Natural Ester Research Articles

Thermal aging performance of soybean insulating oil mixed with glyceryl triacetate

A method of delaying the aging of natural ester oil-paper insulation systems by adding glyceryl triacetate is proposed in this work. A study was conducted on the thermal aging performance of soybean insulating oil mixed with glyceryl triacetate at a volume fraction of 7.5%. Through a 42-day accelerated thermal aging experiment, it was found that the addition of glyceryl triacetate effectively delayed the increase in kinematic viscosity of the insulating oil and reduced the generation of aging products such as moisture and acid. However, the polar compounds in glyceryl triacetate reduced the breakdown voltage of the mixed oil and made the dielectric loss factor higher than that of pure oil. In addition, tests were conducted on the insulating paper immersed in two types of oil, and it was found that the addition of glyceryl triacetate helps to distribute mixed oil molecules on the surface of insulating paper, which effectively helped absorb moisture from the paper, weakening the hydrolysis reaction of cellulose and delaying the aging of insulating paper. In addition, the insulating paper immersed in the mixed oil maintains good power frequency breakdown voltage and dielectric properties throughout the thermal aging experiment.

Exploring the surge current degradation of natural ester oil-based nanofluids

The surge endurance of natural ester oil-based nanofluids against surge events is investigated experimentally. The focus of this work is the examination, through dielectric spectroscopy measurements, of the alteration of the real and imaginary parts of the complex relative permittivity of iron oxide nanofluids as a result of an accelerated degradation test employing a sequence of repetitive current impulses produced via a 12 kV/6 kA combination wave generator. The target is the exploration of a possible implementation of nanofluids as multipurpose liquids that act, in addition to insulation and coolants, as surge absorption media. Promising experimental results are discussed and compared with those of mineral oil that is widely used as a conventional insulating liquid in power transformers.

Up-gradation of the dielectric, physical & chemical properties of cottonseed-based, non-edible green nanofluids as sustainable alternatives for high-voltage equipment's insulation fluids

The use of natural ester oils as electrically insulating fluids has gained significant attention from industries and electrical utilities as they aim to replace traditional mineral oils. However, most natural ester oils are derived from edible products, which has the potential to contribute to the food crisis. Therefore, nonedible green nanofluids made from cottonseed oil (CSO) have been targeted as a keen solution to this issue. However, Al2O3, TiO2, Fe2O3, SiO2, and graphene nanoparticles at (0.025, 0.05, and 0.075 wt/vol%) were used as additives, along with surfactant Olic Ac-id and Ethanol (1:5) due to their promising impact on the dielectric and thermal properties of the nanofluid. The nanofluid synthesis process was practically conducted in HV & Chemical Laboratories using one-step and two-step methods, and their breakdown voltage results and chemical properties (e.g., fire point, flash point, cloud point, pour point, viscosity, acidity, moisture content, resistivity, and dissipation factor) were compared. The physical mechanisms underlying these properties were also analyzed and tested. For the validation of the proposed vegetable oil the results have been compared with traditional mineral oil for high-voltage equipment's. The findings suggest that the proposed nonedible green nanofluids-based cottonseed oil (CSO) has a high potential to be used as electrically insulating fluids, providing a sustainable alternative to conventional mineral oils. Overall, this study provides insights into the use of non-edible green nanofluids as a solution to the potential contribution of natural ester oils to the food crisis. The findings highlight the importance of sustainable solutions in the energy industry and the need for further research in this area.

Microstructure‐ionisation potential relationship analysis for understanding the molecular ionisation difference of natural esters during the impulse discharge via DFT calculation

AbstractUnderstanding the impulse discharge behaviour of natural ester (NE) is crucial for its safe application in high‐voltage transformers. The ionisation potential (IP) of triglycerides plays a significant role in the process of molecular ionisation during impulse discharge for NE. The correlation coefficients between molecular size, frontier orbital, electrostatic potential, polarity, and IP were analysed. And the quantitative microstructure‐IP model for triglycerides were built, which revealed that IP is strongly related to the highest occupied molecular orbital (HOMO) energy EHM, as well as the average value of positive electrostatic potential Vp(+), the average value of negative electrostatic potential Vp(−), and the surface area of negative electrostatic potential S(−). The HOMO and negative electrostatic potentials of saturated triglycerides are predominantly linked to the carbonyl O atoms. Conversely, in unsaturated triglycerides, the influence of C=C double bonds on HOMO and negative electrostatic potentials is more pronounced. Therefore, the IP of unsaturated NE with C=C bonds is lower than that of saturated NE, rendering it more susceptible to ionisation under a strong electric field which is unfavourable for impulse breakdown voltage. The structure‐property correlation analysis is valuable for understanding ionisation mechanism during the impulse discharge breakdown of NE at the microscopic level.

Comparative study of natural ester oil and mineral oil on the applicability of the immersion cooling for a battery module

The immersion cooling for lithium-ion batteries based on insulating oil has gained a great deal of interest and research, while most of them still lie in the exploratory phase with numerical and model-scale experimental efforts, and applicable cooling mediums as well as the cooling mechanisms are still inconclusive. In this paper, an oil-immersed cooling system for a battery module is designed to verify the feasibility of natural ester oil by comparing with the currently popular mineral oil. The thermal behaviors of the battery module immersed in static and dynamic insulating oils are discussed. It is found that both mineral oil and natural ester oil can efficiently decrease the battery temperature and limit the temperature difference among the batteries to less than 2 °C. For both insulating oils, the cooling effect increases with increasing liquid flow rate, but this improvement gradually weakens. With increasing Reynolds numbers, the forced convection replaces the natural convection as the dominant mechanism, especially in the natural ester oil-based system where the forced convection dominates even in the entire Re range. The comparative results demonstrate that natural ester oil can serve as a potential candidate for the battery immersion cooling.

Simulated Thermal Fault: Assessing Dissolved Gas Analysis through Tube Heating Method on Mineral Oils and Natural Ester

Dissolved gas analysis (DGA) is the most widely used technique for monitoring transformer condition and detecting faults at an early stage. The quantity and type of gases that are produced by transformer faults and dissolved in the insulating liquid can reveal a lot about the nature and severity of the fault. To explore the variations in the dissolved gases based on the severity of the fault and the type of insulating liquid, we employed the Tube Heating Technique to simulate thermal faults at regulated temperatures up to 800 °C. To illustrate these differences, DGA data from commercially used insulating fluids such as inhibited and uninhibited mineral oils and a natural ester, will be presented.

Development of transformers with natural ester and cellulose or aramid insulation

This study describes selected research studies performed for developing design rules for power transformers usingnatural esters. The presented simulation results verified adequacy of design rules and allowed for adjustments needed forimplementing the new insulation system vs. the one based on mineral oil and cellulose-based solid insulation. They were alsoused as a base for the next transformer design combining natural ester with aramid insulation.

GÜÇ TRANSFORMATÖRLERİNDE MİNERAL YAĞLARA ALTERNATİF DOĞAL ESTERLERİN UYGULAMALARI

The electrical and environmental disadvantages of mineral oils, traditionally used as insulating fluids in power systems, lead to the search for alternatives. Natural esters produced from vegetable seeds are one of the most important alternatives. Natural esters with high dielectric strength can meet ultra-high voltage transformer design requirements. In addition, they can respond to environmental concerns caused by transformer oils with their biodegradability. This study first compares natural esters with other trans-former oils and explains why natural esters stand out. The basic properties of natural esters are defined in terms of advantages and disadvantages, and power system applications are exemplified. Esterification and synthesis of nanoparticle-added nanofluids, widely used in the literature to improve natural esters' electrical and thermal properties, are presented with experimental applications. Natural esters can have a better oxidation stability with the esterification process. The AC, DC, and lightning impulse (LI) break-down voltages of nanofluids based on natural esters also enhanced by 10% on average. This substation and experimental applications in which natural esters are used show that these environmentally friendly oils can provide insulation requirements in many power system equipment, especially transformers.

Thermal Ageing of Dry Cellulose Paper Impregnated with Different Insulating Liquids—Comparative Studies of Materials Properties

Natural and synthetic esters are increasingly being chosen instead of mineral oil for environmental and fire safety reasons. However, their use in power transformers is limited due to insufficiently well-understood ageing processes affecting their properties and the properties of cellulosic materials impregnated with them. The research results presented in many scientific papers prove that the use of esters slows the ageing process of cellulosic materials. This article presents the results of research aimed at answering the question of whether the effect of slowing the ageing process will also occur in the case of insulation with very low initial moisture. The answer to this question will allow us to better understand the role of water in the ageing process of the transformer’s insulation system. The thermal ageing process was carried out at a temperature of 150 °C in closed systems. The degree of cellulose polymerisation was taken as a measure of the degree of paper ageing. Great attention was paid to measuring the water content in both paper and electro-insulating liquids at various stages of their ageing. Furthermore, measurements of the properties of electro-insulating liquids were made, which are considered markers of ageing. The test results obtained indicate that in the case of a dry insulation system, corresponding to the initial moisture of the new units, the type of liquid used to impregnate the cellulosic material does not significantly affect its depolymerisation process. However, in the case of paper impregnated with natural esters, a lower dynamic of moisture increase in insulation was observed.

Surface-active antibiotic production as a multifunctional adaptation for postfire microorganisms.

Wildfires affect soils in multiple ways, leading to numerous challenges for colonizing microorganisms. While it is thought that fire-adapted microorganisms lie at the forefront of postfire ecosystem recovery, the specific strategies that these organisms use to thrive in burned soils remain largely unknown. Through bioactivity screening of bacterial isolates from burned soils, we discovered that several Paraburkholderia spp. isolates produced a set of unusual rhamnolipid surfactants with a natural methyl ester modification. These rhamnolipid methyl esters (RLMEs) exhibited enhanced antimicrobial activity against other postfire microbial isolates, including pyrophilous Pyronema fungi and Amycolatopsis bacteria, compared to the typical rhamnolipids made by organisms such as Pseudomonas spp. RLMEs also showed enhanced surfactant properties and facilitated bacterial motility on agar surfaces. In vitro assays further demonstrated that RLMEs improved aqueous solubilization of polycyclic aromatic hydrocarbons, which are potential carbon sources found in char. Identification of the rhamnolipid biosynthesis genes in the postfire isolate, Paraburkholderia kirstenboschensis str. F3, led to the discovery of rhlM, whose gene product is responsible for the unique methylation of rhamnolipid substrates. RhlM is the first characterized bacterial representative of a large class of integral membrane methyltransferases that are widespread in bacteria. These results indicate multiple roles for RLMEs in the postfire lifestyle of Paraburkholderia isolates, including enhanced dispersal, solubilization of potential nutrients, and inhibition of competitors. Our findings shed new light on the chemical adaptations that bacteria employ to navigate, grow, and outcompete other soil community members in postfire environments.

Internal Arc Performance of Instrument Transformers Filled with Different Dielectric Liquids

Internal arc testing is still a controversial topic in the instrument transformer world. The main reason for that is the fact that even a fully successful test guarantees only a certain degree of transformer safety. Furthermore, the test does not cover a plethora of operational fault scenarios and has requirements which are not defined clearly enough. In addition, there are very few data available in the literature on the internal arc performance of alternative, biodegradable dielectric liquids. Some liquids (such as natural and synthetic esters) do inherently come with higher flash and fire points compared to conventional mineral oil, but there is insufficient test experience to corroborate the influence this high fire point has on the actual operation. Specifically, to the authors’ knowledge, internal arc tests on instrument transformers were never performed with biodegradable dielectric liquids, making the contributions of this paper a true world premiere. In short, this paper is intended to augment the existing standards, thus providing additional insight into how to test internal arc performance, what to look out for and what level of performance to expect, which is of broad interest to researchers, utility engineers and public alike.

Lightning impulse breakdown behavior of natural ester and modified natural ester under long oil gap: An experiment and first-principles simulation analysis

The investigation of lightning impulse (LI) breakdown characteristics in long oil gaps with insulating liquids is of utmost importance for the design of high-voltage, large-capacity transformers. This study focuses on analyzing the negative LI breakdown characteristics of two types of insulating oils, namely high viscosity natural ester soybean oil (SO) and low viscosity modified natural ester palm fatty acid ester (PFAE), under long oil gap conditions. The research includes testing and analyzing the voltage and current waveforms, LI breakdown voltage, and streamer discharge development speed of these liquids across oil gaps ranging from 25 mm to 105 mm. The findings demonstrate that the breakdown voltage of both insulating oils tends to increase as the oil gap distance widens. At a 25 mm gap, the average breakdown voltage of PFAE is not significantly different from that of SO. However, at a 105 mm gap, the average breakdown voltage of PFAE surpasses that of SO by 46.29%. Weibull distribution analysis is applied to the LI breakdown voltage data of the two insulating liquids, resulting in empirical formulas for breakdown voltage as a function of oil gap width at failure probabilities of 1%, 50%, and 90%. The discharge development rate of PFAE is lower than that of SO, especially in the oil gap of 105 mm. With the increase of the oil gap, the streamer development rate of the two insulating oils showed a trend of increasing. Using density functional theory based on first principles, the study investigates changes and discrepancies in parameters such as ionization potential, electron affinity, softness, excitation energy, and molecular surface electrostatic potential of the two insulating liquids with varying electric field strengths. The atomic and molecular scale analysis reveals the primary factors contributing to the contrasting macroscopic lightning shock breakdown characteristics of SO and PFAE. The comprehensive combination of experimental and simulation results suggests that PFAE exhibits greater potential for implementation in high-voltage, large-capacity transformers compared to SO. This study aims to bridge the gap in knowledge regarding the LI breakdown characteristics of different natural esters in long oil gaps. The experimental and theoretical findings presented in this paper provide a foundation for the practical application of natural esters and modified natural esters in high-voltage and large-capacity transformers.

Natural esters as sustainable alternating dielectric liquids for transformer insulation system: analyzing the state of the art

Natural esters as sustainable alternating dielectric liquids for transformer insulation system: analyzing the state of the art

Performance evaluation of natural Olea europaea (olive oil)-based blended esters with butylated hydroxyanisole and butylated hydroxytoluene: optimization using response surface methodology.

For power transformer applications, this study explores an alternative insulating liquid. With this aim, edible natural esters such as refined Olea europaea (olive oil), rice bran oil, soya bean oil, sunflower oil, and corn oil are investigated as suitable replacements for the mineral oil (MO) used in the transformer. In addition, olive oil and other natural esters are incorporated into the blend for further analysis to obtain a better insulating medium. Blended natural esters were also tested for performance enrichment by antioxidant inclusion. Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) were chosen as antioxidants for this study. In this study, we aimed to investigate the role of key input factors [A-speed, B-time, and C-temperature] on the output response [Y-breakdown voltage]. It was determined that the optimal conditions for [Y] are [A-699.91 rpm, B-49.95 min, and C-88.75 °C]. In order to ensure the desirable properties, the natural esters were subjected to certain experimentations such as breakdown voltage (BDV), viscosity, fire point (FeP), and flash point (FhP). From the results, it is observed that the natural esters and blended natural esters can be used in the transformer as an alternate insulating medium and that the antioxidants have a significant effect on the properties of natural ester combinations.

Methyl Ester-Mineral Oil Mixture under Thermal Aging

Replacement with natural esters (retrofilling) is an alternative solution to extend the life expectancy of an oil-filled transformer containing mineral oil. During the retro-filling process, some portions of the mineral oil remain inside the transformer's tank, forming a mixture between the used mineral oil and the new vegetable oil. In this investigation, methyl ester was mixed with a relatively low percentage of mineral oil to simulate the retro-filling process. The aim is to examine the characteristics of a mixture of mineral and vegetable oils under thermal aging. Thermal aging treatments were carried out at 120°C for 28 days and 140°C for 14 days. Kraft paper and copper wire were incorporated during the aging test. After thermal aging, the characteristics of the oil mixture were evaluated based on electrical, physical, and chemical characteristics. The result shows that physical and chemical characteristics are significantly influenced by the increase in mineral oil content and the temperature of thermal aging. However, the breakdown voltage increased after thermal aging, but at a higher temperature, the breakdown voltage dropped as the mineral oil content increased.

Surface modification boosts dispersion stability of nanoparticles in dielectric fluids

Achieving stable dispersion of nanoparticles in dielectric fluids is a challenging task, as there are complex and diverse influencing factors, requiring molecular-level understanding of the nanoparticle aggregation. In this paper, we conducted long-time molecular simulations of dielectric nanofluids containing fifteen SiO2 nanoparticles, systematically varying the length of alky chains grafted onto their surface to explore their impact on the aggregation process. Our results reveal that appropriate surface modification can dramatically increase the dispersion stability of nanoparticles in dielectric fluids. SiO2 nanoparticles lacking alkyl chains exhibit a strong tendency to approach each other, and form aggregates in natural esters, because of the Coulombic energy from heteroatoms of SiO2 nanoparticles. Despite the differences in the length of grafted alkyl chains on the surface of SiO2 nanoparticles, all of them, regardless of their length, are capable of effectively shielding the Coulombic interactions and increasing the van der Waals interaction with natural esters, thereby reducing the aggregation tendency of nanoparticles. Furthermore, the smaller diffusion ability, caused by the steric hindrance effect, of surface-modified SiO2 nanoparticles also inhibits their collision and subsequent aggregation.

Synthesis of cinnamoyl tethered indoline derivatives with anti-inflammatory and antioxidant activities

Aimed to improve the anti-inflammatory activities of natural antioxidant caffeic acid phenethyl ester, the thirty derivatives of cinnamoyl tethered indoline were synthesized. The structure-activity relationship indicated that the fragments of catechol and 5-Cl-indolinyl were beneficial for the higher dual-activities of antioxidant and anti-inflammation. The most potent compound 4b suppressed the secretions of inflammatory cytokines IL-6 and TNF-α, inhibited inducible nitric oxide synthase (iNOS) expression, upregulated the antioxidant gene HO-1 expression and antioxidant enzyme SOD level, and inhibited oxidative stress marker MDA level. Besides, 4b and its acetate prodrug 4′b could effectively attenuate paw edema more than CAPE. In regard to anti-inflammatory mechanism, 4b suppressed the NF-κB activation associated with phosphorylation of p65 subunit and degradation of IκBα. In summary, this study provided a new anti-inflammatory derivative 4b which was worthy of further research.

Life Expectancy of Transformer Paper Insulation Retrofilled with Natural Ester in the Laboratory.

The use of alternative insulating liquids instead of mineral oil in transformers is spreading around the world due to their superior fire resistance. Furthermore, researchers have demonstrated that these oils increase the lifespan of the solid insulation of the transformers and, thus, the life expectancy of the equipment. Retrofilling of transformers with natural and synthetic esters allows companies to benefit from the properties of using these liquids without making an investment into new machinery. This paper investigated the ageing process of Kraft paper that was retrofilled with a natural ester in the laboratory. The Kraft paper samples were subjected to accelerated thermal ageing in an oven at 130 °C, and markers such as the degree of polymerisation and tensile strength were measured. The ageing tests comprised a first period, where the samples were immersed in mineral oil, followed by a replacement of the oil with a natural ester. As moisture is a determinant factor for paper ageing, two sets of samples with different moisture contents were tested. The results showed that the retrofilling of the transformers may slow down the degradation rate of the solid insulation despite the presence of remaining mineral oil adsorbed in the paper.

A numerical study on the thermal response of biodegradable ferrous oxide/aluminium oxide nanofluid flow past an unsteady contracting permeable cylinder: A comparative analysis

Esters that are considered natural come from renewable sources like vegetable or animal oils or other bio-based materials. Due to natural esters' great biodegradability, lack of toxicity, and high flash point, their use in industrial applications has been expanding quickly in recent years. The current study, thus numerically investigates an unsteady laminar flow and heat transfer of biodegradable nanofluids past over a shrinking cylinder of time dependent radius. Natural Ester (NE) is used as the base fluids, and two nanoparticles such as Fe3O4 (ferrous oxide) and Al2O3 (aluminium oxide) are used to create different combinations of nanofluids. The unsteady Navier-Stokes equations are used to model it, and similarity solutions are introduced to solve the problem. A MATLAB built-in package BVP4c has been employed to tackle the problem. The physical behavior of the solution has been explored in terms of parametric analysis and graphical demonstration and the validation of present solutions is reported by the comparative benchmark with already available results in a limiting sense. Our findings demonstrate that Fe3O4 biodegradable nanofluids are capable of carrying and dispersing thermal energy more effectively, resulting in improved heat transfer rates compared to Al2O3 biodegradable nanofluids.

Molecular Orbital Properties and Insulation Characteristics of Flaxseed Oil

This study aims to analyze the molecular orbital parameters of flaxseed oil (linum usitatissimum) and to measure the AC breakdown voltages at different electrode gaps with various rate of rises. AC breakdown voltages of flaxseed oil are measured at 1.0 and 2.5 mm electrode settings with 0.5 kV/s, 2.0 kV/s and 3.0 kV/s rate of rises, adhering to IEC and IEEE standards. UV-VIS (Ultraviolet–Visible) and FT-IR (Fourier Transform-Infrared) measurement tests carried out after breakdown voltage measurements reveals that the molecular structure of the oil remains stable against electrical discharges. The compounds of flaxseed oil are analyzed using GC-MS and it is determined that the oil mainly consists of seven triglycerides in accordance with the literature. In order to better understand the electrical behavior of these triglycerides, molecular orbital properties such as ionization potential, electron affinity and electron energy gap are analyzed employing Density Functional Theory (DFT) using B3LYP/6-311 + G(d,p) and B3PW91/6-311 + G(d,p) basis sets. The advantages of flaxseed oil such as AC dielectric strength, stability against breakdown mechanism, homogeneous molecular electrical characteristics of its compounds and antioxidant content make this oil as one of the potential natural ester alternatives to mineral oils in the power system industry.