Mixture Of Mineral Oil Research Articles

Continuously stirred tank reactor for oil-suspended thermochemical energy storage systems for CuSO4·5H2O

Thermochemical energy storage can be used for heating applications, thereby helping to cut down on greenhouse gases from burning non-renewable fuels by offering a solution for seasonal heat storage. In the scope of the EU project RESTORE, a thermochemical energy storage is used to store low temperature waste heat and use it for district heating. This study presents the thermochemical energy storage as a new continuously stirred tank three-phase suspension reactor for storing heat from renewable sources or waste heat with almost no losses, in reaction. Therefore, the reactor was built of glass, where process parameters, such as the mean residence time, have been varied to obtain optimized results for thermochemical energy storage operating at the fixed temperature of 125 °C chosen due to project restrictions. The heat is used to dehydrate CuSO4·5H2O in the charging step and recovered by rehydrating CuSO4·3H2O or CuSO4·H2O, respectively, while generating heat in the discharging step. Using a mixture of silicone and mineral oil to prevent foaming, conversion rates of over 94 % to CuSO4·H2O were reached in the charging step with the continuously stirred tank reactor, with 1 kW thermal power, 150 mm diameter and 900 mm height in continuous operation. In discharging operation, 100 % conversion from CuSO4·H2O to CuSO4·5H2O was measured. This paper lays the groundwork for a new technology for thermochemical heat storage in low temperature application.

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.

Investigation of the Stability and Insulating Properties of Mineral Oil-Based Surface Modified Silicon Nanofluid

The requirement for high voltage is growing extensively, which has obligated to enhance the dielectric and thermal properties of the insulators. Nanofluids are a new insulating material class that exhibits exceptional thermal and electrical characteristics. The relative permittivity and conductivity of Si nanoparticles (nSi) of diameter 10-30 nm synthesized from the p-type wafer are ideal values for free charge trapping; hence the mixture of mineral oil and nSi has the potential to replace the standard insulating oil. During the pre-breakdown phenomena of the insulator, the nSi in the base fluid act as a charge trap, capable of capturing about 45 electrons with a significantly shorter relaxation time of 1.42 × 10-14 s relative to the streamer propagation time. Oleic acid, an oil-soluble dispersant, improved the dispersion and stability of the nanofluids. The FTIR analysis determined the type of interaction as chelating bidentate between the oleic acid and the nSi surface. The impulse breakdown voltage of the nanofluids revealed the effect of trapping the free charges generated by the molecular ionization on enhancing the impulse breakdown strength. The relative permittivity measurement of the nanofluid followed the Clausius-Mossotti polarization model of a mixed dielectric. Due to increased nanosized pores (with the number of nanoparticles), partial discharge inception voltage and the AC breakdown voltage were reduced with concentration.

Dielectric Properties and Fire Safety of Mineral Oil and Low-Viscosity Natural Ester Mixtures in Various Concentrations

This paper presents the results of testing the electrical and fire properties of mineral oil and low-viscosity natural ester mixtures. Properties such as breakdown voltage, relative permeability, dispersion coefficient, conductivity, flash and burn point, and lower heating values were investigated in different concentrations of mixtures of the two liquids, as well as for the base liquids. To ensure equal humidity levels, the prepared samples of mixtures and base liquids were conditioned under identical climatic conditions, resulting in samples with similar relative humidity (9 ± 3)%. The obtained measurement results for mixtures of the two fluids were related to the values obtained for the base liquids and analyzed in terms of changes in electrical properties and fire safety when used as insulating liquids in transformers. The presented results are useful for supplementing knowledge on the possibilities of using dielectric liquid mixtures in high-voltage power devices, with to the aim of using mixtures as alternatives to mineral oil.

Performance Analysis of Nyamplung Oil (Calophyllum Inophyl-lum) as an Alternative Liquid Electrical Insulation Material to Replace For Power Transformer Oil

In the operation of electric power distribution, the transformer can be said to be the heart of the transmission and distribution of electric power. In recent years the use of vegetable oil is increasing. The purpose of this study was to test and analyze a mixture of transformer oil and nyamplung oil (Calophyllum Inophyllum) as transformer insulation and also to obtain the best composition of nyamplung oil which can be used as an alternative to transformer oil. This research method tested the parameters of nyamplung oil and a mixture of nyamplung oil and mineral oil (Shell Diala S4), such as; viscosity, flash point, density, pour point, acidity, moisture content and breakdown voltage. The sample test results are then compared with standard mineral oil according to IEC 60296-2003. From the analysis conducted, it was found that TRNY10 oil mixture (10% transformer oil and 90% mineral oil) has the best potential as power transformer oil.

Electrical Analysis of Ceiba Pentandra Oil as a Replacement for Mineral Oil in High Voltage Insulation Application

The application of Ceiba Pentandra Oil is introduced as an alternative to the traditional non-biodegradable insulation oil. Through the recent research in vegetable based insulation oil (coconut oil, palm oil, and olive oil), it is identified that the vegetable insulation oil is biodegradable but edible in nature, which leads to the food crisis. To prevent the insufficiency of food, an interesting non-edible oil is extracted from the seeds of Ceiba Pentandra, which has the capability of biodegradation. This work has focused on the utilization of Ceiba Pentandra seeds for the production of vegetable based insulation oil since it is considered as the sustainable energy resource and. A two-step chemical conditioning method and antioxidants are used to produce the Processed Ceiba Pentandra oil (PCPO). Adding to that, the insulation behavior of Processed Ceiba Pentandra oil (PCPO) with and without antioxidant is analyzed. The different concentrations of PCPO and naphthalene based Mineral oil mixtures have been compared as per the ASTM standard. The two-step chemical conditioning method has provided the enhanced behavior of physical properties like Viscosity, Acidity, Flashpoint, Fire points and AC breakdown voltage. While improving the oxidation stability, the electrical property like AC Breakdown voltage has met the dielectric Standards. Thus this Processed Ceiba Pentandra oil (PCPO) has the potential to be an alternative of traditional insulation oil.

Potential of using mineral oils for the control of the mosquito bugs Helopeltis theivora (Hemiptera: Miridae) in cashew plantations

• Potentials of using an n C24 MO in controlling Helopeltis theivora were investigated. • n C24 MO application significantly reduced egg hatchability of H. theivora. • Oil extended pre-oviposition period and reduced H. theivora fecundity and longevity . • n C24 MO at 1% v/v can be used for H. theivora control in cashew plantations. This study investigated the influence of an n C24 mineral oil (MO) on some biological characteristics of a mosquito bug, Helopeltis theivora, reared on cashew under laboratory and greenhouse conditions. Aqueous emulsions of the oil were applied as sprays to eggs at four daily intervals after oviposition to assess impacts on egg hatch, and to cashew seedlings to assess adult longevity and female fecundity reared on the plants. Field applications were also carried out to assess the impacts of sprays on populations of the bug in a cashew orchard. The results of the laboratory study indicated that 1% (v/v) of the MO application reduced egg hatch when applied to eggs on cashew seedlings, in separate treatments, 1, 2, 3, and 4 days after oviposition (DAO). Egg mortality showed a negative linear correlation with egg maturity (DAO). The pre-oviposition period of adult females placed on sprayed cashew seedling, after deposits of 1% (v/v) sprays dried, was significantly prolonged. The longevity of males and females on dry oil-spray deposits was lower than on seedlings sprayed with water. The fecundity of females was also lower. Field sprays significantly reduced populations of the bug on mature cashew trees. Mixtures of MO and abamectin were more effective than oil alone. The results of the study indicate that mineral oils can be used to suppress populations of H. theivora in cashew plantations.

Process optimization and mechanism of oil-based drilling cuttings treatment based on hydrophilic deep eutectic solvent

Oil-based drilling cuttings (OBDC) are hazardous waste, oil removal treatment must be done before they are re-utilized. Winsor I microemulsion (composed by microemulsion phase and remaining phase) cleaning is one of oil removal methods. However, there are many surfactants in the Winsor I microemulsion, which result in high cleaning cost and high possibility of surfactant contamination. In this paper, hydrophilic deep eutectic solvent (DES) and mineral oil were used to replace the microemulsion phase and remaining phase in Winsor I microemulsion, respectively, and a low-cost and surfactant-free cleaning agent was formed. The recommended DES was the mixture of choline chloride, methanol, and water with a molar ratio of 1:2.5:3, and the best cleaning agent was the mixture of DES and mineral oil with a mass ratio of 3:1. The recommended cleaning process was that added the OBDC into cleaning agent with a mass ratio of solid to liquid of 1:3, and stirred at room temperature for 100 min. At this condition, the oil content of OBDC reduced from 14.57 wt% to 1.34 wt%. In addition, the cleaning mechanism was discussed. The DES has low surface tension and good wetting property, which is similar with the microemulsion.

Computational Fluid Dynamics Analysis of the Influence of Gas Content on the Rotordynamic Force Coefficients for a Circumferentially Grooved Annular Seal for Multiple Phase Pumps

Abstract Pumping efficiency and rotordynamic stability are paramount to subsea multiphase pump operation since, during the life of a well, the process fluid transitions from a pure liquid to a mixture of gas in the liquid to just gas. Circumferentially grooved seals commonly serve as balance pistons in pumps while also restricting secondary flow. Prior experimental results obtained with a grooved seal operating with a mixture of air and mineral oil show the seal rotordynamic force coefficients vary significantly with the gas volume fraction (GVF). This paper, complementing an exhaustive experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage and dynamic force coefficients of a circumferentially grooved seal supplied with air in an oil mixture with a GVF varying from 0 to 0.7. The test seal has 14 grooves, an overall axial length of 43.6 mm, and radial clearance of 0.211 mm. The 127 mm diameter rotor spins at constant angular speed (Ω = 3500 rpm). The mixture enters the seal at a supply pressure (Pin) of 2.9 bar(a), and the seal exit pressure (Pout) is 1 bar(a). The CFD two-phase flow simulations utilize the Euler–Euler multiphase model to predict the mass flowrate and the pressure field as a function of the operating conditions. Using a multi-frequency shaft orbit motion method, the CFD simulations deliver the variations of reaction force on the rotor with respect to the excitation frequency. For a pure liquid condition (GVF = 0), both the CFD and experimental results produce constant stiffness, damping, and added mass coefficients. The experimental and CFD results demonstrate the seal rotordynamic force coefficients are quite sensitive to the GVF. When introducing a small amount of air into the oil (GVF = 0.1), the direct damping coefficient increases by approximately 10%. For operation with a mixture with inlet GVF > 0.1, the cross-coupled stiffness coefficients develop strong frequency-dependent characteristics. In contrast, the direct damping coefficient has a negligible variation with excitation frequency. The CFD predictions, as well as the experimental results, evidence that air injection in a liquid stream can significantly change the seal rotordynamic characteristics, and thus can affect the rotordynamic stability of a pump. An accurate CFD analysis provides engineers to design reliable grooved seals operating under two-phase flow conditions.

Bubble dynamics of R-134a/POE and R-123/MO mixture on enhanced surfaces having pores on sub-tunnels

Structured enhanced surfaces are widely used to promote the nucleate boiling heat transfer in a refrigeration system, where a compressor oil circulates. However, there is a significant lack of understanding of the mechanism or predictive models, especially on the boiling of refrigerant/oil mixtures on enhanced surfaces. In this study, as a building block, the bubble dynamic data as well as the heat transfer coefficients were obtained for the refrigerant/oil mixtures on pored surfaces. The test mixtures included R-134a/polylester (POE) and R-123/mineral oil (MO). The results showed that the oil degraded the size of the departing bubbles. The degradation was more severe for R-123/MO than R-134a/POE, and it increased as the saturation temperature increased. The sequence of degradation among samples generally followed the reverse order to the magnitude of the heat transfer coefficient of the pure refrigerant. Similarly, the oil degraded the frequency. The degradation was, in general, in reverse order to the degradation of the bubble departure diameter. The oil also degraded the nucleation site density. As for the heat transfer coefficient, the degradation was more significant at a higher saturation temperature, and for R-134a/POE than for R-123/MO. The changes of bubble dynamic parameters as well as the thermo-physical properties of the refrigerants were shown to be responsible. A heat transfer prediction model was developed based on the bubble dynamic parameters.

Effect of Concentration of Al2O3 Nanoparticles on Electrical Properties of Mineral Oil

This study aimed to compare the electrical characteristics of mineral oil-based nanoparticles to those of pure mineral oil. Mineral oil used in distribution transformers was mixed with aluminum oxide (Al2O3) nanoparticles, which serve as an insulator, with 0.01, 0.03, and 0.05 % mineral oil volume concentrations. The moisture content in mineral oil was measured beforehand, and the electrical tests were subsequently conducted in accordance with international standards. The moisture content test revealed that the combination of nanoparticles and mineral oil resulted in an increase in moisture content. As regards the test of AC withstanding voltage and negative polarity lightning impulse voltage, it was found that the mineral oil mixed with the nanoparticles had higher dielectric strength than the original mineral oil. In addition, the test results of positive polarity lightning impulse voltage demonstrated that with a mixture of mineral oil and the nanoparticles at a 0.01 % concentration, the positive polarity lightning impulse dielectric strength of the mineral oil increased. However, at concentrations of 0.03 and 0.05 %, it did not rise, regardless of the increasing volume of nanoparticles. The results, thus, showed promising directions for applications of nanoparticles in the development of electrical properties of mineral oil. HIGHLIGHTS The addition of Al2O3 nanoparticles to the mineral oil resulted in an increase in the oil moisture content. However, it was found that the moisture content in the mineral oil tended to decrease with the increase in the amount of nanoparticles The optimum nanofluid combination in terms of increased AC breakdown strength was created by adding Al2O3 nanoparticles to mineral oil at a rate of 0.05 vol% The Al2O3 nanoparticles being added to the mineral oil can give an increase in the impulse breakdown voltage with the negative polarity For the positive polarity of the impulse breakdown voltage, the best nanofluid mixture in terms of increased breakdown strength was produced by the addition of Al2O3 nanoparticles at a rate of 0.01 vol% to the mineral oil GRAPHICAL ABSTRACT

Comparative Study of Microwave Oven-Assisted Tissue Processing with Isopropanol and Mineral Oil Mixture and Propylene Glycol Methyl Ether on Morphological Quality of Tissue Sections

Background: 
 Over several years, xylene has been traditionally utilised as the clearing agent of choice in tissue-processing due to effectiveness in rapidly clearing tissue, facilitating the paraffin infiltration process. However, xylene use adversely impacts the health of personnel with long term exposure due to toxicity. In order to overcome these effects and replace it with a safer alternative agent, the present study aims to compare quality of tissue sections processed using an isopropanol and mineral oil mixture and propylene glycol methyl ether (PGME) as xylene substitutes.
 
 Methods: 
 Rat skeletal muscle tissue samples (n=20) were prepared for each processing protocol with xylene substitutes. Tissue specimens were processed according to the proposed microwave protocol. The clearing steps were performed using isopropanol and mineral oil mixture, and PGME, replacing xylene. From each paraffin-embedded block, one section of 4-5µm thickness tissue was obtained and conventionally-stained with Haematoxylin and Eosin (H&E). The histological sections were microscopically assessed and scored by a pathologist. A qualitative analysis was performed with the results obtained.
 
 Results: 
 The overall score obtained for xylene processed tissue was 100% with a score of 2 for all the 3 parameters assessed. However, the outcome for tissue processed with isopropanol and mineral oil mixture was 28.6% unsatisfactory, 28.6% satisfactory and 42.8% good. In PGME-treated tissues, 14.3% were unsatisfactory sections, 71.4% were satisfactory and 14.3% produced good quality sections. Overall, tissues processed using both substitutes exhibited sufficient staining quality in terms of the aforementioned parameters as compared to xylene-processed tissues, though significant difference in scores were observed.
 
 Conclusion:
 Despite several challenges faced in the study, isopropanol and mineral oil mixture and PGME can be suggested as alternative clearing agents to xylene, provided having access to a more sophisticated microwave oven with precise temperature control for complete tissue-processing.

Water/Oil Emulsions with Controlled Droplet Sizes for In Vitro Selection Experiments.

In the early history of life, RNA might have had many catalytic functions as ribozymes that do not exist today. To explore this possibility, catalytically active RNAs can be identified by in vitro selection experiments. Some of these experiments are best performed in nanodroplets to prevent diffusion between individual RNA sequences. In order to explore the suitability for the large-scale in emulsio selection of water-in-oil emulsions made by passing a mixture of mineral oil, the emulsifier ABIL-EM90, and a few percent of an aqueous phase through a microfluidizer, we used dynamic light scattering to characterize the size of aqueous droplets dispersed throughout the oil. We found that seven or more passes through the microfluidizer at 8000 psi with close to half molar inorganic salts and 10% polyethylene glycol produced droplets with sizes below 100 nm that were ideal for our purposes. We also identified conditions that would produce larger or smaller droplets, and we demonstrate that the emulsions are stable over weeks and months, which is desirable for different types of in vitro selection experiments.

Evaluation of the Properties of Mixtures of Aromatic Mineral Oil and Synthetic Ester for High-Voltage Equipment

This article discusses the possibility of enhancing the insulating characteristics of a mineral oil-based on petroleum with high aromatic hydrocarbon content (23%) by mixing it with the synthetic ester Midel 7131. An assessment of the insulating properties of mixtures with ester content in mineral oil from 0 to 100% is given. The main characteristics of mixtures are described, such as density, kinematic viscosity, flash point, dielectric loss tangent, relative permittivity, breakdown voltage, moisture content and oxidation stability. It is shown that with an increase in the proportion of ester, some parameters of the obtained insulating liquid improve (flash point, relative permittivity, breakdown voltage, oxidation stability, corrosive sulfur), while other parameters (density, kinematic viscosity, dielectric dissipation factor) change to invalid values. Unlike a mixture of pure unused mineral oil with ester, the addition of unused synthetic ester to used high aromatic mineral oil (taken from a transformer in operation) results in an abnormal increase in the dielectric dissipation factor.

Electrophysical properties of mixtures of mineral oil and synthetic ester dielectric liquid

Power transformers are key equipment in power generation, transmission, and distribution systems. The reliability of power transformers is based on the performance of the insulation system, which includes solid cellulose insulation and a liquid dielectric. Modern power engineering requires liquid insulation to have excellent insulating properties, high fire resistance, and biodegradability. Mineral oil that has been in use for over 100 years does not meet certain requirements. Therefore, various methods of enhancing the insulating properties of the oil are currently being considered, including mixing it with other liquid dielectrics, which have excellent properties. Synthetic and natural esters are considered as alternative fluids.This article discusses the possibility of enhancing the insulating characteristics of mineral oil with a high content of aromatic hydrocarbons (for example, T-750 oil) by mixing it with synthetic ester Midel 7131. Assessment is given of insulating parameters of the resulting mixtures with an ester fraction in mineral oil from 0% to fifty%. The main characteristics of the mixtures are described, such as density, kinematic viscosity, flash point, dielectric loss tangent, relative dielectric permittivity, breakdown voltage, and moisture content. It is shown that with an increase in the proportion of ester, some parameters of the obtained insulating liquid improve (flash point, dielectric constant, breakdown voltage), while values of other parameters (density, kinematic viscosity, dielectric loss tangent) with an ester content of more than 10% in the mixture do not meet the requirements for mineral oils.

Suppression of Microdochium patch using rotations of mineral oil, sulfur, and phosphorous acid

AbstractMicrodochium patch is a turfgrass disease caused by the fungal pathogen Microdochium nivale (Fr.) Samuels and I.C. Hallett that occurs in cool, humid conditions, which are commonplace in the U.S. Pacific Northwest and northern Europe. Pesticide restrictions in certain areas make suppressing Microdochium patch challenging, and alternative control methods are desired. Previous research has shown that mineral oil, S, and phosphorous acid (H3PO3) suppress Microdochium patch, but abiotic damage was associated with repeated mineral oil applications. Two field experiments in western Oregon focusing on the suppression of Microdochium patch and turfgrass quality on annual bluegrass (Poa annua L.) greens are presented. The first experiment compared tank mixtures of mineral oil and S or mineral oil and H3PO3 in rotation with a tank mixture of S and H3PO3. The second experiment focused on seasonal rotations that excluded mineral oil in certain months and compared 2‐ and 3‐wk application frequencies. All rotations, in both experiments, suppressed Microdochium patch compared to the non‐treated control, although differences in turfgrass quality were observed. In the first experiment, green cover percentage was used to assess abiotic damage. A mineral oil and H3PO3 tank mixture rotated every 2 wk with S and H3PO3 resulted in the highest green cover percentage. In the second experiment, most of the applications made every 2 wk completely suppressed Microdochium patch. Two treatments applied every 2 wk that withheld mineral oil in the winter months resulted in turfgrass quality ratings considered acceptable for putting greens on all rating dates.

Effects of high oil viscosity on oil‐gas downward flow in deviated pipes. Part 1: Experimental setup and flow pattern transitions

AbstractThis work provides new experimental data on high viscosity oil‐gas flow. A set of 170 downward flow experiments were carried out using a mixture of air and mineral oil (213 mPa · s, 50.8 mm internal diameter, 21.5 m long) for five different elevations: −45°, −60°, −70°, −80°, and −85°. Superficial liquid and gas velocities varied from 0.05 m/s to 0.7 m/s and 0.7 m/s to 7 m/s, respectively. Flow pattern transitions were identified and analyzed. The results helped to evaluate the effects of pipe inclination and liquid viscosity on the stratified‐annular transition, as well as the characterization of subclasses of annular flow pattern, named falling film, liquid slip, and wavy annular. Based on the experimental evidence, the study proposes a constant liquid‐fraction value as a transition between liquid slip and wavy annular flow patterns. A comparison of the present data with the flow pattern predictions of the available models were made. Results show disagreements, which justifies the need for a detailed study of the effects of viscosity and the inclination of the pipe in liquid‐gas downward flow mixtures.

Determination of hydroxy terminated polybutadiene in the blends by liquid critical condition chromatography

A method based on liquid critical condition chromatography (LCCC) was established for the quantification of hydroxy-terminated polybutadiene (HTPB) in polymer blends. The critical conditions for HTPB were investigated using a C18 column as the stationary phase, and tetrahydrofuran (THF)-acetonitrile (ACN) or THF-water as the mobile phase. Irrespective of the relative molecular mass, HTPB was eluted under the critical conditions of THF-ACN (70.7:29.3, v/v) or THF-water (92:8, v/v). Under the optimal conditions, the HTPB exhibited satisfactory linearity in the range of 46.7-216.4 mg/L, with a correlation coefficient (r) of 0.997. The limit of detection reached 4.2 mg/L. The recoveries of HTPB from the prepared mixtures of HTPB and mineral oil ranged from 89.2% to 101.1%, with a relative standard derivation of less than 0.66% (n=6). This method was successfully applied to the quantitative analysis of HTPB in a commercial polyurethane adhesive, and 26.6% of HTPB was detected in the product. This LCCC method is simple, convenient, highly selective, and reliable for quality control and failure studies of formulated products.

Streaming Electrification of Nycodiel 1255 Synthetic Ester and Trafo EN Mineral Oil Mixtures by Using Rotating Disc Method

Power transformers are the main element of an electric power system. The service life of these devices depends to a large extent on the technical condition of their insulation system. Replacing mineral oils with natural or synthetic ester (retrofilling process) may increase the efficiency and operational safety of transformers, and also limit their adverse environmental impact. It is technically unfeasible to completely remove mineral oil from a transformer. Its small residues form a mixture with fluid ester, with different physicochemical and electric properties. Streaming electrification is one of the phenomena which, under unfavorable conditions, may damage the insulation system of a forced oil cooled transformer. It is necessary to run prophylactic tests for the ECT (electrostatic charging tendency) of insulating liquid mixtures from the point of view of transformer retrofilling, which is being used more often than before. The article presents the results of studies on selected physicochemical, and electrical properties, and the ECT of mixtures of fresh and aged Trafo EN mineral oil with Nycodiel 1255 synthetic ester. In this regard, the density, the kinematic viscosity, the conductivity, and the relative dielectric constant were measured. The molecular diffusion coefficient was determined using Adamczewski’s empirical dependency. The streaming electrification was tested in a rotating disc system. The impact of the rotation time, the diameter, and the disc’s rotation speed on the amount of the electrification current generated were analyzed. In addition, the co-relation between the electrification current and the composition of the mixture was determined using fresh and aged mineral oil. On the basis of the electrification model, the volume density of the qw charge was calculated, which is a parameter defining the ECT of insulating liquids. Based on the results, it was concluded that the synthetic ester is characterized by a higher susceptibility to electrification than the mineral oil. However, combining synthetic ester with a small amount (up to 20%) of fresh or aged mineral oil significantly reduces its ECT, which is beneficial from the point of view of retrofilling power transformers.

Electrostatic Charging Tendency Analysis Concerning Retrofilling Power Transformers with Envirotemp FR3 Natural Ester

Natural and synthetic esters are liquids characterized by insulating properties, high flash point, and biodegradability. For this reason, they are more and more often used as an alternative to conventional mineral oils. Esters are used to fill new or operating transformers previously filled with mineral oil (retrofilling). It is technically unfeasible to completely remove mineral oil from a transformer. Its small residues create with esters a mixture with features significantly different from those of the base liquids. This article presents electrostatic charging tendency (ECT) tests for mixtures of fresh and aged Trafo EN mineral oil with Envirotemp FR3 natural ester from the retrofilling point of view. Under unfavorable conditions, the flow electrification phenomenon can damage the solid insulation in transformers with forced oil circulation. The ECT of the insulating liquids has been specified using the volume density of the qw charge. This parameter has been determined using the Abedian–Sonin model on the basis of the electrification current measured in the flow system, as well as selected physicochemical properties of the liquids. It was shown that ECT is strongly dependent on the type of insulating liquid and pipe material, as well as the composition of the mixtures. The most important finding from the research is that a small amount (up to 10%) of fresh and aged mineral oil is effective in reducing the ECT of Envirotemp FR3 natural ester.