absorbs a large amount of oil and swells, leading to significant changes in sample size and shape, thus distorting the test results. In this implementation method, silicone oil is selected as the insulating oil 11. Compared with traditional mineral insulating oil, low-viscosity silicone oil has excellent thermal conductivity, high chemical stability, and a low oil absorption rate for commonly used cable insulation materials such as cross-linked polyethylene. Using silicone oil can effectively suppress the swelling and deformation of the sample at high temperatures, maintaining the stability of the sample's geometric dimensions and shape. At the same time, the low viscosity of silicone oil is conducive to oil bath circulation, and combined with the aforementioned oil outlet 6 layout, it can form a more uniform temperature field in the oil tank, reducing the mechanical interference of oil flow on the sample, thereby ensuring the authenticity and validity of the electrothermal aging life test results of the insulating material.

[0060] To verify the advantages of low-viscosity silicone oil over mineral insulating oil in suppressing sample swelling, five 1mm thick cross-linked polyethylene (XLPE) sheet samples were selected. First, each sample was weighed and marked using a balance. Then, the samples were completely immersed in insulating oil 11 at a set temperature for 15 minutes. After immersion, the samples were removed, their surfaces were gently wiped clean with oil-absorbing paper, and their mass after oil absorption was measured. The oil absorption rate of the material was calculated based on the mass difference before and after oil absorption, and the results are shown in Table 1. The results show that under high-temperature conditions, XLPE insulating materials exhibit a high oil absorption rate for mineral insulating oil, while the oil absorption rate for low-viscosity silicone oil is extremely low. Moreover, the oil absorption rate of XLPE insulating materials for low-viscosity silicone oil remains essentially unchanged with temperature. Therefore, low-viscosity silicone oil is suitable as an insulating and heat transfer medium for long-term high-temperature electro-aging tests of XLPE insulating materials.

[0061] Table 1. Oil absorption rate (%) of cross-linked polyethylene insulation material in different insulating oils 11 Furthermore, the electrothermal aging test device for superimposed harmonics on an insulating sample is provided with a protective resistor R, wherein: the insulating sample is electrically connected to the first end of the high-voltage electrode 12, the second end of the high-voltage electrode 12 is electrically connected to the first end of the protective resistor R, the second end of the protective resistor R is electrically connected to the output end of the power frequency voltage source 3 and the first end of the protective capacitor C, and the second end of the protective capacitor C is electrically connected to the output end of the high-frequency voltage source 4.

[0062] In this implementation, when the insulation sample breaks down or the test circuit experiences an unexpected short circuit during the test, the protective resistor R can limit the amplitude of the discharge current, reduce the arc energy generated at the moment of the short circuit, prevent the generation of a large short circuit current that impacts the power frequency voltage source 3 and the high frequency voltage source 4, avoid damage to the high voltage test power supply due to overcurrent, and ensure the safety of the electrothermal aging test process.

[0063] It should also be noted that the protective resistor R is connected in series with the output terminal of the voltage source, and its resistance value should be selected by comprehensively considering factors such as the short-circuit withstand capability of the voltage source, the rated current of the test circuit, and the allowable voltage drop across the sample terminal under normal test conditions. When the insulation sample breaks down or the circuit is accidentally short-circuited, the protective resistor R can limit the amplitude of the discharge current, protecting the power frequency voltage source 3 and the high-frequency voltage source 4 from the impact of excessive short-circuit current.

[0064] Furthermore, the electrothermal aging test device for superimposed harmonics on insulating samples includes a plurality of insulating samples. The device further includes a plurality of high-voltage electrodes 12 and a protective inductor L corresponding to the plurality of insulating samples, wherein: Each of the insulating samples is electrically connected to the first end of the corresponding high-voltage electrode 12, and the second end of each high-voltage electrode 12 is electrically connected to the first end of the corresponding protective inductor L; The second terminal of each of the protective inductors L is connected in parallel to each other and then electrically connected to the first terminal of the protective resistor R.

[0065] In this implementation, by connecting multiple insulating samples in series with protective inductors L and then in parallel to the same high-voltage test circuit, the lifetime data of multiple sets of samples can be acquired simultaneously in one test cycle, significantly reducing the total time spent testing each sample individually and improving the efficiency of the electrothermal aging test. To address the issue that the transient short-circuit current generated by the initial breakdown of one sample during parallel testing may endanger other samples, this invention connects protective inductors L in series in each branch to limit the rise rate of the breakdown transient current. When a sample breaks down and forms a short-circuit path, the protective inductor L utilizes its characteristic of suppressing sudden current changes to generate an induced electromotive force, limiting the rise rate of the breakdown transient current, thereby suppressing the high amplitude and steepness transient overvoltage induced in the common bus, leads, and power supply internal impedance due to rapidly changing current. Therefore, the transient overvoltage can be blocked from being transmitted to the ends of the remaining intact samples that have not yet broken down, thus preventing the intact samples from experiencing abnormal chain breakdowns due to transient overvoltages. This ensures that the breakdown events of each sample are statistically independent, guaranteeing the statistical independence of the breakdown events of each sample and ensuring the accuracy and validity of the results of multi-sample parallel tests.

[0066] It should also be noted that the number of high-voltage electrodes 12 can be flexibly adjusted according to the number of samples required for each round of electrical aging test.

[0067] Furthermore, the low-voltage electrode 13 has a bulk conductor structure, wherein: Each of the insulating samples is electrically connected to the low-voltage electrode 13, which is grounded.

[0068] In this implementation, a block conductor is used as the low-voltage electrode 13, providing a low-impedance common grounding path for multiple parallel insulating samples. The block structure has a large cross-sectional area and low parasitic inductance, which can ensure that the potential of the grounding terminals of each sample remains consistent, eliminate potential fluctuations caused by differences in grounding impedance, thereby improving the stability of the multi-sample parallel circuit test conditions and ensuring the reliability of the electrothermal aging life test results.

[0069] Please refer to Figure 2 The second aspect of the present invention provides an electrothermal aging test method for superimposed harmonics on an insulating sample, which is applicable to an electrothermal aging test device for superimposed harmonics on an insulating sample. The electrothermal aging test device for superimposed harmonics on an insulating sample includes an insulating oil tank 1, an oil bath heating device 2, a power frequency voltage source 3, a high frequency voltage source 4, and a protective capacitor C. The heat-insulating oil tank 1 is filled with insulating oil 11, which is used to immerse the insulating sample in the insulating oil 11; The oil bath heating device 2 is used to adjust the temperature of the insulating oil 11 so that the insulating sample is within the preset test temperature range; The power frequency voltage source 3 is used to apply a preset power frequency electric stress to the insulating sample; The high-frequency voltage source 4 is used to apply a preset high-frequency harmonic electrical stress to the insulating sample. The protective capacitor C is used to block the power frequency voltage source 3 and the high frequency voltage source 4; This method is executed by the host computer and includes the following steps: S1. Determine the various indicators to be measured; S2. Under the conditions of preset test temperature range, preset power frequency electric stress and preset high frequency harmonic electric stress, the insulating sample is subjected to an electrothermal aging test to obtain the test data of each of the test indicators.

[0070] In a preferred embodiment, the shell of the insulated oil tank 1 is provided with an insulation layer structure to reduce temperature fluctuations during the test and maintain stable oil temperature.

[0071] Furthermore, the oil bath heating device 2 is equipped with an oil bath pot and an oil pump, and the oil bath heating device 2 is connected to the insulated oil tank 1 through several oil inlets 5 and several oil outlets 6; wherein: The oil bath receives insulating oil 11 flowing from the insulated oil tank 1 through the oil inlet 5, and then adjusts the temperature of the insulating oil 11 before pumping the insulating oil 11 back to the insulated oil tank 1 from the oil outlet 6 through the oil pump.

[0072] In this implementation, the oil bath heating device 2 introduces insulating oil 11 from the top of the insulated oil tank 1 through the oil inlet 5. After being heated in the oil bath, the oil is pressurized by the oil pump and then sent back to the insulated oil tank 1 through multiple oil outlets 6 located at the bottom. The evenly distributed distribution of multiple oil outlets 6 distributes the hot oil flow, which can reduce the flow velocity of a single oil outlet 6, avoid the oil flow directly impacting the sample, prevent sample drift, and avoid flashover between electrodes. At the same time, it can make the temperature distribution more uniform, avoid excessive local temperature in the oil tank caused by a single oil outlet 6, and improve the uniformity of oil temperature and heating efficiency in the oil tank.

[0073] Furthermore, the heat-insulating oil tank 1 is provided with a high-voltage electrode 12 and a low-voltage electrode 13. The insulating sample is electrically connected to the power frequency voltage source 3 and the high-frequency voltage source 4 through the high-voltage electrode 12, and the insulating sample is grounded through the low-voltage electrode 13. The insulating sample is located above the low-voltage electrode 13, and the oil outlet 6 is located below the low-voltage electrode 13 so that the low-voltage electrode 13 protects the insulating sample from the impact of hot oil flowing out from the oil outlet 6.

[0074] In this implementation, when heating the insulating oil 11 to achieve a high-temperature electrical aging test, an oil pump is needed to circulate the oil flow to maintain temperature uniformity within the oil tank. However, the circulating oil flow is prone to mechanical disturbances, causing mechanical drift of the sample, which in turn leads to distortion of the electric field between electrodes or even flashover, resulting in test failure. To mitigate the mechanical impact of the circulating oil bath on the sample, this invention places the oil outlet 6 below the low-voltage electrode 13 and uses a large-area low-voltage plate as a shielding and guiding structure. This allows the circulating high-temperature insulating oil 11 to first impact the bottom surface of the low-voltage plate, and then rise smoothly after being buffered and guided by the plate, reducing the direct scouring force of the oil on the sample and ensuring sample stability. At the same time, the low-voltage plate itself plays a good role in guiding and equalizing the flow, forming a gentle laminar flow above the plate, preventing flashover and sample drift caused by oil flow disturbances, and improving test stability.

[0075] Furthermore, the oil bath heating device 2 is equipped with a temperature measuring thermocouple 21, which is in contact with the low-pressure electrode 13 to obtain the electrode temperature of the low-pressure electrode 13; the oil bath adjusts the temperature of the insulating oil 11 based on the electrode temperature to maintain the electrode temperature within the preset test temperature range, thereby enabling the insulating sample to work within the preset test temperature range.

[0076] In this implementation, the temperature-measuring thermocouple 21 is in direct contact with the low-voltage electrode 13, and the electrode temperature is detected in real time and used as a feedback signal for temperature control. Since the insulating sample is placed in close contact with the low-voltage electrode 13, the electrode temperature can reflect the actual temperature that the sample is subjected to. The oil bath adjusts the heating power according to the deviation between the electrode temperature and the preset temperature, so that the electrode temperature is stably maintained within the preset test temperature range, ensuring that the insulating sample is always in a controlled high-temperature environment throughout the test, thereby improving the accuracy of the aging test results.

[0077] Furthermore, the insulating oil 11 is silicone oil.

[0078] It should be noted that in long-term high-temperature electrothermal aging tests, if mineral insulating oil is used, the insulating sample easily absorbs a large amount of oil and swells, leading to significant changes in sample size and shape, thus distorting the test results. In this implementation method, silicone oil is selected as the insulating oil 11. Compared with traditional mineral insulating oil, low-viscosity silicone oil has excellent thermal conductivity, high chemical stability, and a low oil absorption rate for commonly used cable insulation materials such as cross-linked polyethylene. Using silicone oil can effectively suppress the swelling and deformation of the sample at high temperatures, maintaining the stability of the sample's geometric dimensions and shape. At the same time, the low viscosity of silicone oil is conducive to oil bath circulation, and combined with the aforementioned oil outlet 6 layout, it can form a more uniform temperature field in the oil tank, reducing the mechanical interference of oil flow on the sample, thereby ensuring the authenticity and validity of the electrothermal aging life test results of the insulating material.

[0079] Furthermore, the electrothermal aging test device for superimposed harmonics on an insulating sample is provided with a protective resistor R, wherein: the insulating sample is electrically connected to the first end of the high-voltage electrode 12, the second end of the high-voltage electrode 12 is electrically connected to the first end of the protective resistor R, the second end of the protective resistor R is electrically connected to the output end of the power frequency voltage source 3 and the first end of the protective capacitor C, and the second end of the protective capacitor C is electrically connected to the output end of the high-frequency voltage source 4.

[0080] In this implementation, when the insulation sample breaks down or the test circuit experiences an unexpected short circuit during the test, the protective resistor R can limit the amplitude of the discharge current, reduce the arc energy generated at the moment of the short circuit, prevent the generation of a large short circuit current that impacts the power frequency voltage source 3 and the high frequency voltage source 4, avoid damage to the high voltage test power supply due to overcurrent, and ensure the safety of the electrothermal aging test process.

[0081] It should also be noted that the protective resistor R is connected in series with the output terminal of the voltage source, and its resistance value should be selected by comprehensively considering factors such as the short-circuit withstand capability of the voltage source, the rated current of the test circuit, and the allowable voltage drop across the sample terminal under normal test conditions. When the insulation sample breaks down or the circuit is accidentally short-circuited, the protective resistor R can limit the amplitude of the discharge current, protecting the power frequency voltage source 3 and the high-frequency voltage source 4 from the impact of excessive short-circuit current.

[0082] Furthermore, the electrothermal aging test device for superimposed harmonics on insulating samples includes a plurality of insulating samples. The device further includes a plurality of high-voltage electrodes 12 and a protective inductor L corresponding to the plurality of insulating samples, wherein: Each of the insulating samples is electrically connected to the first end of the corresponding high-voltage electrode 12, and the second end of each high-voltage electrode 12 is electrically connected to the first end of the corresponding protective inductor L; The second terminal of each of the protective inductors L is connected in parallel to each other and then electrically connected to the first terminal of the protective resistor R.

[0083] In this implementation, by connecting multiple insulating samples in series with protective inductors L and then in parallel to the same high-voltage test circuit, the lifetime data of multiple sets of samples can be acquired simultaneously in one test cycle, significantly reducing the total time spent testing each sample individually and improving the efficiency of the electrothermal aging test. To address the issue that the transient short-circuit current generated by the initial breakdown of one sample during parallel testing may endanger other samples, this invention connects protective inductors L in series in each branch to limit the rise rate of the breakdown transient current. When a sample breaks down and forms a short-circuit path, the protective inductor L utilizes its characteristic of suppressing sudden current changes to generate an induced electromotive force, limiting the rise rate of the breakdown transient current, thereby suppressing the high amplitude and steepness transient overvoltage induced in the common bus, leads, and power supply internal impedance due to rapidly changing current. Therefore, the transient overvoltage can be blocked from being transmitted to the ends of the remaining intact samples that have not yet broken down, thus preventing the intact samples from experiencing abnormal chain breakdowns due to transient overvoltages. This ensures that the breakdown events of each sample are statistically independent, guaranteeing the statistical independence of the breakdown events of each sample and ensuring the accuracy and validity of the results of multi-sample parallel tests.

[0084] It should also be noted that the number of high-voltage electrodes 12 can be flexibly adjusted according to the number of samples required for each round of electrical aging test.

[0085] Furthermore, the low-voltage electrode 13 has a bulk conductor structure, wherein: Each of the insulating samples is electrically connected to the low-voltage electrode 13, which is grounded.

[0086] In this implementation, a block conductor is used as the low-voltage electrode 13, providing a low-impedance common grounding path for multiple parallel insulating samples. The block structure has a large cross-sectional area and low parasitic inductance, which can ensure that the potential of the grounding terminals of each sample remains consistent, eliminate potential fluctuations caused by differences in grounding impedance, thereby improving the stability of the multi-sample parallel circuit test conditions and ensuring the reliability of the electrothermal aging life test results.

[0087] A third aspect of the present invention provides a computer device, comprising: a memory configured to store instructions; The processor is configured to execute the stored instructions, causing the computer device to perform operations to implement an electrothermal aging test method for superimposed harmonics on an insulating sample as described in the second aspect of the present invention.

[0088] It is worth noting that the electrothermal aging test apparatus, method, and equipment for superimposed harmonics on insulating samples provided by the present invention have at least the following advantages compared with the prior art: In some existing technologies, the test electrode and sample are placed in a beaker, and the wire is routed along the outer wall of the beaker to the top before being grounded. This wiring method results in insufficient insulation between the ground wire and the high-voltage electrode 12, greatly limiting the upper limit of the applied voltage to only 0–25 kV. Moreover, this wiring method also affects the uniformity of the electric field distribution, easily leading to premature sample breakdown. In contrast, in this invention, sufficient insulation margin is reserved between the high-voltage electrode 12, the low-voltage electrode 13, and the ground wire. The structural design meets the safety requirements under high field strength, and a stable voltage of 0–100 kV can be applied according to the electrothermal aging test standard, significantly widening the coverage area, and the electric field distribution in the high-voltage area is more uniform.

[0089] In some existing technologies, beakers are externally jacketed with double layers, and hot oil is circulated through series pipes for sequential heating. However, when the number of parallel samples increases, heat loss along the hot oil path leads to a significant temperature difference between the first and last beakers. To compensate for this deficiency, additional series heating belts and controllers are installed for auxiliary heating, but the series circuit itself cannot independently adjust the temperature of each beaker, making it difficult to ensure that the temperature of each beaker is consistent. This invention integrates all samples and electrodes into the same insulated oil tank 1, and sets separate, dispersed oil outlets 6 at the bottom of each sample. At the same time, it utilizes the high thermal conductivity of the low-pressure metal electrode 13 to shorten the hot oil circulation path and make convection more sufficient, thereby ensuring that all samples age synchronously under strictly identical temperature fields, greatly improving the repeatability and cross-sectional comparability of experimental data.

[0090] In some existing technologies, mainly targeting the insulation materials of dry-type transformers, the insulating oil 11 used in the electrothermal aging test is a conventional mineral oil. When this oil comes into long-term contact with cross-linked polyethylene (XLPE) cable insulation materials, it is prone to causing a swelling effect, affecting the accuracy of the aging evaluation. This invention, considering the actual working conditions of cable insulation materials, specifically selects a low-viscosity silicone oil as the thermally conductive and insulating medium. Its excellent chemical inertness ensures that it will not cause swelling or erosion of the XLPE samples during long-term electrothermal aging, thus ensuring the purity of the aging mechanism study and the validity of the test results.

[0091] In summary, the electrothermal aging test apparatus, method, and equipment for superimposed harmonics on insulating samples provided by the present invention have at least the following technical effects: Traditional electrical aging tests only measure the life index of insulation samples under power frequency voltage, which cannot reflect the composite electrical stress characteristics borne by cable insulation under new energy grid connection conditions, and therefore cannot accurately assess its expected life under actual operating conditions. This invention, by subjecting samples to AC superimposed harmonic electrical aging, accurately simulates the actual operating conditions of cable insulation, resulting in a more reasonable insulation material life index and a more accurate assessment of the cable's expected life.

[0092] This invention employs a multi-channel parallel architecture, which can simultaneously apply the same AC superimposed harmonic voltage waveform to multiple insulating samples. This not only significantly shortens the aging and withstand voltage test cycle, but also ensures that the electrical stress waveform, amplitude, and phase of each sample are strictly consistent. This fundamentally avoids the operating condition deviations introduced by time-sharing tests, making the aging behavior of different samples highly comparable.

[0093] This invention effectively suppresses the rise rate and amplitude of transient short-circuit current by introducing a protective inductor L into the circuit, thus blocking the transmission of overvoltage to other samples. This ensures that the breakdown events of each sample remain statistically independent, and the measured end-of-life is determined solely by the sample's own electrical aging process, eliminating false failures caused by mutual interference between test circuits, thereby guaranteeing the authenticity and validity of the lifetime data.

[0094] This invention uses low-viscosity silicone oil instead of mineral insulating oil as the insulating and heat transfer medium. While ensuring the insulation and heat transfer effects, it significantly reduces the oil absorption rate of cross-linked polyethylene insulating materials, avoids the dimensional deformation caused by oil absorption and swelling of the samples, and ensures the reliability of the long-term high-temperature electrical aging test results.

[0095] The present invention places the oil outlet 6 of the oil bath heating device 2 below the large-size low-pressure electrode 13, adopts a layout of multiple oil outlets 6 to reduce the flow rate of a single oil outlet 6, and uses electrodes to block the oil flow to avoid it directly impacting the sample, thus ensuring the stability of the sample position during long-term testing.

[0096] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0097] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; however, any combination of these technical features that does not contradict each other should be considered within the scope of this specification.

[0098] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the concept of this application, and these improvements and substitutions should also be considered within the scope of protection of this invention. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. An electrothermal aging test apparatus for superimposed harmonics on insulating samples, suitable for insulating samples, characterized in that, include: An insulating oil tank, the insulating oil tank being filled with insulating oil, is used to immerse the insulating sample in the insulating oil; An oil bath heating device is used to regulate the temperature of the insulating oil so that the insulating sample is within a preset test temperature range; A power frequency voltage source is used to apply a preset power frequency electrical stress to the insulating sample. A high-frequency voltage source is used to apply a preset high-frequency harmonic electrical stress to the insulating sample. A protective capacitor is used to block the power frequency voltage source and the high frequency voltage source; The host computer is used to determine the various test indicators, and then to conduct an electrothermal aging test on the insulation sample under the conditions of the test temperature range, the power frequency electric stress and the high frequency harmonic electric stress, so as to obtain the test data of the various test indicators.

2. The electrothermal aging test apparatus for superimposed harmonics on an insulating sample according to claim 1, characterized in that, The oil bath heating device is equipped with an oil bath pot and an oil pump, and is connected to the insulated oil tank through several oil inlets and several oil outlets; wherein: The oil bath receives insulating oil flowing from the insulated oil tank through the oil inlet, and then adjusts the temperature of the insulating oil before pumping it back to the insulated oil tank from the oil outlet through the oil pump.

3. The electrothermal aging test apparatus for superimposed harmonics on an insulating sample according to claim 2, characterized in that, The insulated oil tank is equipped with a high-voltage electrode and a low-voltage electrode. The insulating sample is electrically connected to the power frequency voltage source and the high-frequency voltage source through the high-voltage electrode, and the insulating sample is grounded through the low-voltage electrode. The insulating sample is located above the low-voltage electrode, and the oil outlet is located below the low-voltage electrode so that the low-voltage electrode protects the insulating sample from the impact of hot oil flowing out of the oil outlet.

4. The electrothermal aging test apparatus for superimposed harmonics on an insulating sample according to claim 3, characterized in that, The oil bath heating device is equipped with a temperature measuring thermocouple, which is in contact with the low-pressure electrode to obtain the electrode temperature of the low-pressure electrode; the oil bath adjusts the temperature of the insulating oil based on the electrode temperature to maintain the electrode temperature within a preset test temperature range, thereby enabling the insulating sample to operate within the preset test temperature range.

5. The electrothermal aging test apparatus for superimposed harmonics on an insulating sample according to claim 1, characterized in that, The insulating oil is silicone oil.

6. The electrothermal aging test apparatus for superimposed harmonics on an insulating sample according to claim 3, characterized in that, A protective resistor is provided, wherein: the insulating sample and the first end of the high-voltage electrode are electrically connected; the second end of the high-voltage electrode and the first end of the protective resistor are electrically connected; the second end of the protective resistor is electrically connected to the output end of the power frequency voltage source and the first end of the protective capacitor; and the second end of the protective capacitor is electrically connected to the output end of the high frequency voltage source.

7. The electrothermal aging test apparatus for superimposed harmonics on an insulating sample according to claim 6, characterized in that, The device includes several insulating samples, and the electrothermal aging test apparatus for superimposed harmonics on the insulating samples further includes several high-voltage electrodes and protective inductors corresponding to the insulating samples, wherein: Each of the insulating samples is electrically connected to the first end of the corresponding high-voltage electrode, and the second end of each high-voltage electrode is electrically connected to the first end of the corresponding protective inductor; The second terminal of each of the protective inductors is connected in parallel to each other and then electrically connected to the first terminal of the protective resistor.

8. The electrothermal aging test apparatus for superimposed harmonics on an insulating sample according to claim 7, characterized in that, The low-voltage electrode has a bulk conductor structure, wherein: Each of the insulating samples is electrically connected to the low-voltage electrode, which is grounded.

9. A method for electrothermal aging test of insulating samples with superimposed harmonics, characterized in that, An electrothermal aging test device for superimposed harmonics on an insulating sample is provided. The electrothermal aging test device for superimposed harmonics on an insulating sample includes an insulating oil tank, an oil bath heating device, a power frequency voltage source, a high frequency voltage source, a protective capacitor, and a host computer. The heat-insulating oil tank is filled with insulating oil and is used to immerse the insulating sample in the insulating oil; The oil bath heating device is used to adjust the temperature of the insulating oil so that the insulating sample is within a preset test temperature range. The power frequency voltage source is used to apply a preset power frequency electrical stress to the insulating sample; The high-frequency voltage source is used to apply a preset high-frequency harmonic electrical stress to the insulating sample. The protective capacitor is used to block the power frequency voltage source and the high frequency voltage source; This method is executed by the host computer and includes the following steps: Identify all the indicators to be measured; Under the conditions of preset test temperature range, preset power frequency electric stress and preset high frequency harmonic electric stress, the insulating sample is subjected to electrothermal aging test to obtain test data of each of the test indicators.

10. A computer device, characterized in that, include: The memory is configured to store instructions; The processor is configured to execute the stored instructions, causing the computer device to perform operations that implement the electrothermal aging test method for superimposed harmonics on an insulating sample as described in claim 9.

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