Properties Of Transformer Oil Research Articles

Performance Analysis of Alternative Solid Dielectrics of Power Transformers with a Blend of Mineral and Silicon Oils

ABSTRACTIn the present paper, the influence of accelerated thermal ageing on the performance of thermally upgraded Kraft, Nomex 910 and Nomex 410 alternative solid dielectrics of transformers in conjunction with mineral oil has been investigated. Subsequently, the characteristics of the solid dielectrics which are impregnated in a blend of 80% mineral and 20% silicon oils are also studied. To investigate these properties, accelerated ageing tests have been carried out at different temperatures ranging from 100 to 220 °C. Furthermore, several electrical and thermal properties of transformer oil which include breakdown voltage, interfacial tension, water content, absorption coefficient and colour factor have been determined. It has been revealed from the test results that Nomex oil-impregnated samples have better thermal characteristics and oxidation stability than the thermally upgraded Kraft oil-immersed samples. Moreover, it is also found from the diagnostic test results that a combination of mineral and silicon oils in conjunction with Nomex insulations has improved characteristics than the samples which are composed of these dielectrics and normal mineral oil. Therefore, Nomex insulating materials and a mix of mineral and silicon oils are suggested as alternative solid and liquid dielectrics for power transformers in order to achieve better oxidation stability, improved thermal characteristics for long service run, reduced operating and maintenance costs. It is envisioned that the present experimental study shall be very beneficial for the utility managers and the end-users of transformers.

Discharge characteristics and mechanism of conductive metal particles in function of the oil flow under AC voltages

To obtain the characteristics and mechanism of partial discharge caused by metal particles in function of the oil flow under AC voltages, the author established a mechanical model of metal particles motion in dielectric liquid. The motion trajectory and distribution regularities of metal particles in flowing transformer oil were simulated and calculated. The discharge phenomenon caused by metal particles was explained based on 4 discharge types and discharge mechanism was investigated. Additionally, Experiments were carried out to research the variation of Partial discharge inception voltage (PDIV) with velocity and temperature caused by metal particles. It was observed that discharge amplitude increased within a little scale and discharge number decreased significantly with the increase of velocity. Rise time increased with the increase of velocity while duration time decreased. It was proved that insulating property of transformer oil which was contaminated with metal particles could be improved by increasing the velocity of transformer oil.

Study of Static Magnetic Properties of Transformer Oil Based Magnetic Fluids for Various Technical Applications Using Demagnetizing Field Correction

Static magnetization data of eight transformer oil based magnetic fluid samples, with saturation magnetization ranging in a large interval from 9 kA/m to 90 kA/m, have been subjected to the demagnetizing field correction. Using the tabulated demagnetization factors and the differential magnetic susceptibility of the samples, the values of the radial magnetometric demagnetization factor were obtained in the particular case of VSM880 magnetometer. It was found that the demagnetizing field correction keeps the saturation magnetization values unchanged, but instead the initial magnetic susceptibility of the magnetic fluid samples varies widely. The mean magnetic diameter, obtained through magnetogranulometry from the measured data, is higher than that obtained from the corrected ones and the variation rate increases with the magnetic particle volume fraction growth.

An Investigation on Stability, Electrical and Thermal Characteristics of Transformer Insulting Oil Nanofluids

Transformer insulating oil nanofluid is made to improve dielectric and thermal properties of the oil by employing nanoparticles with proper properties. In the current work, nanofluids based on transformer mineral oil were prepared by three procedures using diamond nanoparticles with high thermal conductivity, as well as high dielectric properties. It was tried to consider the impacts of surfactants’ presence and ball milling process in the preparation procedures. The effects of a variety of stabilizers (the amount and type) and also the ultrasonic time on diamond nanoparticles’ stability in the oil were investigated and optimized experimentally. Using the optimized nanofluids, thermal conductivity and viscosity of the oil nanofluids were compared and discussed. In addition, the consistency of the thermal conductivity results with Maxwell and also Hamilton and Crosser theoretical models was examined. It was revealed that, the nanofluid preparation procedure, temperature and nanoparticles’ concentration have effects on thermal conductivity of the transformer oil nanofluid, while the presence of the nanoparticles has a slight impact on the viscosity of the fluid. Also the effect of diamond nanoparticles’ presence on the electrical properties of transformer oil was studied. Based on the experimental results, adding diamond nanoparticles could lead to an increase in the transformer oil breakdown voltage, while it has nearly no effect on dielectric loss in low concentrations.

Dielectric and Thermal Properties of Transformer Oil Modified by Semiconductive CdS Quantum Dots

In this paper, modified transformer oil semiconductor quantum dots (QDs) are presented. Cadmium sulfide (CdS) quantum dots of radius 4.5 nm with a hexagonal crystal structure are added to transformer oil to improve its dielectric and thermal properties. CdS QDs modified oil is prepared considering different filler loading levels. Alternating current breakdown voltages of the transformer oil samples before and after the modification are measured based on American Society for Testing and Materials D1816 standard. The relative permittivity and dissipation factor are measured for all samples. Also, thermal properties of the oil samples are experimentally evaluated according to the temperature change measurement considering heating and cooling processes. The results show significant improvements in dielectric and thermal properties of the modified transformer oil, as well as an increase in the breakdown strength by about 81% in comparison to the base transformer oil.

Preparation of Three Types of Transformer Oil-Based Nanofluids and Comparative Study on the Effect of Nanoparticle Concentrations on Insulating Property of Transformer Oil

Nanofluids have the potential to become the alternatives of conventional transformer oil for their exquisite electrical and thermal properties. Three kinds of nanoparticles with distinct conductivities, namely, nonconductive nanoparticle Al2O3, conductive nanoparticle Fe3O4, and semiconductive nanoparticle TiO2, with different concentrations from 5% to 40% w/v were selected and suspended into transformer oil to develop nanofluids. The lightening impulse breakdown strengths of the oil samples with and without nanoparticles were measured according to IEC standard methods. The positive impulse breakdown strength indicated that breakdown strength is first increased up to the maximum value at certain concentration and then starts decreasing. The results of negative impulse breakdown manifested that the breakdown voltages of nanofluids with different concentrations were less than the breakdown voltage of pure transformer oil. Different effect mechanisms of dielectric and conductive nanoparticles were also used to describe the difference among three prepared nanofluids.

Unique antioxidant and sulfur corrosion retardant properties of transformer oil blended with turmerone extract

One of the most detrimental effects associated with transformer insulating materials (paper and oil) and copper windings is the corrosive action of certain sulfur components found in transformer oil. Consequently, transformer oil is typically blended with both antioxidant and anti-corrosive agents in an attempt to prolong ageing effects and hinder copper sulfide deposition respectively. This study focusses on the effect antioxidants have on corrosive sulfur deposition on copper metal surfaces. To this end transformer oil was blended with a natural extract from turmeric powder and tested for its ability to act as an antioxidant and to retard copper sulfide deposition. The efficacy of this blended oil was compared with that of oil blended with either of two commonly used antioxidants, namely, 2,6-di-tert-butyl- 4-methylphenol or 2,6-di-tert-butylphenol. Tests for corrosive sulfur showed that for the turmerone oil blend there was a substantial delay in the onset of copper sulfide deposition on the surface of copper metal. Open circuit potential studies showed that the turmerone fraction that was blended into the transformer oil was adsorbed onto the copper surface. This unique property was not observed for the other two antioxidants in this study and can account for the retardation of copper sulfide deposition. In addition, the turmerone-virgin oil blend did not alter the thermal stability of the Kraft insulation paper in direct contact with the oil. The performance of the turmerone oil blend as a dual antioxidant and retardant of copper sulfide deposition renders it eminently suitable for extending the lifetime of insulation in fluid-filled transformers.

English

Transformer is a soul of both transmission and distribution systems. It performs low voltage to high voltage conversion in transmission lines and similarly high voltage to low voltage conversion in distribution lines. The operation of transformer is decided by the cooling provided to the system. The efficient cooling method is achieved by the use of forced (or) natural oil cooling medium. The oils used for the purpose of coolants are the hydrocarbons of paraffin (or) naphtha based petroleum products. The oil is used as coolant is made from highly refined mineral oil and it has high dielectric strength. During the operation of transformer there occurs temperature variation in the oil which causes reduction in dielectric strength with emissions of dissolved gases like sulphur, moisture etc. The mineral oil used in existing system is the dominant material in use but thermal conductivity is less. The insulating property of transformer provides poor results by the use of oil cooling medium. So, to achieve the best cooling the researchers introduced nano based oil, called “Nanofluids”. A nanofluid has attracted much in the field of research and its wide applications in the field of engineering. It is a mixture of nano-sized solid particles and base fluid. The major role of nanofluids is to improve the electrical, physical and chemical parameters of transformer. There are various varities of nanoparticles which improve the electrical and physical properties of transformer oil; among the various nanoparticles available are alumina particle (Al2O3), copper oxide (CuO), titanium oxide (TiO2) etc. Then its performance is being checked by simulation and experimental data.

High thermal conductivity transformer oil filled with BN nanoparticles

Transformer oil is widely used in electric transformers serving the dual functions as insulating medium and cooling material. However, safety and stability of power system is interrupted due to the operation failure of electric transformers in certain case. Therefore efforts should be focused on improving the property of transformer oil for the stable operation of insulating system. The purpose of this paper is to obtain a new type of nanomodified transformer oil with improved dielectric and thermal properties. Boron nitride (BN) nanoparticles with high thermal conductivity were dispersed into transformer oil to form the nanooil. Dielectric and thermal properties of the samples before and after modification were measured. Dielectric property experiments were performed in accordance with IEC standard. Discharge phenomenon in breakdown process was captured by a high speed CCD camera. In order to investigate the effect of BN nanoparticles on thermal property, temperature change and heat distribution of the samples in heat transfer process were measured by an infrared thermal imager and a temperature sensor. It is found that the nanooil has higher dielectric breakdown strength and lower dissipation factor which indicate better dielectric property compared with nonmodified oil. Obtained results show significant improvement in heat transfer process with increasing the concentration of BN nanoparticles. It is proposed that the nanoparticles create an interfacial region which contributes to the enhancement of dielectric strength. For thermal property the ballistic phonon transport of the nanoparticles acts as the key factor in the remarkable improvement. Furthermore, the improved thermal property of the nanooil has an inhibitory effect on the breakdown process according to the bubble theory.

The Study on TiO<sub>2</sub> Nano-Powder’s Influence on the Power Frequency Breakdown Properties of Transformer Oil

There are plenty of intrinsic cation states on the surface of nano-semiconductor crystals. When the crystals contact the transformer oil，surface states that can capture electrons easily are formed. In this paper, TiO2 nano-powders with different surface modifications have been used to improve the property of transformer oil (Karamay 25#). The modification effects of nano-power’s on insulating property of transformer oils have been investigated. And the modifying effects of TiO2 nano-powder with different concentrations on transformer oil have been studied. The breakdown property tests and fitting results show that TiO2 nano-powder can improve the breakdown properties of transformer oil and within some concentrations，the higher the concentration of TiO2 nano-powder，the better the power frequency insulating property of modifying transformer oil. Besides，The modifying agents play a key role in the dispensability of TiO2 nano-powder in the transformer oil. With the increasing of nonpolar segment in the modifying agent, the breakdown property of the modified oils gets more enhancements.

Thermal Conductivity of Transformer Oil From 253 K to 363 K

Transport properties of transformer oil are important parameters for electric equipment designing. In this work, thermal conductivity was measured from 253 K to 363 K by single transient hot-wire technique. And influence of transformer oil's thermal conductivity was investigated. It is found that the thermal conductivity decreases linearly with increasing temperature. When different oils are mixed together, the thermal conductivity shows additive property. For different oils with about the same viscosities, their thermal conductivities are directly related to alkane and aromatic content, while for oils with the same oil source, oil refinery process, similar carbon type, and different boiling range, the thermal conductivity increases with its viscosity.

An Investigation into the Physico-chemical Properties of Transformer Oil Blends with Antioxidants extracted from Turmeric Powder

Abstract The blending of transformer oil (used mainly as an insulating oil) with appropriate synthetic antioxidants, such as BHT (2,6-di-tert-butyl-4-methylphenol) and DBP (2,6-di-tert-butylphenol) have been previously reported. This article is focused on the use of antioxidant extracts from turmeric (Curcuma longa), a natural source. Turmeric is well known for its antimicrobial, antioxidant and anticarcinogenic properties owing to the active nature of its components. Extracts from powdered turmeric were subsequently blended into naphthenic-based uninhibited virgin transformer oil, hereinafter referred to as extract-oil blends (E-OB). Thin-layer chromatography (TLC) of the oil blends revealed that five components extracted from turmeric powder were successfully blended into the oil. Subsequent gas chromatography–mass spectrometry (GC–MS) analysis confirmed the presence of the compounds: curcumene, sesquiphellandrene, ar-turmerone, turmerone and curlone. Thermogravimetric analysis (TGA) of the extract-oil blends, containing various levels of extracts, revealed an average temperature shift of ∼8.21°C in the initial onset of degradation in comparison to virgin non-blended oil. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay showed that an increase in the mass aliquot of turmeric extracts in the transformer oil increased the free radical scavenging activity of the oil. Electrical properties of the oil investigated showed that the dissipation factor in the blended oil was found to be lower than that of virgin transformer oil. Evidently, a lower dissipation value renders the oil blend as a superior insulator over normal virgin non-blended oil. This investigation elucidated improved physico-chemical properties of transformer oil blended with turmeric antioxidant extracts.

Influence of copper ions in transformer oil properties and adsorption treatment

The dissolution of copper with trace acid, oxygen, moisture, nitrogen compounds, and corrosive sulfur in oil formed copper ions. A transformer oil with 7.0 mg/kg copper ion was treated via the adsorption method. The efficiency of adsorbent was raised with the increase of addition amount and temperature. In the adsorption process, the copper ions, interfacial tension, water content, acid value, volume resistivity, and dielectric loss tangent tan δ of oil were tested, and the relationship between copper ions and electrical properties was investigated. In 140 h, the copper ions decreased to 0.5 mg/kg, the dielectric loss tangent from 2.19% to 0.07%, and the volume resistivity from 0.67×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> Ωcm to 7.05×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> Ωcm. Moreover, the antioxidant content, oxidation stability, and transformer insulation resistance before and after the adsorption treatment were analyzed. The adsorption treatment was effective in elevating the transformer insulation resistance from about one to ten thousand.

Dielectric properties of transformer oils for HVDC applications

The knowledge of the behavior of electric conductivity in mineral oils for possible applications in HVDC converter transformers is of paramount importance for proper design of their insulation system. This study presents the results of measurements of dielectric properties of various transformer oils by means of frequency response technique as well as time domain measurements, including measurements of ion mobility using the reversal polarity method. Influences imposed by varying the measurement voltage level and temperature are investigated. Some important parameters of the investigated oils, e.g. their conductivities, ion mobilities, ionic concentrations and effective ionic radiuses are compared and discussed. The results show that despite of similarities in various physical parameters of insulating mineral oils available on the market, the dielectric behavior and especially ionic conduction vary greatly between different oil types. Changes of these properties with temperature are characterized by different activation energies.

Utilization of Date-pits in Transformer Oil Chemical Regeneration

High quality transformer oil is required to increase the reliability and the life time of the transformer. This oil carries information about the operating condition of the transformer. Therefore, the transformer oil properties should be monitored in order to give early warnings and maintain the transformers efficiency. When the oil quality is decreased, it should be either changed or regenerated. Transformer oil regeneration was carried out using adsorption on Activated Carbon (AC) produced from waste date-pits. After adsorption, drop in density, viscosity, neutralization index and metallic contents were observed, whereas adsorption resulted in an increase in interfacial tension. The properties of the regenerated oil after adsorption was found to approach the acceptable standards, which clearly demonstrate the potential of using locally made AC from waste date-pits as an adsorption agent for transformer oil regeneration.

Magneto-dielectric properties of transformer oil based magnetic fluids in the frequency range up to 2 MHz

Magneto-dielectric properties of transformer oil based magnetic fluids in the frequency range up to 2 MHz

Measurement uncertainty evaluation of automatic Tan Delta and resistivity test set for transformer oil

Quality of transformer oil plays vital role in the performance of transformer in electrical appliances. Measurement uncertainty is a general concept associated with any measurement and can be used in professional decision processes as well as judging attributes in many domains, both theoretical and experimental. As the tolerances applied in industrial production become more demanding, the role of measurement uncertainty becomes more important when assessing conformity to these tolerances. Measurement uncertainty plays a central role in quality assessment and quality standards. In an effort to meet national, international and commercial accreditation requirements, users of transformer oil testing machines must establish adequate methods of determining calibration and test measurement uncertainties. Determining measurement uncertainty for transformer oil testing equipments and test data can be a very complex process. Many factors affect the uncertainty of test data produced by testing machines. In this paper, the concepts associated with the procedure for estimation of uncertainty is discussed and the application of these for the determination of uncertainty in transformer oil testing equipments in government testing labs is illustrated. The objective of this study is to develop a methodology for determining the result of measurement concerning electrical properties of transformer oil and their respective uncertainties.

Influence of Artificial Thermal Aging on Transformer Oil Properties

This article presents research results on electrical and physic-chemical properties of insulating oil used for high-voltage applications under accelerated artificial thermal aging. Unlike in previously published work, this article gives an extensive set of test data of artificially aged transformer oil under various temperatures. In addition, the aging effect of test temperature on various properties of the oil was quantified. Continuous thermal aging tests were made on transformer oil (Borak 22, Sonelgaz, Nynas, Austria) using a 5000-hr test at four different temperatures of 80, 100, 120, and 140°C. First, the electrical properties of transformer oil, such as the dielectric dissipation factor and the breakdown voltage, are measured after every 500 hr of aging. Next, the physicochemical parameters, including the acidity degree, water content, color factor, kinematic viscosity, density, and flash point, are quantified in order to find the changes in the chemical composition of the insulating oil. The results show that thermal aging significantly affects the properties of transformer oil by the formation of acidic products and the formation of water in oil, which lead to the degradation of the oil's electrical and physicochemical properties.

Laser interferometric study of the physical properties of transformer oil

This paper describes the optical, thermal, and electrical properties of an important nonpolar dielectric liquid, transformer oil. Applying dual laser (He–Ne and Argon laser of wavelengths 632.8 and 514.5 nm, respectively), and the Mach–Zehnder interferometric technique, the refractive indices and its temperature gradients are determined. Using Maxwell's and Cauchy's equations, the following optical, thermal, and electrical properties are calculated: optical and dielectric dispersion, optical permittivity and its thermal coefficient, thermal coefficient of volume expansion, specific refraction, specific dispersivity, characteristic impedance, electric susceptibility, and the variation of Cauchy's emperical constants with temperature. Additionally, different physical phenomena are studied as functions of wavelength and temperature.

On light scattering in transformer oil

GK transformer oil is studied using the methods of UV and visible spectroscopy, dynamic light scattering, small-angle light scattering, scanning electron microscopy, and element analysis. The effect exerted on the optical properties of transformer oil by colloidal, micelle-like, and solid particles formed in oil during its exploitation is investigated.