Method for detecting refilling residual oil quantity of mineral oil transformer

Abstract

The invention discloses a method for detecting the refilling residual oil quantity of a mineral oil transformer. The method comprises the following steps: cleaning residual mineral oil in the mineral oil transformer through at least three stages of specific cleaning processes, filling natural ester insulating oil, sampling, and detecting the mineral oil content in sample oil by adopting gas chromatography-tandem mass spectrometry; according to the present invention, the residual mineral oil at the difficult-to-clean part is completely adsorbed and eluted by precisely controlling the cleaning process parameters so as to substantially reduce the residual amount of the mineral oil in the transformer, and the gas chromatography-tandem mass spectrometry multi-mode detection method is matched with the refilling process so as to achieve the precise detection of the mineral oil content in the insulating oil sample, the recognition sensitivity of trace mineral oil residues is remarkably improved, and accurate and quantitative refilling is realized; according to the method, the advantages of process collaboration and integration are utilized, the operation performance of the refilled transformer is remarkably improved, the risk of insulation performance reduction caused by oil degradation is effectively inhibited, and the long-term stable operation life of the transformer is prolonged.

Description

Technical Field

[0001] This application relates to the field of power equipment testing and maintenance technology, and in particular to a method for detecting the amount of residual oil in mineral oil transformers after refilling. Background Technology

[0002] In recent years, the use of natural ester (vegetable) insulating oil to replace traditional mineral oil has become an important trend in transformer insulating oil replacement, aiming to reduce the adverse effects of mineral oil residue, oxidation, or deterioration on the long-term operating performance of transformers. However, in actual refilling processes, due to the complex equipment structure and the difficulty in thoroughly cleaning the oil circuit, residual mineral oil is often not completely removed, leaving the transformer potentially still affected by old oil contamination, threatening its insulation performance and operational reliability. Therefore, accurate detection and assessment of the residual mineral oil in the transformer after refilling has become a crucial step in ensuring the safe and stable operation of power equipment.

[0003] In terms of detection methods, traditional gas chromatography and infrared spectroscopy techniques are insufficient to meet the precise detection requirements of trace mineral oil residues. They not only have high detection limits but also weak anti-interference capabilities, making them unsuitable for analyzing complex oil sample matrices. Furthermore, traditional detection technologies are not compatible with the refilling process, making it difficult to establish a standard quantitative model for refilling. This results in imprecise control of the refilling process, compromising the operational performance of the transformer. These problems make it impossible to achieve precise process control and guarantee the final acceptance quality of transformer refilling, necessitating the establishment of a complete technical system for transformer refilling processes and detection. Summary of the Invention

[0004] Therefore, it is necessary to establish a testing method that matches the refilling process of mineral oil transformers, so as to achieve precise control of the refilling process and ensure the long-term stable operation of the transformer.

[0005] Firstly, this application provides a method for detecting the amount of residual oil during refilling of mineral oil transformers, comprising the following steps:

[0006] Clean the internal mineral oil residue of the mineral oil transformer;

[0007] After cleaning, the interior of the mineral oil transformer is filled with natural ester insulating oil;

[0008] After filling, a sample was taken from the inside of the mineral oil transformer, and the mineral oil content in the sample was detected by gas chromatography-tandem mass spectrometry.

[0009] The cleaning pressure is 0.15 MPa-0.40 MPa, and the cleaning temperature is 50℃±2℃;

[0010] The cleaning process includes at least three stages:

[0011] Add 20%-30% of the total oil volume of the mineral oil transformer to the interior of the mineral oil transformer for the first stage of cleaning, and then discharge the waste liquid;

[0012] After the first stage of cleaning is completed, natural ester insulating oil, accounting for 35%-50% of the total oil volume of the mineral oil transformer, is added to the interior of the mineral oil transformer for the second stage of cleaning, and the waste liquid is discharged.

[0013] After the second stage of cleaning, natural ester insulating oil, accounting for 10%-20% of the total oil volume of the mineral oil transformer, is added to the interior of the mineral oil transformer for the third stage of cleaning, and the waste liquid is discharged.

[0014] In some embodiments, during the first-stage cleaning step, the cleaning pressure is 0.25MPa-0.30MPa, and the cleaning time is 25min-35min.

[0015] In some embodiments, during the second-stage cleaning step, the cleaning pressure is 0.20 MPa-0.40 MPa, and the cleaning time is 15 min-70 min.

[0016] In some embodiments, the second-level cleaning step includes at least two cleaning cycles:

[0017] The parameters for the first cleaning are: 0.30MPa ≤ pressure ≤ 0.40MPa, and the time is 25min-40min;

[0018] The parameters for the second cleaning are: 0.20MPa ≤ pressure < 0.30MPa, and the time is 15min-30min.

[0019] In some embodiments, during the third-stage cleaning step, the cleaning pressure is 0.15MPa-0.20MPa, and the cleaning time is 25min-35min.

[0020] In some embodiments, the first stage of cleaning is completed and the sample is left to stand for 3-5 hours; and / or, the second stage of cleaning is completed and the sample is left to stand for 3-5 hours; and / or, the third stage of cleaning is completed and the sample is left to stand for 0.5-2 hours.

[0021] In some embodiments, the voltage rating of the mineral oil transformer is 110 kV; and / or, the mineral oil includes Lamay mineral insulating oil; and / or, the natural ester insulating oil includes FR3 plant-based transformer insulating oil.

[0022] In some embodiments, after the first-stage cleaning, the second-stage cleaning, and the third-stage cleaning, the internal oil paper of the mineral oil transformer is tested, and the dielectric constant change rate of the oil paper is ≤5%.

[0023] In some embodiments, the parameters of the gas chromatography-tandem mass spectrometry include:

[0024] Gas chromatography parameters: DB-5MS column, helium as carrier gas, carrier gas flow rate of 1.5 mL / min, column temperature program of increasing from 60℃ to 280℃ at a rate of 10℃ / min, and injection port temperature of 250℃.

[0025] Mass spectrometry parameters: electron impact ionization source, ionization energy of 70 eV, interface temperature of 280℃, ion source temperature of 230℃, ion monitoring mode SIM, and m / z of quantitatively monitored ions of 57 and 294.

[0026] In some embodiments, the detection method further includes: evaluating the transformer's operational stability and refilling effect based on the mineral oil content in the test sample, wherein the evaluation method includes:

[0027] For Level 1 acceptance, the mineral oil content in the tested sample is ≤1%, and the evaluation is qualified.

[0028] For Level 2 acceptance, if the mineral oil content in the tested sample is ≤3%, it is considered qualified and requires 72 hours of operational monitoring.

[0029] For the third-level acceptance test, the mineral oil content in the tested sample was >3%, which was deemed unqualified and required re-cleaning.

[0030] Compared with the prior art, the beneficial effects of the technical solution of this application are as follows:

[0031] This application provides a method for detecting residual oil content during the refilling of mineral oil transformers. The method involves cleaning the residual mineral oil inside the transformer, refilling it with natural ester insulating oil, sampling, and then using gas chromatography-tandem mass spectrometry (GC-MS) to detect the mineral oil content in the sample oil. This application constructs a complete system matching the refilling process with the detection method, enabling precise control of the refilling process. The refilling process employs a specific cleaning process, including at least three stages, to clean the residual mineral oil inside the transformer. By controlling the pressure, temperature, and amount of cleaning oil added during the cleaning process, residual mineral oil in difficult-to-clean areas inside the transformer is effectively adsorbed and eluted. Furthermore, a GC-MS detection method matching this specific cleaning and refilling process is developed, forming a system of synergistic detection methods for the refilling process. This solves the technical problem of inaccurate control of the refilling process due to the mismatch between traditional refilling processes and detection methods, thereby precisely controlling the refilling process and avoiding the risk of high residual mineral oil content affecting transformer performance due to inaccurate mineral oil quantification during refilling. Detailed Implementation

[0032] To facilitate understanding of this application, preferred embodiments are provided below to provide a more complete description of the application. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a thorough and complete understanding of the disclosure of this application.

[0033] 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 is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0034] As used herein, "optional," "optional," and "optional" refer to either "with" or "without" parallel options. If multiple "optional" entries appear in a technical solution, each "optional" entry is independent unless otherwise specified and there are no contradictions or mutual constraints. The term "and / or" as used herein includes any and all combinations of one or more related listed items. Unless otherwise specified, "multiple," "multiple," etc., as used herein refer to a quantity greater than 2 or equal to 2; for example, "one or more" indicates one, two, or more than two. In open-ended technical features or solutions described herein using words such as "containing," "including," and "comprising," unless otherwise specified, additional members beyond the listed members are not excluded. This can be considered as providing both a closed-ended feature or solution consisting of the listed members and an open-ended feature or solution that includes additional members beyond the listed members.

[0035] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0036] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0037] Transformer oil, also known as insulating oil, is a mineral oil obtained from natural petroleum through distillation and refining. During transformer operation, transformer oil is exposed to high-temperature environments for extended periods. Combined with the influence of oxygen, humidity, and metals such as copper and iron, it is highly susceptible to deterioration, leading to a decrease in breakdown voltage and an increase in surface tension. This significantly reduces the insulating properties of the transformer oil, affecting the normal operation of the transformer and consequently its service life. Natural ester insulating oil, however, possesses excellent properties such as a high ignition point, high flash point, environmental friendliness, and the ability to improve the heat resistance of insulating paper, providing a new solution for extending the insulation life of transformers.

[0038] During the refilling process of a transformer, it is necessary to clean the mineral oil inside the transformer and detect and monitor the residual amount of mineral oil after refilling. However, a complete process system for refilling and testing has not yet been formed, making it impossible to accurately control the refilling process and thus making it impossible to accurately assess the operating performance of the transformer.

[0039] Further, regarding methods for detecting residual mineral oil during the refilling process, traditional gas chromatography, while capable of separating mineral oil from filler oil (natural esters), relies solely on retention time for qualitative analysis and cannot effectively distinguish co-eluting interfering substances, and its detection sensitivity is limited. Infrared spectroscopy, limited by spectral overlap interference, experiences a decrease in signal-to-noise ratio and a significant increase in error at low residual levels. Clearly, traditional detection methods are incompatible with the refilling process. Traditional methods struggle to meet the demand for accurate detection of trace mineral oil residues, failing to achieve precise detection and quantification of low residual mineral oil levels and complex oil samples, thus becoming a critical issue that urgently needs to be addressed to ensure the good operating performance of transformers.

[0040] Firstly, this application provides a method for detecting the amount of residual oil during refilling of mineral oil transformers, comprising the following steps:

[0041] S1. Clean the residual mineral oil inside the mineral oil transformer.

[0042] S2. After cleaning, fill the interior of the mineral oil transformer with natural ester insulating oil.

[0043] S3. After filling, a sample is taken from the inside of the mineral oil transformer, and the mineral oil content in the sample is detected by gas chromatography-tandem mass spectrometry.

[0044] The cleaning pressure is 0.15 MPa-0.40 MPa, and the cleaning temperature is 50℃±2℃;

[0045] The cleaning process includes at least three stages:

[0046] Add 20%-30% of the total oil volume of the mineral oil transformer to the interior of the mineral oil transformer for the first stage of cleaning, and then discharge the waste liquid;

[0047] After the first stage of cleaning is completed, natural ester insulating oil, accounting for 35%-50% of the total oil volume of the mineral oil transformer, is added to the interior of the mineral oil transformer for the second stage of cleaning, and the waste liquid is discharged.

[0048] After the second stage of cleaning, natural ester insulating oil, accounting for 10%-20% of the total oil volume of the mineral oil transformer, is added to the interior of the mineral oil transformer for the third stage of cleaning, and the waste liquid is discharged.

[0049] This application establishes a method integrating refilling process and multimodal detection of residual oil quantity. In the refilling process of a specific cleaning process, it solves the technical problem in traditional refilling processes that rely solely on empirical flushing operations and lack parameter optimization, leading to inconsistent engineering implementation results. This method achieves accurate control of the refilling process and further develops a multimodal detection method to match the specific refilling process, thus solving the problem of unstable transformer refilling performance.

[0050] During the refilling process, a specific multi-stage cleaning process is employed to achieve efficient rinsing, solving the technical problem of high residual mineral oil levels inside transformers during traditional refilling. This reduces residual mineral oil levels, improving transformer performance. Specifically, the refilling process utilizes a dynamically optimized cleaning strategy, employing at least three stages of cleaning. By precisely setting cleaning parameters such as pressure, temperature, and cleaning agent ratios, efficient cleaning is achieved, ensuring the removal of mineral oil adsorbed on materials like cardboard and insulating paper inside the transformer. This reduces residual levels during refilling and avoids over- or under-cleaning issues that may occur with traditional cleaning processes. While ensuring that residual mineral oil levels are below a safe threshold, this process reduces the consumption of cleaning media and process time, effectively controlling the overall cost of the refilling process. It balances technical effectiveness and economic efficiency, achieving a good balance between cleaning efficiency and cost control.

[0051] The multimodal detection method employs gas chromatography-tandem mass spectrometry (GC-MS / MS), which boasts significant advantages such as strong resistance to matrix interference and low detection limits. It can accurately detect and quantify extremely low mineral oil content in refilled insulating oil samples, overcoming the technical challenges of traditional methods, such as high detection limits, weak anti-interference capabilities, inability to adapt to complex oil sample matrices, and difficulty in accurately detecting residual mineral oil. This enables accurate detection of low residual mineral oil in specific refilling processes, achieving a match between the refilling process and the detection method.

[0052] In some embodiments, during the first-stage cleaning step, the swelling effect of natural ester insulating oil on mineral oil is utilized to quickly wet the surface of the insulating paper and desorb the weakly adsorbed surface mineral oil (accounting for 60%-70% of the total residual amount). Further, the first-stage cleaning parameters can better improve the effect of the first-stage cleaning by satisfying at least one of the following pressure, temperature and time: (1) the cleaning pressure is 0.25MPa-0.30MPa; (2) the cleaning temperature is 50℃±2℃; (3) the cleaning time is 25min-35min.

[0053] In some embodiments, in the second-stage cleaning step, satisfying at least one of the following pressure and time parameters can better improve the effect of the second-stage cleaning: (1) the cleaning pressure is 0.20MPa-0.40MPa; (2) the cleaning temperature is 50℃±2℃; (3) the cleaning time is 15 min-70 min. Furthermore, the second-stage cleaning step includes at least two gradient cleanings to achieve better cleaning results, wherein the parameters for the first cleaning are: 0.30MPa≤pressure≤0.40MPa, temperature is 50℃±2℃, and time is 25min-40min; the parameters for the second cleaning are: 0.20MPa≤pressure<0.30MPa, temperature is 50℃±2℃, and time is 15min-30min. The first cleaning uses high pressure to enhance the shear force of the oil flow, peeling off the intermediate adsorbed layer of mineral oil inside the fiber insulation material. The second cleaning reduces the pressure to avoid mechanical damage to the insulation paper and remove residual trace amounts of mineral oil. Gradient pressure cleaning is used to clean the mineral oil in the difficult-to-clean parts inside the transformer and to ensure the integrity of the device structure.

[0054] As a non-limiting example, in the second-stage cleaning step, the cleaning time is 15 min to 70 min, including but not limited to 15 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, or any combination thereof and values ​​within that range. Preferably, it is 15 min to 40 min.

[0055] In some embodiments, the third-stage cleaning step is used to flush out residual oil in the pipeline to prevent secondary contamination. Among them, the effect of the third-stage cleaning can be better improved by satisfying at least one of the following pressure and time parameters: (1) the cleaning pressure is 0.15MPa-0.20MPa; (2) the cleaning temperature is 50℃±2℃; (3) the cleaning time is 25min-35min.

[0056] Traditional methods for detecting mineral oil residue based on gas chromatography or infrared spectroscopy, combined with empirical flushing processes, often rely on fixed-number, fixed-volume flushing. This lack of a scientific and systematic optimization model for flushing parameters leads to unstable flushing results. Insufficient flushing can negatively impact insulation performance, while excessive flushing can waste resources, severely limiting the quality and efficiency of transformer refilling. This application constructs a comprehensive process system integrating cleaning, refilling, and detection methods. This system significantly improves cleaning efficiency, reduces mineral oil residue, and ensures the stability of the transformer's internal structure during cleaning. Furthermore, it provides a precise detection process tailored to the results of this specific refilling process, jointly solving the technical challenges of high residue levels, large detection errors, and unstable transformer performance associated with traditional cleaning methods. This results in a standardized system for refilling processes and detection methods.

[0057] In some embodiments, after the first-stage cleaning is completed, the system is left to stand for 3-5 hours before the second-stage cleaning.

[0058] In some embodiments, after the second-stage cleaning is completed, the system is left to stand for 3-5 hours before the third-stage cleaning.

[0059] In some embodiments, after the third-stage cleaning is completed, the mixture is left to stand for 0.5h-2h before the natural ester insulating oil is filled.

[0060] By setting appropriate settling times between cleaning stages, the mineral oil in difficult-to-clean areas can be better penetrated and dissolved, thus improving the cleaning effect.

[0061] As a non-limiting example, the voltage rating of the mineral oil transformer is 110 kV.

[0062] As a non-limiting example, the mineral oil includes Karamay mineral insulating oil, which may be 25# Karamay mineral insulating oil.

[0063] As a non-limiting example, the natural ester insulating oil includes FR3 plant-based transformer insulating oil.

[0064] In some embodiments, after the first, second, and third stages of cleaning, the internal oil paper of the mineral oil transformer is inspected, and the dielectric constant change rate of the oil paper is ≤5%. Specifically, a frequency domain dielectric spectrometer (FDS) is used to detect the insulation state of the oil paper (understandably, the FDS monitoring results can indirectly reflect the degree of removal of polar residues in the oil paper medium). Only when the dielectric constant change rate is ≤5% can the next stage be proceeded. If the dielectric constant change rate is >5%, the cleaning steps are repeated until the dielectric constant change rate meets the above condition.

[0065] In some embodiments, the parameters of the gas chromatography-tandem mass spectrometry include: a DB-5MS column, helium as the carrier gas, a carrier gas flow rate of 1.5 mL / min, a column temperature program of increasing from 60°C to 280°C at a rate of 10°C / min, and an injection port temperature of 250°C.

[0066] In some embodiments, the parameters of the gas chromatography-tandem mass spectrometry (GC-MS) include: an electron impact ionization source with an ionization energy of 70 eV, an interface temperature of 280°C, an ion source temperature of 230°C, an ion monitoring mode of SIM, and m / z values ​​of 57 and 294 for quantitative ion monitoring. It should be noted that m / z 57 is considered the characteristic peak of mineral oil, and m / z 294 is considered the characteristic peak of natural esters.

[0067] Traditional chromatographic and spectroscopic detection methods are susceptible to interference from the sample being tested, especially in complex oil samples and cases with low mineral oil residue levels. These methods cannot accurately detect residual mineral oil in refilled oil samples, making it difficult to ensure stable transformer operation. This application utilizes a multimodal integrated detection technology combining gas chromatography and mass spectrometry, significantly improving detection accuracy. Compared to traditional detection techniques, it demonstrates a significant advantage in highly accurate quantification of trace residues, enhancing the sensitivity for identifying trace mineral oil residues. It achieves accurate quantification of residual mineral oil in refilled oil samples, effectively overcoming the misjudgment problems caused by spectral overlap or co-eluent interference in traditional detection methods. This enables accurate quantification of extremely low residue levels, providing quantitative filling of insulating oil and offering high-precision data support for transformer operational reliability assessment.

[0068] In some embodiments, the step of detecting the sample using gas chromatography-tandem mass spectrometry further includes sample pretreatment, specifically including: collecting a sample of insulating oil after transformer refilling, allowing it to stand, centrifuging and filtering it, and taking the filtrate for gas chromatography-tandem mass spectrometry detection.

[0069] As a non-limiting example, filtration is performed using a polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.22 μm.

[0070] Understandably, allowing the sample to stand further degasses it, thus improving detection accuracy. As a non-limiting example, the standing conditions are: allowing the sample to stand at room temperature for 30 minutes to allow all bubbles to be released.

[0071] It is understandable that centrifugation further removes insoluble impurities from the sample, reducing the interference of impurities on the detection results, while also reducing the impact of impurity particles on the detection instrument and improving detection stability.

[0072] As a non-limiting example, the centrifugation conditions are: 4000 rpm for 10 min.

[0073] The aforementioned testing method not only aims to accurately quantify the amount of residual mineral oil during insulating oil refilling, but also correlates it with transformer insulation performance indicators such as dielectric loss and breakdown voltage. By accurately detecting the amount of residual mineral oil during refilling, precise refilling of insulating oil is achieved, controlling the degree of contamination of natural ester insulating oil by residual mineral oil. This effectively suppresses the risk of insulation performance degradation caused by oil deterioration, fundamentally extending the long-term stable operating life of transformers, and meeting the core requirement of "ensuring the safe and stable operation of equipment."

[0074] In some embodiments, the detection method further includes: evaluating the transformer's operational stability and the effectiveness of the refilling process based on the mineral oil content in the test sample, wherein the evaluation method includes:

[0075] For Level 1 acceptance, the mineral oil content in the tested sample is ≤1%, and the evaluation is qualified.

[0076] For Level 2 acceptance, if the mineral oil content in the tested sample is ≤3%, it is considered qualified and requires 72 hours of operational monitoring.

[0077] For the third-level acceptance test, the mineral oil content in the tested sample was >3%, which was deemed unqualified and required re-cleaning.

[0078] In some embodiments, acceptance testing is completed within 24 hours ± 2 hours after refilling to ensure more accurate evaluation results.

[0079] This application establishes an integrated "cleaning-detection-feedback" mechanism, simultaneously achieving low residual mineral oil content, accurate filling, and precise detection of complex oil samples with low detection limits during the refilling process. It solves the technical problems of easily interfered test results, lack of quantitative basis for flushing processes, and inconsistent acceptance standards, ultimately leading to inaccurate control of residual content after transformer refilling. This ensures precise process control during transformer refilling and the final acceptance quality. A complete technical system, from flushing parameter optimization to accurate residual content detection, is established, overcoming the core bottlenecks of low detection accuracy and poor process reliability in traditional technologies.

[0080] For experimental parameters not specified in the following specific embodiments, please refer to the guidelines given in this application document first, or refer to experimental manuals or other experimental methods known in the art, or refer to the experimental conditions recommended by the manufacturer.

[0081] The raw materials and reagents involved in the following specific embodiments can be obtained commercially or prepared by those skilled in the art using known methods.

[0082] Example 1

[0083] A 110kV mineral oil transformer sample was selected, and a three-stage flushing scheme was adopted:

[0084] Pre-flushing stage: Add 25% volume (accounting for 25% of the total filling amount of the original mineral oil in the transformer) of natural ester insulating oil (FR3 plant-based transformer insulating oil) into the transformer and circulate and flush for 30 minutes under flushing parameters of pressure of 0.28MPa and temperature (temperature of natural ester insulating oil) of 50℃±2℃. After flushing, drain the waste liquid and keep the transformer stationary for 4 hours.

[0085] Main flushing stage: Add 40% volume (40% of the total mineral oil filling volume) of natural ester insulating oil (FR3 plant-based transformer insulating oil) to the inside of the above transformer, and flush in two cycles. The first flush is performed at a pressure of 0.35 MPa and a temperature (temperature of natural ester insulating oil) of 50℃ ± 2℃ for 30 minutes. After flushing, drain the waste liquid and keep the transformer still for 2 hours. Then, perform the second flush, with a volume of 40%, at a pressure of 0.25 MPa and a temperature (temperature of natural ester insulating oil) of 50℃ ± 2℃ for 20 minutes. After flushing, drain the waste liquid and keep the transformer still for 2 hours.

[0086] Final flushing stage: Add 15% volume (15% of the total oil filling volume of the original mineral oil) of natural ester insulating oil (FR3 plant-based transformer insulating oil) to the inside of the above transformer, and circulate and flush for 30 minutes under flushing parameters of pressure of 0.15MPa and temperature (temperature of natural ester insulating oil) of 50℃±2℃. After flushing, drain the waste liquid and keep the transformer stationary for 1 hour.

[0087] After the above flushing is completed, the transformer interior is filled with natural ester insulating oil (FR3 vegetable-based transformer insulating oil), and then oil samples are taken for analysis using gas chromatography-mass spectrometry (GC-MS). The analysis steps are as follows:

[0088] Sample pretreatment: The oil sample was allowed to stand at room temperature for 30 min, centrifuged at 4000 rpm for 10 min, and the liquid was filtered through a 0.22 μm polytetrafluoroethylene filter membrane. The filtrate was then injected into a gas chromatography-mass spectrometry (GC-MS) instrument for detection.

[0089] The parameters for gas chromatography include: DB-5MS column, helium as carrier gas, carrier gas flow rate of 1.5 mL / min, column temperature program of increasing from 60℃ to 280℃ at a rate of 10℃ / min, and injection port temperature of 250℃.

[0090] The mass spectrometry parameters included: electron impact ionization source, ionization energy of 70 eV, interface temperature of 280℃, ion source temperature of 230℃, ion monitoring mode SIM, and m / z values ​​of 57 and 294 for quantitative ion monitoring. It should be noted that m / z 57 is considered the characteristic peak of mineral oil, and m / z 294 is considered the characteristic peak of natural esters.

[0091] The results of the above gas chromatography-mass spectrometry (GC-MS) detection were processed, and the residual amount was calculated by internal standard method (using n-decane as internal standard, with an addition amount of 50 μL) and external standard method quantitative calibration curve (concentration gradient 0.1%-5%, specifically 0.1%, 0.5%, 1%, 2%, 5% (V / V)). The calculation formula is shown in (i). The relative deviation of parallel samples is required to be ≤5%, and 5 sets of parallel samples are required.

[0092] Residual amount (%) = (Mineral oil peak area × Internal standard concentration) / (Internal standard peak area × Sample volume) × 100% (i)

[0093] The results of the above residual amounts were evaluated and accepted:

[0094] Level 1 Acceptance (High-Quality Project): Residual content ≤1%, acceptance passed and re-inspection recommended after 2 years.

[0095] Level II Acceptance (Qualified Project): 1% < Residual Content ≤ 3%, requiring an additional 72 hours of operational monitoring.

[0096] Level 3 Acceptance (Rectification within a Time Limit): Residual amount >3%, rinse again.

[0097] Example 2

[0098] A 110kV mineral oil transformer sample was selected (the initial mineral oil content was at the same level as in Example 1), and a three-stage flushing scheme was adopted.

[0099] Pre-flushing stage: Add natural ester insulating oil (FR3 plant-based transformer insulating oil) accounting for 20% of the total volume of the original mineral oil in the transformer to the inside of the transformer. Flushing is carried out for 25 minutes under the conditions of pressure of 0.25MPa and temperature of 50℃±2℃. After flushing, the waste liquid is discharged and the transformer is kept still for 3 hours.

[0100] Main flushing stage: Add natural ester insulating oil accounting for 35% of the total oil volume into the transformer, and circulate and flush for 20 minutes under the conditions of pressure of 0.25MPa and temperature of 50℃±2℃. After flushing, drain the waste liquid and keep the transformer stationary for 3 hours.

[0101] Final flushing stage: Add natural ester insulating oil accounting for 10% of the total oil volume into the transformer, and circulate and flush for 25 minutes under the conditions of pressure of 0.15MPa and temperature of 50℃±2℃. After flushing, drain the waste liquid and keep the transformer stationary for 0.5h.

[0102] Sufficient natural ester insulating oil (FR3 vegetable-based transformer insulating oil) was filled into the interior of the cleaned transformer, and samples were taken 24 hours after filling. The oil samples underwent the same pretreatment as in Example 1, and were then detected and analyzed under the same GC-MS instrument parameters.

[0103] Example 3

[0104] Another 110kV mineral oil transformer sample was selected (the initial mineral oil content was at the same level as in Example 1), and a three-stage flushing scheme was adopted.

[0105] Pre-flushing stage: Add natural ester insulating oil (FR3 plant-based transformer insulating oil) accounting for 30% of the total volume of the original mineral oil in the transformer to the inside of the transformer. Flushing is carried out for 35 minutes under the conditions of pressure of 0.30MPa and temperature of 50℃±2℃. After flushing, the waste liquid is discharged and the transformer is kept still for 5 hours.

[0106] Main flushing stage: Add natural ester insulating oil accounting for 50% of the total oil volume into the transformer, and circulate and flush for 60 minutes under the conditions of pressure of 0.35MPa and temperature of 50℃±2℃. After flushing, drain the waste liquid and keep the transformer stationary for 5 hours.

[0107] Final flushing stage: Add natural ester insulating oil accounting for 20% of the total oil volume into the transformer, and circulate and flush for 35 minutes under the conditions of pressure of 0.20MPa and temperature of 50℃±2℃. After flushing, drain the waste liquid and keep the transformer stationary for 2 hours.

[0108] Sufficient natural ester insulating oil was filled into the interior of the cleaned transformer, and samples were taken 24 hours after filling. The oil samples underwent the same pretreatment as in Example 1, and were then detected and analyzed under the same GC-MS instrument parameters.

[0109] Example 4

[0110] The difference from Example 1 is that the main flushing stage is only one flush, and the flushing parameters are: pressure of 0.35 MPa and flushing time of 50 min. The remaining steps are the same as in Example 1.

[0111] Comparative Example 1

[0112] The difference from Example 1 is that no main rinse and final rinse are performed; only a pre-rinse is performed. The pre-rinse time is used to make up for the time of the main rinse and final rinse. The remaining steps are the same as in Example 1.

[0113] Comparative Example 2

[0114] The difference from Example 1 is that only pre-rinse and main rinse are performed, but the main rinse is not performed. The time of pre-rinse is made up for the time of main rinse. The remaining steps are the same as in Example 1.

[0115] Comparative Example 3

[0116] The difference from Example 1 is that only pre-rinse and main rinse are performed, and no final rinse is performed. The remaining steps are the same as in Example 1.

[0117] Comparative Example 4

[0118] The difference from Example 1 is that the pre-rinse, main rinse and final rinse are all carried out using 25% by volume natural ester insulating oil, and the remaining steps are the same as in Example 1.

[0119] Comparative Example 5

[0120] The difference from Example 1 is that the rinsing temperature for the pre-rinse, main rinse, and final rinse is 40°C, while the remaining steps are the same as in Example 1.

[0121] Comparative Example 6

[0122] The difference from Example 1 is that the rinsing temperature for the pre-rinse, main rinse, and final rinse is 58°C, while the remaining steps are the same as in Example 1.

[0123] Comparative Example 7

[0124] The difference from Example 1 is that in the mass spectrometry parameters of gas chromatography-mass spectrometry (GC-MS), the acquisition mode is selected as full scan mode (SCAN), and the acquisition range is 45m / z-800m / z. The remaining steps and other GC-MS parameters are the same as in Example 1.

[0125] Experimental Example 1

[0126] The detection methods of Examples 1-4 and Comparative Examples 1-7 were evaluated, and the evaluation results are shown in Table 1 below:

[0127] Table 1: Evaluation Results of the Detection Method for Residual Oil Content During Refilling of Mineral Oil Transformers

[0128]

[0129] As shown in Table 1 above, the detection method for residual mineral oil in mineral oil transformers provided in this application can accurately quantify the amount of residual mineral oil during the refilling process. This achieves a complete system matching the transformer refilling process and the detection method, enabling targeted detection of specific refilling processes and precise control over the refilling process, thus ensuring the long-term stable operation of the transformer. Furthermore, as shown in Table 1, the refilling process in the detection method provided in this application includes a specific cleaning process. This cleaning process can thoroughly clean the mineral oil in the transformer, significantly reducing the amount of residual mineral oil, thereby further ensuring the long-term stable operation of the transformer.

[0130] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0131] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for detecting the amount of residual oil during refilling of a mineral oil transformer, characterized in that, Includes the following steps: Clean the internal mineral oil residue of the mineral oil transformer; After cleaning, the interior of the mineral oil transformer is filled with natural ester insulating oil; After filling, a sample was taken from the inside of the mineral oil transformer, and the mineral oil content in the sample was detected by gas chromatography-tandem mass spectrometry. The cleaning pressure is 0.15 MPa-0.40 MPa, and the cleaning temperature is 50℃±2℃; The cleaning process includes at least three stages: Add 20%-30% of the total oil volume of the mineral oil transformer to the interior of the mineral oil transformer for the first stage of cleaning, and then discharge the waste liquid; After the first stage of cleaning is completed, natural ester insulating oil, accounting for 35%-50% of the total oil volume of the mineral oil transformer, is added to the interior of the mineral oil transformer for the second stage of cleaning, and the waste liquid is discharged. After the second stage of cleaning, natural ester insulating oil, accounting for 10%-20% of the total oil volume of the mineral oil transformer, is added to the interior of the mineral oil transformer for the third stage of cleaning, and the waste liquid is discharged.

2. The method for detecting the amount of residual oil during refilling of a mineral oil transformer according to claim 1, characterized in that, In the first stage of cleaning, the cleaning pressure is 0.25MPa-0.30MPa, and the cleaning time is 25min-35min.

3. The method for detecting the amount of residual oil during refilling of a mineral oil transformer according to claim 1, characterized in that, In the second stage of cleaning, the cleaning pressure is 0.20MPa-0.40MPa, and the cleaning time is 15 min-70 min.

4. The method for detecting the amount of residual oil during refilling of a mineral oil transformer according to claim 3, characterized in that, The second-level cleaning process includes at least two cleaning steps: The parameters for the first cleaning are: 0.30MPa ≤ pressure ≤ 0.40MPa, and the time is 25min-40min; The parameters for the second cleaning are: 0.20MPa ≤ pressure < 0.30MPa, and the time is 15min-30min.

5. The method for detecting the amount of residual oil during refilling of a mineral oil transformer according to claim 1, characterized in that, In the third-stage cleaning process, the cleaning pressure is 0.15MPa-0.20MPa, and the cleaning time is 25min-35min.

6. The method for detecting the amount of residual oil in a mineral oil transformer after refilling, according to any one of claims 1 to 5, is characterized in that, After the first stage of cleaning, let it stand for 3-5 hours; and / or, after the second stage of cleaning, let it stand for 3-5 hours; and / or, after the third stage of cleaning, let it stand for 0.5-2 hours.

7. The method for detecting the amount of residual oil in a mineral oil transformer after refilling, according to any one of claims 1 to 5, is characterized in that, The voltage rating of the mineral oil transformer is 110 kV; and / or, the mineral oil includes Karamay mineral insulating oil; and / or, the natural ester insulating oil includes FR3 plant-based transformer insulating oil.

8. The method for detecting the amount of residual oil in a mineral oil transformer after refilling, according to any one of claims 1 to 5, is characterized in that, After the first, second, and third cleaning stages, the internal oil paper of the mineral oil transformer was tested, and the dielectric constant change rate of the oil paper was ≤5%.

9. The method for detecting the residual oil content during refilling of a mineral oil transformer according to any one of claims 1 to 5, characterized in that, The parameters of the gas chromatography-tandem mass spectrometry include: Gas chromatography parameters: DB-5MS column, helium as carrier gas, carrier gas flow rate of 1.5 mL / min, column temperature program of increasing from 60℃ to 280℃ at a rate of 10℃ / min, and injection port temperature of 250℃. Mass spectrometry parameters: electron impact ionization source, ionization energy of 70 eV, interface temperature of 280℃, ion source temperature of 230℃, ion monitoring mode SIM, and m / z of quantitatively monitored ions of 57 and 294.

10. The method for detecting the amount of residual oil in a mineral oil transformer after refilling, according to any one of claims 1 to 5, is characterized in that, The testing method also includes: evaluating the transformer's operational stability and refilling effect based on the mineral oil content in the test sample; the evaluation method includes: For Level 1 acceptance, the mineral oil content in the tested sample is ≤1%, and the evaluation is qualified. For Level 2 acceptance, if the mineral oil content in the tested sample is ≤3%, it is considered qualified and requires 72 hours of operational monitoring. For the third-level acceptance test, the mineral oil content in the tested sample was >3%, which was deemed unqualified and required re-cleaning.

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