Cellulose Insulation Research Articles

Method for assessing unevenness of cellulose insulation layers aging of power transformers winding

Introduction. Improving the methods of estimating the insulation aging of the oil-immersed power transformer windings is an urgent task for transformer condition monitoring systems. The scientific novelty of the work is to take into account the uneven distribution of temperature and humidity along the vertical axis of the winding in modeling the aging of insulation and to develop methods for determining the conditions under which the aging rate of insulation in the intermediate layer will exceed aging rate in the hottest layer. The purpose of the work is to evaluate the wear unevenness of cellulose insulation based on modeling the distribution of temperature and humidity along the vertical axis of the power transformer winding. Methods. The transformer winding is mentally divided into horizontal layers of equal height, the reduction of service life is calculated in parallel for all horizontal layers. Layer with the maximum degree of aging for the entire period of operation and storage of the transformer is recognized as determining the reduction in the service life of the insulation of the transformer as a whole. A model of the interaction of winding layers is developed, with determination of temperatures, humidity, relative rate of aging of each layer due to temperature and humidity as a function of traditional design parameters such as load, cooling temperature, heat capacity and thermal resistance of transformer. The index of exceeding the aging rate by the layered method in comparison with this rate for the hottest layer is offered. The method of genetic algorithms determines the conditions for obtaining the maximum value of this index. Results. A computer model has been developed to predict the aging of the cellulose insulation of transformer windings. According to the proposed method, a layer with significantly shorter insulation aging time (in the example, time reduced by 39.18 %) than for the upper layer was determined, which confirms the feasibility of layer-by-layer monitoring and modeling of insulation aging processes of power oil-immersed transformer windings.

The application of a molecular sieve for drying the insulation system of a power transformer in terms of improving its perational reliability

The first research objective was the assessment of the selectivity of water and hydrogen adsorption by the 3A molecular sieve (MS) in the terms of the safety of using the DGA (Dissolved Gas Analysis) method as a diagnostic technique. The second objective was to demonstrate the efficiency of drying the insulation system consisting of cellulose insulation impregnated with various insulating liquids in terms of improving safety and extending the service life of power transformers. In order to achieve the assumed objectives, measurement systems were prepared and material tests were carried out, based mainly on chromatographic analyzes and measurements of water content using the Karl Fischer titration method. On the basis of the obtained test results and the conducted physical analyzes, the selectivity of MS sorption was shown and it was explained that the facilitator of the adsorption of water molecules is their polar nature related to their large dipole moment. The high efficiency of drying cellulose insulation impregnated with various insulating liquids using MS was also demonstrated

Life Cycle Environmental and Cost Analysis of Building Insulated with Hemp Fibre Compared to Alternative Conventional Insulations – a Swedish Case Study

This study presents a comparative life cycle analysis (LCA) and life cycle costing (LCC) assessments of hemp fibre and conventional alternative insulations for the climate shell of a building. The conventional alternative insulations compared to the hemp fibre are cellulose and glass wool. The object of the analysis is a one-story single-family house, in Växjö, Sweden, and the lifetime of the house is set to 50 years. The LCA focuses on the Global Warming Potential (GWP) impact and the LCC during the lifetime of the different insulations for the building are calculated using the net present value method. The results show that the net GWP-impact for hemp fibre insulation is about 10 % lower and the cost is about 20 % higher than the conventional glass wool alternative. Furthermore, the analysis shows that cellulose insulation has slightly lower GWP-impact and nearly the same cost as the glass wool alternative. Sensitivity analyses regarding five different issues were performed and these show that: for cellulose coming from recycled paper, it contributed to less fossil emissions than non-recycled paper. If the data source for glass wool insulation is changed from environmental product declarations (EPD) to generic data, the greenhouse gas emissions increased. By replacing district heating system with geothermal heating system, fossil GWP-impacts also increased while the LCC analysis shows that operating costs is reduced. If the fuel is changed from diesel to electricity, fossil emissions are reduced over the life cycle of the building. If only part A1 – A5 is reported, as required for the Swedish climate declaration, the results point to the outcomes that glass wool insulation gives the least fossil GWP-impact while the hemp fibre gives the least net GWP-impact.

Improved Fire Retardancy of Cellulose Fibres via Deposition of Nitrogen-Modified Biopolyphenols.

Driven by concerns over the health and environmental impacts of currently used fire retardants (FRs), recent years have seen strong demand for alternative safer and sustainable bio-based FRs. In this paper, we evaluated the potential of nitrogen-modified biopolyphenols as FRs for cellulosic natural fibres that could be used in low-density cellulose insulations. We describe the preparation and characterisation of nitrogen-modified lignin and tannin containing over 10% nitrogen as well as the treatment of cellulose pulp fibres with combinations of lignin or tannin and adsorption-enhancing retention aids. Combining lignin or tannin with a mixture of commercial bio-based flocculant (cationised tannin) and anionic retention chemical allowed for a nearly fourfold increase in lignin adsorption onto cellulosic pulp. The nitrogen-modified biopolyphenols showed significant improvement in heat release parameters in micro-scale combustion calorimetry (MCC) testing compared with their unmodified counterparts. Moreover, the adsorption of nitrogen-modified lignin or tannin onto cellulose fibres decreased the maximum heat release rate and total heat release compared with cellulose reference by 15–23%. A further positive finding was that the temperature at the peak heat release rate did not change. These results show the potential of nitrogen-modified biopolyphenols to improve fire-retarding properties of cellulosic products.

Prediction of the Degree of Polymerization in Transformer Cellulose Insulation Using the Feedforward Backpropagation Artificial Neural Network

The life expectancy of power transformers is primarily determined by the integrity of the insulating oil and cellulose paper between the conductor turns, phases and phase to earth. During the course of their in-service lifetime, the solid insulating system of windings is contingent on long-standing ageing and decomposition. The decomposition of the cellulose paper insulation is strikingly grievous, as it reduces the tensile strength of the cellulose paper and can trigger premature failure. The latter can trigger premature failure, and to realize at which point during the operational life this may occur is a daunting task. Various methods of estimating the DP have been proposed in the literature; however, these methods yield different results, making it difficult to accurately estimate a reliable DP. In this work, a novel approach based on the Feedforward Backpropagation Artificial Neural Network has been proposed to predict the amount of DP in transformer cellulose insulation. Presently, no ANN model has been proposed to predict the remaining DP using 2FAL concentration. A databank comprising 100 data sets—70 for training and 30 for testing—is used to develop the proposed ANN using 2-furaldehyde (2FAL) as an input and DP as an output. The proposed model yields a correlation coefficient of 0.958 for training, 0.915 for validation, 0.996 for testing and an overall correlation of 0.958 for the model.

Novel Characteristic Quantities for Determining the Moisture State of Oil-Impregnated Cellulose Insulation Using the Extended Debye Model

Despite the technical popularity of the dielectric response (DR) methods used for the nonintrusive diagnosis of the cellulose insulation condition, it is still considered a challenging and tough task so far to trustworthily interpret the details of the measurement results for further understanding and tracing the insulation changes behind. From a novel perspective of parametric study on the circuital DR equivalence of cellulosic insulation—extended Debye model (EDM), the new dielectric characteristic quantities and the quantification approach to determine the cellulosic moisture condition are investigated in the present study. First, a kind of tailor-made scale-down bushing model is prepared, with its cellulosic condenser body absorbing differently controlled quantities of water to simulate the dampness of real-life insulation, of which the frequency-domain spectroscopy (FDS) is measured under controlled temperatures. Then, the EDM is employed for a parameterized study on the FDS details with the moisture changes, by identifying the model parameters against the FDS curves, whereby the two time-domain dielectric spectra—polarization/depolarization current and return voltage—are transferred from the FDS so that a set of hybrid time–frequency characteristic quantities is proposed, which is revealed to be indicative of the dampness variations of cellulosic insulation. Finally, the principal component analysis and the feature recognition algorithm based on minimum distance are applied to determine the moisture content of the condenser body, which verifies the holistic effectiveness of the proposed method.

Analysis of the Impregnation Process of Cellulose Materials by Using Ester-Based Liquids and Mineral Oil

Nowadays, new alternative of dielectric liquids with biodegradable characteristics has been considered to replace conventional mineral oil in both distribution and power transformer applications. However, there are some manufacturing processes that need to be modified to incorporate these ecological fluids, mainly in power transformers. Ester liquids, either natural or synthetic, show higher viscosity than mineral oil; therefore, a significant impact on the impregnation process of insulation materials is expected. In this work, the impregnation process of cellulose insulation is investigated by using three different liquids: natural ester (NE), synthetic ester (SE), and mineral oil. Laboratory tests were carried out using insulation blocks and pressboard samples to evaluate the influence of each fluid in the cellulose material. It is shown that the impregnation process with ester liquids is longer than mineral oil, at room temperature; however, it could be reduced by increasing the temperature of the ester liquid.

Impact of the Use of Vegetable Oil on the Mechanical Failure of the Cellulosic Insulation of Continuously Transposed Conductors in Power Transformers

Natural esters have become of interest for the industry in recent years as dielectric liquids for power transformers, and many studies are focused on their dielectric and chemical properties and on their influence in the degradation of the solid insulation due to aging. However, very little is known about their impact on the evolution of the mechanical properties of the paper insulation, which are acknowledged to have a considerable influence in their overall performance and reliability during the operating life of power transformers. This work studies the effects of thermal aging with vegetable oil in some commercial components, which are commonly used in power transformers, such as an insulated continuously transposed conductor (CTC) and samples of thermally upgraded crepe insulation. The changes in the properties of the crepe paper insulation are characterized through the degree of polymerization and tensile testing. Failure initiation and propagation in the insulation of the CTC is analyzed macroscopically. The results are compared with those obtained when using mineral oil, showing that the use of vegetable oil has a protective effect over mechanical properties of the studied types of paper insulation.

Protocol for characterizing the molar mass distribution and oxidized functionality profiles of aged transformer papers by gel permeation chromatography (GPC)

Oil-immersed paper insulation and paper pressboards for structural support are widely used in electrical power transformers. Cellulose thus fulfills an essential task for the smooth power supply of our societies. However, the prevailing temperatures in such equipment, combined with a targeted service life of several decades, pose a serious challenge to the long-term integrity of cellulosic paper insulation. Therefore, numerous studies have been conducted to obtain kinetic data on the degradation processes that contribute to the thermally induced decomposition of cellulose. These studies usually rely on the assessment of the average degree of polymerization by viscosity measurements. In this work, we applied and optimized more advanced methods for the characterization of cellulosic materials based on gel permeation chromatography for the special case of thermally stressed unbleached Kraft paper samples. This allowed studying the molar mass distributions of paper polymers upon exposure to heat, as well as the investigation of changes in their conformation in solution and the observation of thermally induced cross-linking. In combination with group-selective fluorescence labeling, it was possible to track over time the changes in molar mass-dependent profiles of carbonyl and carboxyl groups of authentic Kraft insulator paper samples under thermal stress. In addition, changes of the hemicellulose composition were quantified. We hope that this analytical approach to the in-depth characterization of thermally stressed insulator paper will prove useful for future studies of this important cellulose product, and that our findings will contribute to a better understanding of the thermal decomposition of paper in general.Graphical abstract

Influence of Ester Liquids on Dielectric Strength of Cellulose Kraft Paper

Generally, impregnation of solid insulation is performed to increase the dielectric strength and reduce the dielectric losses of solid insulants. This increase in dielectric strength depends on the oil’s diffusion and dielectric properties. This paper investigates the diffusion behavior of mineral oil and ester fluids (synthetic, natural, and mixed) to understand the influence of oil diffusion on paper breakdown voltage. To better understand this phenomenal influence, cellulose insulation paper of different thicknesses has been considered. Wetting characteristics of various oil-paper insulation systems were investigated with and without thermal stressing. Thermal aging was carried out as per modified ASTM D1934 at 110 °C, 140 °C, 160 °C, and 185 °C respectively for 2 weeks. The wetting characteristics and influence of different oils on paper breakdown voltage were explicitly reported. It is inferred that paper wetting characteristics are attributable to the type of oil, the thickness of paper, and the aging factor of oil-paper insulation. Importantly, the increase in paper dielectric strength and diffusion behavior for ester fluids is found to be superior to that of the mineral insulating oils.

Designing highly insulated cross-laminated timber external walls in terms of hygrothermal performance: Field measurements and simulations

Keeping wood dry both under construction and service is important to prevent possible moisture damages in wooden buildings. However, practice has shown that without weather protection, wooden structures may get soaked during construction. Therefore, our aim was to evaluate the impact of vapour permeable and low permeable highly insulated external wall assemblies, façade orientation, and initial moisture content on the hygrothermal performance of cross-laminated timber (CLT) external walls. We carried out field measurements in the cold and humid Estonian climate, for which five types of test walls were designed and manufactured. Simulation models for future research were also created and validated. Field measurements showed that the CLT external walls were hygrothermally safe in the observed cold and humid climate and the CLT panel provided sufficient control of the water vapour diffusion. The use of low vapour permeable external insulation can be beneficial against vapour permeable insulation if low moisture content of the CLT panel (factory dry) during construction is maintained and insulation is installed airtightly. Cellulose insulation can be a safe choice when selecting water vapour permeable insulation for the external wall in case the construction is planned without weather protection. Mould growth risk calculations based on measured hygrothermal conditions showed that the high moisture content in the thin surface layer of the CLT panel may not be critical when dry-out time is short. The probability of failure must be determined by stochastic analysis using a variety of influencing parameters.

Charge Carriers Relaxation Behavior of Cellulose Polymer Insulation Used in Oil Immersed Bushing.

Cellulose polymer insulation material is widely used in oil immersed bushing. Moisture is one of the important reasons for the deterioration of cellulose polymer insulation, which seriously threatens the safe and stable operation of bushing. It is significant to study the polarization and depolarization behavior of oil-immersed cellulose polymer insulation with different moisture condition under higher voltage. Based on polarization/depolarization current method and charge difference method, the polarization/depolarization current, interfacial polarization current and electrical conductivity of cellulose polymer under different DC voltages and humidity were obtained. Based on molecular-dynamics simulation, the effect of moisture on cellulose polymer insulation was analyzed. The results show that the polarization and depolarization currents become larger with the increase in DC voltage and moisture. The higher applied voltage will accelerate the charge carrier motion. The ionization of water molecules will produce more charge carriers. Thus, high DC voltage and moisture content will increase the interface polarization current. Increased moisture content results in more charge carriers ionized by water molecules. In addition, the invasion of moisture will reduce the band width of cellulose polymer and enhance its electrostatic potential, so as to improve its overall electrical conductivity. This paper provides a reference for analyzing the polarization characteristics of charge carriers in cellulose polymer insulation.

Study on Aging Assessment Model of Transformer Cellulose Insulation Paper Based on Methanol in Oil

Methanol is considered to be a new chemical marker to estimate the aging state of transformer cellulose insulation paper. The key to improve the assessment accuracy is to establish the precise relationship between the concentration of methanol in oil and degree of polymerization (DP) of insulation paper. The previous research in this area has shortcomings and needs to be further improved. In this article, first, an aging assessment basic model (temperature 20 °C, moisture content of insulation paper 0.637%) is established based on the theoretical derivation of cellulose degradation kinetics, and is calculated by 130 °C thermal aging experiment. Furthermore, the effects of different temperatures (20 °C–90 °C) and moisture contents of insulation paper (0.6%–3.4%) on methanol in oil are studied by diffusion experiment. Based on the above effects, the temperature and moisture correction factors are established by mathematical reduction. What is more, a modified model is proposed by integrating the basic model and the correction factors. Eventually, the verification experiment is randomly prepared to test the accuracy of modified model and the result shows that the relative error of DP is within 7%. The physical meaning and accuracy of aging assessment are improved by model derivation and modification of influencing factors.

A review on the research progress and future development of nano‐modified cellulose insulation paper

Focussing on the insulating material of power transformer—cellulose insulation paper, this paper first introduces the basic characteristics and engineering application background of insulation paper. Then, the research progress of improving the mechanical properties, thermal stability and electrical properties of insulation paper by nano modification in recent years is compared, and the promotion mechanism is analysed. In addition, in practical engineering application, the oil–paper composite insulation system composed of insulation paper and insulating oil is used for the internal insulation of oil immersed transformer. Therefore, the influence of modified insulation paper on the performance of oil–paper composite insulation system is analysed. Finally, the newly reported new insulation paper is introduced, and the future development trend of modification of traditional insulation paper is analysed.

농촌주택 및 목조주택 표준모델 구조체의 습·열 환경 성능 개선 방안

The purpose of this study was to investigate whether the standard models for rural housing and wooden housing model have performance for hygrothermal and to propose a way of improvement relevant to hygrothermal performance for those models. All of the models to be analyzed were found to have some parts that were absent of stability in terms of performance for hygrothermal. In the process of analyzing the causes and proposing improvement measures, the following conclusions were derived. Fist, The exterior surface of the structure should be composed of a structure with good moisture permeability, and for the interior surface, a variable vapor retarder paper should be applied in consideration of the reverse condensation phenomenon in summer. Second, in terms of performance for hygrothermal, applications of external insulation plaster finish to the exterior wall or of ventilation method using a rafter vent on the roof should be avoided. Third, a rain screen method with a ventilation layer should be applied to the exterior wall, and a method of constructing ventilation layer separated from the insulation layer with a vapor retarder paper should be applied to the roof. Fourth, the application of insulation materials having capillary action, such as wood fiber insulation board or cellulose insulation board, contributes to more stable performance for hygrothermal.

Assessment of Transformer Cellulose Insulation Life Expectancy Based on Oil Furan Analysis (Case Study: South African Transformers)

Assessment of Transformer Cellulose Insulation Life Expectancy Based on Oil Furan Analysis (Case Study: South African Transformers)

Fracture toughness as an alternative approach to quantify the ageing of insulation paper in oil

Oil-immersed transformers use paper and oil as insulation system which degrades slowly during the operation of these machines. Cellulose materials are used generally as insulation solid in power transformers. The degree of polymerization (DP), defined as number of repeating β-glucose residues in the cellulose molecule, is a critical property of cellulosic insulation material used in transformers, since it provides information about paper ageing and its mechanical strength. The fast-developing electric power industry demanding superior performance of electrical insulation materials has led to the development of new materials, as well as different drying techniques performed during transformer manufacturing and service when required. Both developments have caused some practical difficulties in the DP measurement. Moreover, the increasing interest in synthetic dielectric materials replacing cellulose materials requires measuring alternative properties to the DP to quantify the degradation of insulation solids over time. In this sense, this paper proposes the possibility of analyzing paper degradation through fracture toughness. This approach is different from the study of mechanical properties such as tensile strength or strain because it provides a tool for solving most practical problems in engineering mechanics, such as safety and life expectancy estimation of cracked structures and components which cannot to be considered through the traditional assessment of the mechanical resistance of the material. An accelerated thermal ageing of Kraft paper in mineral oil was carried out at 130 °C during different periods of time, to obtain information on the kinetics of the ageing degradation of the paper. Double-edged notched specimens were tested in tension to study their fracture toughness. The evolution of the load–displacement curves obtained for different ageing times at the ageing temperature of 130 °C was utilized to the determination of the stress intensity factor. Furthermore, different kinetic models based on this stress intensity factor were applied to relate its evolution over time as a function of the temperature. Finally, the correlation between the DP and stress intensity factor, which depends on the fiber angle, was also defined.Graphic abstract

Examination on Water Management Method in the Same Electrode in PEFC

Recently, Polymer Electrolyte Fuel Cells (PEFCs) are beginning to be used in various fields as a clean energy source because they don’t emit carbon dioxide during operating. However, PEFCs have some problems such as a cost reduction and durability etc. Generally, PEFCs need a humidification system to avoid dryness of membrane during operating, but the amount of energy supplied to the humidifier is large, and reduces a system efficiency, and the cost of the humidification system is also necessary. And, the steam in the cathode gas becomes supersaturation in the vicinity of gas outlet, and thereafter it is condensed because the steam is generated by the cell reaction and is multiplied toward the gas outlet. Because the use of humidifier increases the amount of condensation and causes the water management issues such as the flooding phenomenon and the plugging phenomenon in the vicinity of gas outlet, these issues make the cell voltage unstable. Our laboratory has proposed the Self Water Management Separator (SWMS) with a bypass channel to solve these issues. The SWMS moves excess water from gas outlet to gas inlet through the bypass channel where filled water absorption material. Excess water was absorbed by a capillary phenomenon of water absorption material, and it moved from gas outlet to gas inlet by a concentration difference of water. The previous study clarified that the bypass position depended on the operating condition, and the optimum bypass position under non-humidifying and non-heating conditions (w/o humidifier and heater) was at gas inlet. Therefore, this study aims to select the optimum water absorption material for SWMS. The specification demanded for the water absorption material is a water supply and drainage ability and a handling ability. We prepared four water absorption material such as polyvinyl alcohol sponge (PVA), diatomite powder, cellulose fiber insulation (CFI), and EM diatomite grain. Here, cellulose insulation is a wood fiber insulation material. The SWMS was installed in only cathode side and a single serpentine was applied to both separators as a gas channel. The cell performance was evaluated by IV performance and Cole-Cole plots of AC impedance method under the standard condition and a durability test condition. Here, the standard condition and the durability test condition mean 0.3A/cm2 of the current density and Uf/Uox=70%/40% of the fuel/oxidant gas utilization, and 0.2A/cm2 and 45%/25%, respectively. The cell temperature of both conditions was 30°C. As a result, the resistance polarizations of the cell with SWMS on all water absorption material were equivalent or smaller than that of the cell w/o bypass channel as shown in Fig.1. Especially, the initial performance of the cell where PVA or CFI was filled in the bypass channel was better than that of others in a high current density region. The activation polarization of the cell with PVA was the smallest, and it has hardly changed on the durability test. Therefore, because PVA uniforms the humid condition in the cell, consequently the activation and resistance polarizations are improved by the increases of three phase interface and the ion conductivity. However, although the IV performance of the cell with CFI was almost the same as that of PVA, the resistance and activation polarizations were a little large compared with others and the diffusion polarization began to grow up. Because CFI has a high water supply and drainage ability, it deprived the membrane and three phase interface of necessary water, consequently it deteriorated the cell performance. Therefore, we decided that PVA is the most suitable as the water absorption material of the bypass channel from viewpoints of cell performance and handling ability. Figure 1

Solubility analysis of nano particles, cellulose crystalline region and cellulose molecule, and the impact study of crystalline region on properties of cellulose insulating paper

ABSTRACT For the first time, molecular dynamics simulation was used to analyse the solubility of five kinds of nanoparticles (SiO2, ZnO, Al2O3, Fe2O3, TiO2), cellulose crystalline region and cellulose molecules in this paper. The results show that the solubility of cellulose nanoparticles is positively related to the number of –OH groups on the surface of nanoparticles. The solubility between nano particles and cellulose molecules is smaller than that between cellulose crystalline region and cellulose molecules, which leads to the direct introduction of nano particles for physical modification reducing the solubility parameters of insulating paper. Through the analysis of mechanical properties, thermal stability and insulation properties, it is concluded that the comprehensive performance of the model with 70% crystalline region ratio is the best. The proportion of crystalline region further increased, the improvement of thermal stability is not obvious; the relative permittivity and the content of crystalline region are in line with the binomial fitting curve, and the constant term in the fitting curve is the relative permittivity of the amorphous region model; increasing the proportion of crystalline region is beneficial to improve the insulation performance of cellulose insulation paper.

Experimental and molecular level analysis of natural ester delaying degradation of cellulose insulation polymer

Developing green insulation materials has become an important direction for future research. As a new environmental insulation liquid, natural ester can effectively delay cellulose insulation polymer ageing. Mastering the mechanism of natural ester delaying the cellulose ageing could promote its application in power transformers. In this study, based on the accelerated thermal ageing of pressboard immersed in natural ester and 25# mineral oil at 120°C for 221 days, the thermal ageing rate and the levelling off degree of polymerisation (LODP) for two kinds of oil-impregnated pressboards were compared. The molecular level mechanism of natural ester delaying cellulose degradation and keeping higher LODP value was proposed using molecular dynamics simulation. At the early stage of thermal ageing, cellulose with a higher degree of polymerisation (DP) can form many hydrogen bonds with hydronium ions, and their binding energy is stronger, which can accelerate the acid hydrolysis of cellulose, causing the DP of pressboard immersed in natural ester and mineral oil to decrease rapidly. With the breaking of the cellulose molecular chain, the number of hydrogen bonds and binding energy between cellulose and hydronium ions becomes smaller and the thermal ageing rate decreases gradually. At the end stage of ageing, it is difficult for the hydronium ions to enter the crystalline cellulose, acid hydrolysis of crystalline cellulose is hard to conduct, leading to the occurrence of the LODP phenomenon. The degradation rate of cellulose in natural ester is only 50% of that in mineral oil. The cellulose LODP value in natural ester is over 200 larger than that in mineral oil. Compared with the mineral oil-cellulose system, natural ester can form hydrogen bonds with hydronium ions and lead to fewer hydronium ions in cellulose, fewer hydrogen bonds and smaller binding energy between cellulose and hydronium ions, which can reduce the acid hydrolysis reaction of cellulose. This study provides a theoretical explanation for natural esters to delay the ageing of insulation paper.