Pure Transformer Oil Research Articles

Influence of thermal aging on dielectric characteristics of transformer insulating oils

Transformer oil is a liquid insulating material used in transformers as insulation and coolant. Particular characteristics insulating oil materials must be able to withstand breakdown voltages, while transformer oil as a coolant must be able to minimize heat generated, so that transformer oil is expected to protect the transformer from disturbances with these two characteristics. In order to reduce the percentage of transformer failures, it is necessary to maintain the purity of the oil. The features of aged transformer oil and pure transformer oil are investigated in this study. Pure transformer oil is heated to a particular temperature and cycled to create samples of aged transformer oil. The electric field intensity of transformer oil is measured to estimate the dielectric strength of aged transformer oil. FEM analysis is used to determine the intensity of an electric field. At aging temperatures of 130°C and 150°C, the dielectric characteristics of transformer oil for both Shell Diala and Triapar types are investigated. As a result, not only the electrical characteristics but also the effects of thermal aging on the physical and chemical properties of transformer oil are reported in this study.

Lubricated sliding wear of gear material under electrification – A new approach to understanding of the influence of shaft currents in the wear of EV transmissions

Electrification of drivelines of electric vehicles (EVs) can give rise to damaging shaft voltages/currents that can potentially impair the tribological performance of sliding and rolling elements in these driveline systems. In fact, previous research has shown that the existence of shaft voltages/currents in electric machines is indeed highly detrimental for the service life of tribological components of EVs. Such currents/voltages originate from magnetic flux asymmetry, inverter-induced voltage and triboelectrification and may also interfere with the normal sliding condition of other electrically conductive tribological components connected to the electric motors in addition to those that are comprised in the driveline, e.g., gears. In the past, the influence of shaft voltages/currents in gear systems has been explored scarcely. Accordingly, this work aims to investigate specifically the lubricated sliding friction and wear behavior of gear materials under the influence of DC electrification. For this, many tests were conducted on a gear material in a two-electrode-cell-based pin-on-disc tribometer representing the sliding contact of a gear interface. The tests were run under different currents (0, 1.5 and 3 A) and using different lubricants (pure mineral base oil, gear oil and transformer oil). The differences in sliding contact temperature, coefficient of friction (CoF), wear volumes and underlying mechanisms, as well as the chemical changes occurred in the lubricating oils by electrification are analyzed and discussed. Overall, the results confirmed that electrification can indeed have a strong influence on friction and wear of gear materials besides increasing contact temperature and thus accelerating the oxidation at the sliding interfaces for all the lubricants. The increase in wear is most likely due to three-body abrasion caused by increased oxidation and/or oxide-based debris formation under electrification. CoF was found to decrease by electrification, which was ascribed to the formation of a larger wear scar (that reduced contact pressure) and continuous replenishment of an oxide layer affording Lower Friction To Sliding Surfaces.

Experimental study of specific heat capacity and thermal conductivity of Al2O3-nanotransformer oil

The Al2O3-nanotransformer oil is regarded as one of the most compatible nanofluids that can function well in transformers. The Al2O3-nanofluids are rich in insulation properties, heat resistance and possess high thermal characteristics. The information gathered for this study outlines the contribution made by the Al2O3 nanoparticles in improving the specific heat capacity and thermal conductivity of the base transformer oil (mineral). The volume of the transformer oil reservoir is measured to be 15 L. When conducting the experimental work, a range of flow rates from (0.20, 0.30, 0.40, 0.50 and 0.60 L/min) and temperatures (35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C & 70 °C) have been used. The nanoparticle size used is fixed at 50 nm. It has been demonstrated that the Al2O3-nanoparticles have better thermal properties than pure transformer oil. At 40 and 50 °C, the overall heat transfer coefficient scored 10.2 and 12.1%. When using the thermal conductivity equation, the nanofluids thermal conductivity is seen to increase with the increase in nanoparticle volume concentration. The availability of nanofluids with high specific heat capacity can be viewed as one of the possible solutions that can be used to reduce energy consumption. The greatest value of the Nusselt achieved is 49% at the temperature of 35 °C and a volume concentration of 0.015% vol.

Dielectric response of a hybrid nanofluid containing fullerene C60 and iron oxide nanoparticles

Dielectric nanofluids based on transformer oil and magnetic nanoparticles are attractive due to the controllability of their physical properties by magnetic fields. Fullerene-based nanofluids often exhibit superior dielectric performance. In this study, we combine both iron oxide and fullerene nanoparticles into a transformer oil-based hybrid nanofluid. Using the method of dielectric relaxation spectroscopy, we examine the dielectric response of six samples with different fullerene-magnetic nanoparticle concentrations in the frequency range 0.1 mHz – 10 kHz. The study reveals that the dielectric response of magnetic nanoparticles dominates the dielectric spectrum of the hybrid nanofluids. The spectrum is characterized by a low-frequency Debye-like relaxation process associated with the interfacial polarization mechanism. The process is analyzed in the complex permittivity, electric modulus, and impedance plane. A logarithmic increase in relaxation times is observed with a linearly increasing concentration of fullerenes. The hybrid nanofluid with the highest fullerene concentration of 0.03 %w/V shows the lowest dielectric losses at the mains frequencies. When magnetic nanoparticles are absent, the dielectric spectrum of the fullerene nanofluid resembles that of the pure transformer oil. Around the mains frequencies, the dielectric losses of nanofluid containing only 0.01 %w/V of fullerene have been found lower than those of pure transformer oil. The complex impedance analysis revealed that the electrical conductivity of the hybrid nanofluids has a purely unidirectional character.

Stability, thermo-physical and electrical properties of naphthenic/POME blended transformer oil nanofluids

This study aims to investigate the stability, thermo-physical properties and electrical properties of pure transformer oil (naphthenic), palm oil methyl ester (POME) and blend oils suspended with SiO2-graphene nanoparticles. The hybrid SiO2-graphene was synthesized via sol–gel technique with pH varying from 10 to 12. Simultaneously, the transformer oil blend was prepared by homogenizing transformer oil and POME with various mass ratios ranging from 0 to 100%. Later, the nanofluids were synthesized by dispersing SiO2-graphene nanoparticles via high-speed homogenization (25000 RPM) followed by water bath sonication for 5 h. The stability of the nanofluids was measured by visual observation and UV–Vis spectrometer. Optimization of blend oils and hybrid nanofluids was performed using Minitab 18 for higher thermal conductivity and lower viscosity as the criteria for faster heat dissipation and fluid flow. Hybrid nanoparticles synthesized at pH 10 showed the lowest sedimentation rate than pH 11 and 12 and were therefore selected for further studies. Results show the thermal conductivity of nanofluids increased with hybrid nanoparticle concentration and temperature. The viscosity of nanofluid decreased with temperature with POME-based resulted in the lowest. Oxidation induction time (OIT) decreased with temperature but increased with the addition of hybrid nanoparticles. The optimized nanofluid blend was found to be 81.51 wt% mineral oil, 18.48 wt% POME and 0.10 wt% hybrid nanoparticle concentration. Further, the optimized sample resulted in lower dissipation dielectric factor than pure transformer oil. However, the breakdown voltage and resistivity of pure transformer oil is higher than optimized sample.

Degradation studies of electrical, physical and chemical properties of aged transformer oil

Transformer is crucial equipment in the transmission of electric power. Various types of insulating materials used in the transformer among those mineral oil or transformer oil is used for the insulation. To reduce the failure percentage of transformer it is necessary to maintain the purity of oil. This paper investigates work on different properties of aged transformer oils and pure transformer oil. The aged oils are taken as filtered and unfiltered after using in the transformer. The electrical, physical and chemical properties are investigated for pure and aged transformer oils. UV-spectroscopy is used to test the quality of oil based on the absorbance value and FTIR analysis is performed to determine the functional groups existing in the pure and aged transformer oils. The results showed that breakdown strength is less for used transformer oil due to formation of acidic functional groups. The absorption peak is high for unfiltered oil followed by filtered oil and pure oil.

The Modification Mechanism of Nano-Liquids on Streamer Morphology and Breakdown Strength under Microsecond Pulse

In liquid mediums, whether the breakdown strength can be greatly improved after introducing the nano-particles has been widely investigated, however, there has been no scientific consensus on the modification mechanism of this anomalous phenomenon. In this paper, we first experimentally measured the streamer morphology and breakdown strength in pure transformer oil, TiO2 nano-liquids and Al2O3 nano-liquids under microsecond pulse. The results demonstrated that there are significant differences in streamer morphology between pure transformer oil and nano-liquids, as the streamers in pure transformer oil exhibit thick bush-like qualities, while in nano-liquids they exhibit tree-like qualities. Moreover, the breakdown voltage results show that the breakdown strength of transformer oil is improved after nano-modification, and the TiO2 nano-liquids and Al2O3 nano-liquids have nearly the same optimal volume fraction. The results of the analysis indicate that the modification mechanism of nano-particles is significantly linked to the trapped electrons process. Specifically, the addition of nano-particles can affect the electrons’ density and thus affect the breakdown process and streamer morphology.

Improving the thermal performance of electrical transformers using hybrid mixture of (transformer oil, nanoparticles, and PCM)

In this paper, an experimental electrical distribution transformer was studied and a new technique was proposed to improve the performance of a new mixed cooling consisting of pure transformer oil, paraffin wax and nanoparticles. The experiment was carried out on a small transformer that was done by taking a model with dimensions (15 * 10 * 10) cm to facilitate calculations. Paraffin wax absorbs the heat generated in the transformer due to the smelting process that can be used to cool electrical appliances. Nanoparticles have good thermal properties and lead to increased oil insulation to thermal improvements in transformer oil with dispersal of solid nanoparticles and their effects on transformer cooling. Three types of solid nanoparticles were used in this experiment (Al2O3, TiO2, and Sic) with a different volume concentration (1%, 3%, and 5%) and 4% paraffin wax as a certified added percentage for each process. The obtained results showed that when mixing paraffin wax and solid nanoparticles with transformer oil, the transformer cooling performance is improved by reducing the temperature. The best selected nanoparticles were found to be Sic and the reason for this is that Sic has a higher thermal conductivity compared to (Al2O3 and TiO2). The proposed hybrid oil reduces the temperature by 10 ° C (in the case of PCM and Sic) and it is possible to improve the cooling performance of electrical transformers.

On evaluation of thermophysical properties of transformer oil-based nanofluids: A comprehensive modeling and experimental study

Transformer oil-based nanofluids are known to have higher thermal conductivity and heat transfer performance compared to conventional transformer oils. In this study, four different types of transformer oil-based nanofluids are synthesized using the well-known two-step method. The first nanofluid contains pure multi-walled carbon nanotubes (MWCNTs), while other samples consist of 20 Vol% of MWCNTs and 80 Vol% of different oxide nanoparticles (i.e., Al2O3, TiO2, and SiO2). The dynamic viscosity and thermal conductivity of prepared samples are investigated in seven different volume fractions of 0.001, 0.0025, 0.005, 0.01, 0.025, 0.05, and 0.1%. Besides, the breakdown voltage of the pure transformer oil and nanofluids containing 0.05 and 0.1 Vol% of nanoparticles is investigated. The outcomes show that dielectric properties of hybrid carbon-based nanofluids are far better compared to those properties of the pure MWCNTs nanofluids. Finally, eight different soft computing approaches, including group method of data handling (GMDH), support vector machine (SVM), radial basis function (RBF) neural network, multilayer perceptron (MLP), and MLP and RBF models optimized with bat and grasshopper optimization algorithm (GOA), are used to model the viscosity and thermal conductivity of synthesized nanofluids. The outcomes show that the GMDH approach significantly outperforms all other models in terms of predicting the thermal conductivity and dynamic viscosity of transformer oil-based nanofluids.

Analysis and design of nanofluid-filled power transformers

To alleviate the adverse impact due to the deterioration of electrical insulation, this paper presents an electromagnetic-thermal-fluid analysis for the prediction of temperature distribution in transformers with oil-based nanofluids or pure oil. The core loss and copper loss are taken as the heat sources for the temperature analysis using computational fluid dynamics. To strive for computing the temperature distribution accurately in the nano-oil, an effective numerical method using finite volume method and improved physical parameter model are employed. Numerical simulation of the thermal performance of the nanofluid with different volumetric fractions with Al2O3 nanoparticles is compared with those using pure transformer oil in a 500 VA single-phase transformer. From the comparisons of the simulation results, it is found that the volumetric fraction 0.01% is an optimum concentration in reducing the transformer size for the same power rating. The observation is served as useful guidelines and detailed process for the design of oil-based power transformers.

Space charge injection behaviors and dielectric characteristics of nano-modified transformer oil using different surface condition electrodes

Electrodes are damaged by external forces, mechanical wear, and electrochemical corrosion during long-term operation in power systems, resulting in rough electrode surfaces. Space charge injected into the liquid by a rough electrode under a strong electric field causes electric field distortion and leads to breakdown. Moreover, the charge injection is associated with the energy barrier at the electrode-liquid interface. The combined effect mechanism of nanoparticles and electrode surface condition on the insulating characteristics of transformer oil was investigated using various surface condition aluminum plate electrodes. The breakdown voltages and space charge patterns in pure transformer oil and Al2O3 nano-modified transformer oil under impulse voltage were measured in this study through Kerr electro-optic field mapping measurement. The test results indicate that the breakdown voltage of nano-modified transformer oil depends on voltage polarity and electrode surface conditions and the charge injection shows the same mode in pure transformer oil using different surface condition electrodes, but the magnitude of charge injection differs considerably. Due to nanoparticle’s ability of shielding space charges of different polarities and the charge injection of different surface condition electrodes, they have different effects on the breakdown process of transformer oil between different surface condition electrodes. An interfacial model was formed to explore the mechanism of the effect of nanoparticles and electrode surface conditions on the insulation performance of liquid dielectrics and analyze the breakdown process using the space charge injection behaviors.

Electric Field Distribution Characteristics and Space Charge Motion Process in Transformer Oil Under Impulse Voltage

The electric field and space charge dynamics characteristics in oil under impulse voltage are key factors to the transformer insulation design, which are mainly obtained through simulation, falling short of experimental verifications. Applying the Kerr electro-optic method, the present paper carried out an actual measurement for the electric field characteristics in transformer oil under impulse voltage and managed to obtain their correlations with an electrode material, voltage amplitude, and wave-front time, respectively. First, it was found that, under impulse voltage and in pure transformer oil, the aluminum electrode had the largest amount of charge injection, followed by stainless steel and then copper, which was attributed to the different work functions of metal elements in electrodes. Second, with the increase of voltage amplitude, the effect of the space charge on the intermediate electric field of the oil gap was first enhanced, then weakened, and eventually enhanced. Third, as the wave-front time was prolonged, the peak of electric field in transformer oil showed a downward trend. For instance, the peak value of the electric field was reduced by 17.6 % when the wave-front time was increased from 0.5 μs to 40.0 μs. The reason is that when the wave-front time is longer, the amount of injected charge grows larger and the weakening effect becomes stronger. Fourth, a charge dynamic motion model in transformer oil under impulse voltage was established to demonstrate its spatial-temporal effects on the electric field. Besides, this paper has clarified the source of the negative and positive charges in the transformer oil under impulse voltage by using the theories of field emission and field ionization. Moreover, the variation of electron mobility over-voltage amplitude, wave-front time, and spatial distribution was worked out to present the quantitative results of its motion process.

Natural convection heat transfer of nanofluid in a cavity under an inhomogeneous electric field

Natural convective heat transfer of nanofluid consisted of transformer oil and Al2O3 nanoparticles in a cavity under a non-uniform high electric field intensity was experimental investigated. The main objective is looking for a coupling enhanced method by nanofluid and electric field. It is found that when the effect of gravity is ignored, the electric field forces applied on the working fluids induce an electric convection and thence induce significant heat transfer enhancement. This enhancement effect increases rapidly with the increase of electric field intensity, the nanoparticles mass concentration of nanofluid and the heat flux. When the effect of gravity exists, a coupled convection is caused by both gravity and electric field force together. For pure transformer oil, the influences of electric field force and gravity on the heat transfer almost offset each other. However, for nanofluid, the impact of the electric filed force is dominant. The study results revealed the enhanced mechanism of natural convection heat transfer of nanofluid under electric field and provided some useful technical support for practical application.

Affecting Factors Titanium Oxide of Nanoparticles for the Electrical Effect on Insulation Resistance of the Transformer Oil

In most cases, The electrical insulation of the transformer oil will be exposed to different internal problems, such as short circuit , over voltage, over load, over excitation and etcetera. The insulation of transformer will be sever decreased into minimum value. This requires some treatments of oil liquid ,such as refining or replacing the damaged oil with a new, which is a very expensive process. In this paper, the Insulation Resistance (IR) of transformer oil will be enhanced by using nanoparticles NPs. Titanium oxide (TiO2) one of them, which will be used in this experiment. The (NPs) improve the insulation, physical and chemical properties of transformer oil. The breakdown voltage will be tested for pure oil and after the addition (TiO2) according to IEC standard methods. The results of this study indicated that addition of TiO2 in certain quantities of pure oils can be affected the Insulation Resistance (IR) and electrical breakdown voltage. A comparative study was conducted to identify the effects of using nanoparticles in pure transformer oils to ensure their effect on electrical Insulation Resistance (IR). The results are indicated an increasing in the breakdown voltage and the dissipation factor of the transformer oil, thus results using nanoparticles oil higher than pure oil.

Electrical conduction in a transformer oil-based magnetic nanofluid under a DC electric field

In this paper, we report on the experimental study of the direct current electrical conduction in a magnetic nanofluid based on transformer oil and iron oxide nanoparticles stabilized with oleic acid. We present the current–voltage characteristics of the pure transformer oil and the magnetic nanofluid with various particle volume fractions. From the Ohmic region, we calculate the electrical conductivity values and confirm the effect of increasing conductivity with increasing particle volume fraction. A few sources of space charge have been taken into account, among which the ion impurities play the key role. It was found that the current–voltage characteristics exhibit the inverse hysteresis-like behavior. Then, we focus on the magnetic field influence on the hysteresis behavior of a selected sample. The external magnetic field was applied in both, parallel and perpendicular configuration in regard to the electric field direction. It is shown that the magnetic field acting on the magnetic nanofluid in the perpendicular configuration results in the remarkable thinning of the current–voltage inverse hysteresis loop.

Effect of electrode materials on the space charge distribution of an Al2O3 nano-modified transformer oil under impulse voltage conditions

The combined effect mechanism of electrode materials and Al2O3 nanoparticles on the insulating characteristics of transformer oil was investigated. Impulse breakdown tests of pure transformer oil and Al2O3 nano-modified transformer oil of varying concentrations with different electrode materials (brass, aluminum and stainless steel) showed that the breakdown voltage of Al2O3 nano-modified transformer oil is higher than that of pure transformer oil and there is a there is an optimum concentration for Al2O3 nanoparticles when the breakdown voltage reaches the maximum. In addition, the breakdown voltage was highest with the brass electrode, followed by that with stainless steel and then aluminum, irrespective of the concentration of nanoparticles in the transformer oil. This is explained by the charge injection patterns from different electrode materials according to the results of space charge measurements in pure and nano-modified transformer oil using the Kerr electro-optic system. The test results indicate that there are electrode-dependent differences in the charge injection patterns and quantities and then the electric field distortion, which leads to the difference breakdown strength in result. As for the nano-modified transformer oil, due to the Al2O3 nanoparticle’s ability of shielding space charges of different polarities and the charge injection patterns of different electrodes, these two factors have different effects on the electric field distribution and breakdown process of transformer oil between different electrode materials. This paper provides a feasible approach to exploring the mechanism of the effect of the electrode material and nanoparticles on the breakdown strength of liquid dielectrics and analyzing the breakdown process using the space charge distribution.

Study of Dielectric Breakdown Performance of Transformer Oil Based Magnetic Nanofluids

Research on the transformer oil-based nanofluids (NFs) has been raised expeditiously over the past decade. Although, there is discrepancy in the stated results and inadequate understanding of the mechanisms of improvement of dielectric nanofluids, these nanofluids have emerged as a potential substitute of mineral oils as insulating and heat removal fluids for high voltage equipment. The transformer oil (TO) based magnetic fluids (ferrofluids) may be regarded as the posterity insulation fluids as they propose inspiring unique prospectus to improve dielectric breakdown strength, as well as heat transfer efficiency, as compared to pure transformer oils. In this work, transformer oil-based magnetic nanofluids (MNFs) are prepared by dispersal of Fe3O4 nanoparticles (MNPs) into mineral oil as base oil, with various NPs loading from 5 to 80% w/v. The lightning impulse breakdown voltages (BDV) measurement was conducted in accordance with IEC 60897 by using needle to sphere electrodes geometry. The test results showed that dispersion of magnetic NPs may improve the insulation strength of MO. With the increment of NPs concentrations, the positive lightning impulse (LI) breakdown strength of TO is first raised, up to the highest value at 40% loading, and then tends to decrease at higher concentrations. The outcomes of negative LI breakdown showed that BDV of MNFs, with numerous loadings, were inferior to the breakdown strength of pure MO. The 40% concentration of nanoparticles (optimum concentration) was selected, and positive and negative LI breakdown strength was also further studied at different sizes (10 nm, 20 nm, 30 nm and 40 nm) of NPs and different electrode gap distances. Augmentation in the BDV of the ferrofluids (FFs) is primarily because of dielectric and magnetic features of Fe3O4 nanoaprticles, which act as electron scavengers and decrease the rate of free electrons produced in the ionization process. Research challenges and technical difficulties associated with ferrofluids for practical applications are mentioned. The advantages and disadvantages linked with magnetic fluids are also presented.

Transformer oils-based graphene quantum dots nanofluid as a new generation of highly conductive and stable coolant

Transformer oil-based graphene quantum dots (GQD) nanofluid with superior colloidal stability has great potentials as a new generation of high performance transformer oil. To this end, graphene quantum dots were initially synthesized with a novel and cost-effective exfoliation approach. To eliminate the acidity, a covalently-functionalization process was employed to change GQD to amine-treated graphene quantum dots (AGQD). The morphological analysis confirmed that the diameter and average height of the mono-layered AGQD were mostly in the range of 5–17nm and <1nm, respectively. Transformer oil-based AGQD nanofluid at very low weight fraction has been shown experimentally to have substantially higher positive voltage breakdown, thermal conductivity, natural and forced heat transfer rate, and flash point levels compared to that of pure transformer oil. A comprehensive rheological and electrical analysis of the transformer oil-based AGQD nanofluid showed no significant enhancement in its viscosity compared to pure transformer oil, which is a great advantage of this new generation of transformer oil. Case studies showed that the transformer oil-based AGQD nanofluid has a superior colloidal stability, offering improved high voltage equipment performance and reliability.

Performance Analysis of Nanomaterials based Transformer Oil

The nanomaterials based transformer oil can be considered as next-generation insulation fluids because they offer exciting new possibilities to enhance dielectric breakdown voltage as well as heat transfer performance compared to pure transformer oils. Transformer oil (TOL) is a liquid dielectric which acts as an insulating medium as well as coolant. A colloidal mixture of nano-sized particles in base fluid is called nanofluids. Nanofluids are prepared by mixing the nanomaterials for different volume concentrations with TOL as base fluid. Nanofluids are significant potential heat transfer fluids with enhanced thermo physical properties can be applied in many devices for better performances. Nanofluids play an important role in cooling of transformer oil, engine cooling, in nuclear reactor, defense and space. Our effort focused on increasing dielectric breakdown voltage of transformer oil-based nanofluids with different volume concentrations of nanoparticles.

Improving the cooling performance of electrical distribution transformer using transformer oil – Based MEPCM suspension

In this paper the electrical distribution transformer has been studied numerically and the effect of outside temperature on its cooling performance has been investigated. The temperature range studied covers the hot climate regions. 250KVA distribution transformer is chosen as a study model. A novel cooling fluid is proposed to improve the cooling performance of this transformer, transformer oil-based microencapsulated phase change materials suspension is used with volume concentration (5–25)% as a cooling fluid instead of pure transformer oil. Paraffin wax is used as a phase change material to make the suspension, in addition to the ability of heat absorption due to melting, the paraffin wax considered as a good electrical insulator. Results obtained show that, using of MEPCM suspension instead of pure transformer oil lead to improve the cooling performance of transformer by reducing its temperature and as a consequence increasing its protection against the breakdown. The melting fraction increased with increasing outside temperature up to certain temperature after which the melting fraction reach maximum constant value (MF=1) which indicate that, the choosing of PCM depend on the environment in which the transformer is used.