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Characterized by its exceptional electrical, physical, and chemical properties, 1-phenyl-1-xylylethane (PXE) insulating oil finds extensive application in the realm of power capacitor insulation. In this study, molecular simulation is employed to investigate the reactivity of PXE insulating oil molecules and the impact of temperature on water diffusion behavior in PXE insulating oil, as well as its solubility. The findings demonstrate a higher propensity for hydrogen atoms in nucleophilic and electrophilic positions within PXE insulating oil molecules to interact with water molecules. The inclusion of a temperature field enhances the Brownian motion of water molecules and improves their diffusion ability within the oil. Furthermore, the temperature field diminishes the interaction force between water molecules and the oil medium. Under the influence of this temperature field, there is an increase in the free volume fraction of PXE insulating oil, leading to a weakening effect on hydrogen bonds between oxygen and hydrogen atoms within PXE insulating oil. Additionally, with increasing temperature, there is an elevation in moisture solubility within insulating oil, resulting in a transition from a suspended state to a dissolved state. [ABSTRACT FROM AUTHOR]

The study determines the frequency–temperature dependence of the conductivity of a moist solid insulation component of power transformers, impregnated with the innovative bio-oil NYTRO® BIO 300X, manufactured from plant-based raw materials. The research was conducted for six moisture levels ranging from 0.6% to 5% by weight, within a frequency range from 10−4 Hz to 5 · 103 Hz and measurement temperatures from 20 °C to 70 °C, with a 10 °C step. The conduction model for both DC and AC, based on the quantum mechanical phenomenon of electron tunneling between water nanodroplets, was used to analyze the obtained results. It was determined that the frequency dependence of the conductivity of pressboard-bio-oil-moisture composites is influenced by two factors as follows: the activation energy of conductivity and the activation energy of relaxation time. For each moisture content, 16 values of the activation energy of the relaxation time and 16 values of the activation energy of conductivity were determined. It was found that the values of activation energy of conductivity and relaxation time are equal and independent of moisture content, frequency, and temperature. Based on 192 residual activation energy values, the mean generalized activation energy value for the relaxation time and conductivity was calculated with high precision, resulting in ΔE ≈ (1.02627 ± 0.01606) eV. The uncertainty of its determination was only ±1.6%. This indicates that electron tunneling from the first nanodroplet to the second, causing AC conductivity, and their return from the second nanodroplet to the first, determining the relaxation time, occur between the same energy states belonging to the water nanodroplets located in the pressboard impregnated with bio-oil. For each moisture content, the curves obtained for different measurement temperatures were recalculated to a reference temperature of 20 °C using the generalized activation energy. It was found that the shifted curves obtained for different temperatures perfectly overlap. Increased moisture content shifts the recalculated curves toward higher conductivity values. It was established that for all moisture contents in the lowest frequency range, conductivity is constant (DC conductivity). A further increase in frequency causes a rapid rise in conductivity. The increasing period can be divided into two stages. The first stage occurs up to about 100 Hz–101 Hz, depending on the moisture content. In the second stage, the rate of conductivity increase is higher, and its value depends on moisture content. The lower the moisture content, the faster the conductivity increases. Recalculation using the generalized activation energy eliminated the effect of temperature on the curves. It was found that the shapes of the recalculated curves and their position relative to the coordinates depend only on the moisture content in the composite. The equality of the activation energy of the relaxation time and conductivity established in the study, as well as their independence from frequency and moisture content in the pressboard impregnated with NYTRO® BIO 300X bio-oil, allows for recalculating the curves of electrical parameters determined at any operating temperatures of the transformer to a reference temperature, for example, 20 °C. Comparing the curve obtained for the transformer, recalculated to the reference temperature, with reference curves determined by us in the laboratory for different moisture contents, will allow for the precise determination of the moisture content of the solid insulation component impregnated with NYTRO® BIO 300X bio-oil. This will contribute to the early detection of approaching critical moisture content, threatening catastrophic transformer failure. [ABSTRACT FROM AUTHOR]

Power transformers are critical to electrical power systems but are prone to failures due to factors such as heat, electricity, chemical reactions, mechanical stress, and adverse environmental conditions. Moni-toring the insulating oil effectively is key to preventing these failures. A major challenge in this process is determining the optimal weights for the oil quality index, which lacks a standardized benchmark and often relies on subjective expert assessments. To reduce expert bias and subjectivity, this research utilizes a genetic algorithm to optimize the weightings for five essential parameters: color, water content, break-down voltage (BDV), interfacial tension (IFT), and acidity. The algorithm operates through three stages: crossover, mutation, and selection, and analyzes data from 504 oil tests across various transformers. The mean absolute percentage error (MAPE) is used as the fitness value to assess the algorithm's effective-ness. The optimization process determined the best conditions as 132 iterations, a population size of 180, a crossover rate of 0.2, and a mutation rate of 0.8. These parameters achieved an average MAPE of 1.799% over ten trials, indicating high accuracy. This research not only optimizes the weighting of the oil quality index but also significantly reduces the need for expert input and subjective judgments in trans-former maintenance. The findings are expected to improve the efficiency and reliability of power trans-formers, thereby minimizing failures and associated economic costs.

Mineral oils and synthetic and natural esters are the predominant insulating liquids in electrical equipment. Structure–activity relationship models to predict the key properties of pure insulating liquids, including pulse breakdown strengths, AC breakdown voltages, dielectric constants, flash points, and kinematic viscosities, have been proposed for the first time. Dependence of the specific properties on the molecular structures has been illustrated quantitatively in terms of surface area, statistical total variance, and average deviation of positive and negative electrostatic potentials, as augmented by molecular weight, volume, and ovality. Moreover, the individual contribution of the functional groups to viscosity has been revealed by an additive approach. The predicted properties are in good agreement with the experimental data. The present theoretical work provides new insights on the development of novel dielectric fluids. [ABSTRACT FROM AUTHOR]

A transformer plays a key role in electric power distribution system; therefore, when the transformer fails, several electrical components may get affected. As a result, diagnosing the deterioration of transformers is important for the management of electric power distribution system. The furfural content in the insulating oil of a transformer is widely used as an indicator of deterioration because furfural is generated by the decomposition of insulating paper. However, analyzing the furfural content is time consuming because of the requirement of a professional and the complexity of the diagnosis process. In this study, we propose a novel method for analyzing the amount of furfural in the insulating oil based on near‐infrared spectroscopic data obtained using the developed portable spectrometer, which can be used for the on‐site analysis at transformer installation sites. We selected wavenumbers with high correlation coefficients between the furfural content of oil and the spectroscopic data and estimated the furfural content by partial least squares regression. The results suggest that the furfural content can be analyzed in a few minutes using a small amount of oil through a portable diagnostic device. [ABSTRACT FROM AUTHOR]

Abstract The lifetime of power transformers is closely related to the insulating oil performance. This latter can degrade according to overheating, electric arcs, low or high energy discharges, etc. Such degradation can lead to transformer failures or breakdowns. Early detection of these problems is one of the most important steps to avoid such failures. More efficient diagnostic systems, such as artificial intelligence techniques, are recommended to overcome the limitations of the classical methods. This work deals with diagnosing the power transformer insulating oil by analysis of dissolved gases using new techniques. For this, we have proposed intelligent techniques based on Multilayer artificial neural networks (ANN). Thus, a multi-layer ANN-based model for fault detection is presented. To improve its classification rate, this one was optimized by a meta-heuristic technique as the particle swarm optimization (PSO) technique. Optimized ANNs have never been used in transformer insulating oil diagnostics so far. The robustness and effectiveness of the proposed model is demonstrated, and high accuracy is obtained.

Battery thermal management system (BTMS) is very critical to a high-performance electric vehicle. Compared with other cooling methods, the immersion cooling with heat transfer efficiency has received comprehensive attentions recently, especially that with single-phase insulating oil, since it can not only guarantee the heat transfer efficiency but also simplify the system. This article reviews the latest research progress in oil-immersed BTMS based on single-phase insulating oil. Firstly, the development of insulating oils is introduced, and their basic cooling properties are compared and analyzed. Then, the influences of different factors on the effectiveness of the oil-immersed battery cooling system are analyzed from the aspects of immersion degree, flow channel configuration, thermal property parameters, and others. Finally, challenges with using insulating oil as the immersion cooling medium for lithium batteries (LIBs) are discussed, and potential future research directions are outlined. Ultimately, the insights of this paper will hopefully provide some references for researchers to further develop and design more efficient and reliable BTMSs, thus driving the development of LIBs. [ABSTRACT FROM AUTHOR]

The lifetime of power transformers is closely related to the insulating oil performance. This latter can degrade according to overheating, electric arcs, low or high energy discharges, etc. Such degradation can lead to transformer failures or breakdowns. Early detection of these problems is one of the most important steps to avoid such failures. More efficient diagnostic systems, such as artificial intelligence techniques, are recommended to overcome the limitations of the classical methods. This work deals with diagnosing the power transformer insulating oil by analysis of dissolved gases using new techniques. For this, we have proposed intelligent techniques based on Multilayer artificial neural networks (ANN). Thus, a multi-layer ANN-based model for fault detection is presented. To improve its classification rate, this one was optimized by a meta-heuristic technique as the particle swarm optimization (PSO) technique. Optimized ANNs have never been used in transformer insulating oil diagnostics so far. The robustness and effectiveness of the proposed model is demonstrated, and high accuracy is obtained. [ABSTRACT FROM AUTHOR]

This paper presents the results of the study of the direct current (DC) and alternating current (AC) electrical properties of an electrical pressboard–bio-insulating oil–water composite in a wide range of water content and temperatures used in electric power transformers. These parameters allow the level of insulation reliability to be determined after many years of operation of power transformers. To analyse the experimental results, a model of the DC and AC conductivities of nanocomposites based on the quantum-mechanical phenomenon of electron tunnelling was used. It was found that in a low-frequency region, the conductivities of AC and DC and their activation energy are equal. The relaxation times of AC conductivity and permittivity are also equal. It was found that the dependence of the DC conductivity on the distance between water molecules is an exponential function. On the basis of the model of conductivity by electron tunnelling between potential wells, the average number of water molecules in a nanodroplet, located in a composite of electrical pressboard–bio-insulating oil–moisture was determined to be (126 ± 20). It was found that the measured dependencies of DC and AC conductivity, permeability and dielectric relaxation times are consistent with the results of computer simulations performed on the basis of the model. This study showed that the composite of pressboard impregnated with bio-oil spontaneously transforms through water absorption into a pressboard–bio-oil–water nanocomposite. These will serve as the basis for the application of actual conductivity and dielectric relaxation mechanisms to improve the accuracy of moisture estimation in the solid component of power transformer insulation carried out on the basis of measurements of DC and AC properties. This will improve the operational safety of the transformers, minimise the occurrence of transformer failure and the associated environmental pollution. [ABSTRACT FROM AUTHOR]

Characterized by its exceptional electrical, physical, and chemical properties, 1-phenyl-1-xylylethane (PXE) insulating oil finds extensive application in the realm of power capacitor insulation. In this study, molecular simulation is employed to investigate the reactivity of PXE insulating oil molecules and the impact of temperature on water diffusion behavior in PXE insulating oil, as well as its solubility. The findings demonstrate a higher propensity for hydrogen atoms in nucleophilic and electrophilic positions within PXE insulating oil molecules to interact with water molecules. The inclusion of a temperature field enhances the Brownian motion of water molecules and improves their diffusion ability within the oil. Furthermore, the temperature field diminishes the interaction force between water molecules and the oil medium. Under the influence of this temperature field, there is an increase in the free volume fraction of PXE insulating oil, leading to a weakening effect on hydrogen bonds between oxygen and hydrogen atoms within PXE insulating oil. Additionally, with increasing temperature, there is an elevation in moisture solubility within insulating oil, resulting in a transition from a suspended state to a dissolved state.

The study determines the frequency–temperature dependence of the conductivity of a moist solid insulation component of power transformers, impregnated with the innovative bio-oil NYTRO® BIO 300X, manufactured from plant-based raw materials. The research was conducted for six moisture levels ranging from 0.6% to 5% by weight, within a frequency range from 10−4 Hz to 5 · 103 Hz and measurement temperatures from 20 °C to 70 °C, with a 10 °C step. The conduction model for both DC and AC, based on the quantum mechanical phenomenon of electron tunneling between water nanodroplets, was used to analyze the obtained results. It was determined that the frequency dependence of the conductivity of pressboard-bio-oil-moisture composites is influenced by two factors as follows: the activation energy of conductivity and the activation energy of relaxation time. For each moisture content, 16 values of the activation energy of the relaxation time and 16 values of the activation energy of conductivity were determined. It was found that the values of activation energy of conductivity and relaxation time are equal and independent of moisture content, frequency, and temperature. Based on 192 residual activation energy values, the mean generalized activation energy value for the relaxation time and conductivity was calculated with high precision, resulting in ΔE ≈ (1.02627 ± 0.01606) eV. The uncertainty of its determination was only ±1.6%. This indicates that electron tunneling from the first nanodroplet to the second, causing AC conductivity, and their return from the second nanodroplet to the first, determining the relaxation time, occur between the same energy states belonging to the water nanodroplets located in the pressboard impregnated with bio-oil. For each moisture content, the curves obtained for different measurement temperatures were recalculated to a reference temperature of 20 °C using the generalized activation energy. It was found that the shifted curves obtained for different temperatures perfectly overlap. Increased moisture content shifts the recalculated curves toward higher conductivity values. It was established that for all moisture contents in the lowest frequency range, conductivity is constant (DC conductivity). A further increase in frequency causes a rapid rise in conductivity. The increasing period can be divided into two stages. The first stage occurs up to about 100 Hz–101 Hz, depending on the moisture content. In the second stage, the rate of conductivity increase is higher, and its value depends on moisture content. The lower the moisture content, the faster the conductivity increases. Recalculation using the generalized activation energy eliminated the effect of temperature on the curves. It was found that the shapes of the recalculated curves and their position relative to the coordinates depend only on the moisture content in the composite. The equality of the activation energy of the relaxation time and conductivity established in the study, as well as their independence from frequency and moisture content in the pressboard impregnated with NYTRO® BIO 300X bio-oil, allows for recalculating the curves of electrical parameters determined at any operating temperatures of the transformer to a reference temperature, for example, 20 °C. Comparing the curve obtained for the transformer, recalculated to the reference temperature, with reference curves determined by us in the laboratory for different moisture contents, will allow for the precise determination of the moisture content of the solid insulation component impregnated with NYTRO® BIO 300X bio-oil. This will contribute to the early detection of approaching critical moisture content, threatening catastrophic transformer failure.

Insulating oil is an important component of transformers. Its quality directly affects the performance of the insulation system and the operation safety of the transformer. As working years increase, insulating oil interacts with oxygen, water, and other impurities in the environment to form a variety of aging products. This results in a decrease in its insulation and heat dissipation performance, which in turn causes failures. Therefore, analyzing and detecting transformer insulating oil is an important means to understand the working status of transformers. The analysis results are the reference basis for transformer maintenance and replacement of new oil. The ultraviolet-visible absorption spectrum was used to analyze insulating oil of different working years. The correlation between the aging degree of insulating oil and its ultraviolet spectral characteristics was obtained. The ultraviolet spectrum of furfural, a symbolic aging product, was studied by quantum chemical calculation. The mechanism corresponding to the ultraviolet-visible spectral characteristics of furfural was analyzed. The research results confirm the effectiveness of UV-visible spectroscopy in analyzing the aging degree of transformer insulating oil. The relevant results can be used as a reference for transformer detection. [ABSTRACT FROM AUTHOR]

Mineral oils and synthetic and natural esters are the predominant insulating liquids in electrical equipment. Structure–activity relationship models to predict the key properties of pure insulating liquids, including pulse breakdown strengths, AC breakdown voltages, dielectric constants, flash points, and kinematic viscosities, have been proposed for the first time. Dependence of the specific properties on the molecular structures has been illustrated quantitatively in terms of surface area, statistical total variance, and average deviation of positive and negative electrostatic potentials, as augmented by molecular weight, volume, and ovality. Moreover, the individual contribution of the functional groups to viscosity has been revealed by an additive approach. The predicted properties are in good agreement with the experimental data. The present theoretical work provides new insights on the development of novel dielectric fluids.

With the application of ultra-high voltage (UHV) technology, a substantial amount of energy released from an internal arc fault in the transformer leads to the instantaneous decomposition of insulating oil into various flammable gases. This results in a rapid increase in internal pressure, making it highly probable for the transformer casing to rupture. Consequently, the insulating oil and its decomposition products disperse in the air, which in the presence of an ignition source, can trigger an explosive accident. To reveal the explosion characteristics of insulating oil, experiments and simulations are conducted under unconfined conditions. Besides, a quantitative explosion risk assessment is conducted. The results indicate that, at 20 ms, a high temperature and strong turbulence region appears at about 0.9 m from the center of the cloud and 0.7 m in height, and the combustible cloud is initiated near the region. The safety distances for humans free from the hazard of shock waves are 11.79 m, 13.74 m, and 21.63 m with the amount of insulating oil of 10 L, 15 L, and 20 L, respectively, and the safety distances for humans free from the hazard of thermal radiation are 21.2 m, 26.4 m, and 29.2 m respectively.

This paper presents the results of the study of the direct current (DC) and alternating current (AC) electrical properties of an electrical pressboard–bio-insulating oil–water composite in a wide range of water content and temperatures used in electric power transformers. These parameters allow the level of insulation reliability to be determined after many years of operation of power transformers. To analyse the experimental results, a model of the DC and AC conductivities of nanocomposites based on the quantum-mechanical phenomenon of electron tunnelling was used. It was found that in a low-frequency region, the conductivities of AC and DC and their activation energy are equal. The relaxation times of AC conductivity and permittivity are also equal. It was found that the dependence of the DC conductivity on the distance between water molecules is an exponential function. On the basis of the model of conductivity by electron tunnelling between potential wells, the average number of water molecules in a nanodroplet, located in a composite of electrical pressboard–bio-insulating oil–moisture was determined to be (126 ± 20). It was found that the measured dependencies of DC and AC conductivity, permeability and dielectric relaxation times are consistent with the results of computer simulations performed on the basis of the model. This study showed that the composite of pressboard impregnated with bio-oil spontaneously transforms through water absorption into a pressboard–bio-oil–water nanocomposite. These will serve as the basis for the application of actual conductivity and dielectric relaxation mechanisms to improve the accuracy of moisture estimation in the solid component of power transformer insulation carried out on the basis of measurements of DC and AC properties. This will improve the operational safety of the transformers, minimise the occurrence of transformer failure and the associated environmental pollution.

Integrating nanotechnology in dielectric fluid significantly inhibits losses and boosts overall dielectric fluid performance. There has been research done on the effects of introducing various nanoparticles, such as titania, alumina, silica nanodiamonds, etc. In this paper, a novel nanoparticle, Ceria (CeO2), has been used, and its properties were examined using the FTIR (Fourier Transform Infrared) spectrum, the XRD (X-ray Diffraction) spectrum, the SEM (Scanning Electron Microscopy), and the TEM (Transmission Electron Microscopy). This paper illustrates an efficient dielectric fluid prepared by the successful dispersion of Cerium Oxide (CeO2) nanoparticles in various concentrations into four commercial oils, namely mineral oil, rapeseed oil, synthetic ester oil, and soybean oil, to enhance and improve their dielectric characteristics. The performance investigation emphasises breakdown strength enhancement and other dielectric properties of the colloidal solution comprising different nanoparticle (NP) concentrations. Various commercial oils are used as a base in nano-oil to diversify their applicability as dielectric fluids by measuring the correlation in dielectric parameters and statistically assessing their applicability with normal and Weibull distributions. The obtained experimental data sets were analyzed using the Statistics and Machine Learning Toolbox in MATLAB. The aging measurement has been done only on mineral oil, and results were matched using a predictive model of statistics and the Machine Learning Toolbox in MATLAB. Well-dispersed CeO2 NPs in the insulating oils lead to a significant increase in AC breakdown strength. The effect of ageing on the dielectric properties of nano oils yields better results than conventionally aged oil. It has been observed that the breakdown voltage is enhanced by up to 30% for mineral oil at an optimal concentration of 0.01 g/L, 9% for synthetic ester oil at 0.03 g/L, 18% for rapeseed oil at 0.02 g/L, and 19% for soybean oil at 0.03 g/L nanoparticle concentration. Following the dispersion of CeO2 nanoparticles, the dielectric constant of all insulating oils has also significantly improved.The overall experimental results are promising and show the potential of the CeO2 NPs-based nano oil as an efficient and highly performing dielectric oil for different power applications.

The enhancement of the thermal properties of insulating oils has positively reflected on the performance of the electrical equipment that contains these oils. Nanomaterial science plays an influential role in enhancing the different properties of liquids, especially insulating oils. Although a minimum oil circuit breaker (MOCB) is one of the oldest circuit breakers in the electrical network, improving the insulating oil properties develops its performance to overcome some of its troubles. In this paper, 66 kV MOCB is modeled by COMSOL Multiphysics software. The internal temperature and the internally generated heat energy inside the MOCB during the making process of its contacts are simulated at different positions of the movable contact. This simulation is introduced for different modified insulating oils (mineral oil and synthetic ester oil) with different types of nanoparticles at different concentrations (0.0, 0.0025, 0.005, and 0.01 wt%). From the obtained results, it is noticed that the thermal stress on the MOCB can be reduced by the use of high thermal conductivity insulating oils. Nano/insulating oils decrease internal temperature and generate heat energy inside the MOCB by about 17.5%. The corresponding physical mechanisms are clarified considering the thermophoresis effect. [ABSTRACT FROM AUTHOR]

This article reviews the application of the Reactive Molecular Dynamics (ReaxFF-MD) method in the field of insulating oil. It introduces the commonly used methods for constructing models of insulating oil and oil-paper, summarizes the pyrolysis mechanisms and influencing factors of insulating oil, analyzes the performance differences and advantages of different types of insulating oil, discusses the interactions and coupling effects in the oil-paper system. The paper points out the current status and existing issues in this field, providing a reference for further theoretical and experimental research.

The enhancement of the thermal properties of insulating oils has positively reflected on the performance of the electrical equipment that contains these oils. Nanomaterial science plays an influential role in enhancing the different properties of liquids, especially insulating oils. Although a minimum oil circuit breaker (MOCB) is one of the oldest circuit breakers in the electrical network, improving the insulating oil properties develops its performance to overcome some of its troubles. In this paper, 66 kV MOCB is modeled by COMSOL Multiphysics software. The internal temperature and the internally generated heat energy inside the MOCB during the making process of its contacts are simulated at different positions of the movable contact. This simulation is introduced for different modified insulating oils (mineral oil and synthetic ester oil) with different types of nanoparticles at different concentrations (0.0, 0.0025, 0.005, and 0.01 wt%). From the obtained results, it is noticed that the thermal stress on the MOCB can be reduced by the use of high thermal conductivity insulating oils. Nano/insulating oils decrease internal temperature and generate heat energy inside the MOCB by about 17.5%. The corresponding physical mechanisms are clarified considering the thermophoresis effect.

This work studied the lubrication performances of polyalkylene glycols, which are insulating oils, at the steel interface under external electric fields. The results show that external electric fields greatly affect the lubrication performances of polyalkylene glycols, and there is an optimal voltage (−1.0 V) for the improvement in friction reduction performance. The surface analysis and experiment results indicate that the polyalkylene glycol adsorption film and the reduction in the amount of FexOy and FeOOH in the tribochemical film contribute to improved friction performance under the negative voltage condition. This work proves that the lubrication performances of insulating oils can be affected by external electric fields as well. A lubrication model was proposed, hoping to provide a basic understanding of the lubrication mechanisms of ether-bond-containing insulating oils in the electric environment. [ABSTRACT FROM AUTHOR]

During operation of the transformer, the oil in it undergoes profound changes usually referred to as aging. The electrical insulating properties of it deteriorate, and sediments accumulate on the active part, which makes it difficult to remove heat. Inhomogeneous solid formations can induce not only the voltage breakdown, but also impair the parameters such as viscosity and other char-acteristics of the oil, which are important for the reliable operation of the power transformers. Aromatic groups initially is present in the transformer oil composition during the operation of the oil, and because of the aging processes, the concentration of the unsaturated cyclic com-pounds increases. The aim of this work is to develop a new method for the determination of the aromatic compounds and colloidal particles. This goal is achieved using a visual inspection of the transformer oil samples in the visible range. The most significant result of the paper is the establishment of a correlation between the acid number of the transformer oil (KOH), the tan-gent of the dielectric loss angle and the type of oil image under the visible light illumination. The significance of the obtained results lies in the fact that the presented method based on the analy-sis of the scattered and transmitted radiation, makes it possible to determine the presence of the aromatic compounds and colloidal particles in the transformer oil, as well as to define their con-centration and size. This method simplifies the analysis of the transformer oil quality, and re-duces the cost of the research, which is an important factor for the electric power industry.

Assessing the levels of furfural in insulating oils is a crucial technical method for evaluating the degree of aging and mechanical deterioration of oil-paper insulation. The surface-enhanced Raman spectroscopy (SERS) technique provides an effective method for enhancing the sensitivity of in-situ detection of furfural. In this study, a homogeneous three-dimensional (3D) urchin-like Au@W 18 O 49 heterostructure was synthesized as a SERS substrate using a straightforward hydrothermal method. The origin of the superior Raman enhancement properties of the 3D urchin-like heterostructures formed by the noble metal Au and the plasmonic semiconductor W 18 O 49 , which is rich in oxygen vacancies, is analyzed experimentally in conjunction with density-functional theory (DFT) calculations. The Raman enhancement is further amplified by the remarkable dual localized surface plasmon resonance (LSPR) effect, which generates a strong local electric field and creates numerous "hot spots," in addition to the interfacial charge transport (CT). The synergistic effect of these factors results in the 3D urchin-like Au@W 18 O 49 heterostructure exhibiting exceptionally high SERS activity. Testing the rhodamine 6G (R6G) probe resulted in a Raman enhancement factor of 3.41 × 10−8, and the substrate demonstrated excellent homogeneity and stability. Furthermore, the substrate was effectively utilized to achieve highly sensitive in-situ surface-enhanced Raman scattering (SERS) detection of dissolved furfural in complex plant insulating oils. The development of the 3D urchin-like Au@W 18 O 49 heterostructure and the exploration of its enhancement mechanism provide theoretical insights for the advancement of high-performance SERS substrates. [Display omitted] • 3D urchin-like Au@W 18 O 49 heterostructure as a high-performance SERS substrate. • The SERS substrate exhibits a high SERS enhancement factor, excellent homogeneity and long-term durability. • The substrate can be used for the in-situ detection of furfural in complex insulating oil environments. • Experiments combined with DFT calculations reveal the synergistic enhancement mechanism of dual LSPR and CT. [ABSTRACT FROM AUTHOR]

Moisture content is one of the parameters of transformer oil that determine its quality. This parameter is one of the most critical, which is closely monitored. During the operation of transformer oil in the power equipment of electric power systems, about 10 grams of water per ton of oil is allowed, i.e. the permissible proportion of water is 10 ppm (ppm). The aim of the work is to develop a new method for determining the permissible proportion of water in transformer oil in small quantities. This goal is achieved by performing spectral studies of transformer oil samples in the UV and visible range with the addition of cobalt (II) chloride (CoCl2) powder. Сobalt (II) chloride has the ability to change its color depending on the amount of water of crystallization. The most significant result of the article is the conclusion, obtained on the basis of the recorded spectra, about the relationship between the optical density of the spectrum in the range of 360-490 nm and the moisture content of transformer oil when adding cobalt chloride powder. The significance of the results obtained is that the authors have proposed a new optical method for determining small values of the proportion of water in transformer oils, based on the dependence of the optical properties of cobalt (II) chloride on moisture content.This method has a very high sensitivity, low cost for determining the proportion of water and is very promising for solving problems of power energy.

• Synthetic ester insulating oil is a dielectric liquid with balanced properties. • A strategy to improve the lightning breakdown characteristics based on the design of molecular chain length. • Revealing the correlation between microscopic electron structural parameters and macroscopic discharge behavior. The high flash point and biodegradability of synthetic ester insulating oil offer transformers both operational stability and environmental protection. However, its poor lightning breakdown characteristics under long oil gaps and inhomogeneous electric field often lead to rapid streamer discharges, posing challenges and limits to the use of synthetic ester insulating oil and hinders the development of low-carbon, eco-friendly high voltage power transformers. To address this issue, we propose improving the lightning breakdown characteristics through molecular chain length design. Using density functional theory, time-dependent density functional theory, and wave function analysis, we investigate how microscopic factors like molecular polarity, discharge active sites, frontier orbitals, traps, ionization and electron affinity, and excitation processes influence macroscopic discharge characteristics. Our findings show that under an electric field, chain length is positively correlated with electron transfer, enhancing charge polarization. Chain length also correlates positively with dipole moment, facilitating the formation of space charge centers. While chain length minimally affects discharge active sites, the electric field can intensify their formation. Additionally, a longer chain length decreases the energy gap, increasing electron trap levels more than hole trap levels, thus capturing charges longer. Chain length is negatively correlated with ionization energy, promoting electron impact ionization, and has little effect on the excitation energy of S(0) → S(1), making excitation under high electric fields unlikely. [ABSTRACT FROM AUTHOR]

The transformer is the most essential component in electrical power transmission. Once a transformer is installed, it is generally used for decades. When failure occurs in a transformer, serious problems can arise, and numerous electrical components that depend on the transformer may be affected. Thus, deterioration diagnosis of transformers is important. The furfural content in the insulating oil of a transformer is widely used as an indicator of transformer deterioration, as furfural is generated by decomposition of the insulating paper. Although the degree of transformer deterioration can be estimated by measuring the furfural content, this measurement is time‐consuming. This paper proposes a novel method for estimating the amount of furfural contained in insulating oil within a short time. The method is realized by combining spectroscopic analysis in the visible region with a pattern recognition technique. The effectiveness of the proposed method is verified through a series of experiments. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The investigation on the aging marker for palm fatty acid ester (PFAE)-filled transformer was performed. Sealed aging stainless steel tanks containing transformer components in the same ratio as a 27-MVA power transformer, were aged at 151 °C–168.5 °C for 48–2880 h in a strictly controlled oxygen-free and low initial moisture environment. The generation of 2-furaldehyde (2FAL) and other four kinds of furans including 5-hydroxymethylfurfural (5HMF), 2-furfuryl alcohol (2FOL), 2-acetylfuran (2ACF), and 5-methyl furfural (5MEF) from cellulosic insulating components impregnated in mineral oil (MO) and PFAE after thermally aging tests are determined and compared. The results indicate that the concentration of 2FAL, 2ACF, and 5MEF maintains an increasing trend with the aging time and temperature for both fluids. The correlations between 2FAL and the degree of polymerization (DP) of high-density pressboard (HPB) in both fluids are established. The results demonstrate that 2ACF and 5MEF can also be used as aging markers for transformer in spite of their much lower concentrations in the aged fluids. [ABSTRACT FROM AUTHOR]

This article aims at developing a gradient boosting (GB) model with parameters optimized by the Bayesian optimization (BO) method for detecting various types of fault in an oil-immersed transformer and reactor. The developed model depicts higher accuracy in comparison with other machine learning (ML) techniques, such as XGBoost, AdaBoost, random forest, and support vector machine parameters being optimized by BO. A comparison of the skill score depicts the superiority of the developed Bayesian optimization-based gradient boosting (BO-GB) model with respect to Bayesian optimized other ML techniques. Further comparison of the model with conventional Duval pentagon verifies the accuracy of detecting the faults, which were missed by the former. Also, the software has been developed based on the proposed BO-GB method for the on-site detection of the fault. In addition, actual values of dissolved gases with respect to fault confirmed after the internal inspection of the transformer and reactor are tabulated and compared. The data so presented will help in utilizing the authentic dissolved gas data in addition to the already available IEC TC10 databases for future works. The study undertaken in this article will help utilities in diagnosing the incipient faults more accurately and precisely, thereby preventing hazardous operating conditions along with minimizing the downtime cost. [ABSTRACT FROM AUTHOR]

A new procedure to optimally identifying the prediction equation of oil breakdown voltage with the barrier parameters’ effect is presented. The specified equation is built based on the results of experimental works to link the response with the barrier parameters as the inputs for hemisphere-hemisphere electrode gap configuration under AC voltage. The AC HV is applied using HV Transformer Type (PGK HB-100 kVAC) to the high voltage electrode in the presence of a barrier immersed in Diala B insulating oil. The problem is formulated as a nonlinear optimization problem to minimize the error between experimental and estimated breakdown voltages (VBD). Comprehensive comparative analyses are addressed using three recent innovative marine predators, grey wolf, and equilibrium optimization algorithms to reduce the error between the experimental and estimated breakdown voltages. In addition, the experimental results are expressed in two different models via grey and real coding. Finally, simulation results are conducted with statistical indices that show the effectiveness of the proposed models for experimental verification. The total percentage errors of the tested samples between the observed and estimated VBD are 1.207, 1.222, and 1.207 for EO, GWO, MPA, respectively. The marine predator algorithm has the best performance compared with the other two competitive algorithms for grey and actual codes. [ABSTRACT FROM AUTHOR]

The early detection of the transformer faults with high accuracy rates guarantees the continuous operation of the power system networks. Dissolved gas analysis (DGA) is a technique that is used to detect or diagnose the transformer faults based on the dissolved gases due to the electrical and thermal stresses influencing the insulating oil. Many attempts are accomplished to discover an appropriate technique to correctly diagnose the transformer fault types, such as the Duval Triangle method, Rogers' ratios method, and IEC standard 60599. In addition, several artificial intelligence, classification, and optimization techniques are merged with the previous methods to enhance their diagnostic accuracy. In this article, a novel approach is proposed to enhance the diagnostic accuracy of the transformer faults based on introducing new gas concentration percentages limits and gases' ratios that help to separate the conflict between the diverse transformer faults. To do so, an optimization model is established which simultaneously optimizes both gas concentration percentages and ratios so as to maximize the agreement of the diagnostic faults with respect to the actual ones achieving the high diagnostic accuracy of the transformer faults. Accordingly, an efficient teaching-learning based optimization (TLBO) is developed to accurately solve the optimization model considering training datasets (Egyptian chemical laboratory and literature). The proposed TLBO algorithm enhances diagnostic accuracy at a significant level, which is higher than some of the other DGA techniques that were presented in the literature. The robustness of the proposed optimization-based approach is confirmed against uncertainty in measurement where its accuracy is not affected by the uncertainty rates. To prove the efficacy of the proposed approach, it is compared with five existing approaches using an out-of-sample dataset where a superior agreement rate is reached for the different fault types.

This article performs a thermal study through the application of Computational Fluid Dynamics (CFD) of a transformer prototype considering six different cooling configurations. Each configuration was computationally designed and simulated in the ANSYS CFX © software. It was possible to analyze the temperature data of the hotspot, at the top oil and at the average temperature, thus comparing the thermal performance of each system and implementing the data in a simplified methodology for estimating the transformer lifespan standardized by IEEE C57.100-2011. In addition, the rendering of the results allows visualizing the temperature distribution and, consequently, the performance for each cooling system. Finally, the advantages and disadvantages of each cooling system were summarized, providing useful information for transformer designer's decision. As some results, the forced air-cooled transformers have a thermal reduction of approximately 8.81% compared to natural air-cooled and the directed oil system transformers have superior cooling performance than forced oil and natural oil. The directed oil and forced air combination means a useful life 52.76% longer than the natural oil and natural air combination. [ABSTRACT FROM AUTHOR]

This paper reports the AC dielectric‐breakdown characteristics of a rice‐oil‐based electrical insulating oil as a function of oil temperature as well as the influence of thermal degradation on its performance (kinematic viscosity, AC dielectric breakdown, moisture amount, total acid number, and pour point). We manufactured rice ester oil using the ester‐exchange reaction. The results demonstrated the following. (i) The kinematic viscosity of the rice ester oil was lower than that of the rice and mineral oils. (ii) The AC breakdown strength of the rice ester oil was higher than that of the mineral oil. The AC breakdown strength of both insulating oils increased with the increase in the oil temperature. (iii) The moisture content of the rice ester oil was larger than that of the mineral oil. (iv) The total acid numbers of the rice ester and mineral oils were almost the same. (v) The pour point of the rice ester oil was higher than that of the mineral oil. In addition, the rice ester oil exhibited high resistance to heat stress compared with the mineral oil, but the former was unsuitable for use in cold climates. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The paper presents a new test stand for ivestigating the rate of penetration of transformer oil through electrotechnical pressboard. The stand consists of a pipe, to the lower end of which is glued a pressboard plate. The pipe is filled with insulating oil. A mirror is placed under the plate, which directs its image to the lens of the camera, which takes a series of photographs at a given time interval. After being saturated with the insulating oil, the pressboard changes colour from light to dark yellow. The absorbing time is defined as the time in which a dark yellow spot appears on the lower light surface of the pressboard after the pipe is filled with oil.A new way of determining capillary diameters has been developed when the number of capillaries is unknown and the volume of liquid flowing through them is not measurable. The distribution of the times of penetration of transformer oil through 2 mm thick electrotechnical pressboard was determined, the values of which range from about 220 min to about 550 min. It was found that the radii of capillaries through which the insulating oil penetrates are within the range from about 45 nm to about 70 nm. Due to the structure of the pressboard, which consists of cellulose fibres, arranged more or less tightly, there are capillaries in the structure of the board, each of which has sections of varying lengths of radii. This means that short sections of a single capillary can have radii both smaller than 45 nm and larger than 70 nm.The developed stand and the new analysis method can be used for testing various porous materials for penetration by various liquids.

In order to study the removal performance of pollutants in contaminated soil by microsecond pulsed dielectric barrier discharge technology, the effects of treatment time, initial concentration of pollutants, soil moisture content, soil thickness and carrier gas flow rate on the removal rate of insulating oil were investigated. The removal rate of insulating oil in soil increases with the increase of treatment time; The initial concentration of pollutants in soil and the increase of soil thickness inhibit the removal of insulating oil; When the water content in soil is 15%, the optimum removal effect of insulating oil is reached; Excessive carrier gas flow rate is not conducive to the reaction between active substances and insulating oil, which reduces the degradation effect of insulating oil. Using the microsecond pulsed dielectric barrier discharge technology to treat the soil polluted by insulating oil could achieve good remediation effect and high energy utilization efficiency, which provides a reference for the remediation of organic pollutants by this technology. [ABSTRACT FROM AUTHOR]

Analytical science has always been calling for simple, fast and ultra-sensitive methods to sense molecules of interest. Surface-Enhanced Raman Spectroscopy (SERS) has drawn much attention as a convenient tool for molecular fingerprint characterization. In addition to sample preparation, the key point of sensitive SERS detection is the preparation of highly reproducible and sensitive SERS substrates. In this paper, 2D gold nanoclusters are grown on surfaces of glass slips using an in-situ cyclic growth method in aqueous solutions to prepare high-quality SERS substrates, whose surface morphology can be effectively modulated by adjusting a few parameters during preparation. Substrates prepared with optimized parameters exhibit high SERS activity, uniform response, and good batch-to-batch reproducibility. Due to their strong absorption in the near-infrared range, the substrates can be combined with a portable Raman spectrometer with 785 nm excitation wavelength to detect traces of dibenzyl disulfide (DBDS), a major source of corrosive sulfur in mineral insulating oil. A detection limit lower than 1 mg/L can be achieved with the aid of a simple sample pretreatment method, representing a promising on-site insulating oil analysis method for electric power industry.

The current calculation method of fluid–structure interaction (FSI) has a defect for oilimmersed transformers for distributed energy resources (DERs). In order to solve this problem, a calculation method is proposed for the temperature rise of oil-immersed transformers in this article. The vibration of insulating oil is considered in this method. Different from the temperature field model established by FSI, the effect of insulating oil vibration on the temperature field is considered. The structure field is introduced to establish the insulating oil vibration model. The temperature field correction coefficient is introduced by coupling the insulating oil vibration and the natural convection of the insulating oil. The result shows that compared with FSI, the results of the calculation method in this study are consistent with the experiment, and the temperature field distribution in the oil-immersed transformer can be calculated more accurately.

This paper presents the potential of using treated used cooking oil as a potential dielectric liquid for high-voltage power transformers. The acidity of used cooking oil is higher than the prescribed limit of natural ester for power transformers. Hence, this paper proposes a combination of treatment methods to reduce the acidity of used cooking oil to less than 0.06 mg KOH/g. The treatment methods are: (1) alkaline refining, (2) bleaching and (3) synthetic silicate treatment. The physicochemical and electrical properties (acidity, color, density, flash point, viscosity, water content, breakdown voltage and dissipation factor) of the treated used cooking oil are measured according to standards. The results show that the acidity of the treated used cooking oil is 0.0182 mg KOH/g, which is 99.67% lower than the initial value of 5.4664 mg KOH/g. This acidity is achieved by implementing the following treatment methods: (1) alkaline refining using caustic soda (normality: 2.0N); (2) two cycles of bleaching with Fuller earth's adsorbent (concentration: 10 wt%) in each cycle; and (3) treatment with synthetic silicate absorbent (concentration: 15 wt%). In addition, combined treatment methods affect the color rating of the treated used cooking oil, where the color rating is L0.5. The breakdown voltage and dissipation factor at 90 °C of the treated used cooking oil are found to be 100 kV and 0.00688, respectively. The other physicochemical properties (density, viscosity and water content) of the treated used cooking oil fulfills the BS EN 62770 standard except for the flash point, with a value of 234 °C. [ABSTRACT FROM AUTHOR]

This study proposes a novel method for estimation of the acid value and the furfural contained in the insulating oil of an oil‐filled transformer based on the information received from the color of the insulating oil. A spectrometer analysis is carried out on insulating oils. The color data, represented as L*, a*, and b*, are measured, and it is found that these values change on a certain trajectory in accordance with the degradation of the insulating oil. Subsequently, a method for the estimation of acid value and the furfural is proposed based on the trajectory. Finally, the effectiveness of the proposed method is verified through experimental procedures. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This work studied the lubrication performances of polyalkylene glycols, which are insulating oils, at the steel interface under external electric fields. The results show that external electric fields greatly affect the lubrication performances of polyalkylene glycols, and there is an optimal voltage (−1.0 V) for the improvement in friction reduction performance. The surface analysis and experiment results indicate that the polyalkylene glycol adsorption film and the reduction in the amount of FexOy and FeOOH in the tribochemical film contribute to improved friction performance under the negative voltage condition. This work proves that the lubrication performances of insulating oils can be affected by external electric fields as well. A lubrication model was proposed, hoping to provide a basic understanding of the lubrication mechanisms of ether-bond-containing insulating oils in the electric environment.

In this study, an alternative method was applied to evaluate the accelerated oxidation of mineral insulating oils using continuous real time monitoring, with smaller samples and lower experimental times than the standard ASTM D2440 method. Using this method, the influence of temperature and presence of a metal catalyst on the oxidation behavior was evaluated. The activities of commercial metal passivators and antioxidants were also studied at different conditions. The addition of the metal passivators (BTA: 1,2,3-benzotriazole, and Irgamet-39: n-(1,2,3-benzotriazol-1-methyl)-n-alkylamine) at low concentrations (8 mg/kg) increased the induction period (IP) of doped samples. Furthermore synergetic effects on retarding the oxidation reactions when using both metal passivators and two commercial antioxidants (DBPC, 2,6-di-tert-butyl-p-cresol, and Irganox L115, 2,2’-thiodiethylen-bis(3,5-di-tert-butyl-4 hydroxyphenyl-proprionate) were observed, increasing the IP values by up to 25 times when compared to a fresh oil sample. Experimental IP values from this newly proposed technique (up to 10 h) may be used to estimate the Total Acid Number values obtained when using the ASTM D2440 method (164 h). [ABSTRACT FROM AUTHOR]

This paper focuses on the effects of dielectric strength on transformer oil reliability and on a reproduction of a voltage breakdown simulation during a dielectric strength test. A typical Foster test cell was used in order to measure the dielectric strength of a variety of oils. For a more complete picture, it requires the identification of more parameters but this paper examines only the above one as a result of the operation of a testing apparatus. It is shown that FEM/FDM analysis provides same information for the electrode gap. Bruce electrode provides highly uniform electric field. Factors such as voltage rate, relaxation time between measurements as well as the shape of the testing electrodes influences the dielectric strength of the liquid. [ABSTRACT FROM AUTHOR]

The DC conductivity of insulating oil is key to converter transformers, in which AC and DC electrical fields simultaneously exist. Research on the influence of the electric field on oil conductivity can optimise the insulation design of converter transformers. Although numerous studies have been conducted on the conductance mechanism of non‐polar liquids, the explicit mechanism and properties of oil conductivity under a high electrical field remain unclear. This study developed an optimised conductance model considering charge carrier elimination, dissociation, and charge injection process. Thereafter, the authors chose three types of oils for converter transformers and measured the variations in oil conductivity and ion mobility under different electric fields with 0–10 kV/mm range. The result indicates that ion mobility will increase under a high electric field owing to the EHD effects. The conductivity of the insulating oil follows a U‐shaped pattern with an increasing electric field, thereby generally matching the optimised theoretical model. Therefore, the decrease in conductivity is mainly the result of the elimination process of free ions, whereas the increase is the result of the injection process that occurs on the electrodes. [ABSTRACT FROM AUTHOR]

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.

Current transformers (CTs) are extensively used in electrical switchyards and substations for metering and protection purposes [1] and are expected to operate properly for at least 30 years [2]. Normally, aging of CTs under service conditions is relatively slow, but they also may fail prematurely due to various reasons, such as design faults, inadequate quality during manufacture, lightning strikes, operation beyond rated conditions and inadequate maintenance [3]. Compared with other high voltage apparatus, failure of a CT can be violent or even catastrophic, causing damages to the CT itself as well as to nearby located assets and humans [4–9]. Build-up of internal pressure during a failure of a CT results in an instant fire due to burning of oil and explosion of porcelain housing, where porcelain pieces can spread to a distance up to 100 m [4], [6]. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study of the behavior of an antioxidant additive (ionol) in insulating oil from existing high-voltage equipment. Decomposition products of the inhibitor (ionol), the concentration of which changes as the oil ages, were found in the oil samples. These compounds can be attributed to impurity compounds, which can also serve as additional markers of aging of a liquid dielectric. The ionol degradation products were analyzed by gas chromatography with a flame-ionization detector (FID) and a mass spectrometric detector (MSD). The advantages of the gas chromatography-mass spectrometric method over gas chromatography with an FID are shown. Compounds that are formed as the oxidation inhibitor (ionol) is consumed are identified using chromatography-mass spectrometry. It has been found that the ionol concentration decreases as the mineral oil ages. At the same time, the concentration of ionol "metabolites" increases and becomes much higher than the concentration of the additive itself. [ABSTRACT FROM AUTHOR]

The present work aims at the preparation and characterization of a stable soybean natural ester nanofluid using alumina nanofiller, as an alternative to the conventional mineral oil. Stability using UV-Vis spectrophotometer and turbidity meter for various concentrations of nanofluids is reported and analyzed. Natural ester nanofluids with 0.02 wt% nanofiller concentration shows the highest stability. AC breakdown voltage shows a 21.5 and 27.9% increase for unfilled and 0.02 wt% nanofilled natural ester, respectively, when compared to the unfilled mineral oil. An improvement of 5.4 and 14.6% in the thermal conductivity can be observed for unfilled and 0.1 wt% nanofilled natural ester, respectively, when compared to that of unfilled mineral oil. [ABSTRACT FROM AUTHOR]