Transformer Oil-based Nanofluids Research Articles

Production and characterization of CuNiZnFe2O4 dispersed transformer and kerosene oil based magnetic nanofluids for heat transfer applications

This study produced nanofluids via a two-step method by dispersing copper–nickel–zinc (CuNiZnFe2O4) ferrite nanocomposites in transformer and kerosene oils. A sol–gel auto-combustion approach was adopted to synthesize ferrite nanoparticles. The prepared nanoparticles were analyzed through scanning electron microscopy, photoluminescence spectroscopy, and x-ray diffraction. The measured crystallite size varied between 11 and 13 nm. The SEM images show that the structures of the developed CuNiZn nanoparticles are irregular. The photoluminescence results give a bandgap of 1.91 eV and the emission lines of the nanoparticles. Transient hot wire analysis was performed to determine the thermal conductivity of the base fluid and the prepared nanofluids. It is observed that nanoparticles in the nanofluid enhance the heat transfer rate. It has been proven that CuNiZn/kerosene-based nanofluids have greater thermal conductivity than CuNiZn/transformer oil-based nanofluids. The viscosity of transformer oil-based nanofluids at room temperature is 12.53 mm2 s−1, which decreases to 12.49 mm2 s−1 at 40 °C. Similarly, the viscosity of kerosene-based nanofluids is 1.49 mm2 s−1 at room temperature and 1.16 mm2 s−1 at 40 °C. The sedimentation method revealed that CuNiZn/transformer oil-based nanofluids have greater stability than CuNiZn/kerosene-based nanofluids.

Dielectric and thermal behavior investigation of Mn-Zn nano ferrite-fluid for transformer oil applications

Manufacturing of novel transformer oil-based nanofluids has become necessary to improve dielectric and cooling properties. The current study was carried out to examine the dielectric and thermal characteristics of transformer oil incorporated by Mn0.5 Zn0.5 Fe2O4 nanoparticles (Mn-Zn ferrite NPs) that were synthesized by an auto-combustion technique. The microstructure and morphology of the synthesized Mn-Zn ferrite NPs were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and high-resolution transmission electron microscopy (HRTEM). The formation of a single-phase cubic spinel structure for the Mn-Zn ferrite NPs was confirmed by XRD results. The average crystallite sizes of about 26.7 nm obtained from XRD are very close to the measured value obtained from HRTEM. VSM measurements ensure a high saturation magnetization of 57 emu/g for the Mn-Zn ferrite sample and which makes it a very good candidate as a transformer oil filler. The as-synthesized Mn-Zn ferrite NPs were then introduced into transformer oil with concentrations up to 0.4 g/L to form Mn-Zn nano ferrite-fluid. The dielectric properties of the prepared nano ferrite-fluid samples were investigated by measuring the dielectric constant (ε′) and dissipation factor (tan δ) in the frequency range of 30 Hz − 1 MHz. Moreover, the AC breakdown voltage of the investigated nano ferrite-fluid samples was measured at a constant 500 V/s ramp, and it showed a pronounced enhancement with the addition of Mn-Zn ferrite NPs. It reached 80 % for 0.2 g/L of NPs. Moreover, the convective heat transfer of the nano ferrite-fluid was examined through the heating–cooling process, which is indicating a significant reduction in the thermal time constant in cooling with the introduction of the Mn-Zn ferrite NPs into the oil.

Fabrication of AlN nanoparticles by arc discharge method and investigation of thermal conductivity of AlN transformer oil-based nanofluid

Fabrication of AlN nanoparticles by arc discharge method and investigation of thermal conductivity of AlN transformer oil-based nanofluid

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.

Titania‐based transformer nanofluid: a study on the synthesis for enhanced breakdown strength and its humidity ageing

Researches on the transformer oil-based nanofluids to determine its suitability for replacing the conventional liquid insulation has been consistently happening for more than a decade. Yet, to prepare an optimum blend of transformer oil-based nanofluid with the stability compliance and superior breakdown (BD) characteristics is still a key issue to be addressed. So to achieve the higher BD voltages (BDVs) with good stability, the nanoparticle and surfactant weights dispersed in the oil should be optimised to at least possible critical levels. In this work, dielectric BD characteristic of mineral oil dispersed with TiO2 nanoparticle and surfactant cetyl trimethyl ammonium bromide (CTAB) is been studied with the applied AC and DC high voltages, which is termed as titania-based transformer nanofluid (TTNF) for this study. Series of TTNF samples were synthesised with different weights of TiO2 nanoparticle and CTAB, and the partial discharge inception voltage, AC and DC BDV were experimented to ascertain the optimum concentration level. Results show that the AC and DC BDV enhanced up to 36.23 and 43.07%, respectively, for the TTNF prepared with 0.00562 wt% of TiO2 and its 1% weight of CTAB, which was stable for around eight weeks.

Nanofluid from Palm Kernel Oil for High Voltage Insulation

A clean alternative insulating oil has been the quest of researches over the years due to non-degradability of mineral oil and safety issues. With the application of nanoscience and nanotechnology, the potential of transformer oil-based nanofluids has been thoroughly investigated with signs of significant improvement. Attention was placed on natural ester as a green alternative and it was realized that it has the potential to become a replacement for mineral oil. However, for natural ester-based nanofluids, the performance analysis is not well explored and there is still room for more investigations. This paper focused on the improvement of the physicochemical properties, dielectric loss and breakdown voltage of palm kernel oil ester using Al2O3 and TiO2 nanoparticles. The nanoparticles were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Scanning electron microscopy (SEM) equipped with electron dispersive X-ray analysis (EDX). The physicochemical properties, relative permittivity, dielectric loss, and high voltage DC conductivity of the nanofluid samples were studied with varying weight percentages of Al2O3 and TiO2 nanoparticles ranging from 0.2 wt% to 1 wt% in a step of two to understand the behaviour of the materials. The adequacy of the fluid samples as an electrical insulating fluid in oil-filled high voltage (HV) electric equipment was explored and compared. For both types of nanoparticles, the dielectric loss was observed to decrease at 1 wt% but with a more noticeable decrease when considering Al2O3 nanoparticle. Measurement of DC electrical breakdown voltage of the ester-based nanofluids revealed that the dispersion of nanoparticles in the fluid result in an increase in the breakdown voltage of the base fluid with the optimum value obtained at 0.6 wt%. The study indicated a decrease in the dielectric loss of the nanofluid sample and exhibited improved breakdown voltage when compared with the base alkyl ester.

Effects of magnetite and titania nanoparticles on properties of transformer insulating oil

Transformer oil-based nanofluids have become popular research topic due to their enhanced dielectric and thermal properties. Considering the sustainability aspects of extending the life of transformer oil, it is imperative to conduct research on the effect of transformer oil with nanofillers. In the present work, the influence of conducting magnetite (Fe3O4), semiconducting titania (TiO2) nanoparticles and combination of Fe3O4 and TiO2 nanoparticles (multi-nanoparticle) on AC breakdown voltage are investigated for various concentrations. Nanofluid prepared using multi-nanoparticle shows enhanced AC breakdown voltage (BDV) of transformer oil compared with unfilled oil. Enhancement in BDV of 22% is observed with combination of 0.0025 wt% Fe3O4 and 0.0075 wt% TiO2. In addition, the effect of titania nanoparticles dispersed into service-aged transformer oil with a weight percentage of 0.01% is investigated. Comparative study of breakdown strength and viscosity of nanofluid with unfilled oil is performed. Service-aged oil sample shows increased BDV of 15% with TiO2 nanoparticles. The degradation in service-aged transformer oil is analyzed using UV–vis and Fourier Transform Infrared (FTIR) spectroscopy. The characteristics of oil samples are analyzed using fluorescence spectroscopy.

Statistical analysis of AC dielectric breakdown in transformer oil-based magnetic nanofluids

Insulating nanofluids often exhibit better insulating properties than their base liquids. In particular, dielectric breakdown performance of insulating liquids may be remarkably enhanced by the presence of nanoparticles. The purpose of this paper is to demonstrate experimental evidence of the missing enhancing effect of the magnetic nanoparticles dispersed in transformer oil and to find potential reasons for the unimproved AC dielectric breakdown. The research is conducted on a long-term stable magnetic nanofluid with three different volume fractions of iron oxide nanoparticles coated with oleic acid. The AC dielectric breakdown voltage is investigated at various temperatures and statistically treated. Temperature-dependent viscosity, dissipation factor, and AC electric current are presented as supporting experimental results. In searching for the reason of the unimproved dielectric breakdown, we focus on the nanoparticle interface and consider the limited ability of the modified nanoparticles to act as charge trapping centers under the AC dynamic conditions.

The impacts of nanotechnology on the improvement of liquid insulation of transformers: Emerging trends and challenges

The rise in transmission voltages levels, the demand for insulating reliability of the transformer is getting more and more critical. The mineral oil (MO) together with paper is the main insulation constituents in oil-immersed transformers. To enhance the insulation level of ultra-high voltage (UHV) transformers and to decrease its weight and size, it is highly required to increase the insulating conduct of transformer oil (TO) and oil-impregnated cellulose. Lately, a distinctive novel venture of application of nanotechnology with liquid insulation of transformer has been conducted and the results have displayed marvelous enhancement in the insulation properties of transformer oil. The transformer oil-based nanofluids research domain (i.e., NFs) has been attracting huge attention during recent years both in theoretical and practical fields. NFs may be applied as a potential substitute for MO in the near future. To recognize various brunts of NFs and show evolving developments and challenges, the study demonstrates a scientometric review established on 210 published features from 2004 to 2019 through co-author, co-occurring and co-citation investigations. The significance of the editorial lies in compiling former inquiries, categorizing research nature, motivations and forecasting impending research orientations. Lastly, some recommendations for future NFs research and application are suggested.

Seeking optimized transformer oil-based nanofluids by investigation of the modification mechanism of nano-dielectrics

The modification mechanism of nano-additives on the electrical properties of transformer oil-based nanofluids has systematically been studied from a micro-perspective.

Effect of Al2O3 nanorods on the performance of oil-impregnated pressboard insulation

The mineral oil (MO) in conjunction with paper is the main insulation components in oil-immersed transformers; their insulation properties play a significant role in the safe and stable operation of power transformers. To strengthen the insulation level of ultra-high voltage transformer and to reduce its size and weight, it is imminent to enhance the insulating performance of transformer oil and oil-impregnated cellulose. Recently, a unique novel effort of suspension of nanorods (NRs) into MO has been carried out and the results have exhibited improved insulation characteristics of transformer oil. The Al2O3 NRs with favorable features were prepared in our laboratory to develop transformer oil/paper insulation system with better insulation performance. The transformer oil-based nanofluids (NFs) were prepared with nanorod shape, oleic acid surface modification and 0.8 g/L concentration of NRs. The impregnated pressboards were prepared by impregnating them into dried oil and NF under vacuum beneath 1 kPa at 80 °C for almost 48 h to obtain the oil-impregnated pressboard (OIP) and nanofluid-impregnated pressboard (NIP), respectively. The interface at solid/liquid is considered weak link and is the main reason of oil-filled transformer collapse. The effect of Al2O3 NRs on creeping discharge and flashover traits of oil/pressboard (OP) interface under AC and impulse voltages were studied. Partial discharge and creeping flashover test of OIPs and NIPs were conducted. TSDC and PEA tests were applied to examine the space charge properties of OP interface before and after suspension of Al2O3 NRs.

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.

Numerical study on nanofluids natural convection heat transfer inside power transformer windings

As an innovative approach to improve the cooling efficiency of fluid, the use of nanofluids has attracted increasing attention in engineering applications. In this paper, the impact on the natural convective heat transfer in disc-type transformer windings due to transformer oil-based nanofluids is studied numerically. A low-voltage winding using nanofluid (SiC/oil) as the coolant is modelled two-dimensionally and simulated by computational fluid dynamics and the multi-phase mixture model. The numerical method is validated with the existing results of transformers using conventional oil cooling, and grid-independence study is carried out for the nanofluid flow. Compared with transformer oil cooling, the temperature of nanofluid cooled winding is significantly reduced, while the temperature trend along the flow direction remains essentially the same. Moreover, the effects of nanofluid on the mass flow rate and the coolant temperature have been taken into consideration in the heat transfer analysis.

Preparation and Characterization of Transformer Oil Based Nano Fluids

This paper is concerned with the preparation and characterization of transformer oil based nanofluids with the suspensions of Al2O3 and CuO nanoparticles . As a part of experimental study the transformer oil based nanofluids for heat exchangers in transformer cooling application, preparation and characterization has been performed. The preparation of nanofluids is the first key step in experimental studies with nanofluids. One step technique and two step technique are generally used for preparing the nanofluids. This work deals with the preparation methods of (Al2O3-Transformer oil ,CuO-Transformer oil) and characterizing the transformer oil based nanofluids of different volume concentrations (0.05%, 0.1%, 0. 5%, 1.0% and 1.5%).From the results it is revealed that increasing the volume concentration resulted in increase in thermal conductivity, viscosity of the nanofluid and decrease in density and specific heat of nanofluid.

Effect of magnetic nanoparticles on partial discharges in transformer oil

We report on an experimental study of partial discharges (PD) in transformer oil with four different volume concentrations of superparamagnetic iron oxide nanoparticles (SPION) ranging from 0 to 0.0004 vol%. To investigate the PD, a specific high-voltage setup was designed. Thanks to the small amount of SPION in the oil (transparency), the PD events in the form of visible corona and streamer discharges were visualized by a CCD camera. Furthermore, the PD inception and extinction voltage, apparent charge and quantities derived from the PD recurrence, as pulse repetition rate and phase resolved patterns, were analyzed in dependence on SPION concentration. It was found that the PD inception voltage increases quasi linearly with increasing SPION concentration but the extinction voltage is practically unaffected. The pulse repetition rate decreases as a result of the increasing SPION concentration. The decreased PD activity is clearly concluded also from the reducing shape and growth of the visual corona discharge patterns. To interpret the observed suppression of PD in transformer oil-based magnetic nanofluids, the electric field modification and injected charge trapping by the dispersed nanoparticles is considered. Moreover, a possible effect of the local magnetic fields around the SPION on the space charge migration is taken into account, too.

Transformer oil-based magnetic nanofluid with high dielectric losses tested for cooling of a model transformer

An experimental study of dielectric permittivity and dissipation factor of transformer oil-based magnetic nanofluid is reported in this paper. The investigated nanofluid consists of a commercial transformer oil and iron oxide nanoparticles (0.93 % solid volume fraction) coated with oleic acid as a stabilizing agent. Both, the transformer oil and the nanofluid were subjected to measurements of dielectric permittivity and dissipation factor under 1 kV at a power frequency of 50 Hz in the temperature range from 303 to 373 K. The compared results show that the magnetic nanofluid exhibits approximately 4 orders of magnitude greater dielectric losses than the transformer oil. This raised a question about the suitability of such a nanofluid for cooling applications in a transformer. Therefore, the cooling effectiveness of the nanofluid was tested in a model single-phase power transformer under 4.3 kVA load. The prototype transformer was designed with the aim to monitor its temperature at various locations during the load test. It was found that the cooling with the lossy nanofluid does not result in the deterioration of the thermal conditions of the transformer as compared to the cooling with the transformer oil. On the contrary, the tested nanofluid provides a slight decrease in the average transformer temperature rise. Possible reasons accounting for the slight enhancement in the transformer cooling are discussed. The increased thermal conductivity and development of thermomagnetic convection are considered as primary reasons of the cooling effect.

Effect of Al2O3 nanorods on dielectric strength of aged transformer oil/paper insulation system

With the commencement of high voltage alternating current (HVAC) and high voltage direct current (HVDC), the demands on insulating reliability of power transformer is getting more and more imperative. The mineral oil (MO/TO) in conjunction with paper is the main insulation components in oil-immersed transformers; their insulation properties play a significant role in the safe and stable operation of power transformers. To strengthen the insulation level of ultra-high voltage transformer and to reduce its size and weight, it is imminent to enhance the insulating performance of transformer oil and oil-impregnated cellulose. Recently, a unique novel effort of suspension of nanoparticles (NPs) into mineral oil (MO) has been carried out and the results have exhibited improved insulation characteristics of transformer oil. The Al2O3 nanoparticles with favorable features were prepared in our lab to develop transformer oil/paper insulation system with better insulation performance. The transformer oil-based nanofluids (NFs) were prepared with nanorod shape, oleic acid (OA) surface modification and 0.8 g/L concentration of NPs. The pressboards were cut into the desired sizes (85 mm.55 mm). The thickness of the pressboards was 2 mm applied in flashover tests. The prepared pressboards were put into an oven at 105 °C for almost 48 h to carry out the hot air drying operation. Then they were put in the vacuum drying at 85 °C for 48 h. The impregnated pressboards were prepared by impregnating them into dried oil and NF under vacuum beneath 1 kPa at 80 °C for almost 48 h to obtain the oil-impregnated pressboard (OIP) and nanofluid-impregnated pressboard (NIP) respectively. Additionally, the prepared insulation system samples of liquid (MO and NFs) and solid (OIPs, NIPs) were thermally aged at 130 °C for 30 days. The effect of alumina NPs on thermal aging of transformer oil and pressboard were also investigated. The results showed that Al2O3 NPs can slow down the aging of oil and pressboard. The average AC and positive LI BDV of aged NFs was 11% higher than aged MOs. The average LI creeping FOVs of NIPs were 6% higher than OIPs. Additionally, average AC creeping FOVs of NIPs were 8% higher than that of OIPs. The enhancement in insulating performance of aged NFs and NIPs as compared to MO and OIPs is interpreted in light of electron traps theory.

Slowing Positive Streamer Propagation in Silicon and Ester Transformer Oil Using Multi-nanoparticles Technique

This paper formulates a new multi-nanoparticles technique for reducing positive streamer propagation in silicon and vegetable oils nanofluids; transformer oil nanofluids with multi-nanoparticles suspensions are blended to slow thepropagation of positive streamer more than using individual nanoparticles, hence the insulation qualities are improved andthe breakdown voltage of nanofluid is expanded. This study indicated the influence of nanoparticle radius, nanoparticles’ polarization, the relative permittivity of oil, applied field, and the charge density of nanoparticles interface. It is deduced that transformer oil-based nanofluids with conductive individuals and multi-nanoparticles suspensions have considerably higher impacts on slowing positive streamer than non-conductive nanoparticles. A comparative study has demonstrated the magnitude of deposited charge and charging time as a result of using individual nanoparticles and multi-nanoparticles inside transformer oil.

Numerical Study on Natural Convective Heat Transfer of Nanofluids in Disc-Type Transformer Windings

Nanofluid is an innovative approach to improve the thermal conductivity of fluid by adding nanoparticles. Transformer oil-based nanofluids have been prepared and measured, which verifies the concept and demonstrates the potential in oil-immersed power transformer applications. In this paper, the effect that nanofluids (oil/SiC) have on the natural convective heat transfer in disc-type transformer windings is investigated numerically. The multi-phase mixture model is employed for the first time to analyze such a nanofluid flow field, and the single-phase model is also used for comparison and mutual authentication. After using the nanofluid, significant temperature drops inside the windings are observed, and in some cases, the heat transfer performance is further improved by the adjusted mass flow rate distribution. The impact of nanofluids is enhanced with the rising volume fraction of nanoparticles. Before performing the study, the numerical model is validated using the existing results of the referenced windings cooled by transformer oil.

Effect of Surfactant on Breakdown Strength Performance of Transformer Oil-Based Nanofluids

Many approaches to improve the transformer oil characteristics have been made by adding nanofillers into the liquids, but it has caused the existence of sedimentation and agglomeration thereby resulting in incompatibility of transformer oil. In view of foregoing, this paper aims to study the impact of cetyl trimethyl ammonium bromide (CTAB) surfactant added with the nanofiller in improving the compatibility and agglomeration issues towards improvement of breakdown voltage (BDV) characteristics of oil nanofluids. This study was carried out by implementing three different percentages of silica (SiO2) and alumina (Al2O3) nanofillers along with CTAB as surfactant into the mineral oil. The breakdown voltage test was carried out accordance to IEC 60156 standard. The results show that the inclusion of 0.1 wt% SiO2 and 0.1 wt% Al2O3 nanoparticles into mineral oil have improved the BDV. Meanwhile, Al2O3 nanofluids with 0.075 wt% CTAB had good impact on BDV but not on SiO2. This case has reverse behavior with the sedimentation which 0.1 wt% CTAB in SiO2 nanofluids has a good response but not the whole in Al2O3 nanofluids. This could be mainly due to the limitation stability of the nanofluids.