Dielectric Strength Of Transformer Oil Research Articles

Study of Dependence of Electric Strength of Transformer Oil on Humidity and Presence of Mechanical Impurities

The results of additional studies of quantitative estimates and analytical dependence of the influence of moisture and mechanical impurities on the dielectric strength of transformer oil are presented. The results obtained made it possible to draw a conclusion about a similar breakdown mechanism in the form of an exponential character.

Fe3O4/TiO2/Graphene Hybrid Nanocomposite to Improve the Lifespan of Distribution Transformers

The actual lifetime of a transformer is between 30-50 years, while a foundation can be in service for 100 years. The aim of this research is to get the exact remaining lifetime of the transformers and to suggest a method to improve it. Hybrid nanoparticles are used to improve the thermal properties and dielectric strength of transformer oil. Titanium oxide (TiO2), Iron oxide (Fe3O4), and Graphene is used in specific concentration to prepare the hybrid nanoparticles. Energy Dispersive X-Ray Analysis (EDX), X-Ray Diffraction Analysis (XRD), Fourier Transform Infrared Spectroscopy (FTIR) are carried out to know whether the nanoparticles are properly synthesized. Initially Infrared thermography analysis using Fluke TiX-580 is being carried out to measure the surface temperature of the transformers and transformers under analysis are grouped. Nanofluid Transformer oil is prepared and Break Down Voltage (BDV) Test is taken to analyse the strength. Transformers are filled with nanofluid transformer oil and Infrared Thermography analysis is performed again to analyse the surface temperature. It is showing that lifetime of transformers is increased from 6 to 8% after using nanofluid transformer oil.

Dielectric Strength of Transformer Oil of Various Qualities

Dielectric Strength of Transformer Oil of Various Qualities

Method of calculating the electric strength of oil channels of the main insulation of power transformers

The most damage-sensitive unit of power transformers is the main insulation of the oil barrier type. The breakdown of such insulation occurs as a result of the breakdown of the oil channel near the high voltage winding. In accordance with traditional methods of calculating the dielectric strength of insulation, the value of the breakdown strength is determined by empirical formulas depending on the selected width of the oil channel. The existing methods do not consider the influence of the oil channel volume, of the electric strength the statistical characteristics of the oil, the design features of the insulation of power transformers, and do not contain recommendations for creating design models. Thus, to improve the calculation accuracy, it is relevant to develop the evaluation method of dielectric strength of the main insulation of power transformers taking into account the volume and parameters of the breakdown voltage distribution of transformer oil, design features. The research results of the breakdown tension in oil channels with different volumes of transformer oil were used. To improve the accuracy of the calculation and taking into account the design features, the model of the main insulation of power transformers was made in the ANSYS program. Boundary data and assumption of linear stress distribution of transformer coils were considered. A method for calculating the dielectric strength of oil channels of the main insulation of power transformers, considering the volume and parameters of the breakdown voltage distribution of transformer oil was proposed. Unlike the existing methods, when calculating the minimum breakdown strength in the model of the main insulation, the design features of power transformers are taken into account and assumptions are justified to improve the accuracy of the calculation. In accordance with the methodology, the parameters of the dielectric strength of the transformer oil in the oil channel of the high voltage winding of the transformer were calculated. It was concluded that with increase of relative value of breakdown tension, dielectric strength of oil channel is decreasing, and it corresponds to physical sense of breakdown. The method for calculating the dielectric strength of transformer oil can be used when choosing the main insulation of power transformers in design.

Study of the effect of cellulose fibers on the electrical strength of transformer oil

The electrical strength of transformer oil is the first parameter in transformer insulation tests. Such tests are carried out in a standard discharger according to the values of breakdown voltage. An abrupt decrease in electrical strength occurs when oil is contaminated with mechanical impurities. The greatest influence on the electric field is exerted by highly conductive cellulose fibers. The field between the electrodes may be severely distorted bya «bridge» of such fibers. At the same time, the influence of such particles is not taken into account in the tests. The problem is to experimentally determine the effect of such impurities on the breakdown strength. Thereby, this research poses and solves the problem of determining the dielectric strength of transformer oil in a standard discharger in the presence of cellulose fibers.To simulate electric field strengths, the ANSYS software package has been used. The basis of the 3D model was a standard measuring cell for determining breakdown voltage, which takes into account the boundary conditions in the form of a cube in which the electrode system is located, and the values of the electric field strength in the center of the electrode system.The electric field tension between the electrodes has been calculated, taking into account the influence of increased conductivity of cellulose fibers. It has been found that the electrical strength of oil gaps of moistened fibers with a length of more than 200 μm is significantly reduced, which is not taken into account when testing transformer oil for breakdown in a standard cell. This leads to inaccuracy in determining the electric strength of transformer oil in existing equipment.The results of the study can be used by operational services to improve the assessment of the quality of transformer oil used in power transformers as insulation. The results also can be used to study the mechanisms of electrophysical processes occurring in liquid dielectrics in the presence of fibers.

Synthesis and Application of Ceo2 and Zro2 Nanoparticles for Enhancement of Dielectric Strength of Transformer Oil

Power and Distribution transformers are the key devices to maintain power system reliability. Thus in-order to have continuous power supply ,a fault tolerant system is to be developed by avoiding the failures on major devices like transformers. As insulation failure is accounted as 13.0% occurrence of all the faults on transformer, there is always a point of interest to enhance the breakdown strength of the transformer oil. Also to cater to the demand , an increase in the number and unit capacity of high voltage transformers require transformer oil with high oxidation stability and good electric properties. In this work , ceramic nanomaterials zirconia(ZrO2) and Ceria ( CeO2) are preferred due to their strong insulating property and high relative permittivity. The synthesized nanomaterials of concentration (0.5%wt) are dispersed into the transformer oil by sonication and AC breakdown measurements have been performed on the prepared nano transformer oil. The obtained results clearly indicates a remarkable increase in the dielectric strength of transformer oil filled with ZrO2 and CeO2nanoparticle.

Breakdown performance of transformer oil in the presence of single‐phase nanocrystalline ZnO and nano‐partial substitution

In this study, newly structured nanoparticles are synthesised and incorporated in the transformer oil for enhancing the dielectric properties. A new nanocrystalline series of zinc oxide (ZnO) and ZnO partially substituted by lanthanum oxide is presented for the first time, where the precursor technique is utilised to create the nano-powders. Different partial substitutions facilitate to manipulate nanocrystalline sizes, and therefore the effect on nanofluid dielectric characteristics is attained. Another factor during the laboratory nanoparticles preparation is considered that the precursor is annealed at different temperatures. The nanocrystalline phase compositions are experimentally examined and evaluated using X-ray diffraction and transmission electron microscope. Accordingly, single-phase and multi-phase nanocrystalline powders are ascertained. The transformer oil incorporated with nanoparticles is prepared and its dielectric strength is measured using an oil breakdown voltage tester. The measured dielectric strength of transformer oil with and without nanoparticles is statistically evaluated using Weibull distribution. The most appropriate nanofluid and concentration are estimated experimentally. Toward interpreting the nanofluid dielectric enhancement, their electric field distribution is numerically evaluated at different nanoparticle concentrations using COMSOL multiphysics. This study supports the analysis and optimisation of transformer oil dielectric performance.

Investigation of Dielectric Strength of Transformer Oil Based on Hybrid TiO2/Al2O3/MoS2 Nanofluid Using Taguchi and Response Surface Methodology

ABSTRACT Transformers play a vital role in transmission and distribution systems, still 75% of the transformers fail because of inappropriate dielectric insulation. Almost a century alone, mineral oil and vegetable oil were used as insulation and coolant, but they failed because of extra power requirement. After the introduction of nanofluids, massive research work has been carried out to improve the thermal and dielectric characteristics of transformer oil. In this work, a novel approach has been used to investigate dielectric strength by adding hybrid nanoparticles TiO2/Al2O3/MoS2 with 0.01, 0.025, 0.05, and 0.1 volume percentage in transformer oil with 16 different combinations based on Taguchi L16 orthogonal array. The dielectric strength was measured for transformer oil on the basis of the design matrix and a statistical analysis was done to predict the best combination of parameters. ANOVA also showed that the weight percentage of TiO2 and Al2O3 had a significant effect on dielectric strength. Further, the second-order quadratic equation was developed to predict the best suitable combination of nanoparticles using Response Surface Methodology. The predicted results revealed that the TiO2 had a significant effect on dielectric strength.

Wavefront dependent dielectric strength of transformer oil under double-exponential impulse voltage

Lightning impulse withstand test is extremely important to the insulation examination of oil-immersed equipment, but the increase of the entrance capacitance of ultrahigh voltage equipment usually makes the front time T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> of test impulses exceed the upper limit regulated by IEC 60060-1. In order to evaluate the equivalency between the withstand tests under standard lightning impulses and impulses with longer front time (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <; 6 μs), as well as to explore the effect of wavefront on dielectric strength of transformer oil, the breakdown characteristics of transformer oil under impulses with different front time in quasi-uniform and non-uniform field were studied. The results show that, in quasi-uniform field, the 50% breakdown voltages U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> % are almost independent of the front time, but the minimum breakdown voltages slightly increase as the front time increases. In a highly inhomogeneous field, the front time has remarkable effects on the 50% breakdown voltages under positive impulses, contrary to the weak influences under negative impulses. Light signals and shadow images of streamers were recorded to analyze the influence of wavefront on the initiation and propagation characteristics. It is found that an increase in front time would increase the initiation voltages of both positive and negative streamers, but their shapes do not change much as front time varies. The dependence of light signals of streamers on front time was only observed under positive impulses. The mechanism underlying the differences between the front time related breakdown characteristics of transformer oil under positive and negative impulses is discussed, as well as the waveform equivalency for impulse withstand tests of oil-immersed equipment.

Breakdown Voltage of Transformer Oil Contaminated with Iron Particles at Pulsating DC Voltage

It is well known that particles, especially conducting particles, have a detrimental effect on the dielectric strength of transformer oil. This article investigates the influence of iron particles on the breakdown voltage of transformer oil. The breakdown voltage of transformer oil contaminated with iron particles of different median diameters and quantities was measured at pulsating DC voltage. For comparison, identical experiments were performed at AC and DC voltage, respectively. The Weibull distribution was adopted to analyze the breakdown voltage data and thus the effect of particle number and particle size on the breakdown voltage of transformer oil was obtained. The experiment results showed that the breakdown voltage of transformer oil decreases with an increase of the particle number and particle size. The breakdown voltage of contaminated oil is smaller when there is DC component contained in the applied voltage, which is because of the increasing possibility of bridge formation in transformer oil with the presence of DC voltage. The limit of particle number was also calculated for transformer oil subjected to pulsating DC voltage and found to be lower than that at AC voltage, suggesting that the limit of particle number should be individually defined for converter transformer oil.

Recent progress in nanofluids based on transformer oil: preparation and electrical insulation properties

Given the adoption of ultrahigh-voltage ac and dc power transmission, it is desirable to develop a new kind of oil-paper insulation system, with higher dielectric strength and smaller volume compared with conventional insulation systems, in order to reduce the volume and mass of high-voltage power transformers and improve their long-term operational reliability [1], [2]. Methods of improving the dielectric properties of the oil-paper insulation have therefore been widely investigated [3], [4]. The most influential factors affecting the performance of oil-paper insulation systems are the low dielectric strength of transformer oil and its degradation caused by water and other contaminants [5]. The dielectric strength of oil-paper insulation may be increased by filtering the oil in order to remove water and other contaminants [6]. However, further increase in the dielectric strength of the oil is required in order to achieve reduction of transformer volume and mass.

Comparison of the dielectric strength of transformer oil under DC and repetitive multimillisecond pulses

The dielectric strength of fresh and contaminated transformer oil under repetitive millisecond pulses was compared with that at DC voltage. The pulsed breakdown voltage was found to be higher than its DC counterpart by 10 to 20%.

Barrier effect on breakdown of point–plane oil gaps under alternating current voltage

This study deals with the influence of insulating barriers on AC dielectric strength of transformer oil in point–plane electrode configuration. The influence of the characteristics of barrier such as its position with regard to the point electrode, its thickness and dimension as well as its constituting material is investigated. It is shown that the insertion of barrier near the point electrode generally leads to the increase of breakdown voltage; this later also increases with the dimensions of barrier. The optimal position of barrier is at about 20% of gap starting from the sharp electrode (i.e. the point). The barrier acts as a geometrical obstacle against the direct propagation of discharge. There is an equivalency between distances of systems with barrier and without barrier.

Breakdown of transformer oil

Some of the factors affecting the dielectric strength of transformer oil are investigated. These factors include the stabilization phenomenon, oil and electrode pretreatment, the effect of oil velocity, the effect of a capacitance parallel to the test cell, and the effects of electrode area and gap spacing. The experimental apparatus and procedure are described, and the results are presented for each of the above factors. Suggestions for future research are offered. >

Statistical Dielectric Degradation of Large-Volume Oil-Insulation

In an attempt to clarify the persisting controversy over the effect of the electrode area versus that of the stressed oil volume in large-oil-volume- breakdown, a study was carried out under well defined conditions of the oil quality, particularly with regard to the degree of particle contamination. The results indicate that both the electrode area and the stressed oil volume can affect the dielectric strength of transformer oil, with the stressed-oil-volume effect being most pronounced under particle contamination conditions. Test results with technically clean transformer oil as currently accepted for use in power apparatus indicate that the degree of particle contamination in these oils is sufficient to produce an observable stressed-oil-volume effect. Finally, it is demonstrated that the observed phenomenon can be interpreted in terms of an apparent effect of either the electrode area or the stressed oil volume. This has led to the development of a semi-empirical method of quantitatively assessing the breakdown phenomenon in large oil volumes with reasonable accuracy.

Particles and Moisture Effect on Dielectric Strength of Transformer Oil Using VDE Electrodes

The effect of particles and moisture on the 60 Hertz breakdown strength of tranformer oil was investigated. Different sizes and concentrations of iron, copper and cellulose particles were used. The breakdown voltage was determined according to ASTM D1816 using VDE electrodes with an 80 mil (2 mm) gap. The breakdown strength of oil decreased approximately 25 percent when the moisture content was increased from 5 ppm to 20 ppm. A further reduction in the breakdown strength of oil occurred when iron, copper or cellulose particles were added to the oil. The transformer oil showed very low values of 60 Hertz breakdown strength as the result of the combined effects of moisture and particles' type, size and concentration.

Particles and Moisture Effect on Dielectric Strength of Transformer Oil Using VDE Electrodes

Particles and Moisture Effect on Dielectric Strength of Transformer Oil Using VDE Electrodes

Gas Bubbles In Distribution Transformers

Gas bubbles are known to have a deleterious effect on the dielectric strength of transformer oil. The possibility that such bubbles may develop in oil-filled distribution transformers and may cause excessive failure rates is thus of concern to both manufacturer and user. The paper presents new information relative to failure mechanisms in transformers. It describes some of the operating conditions which may lead to gas bubble formation and it gives limited data showing the effect of bubbles on insulation breakdown strength.

Influence of Specimen Size on the Dielectric Strength of Transformer Oil

The results of some specimen size effect experiments on technical grade transformer oil are reported. Four electrode areas (1.77, 8.19, 37.9 and 177 cm2) and four gap spacings (0 .215 0.464, 1.0 and 2.15 mm) were investigated using a fast ramp (5.5 x 1012 V.cm-1.sec-1) and an ac ramp (12 kV. cm-1.sec-1). Whilst the results are in general agreement with weak link theories, it is suggested that physical specimen size factors play a significant part. Examples of physical size factors are spark conditioning, electrode profile, and liquid motion.

Dielectric Strength of Transformer Insulation

This paper presents a summary of the results of over 2,000 tests on the dielectric strength of transformer oil and insulating material for impulse, switching, and 60-cycle voltages. From these tests the voltage-time characteristics of the 2 insulations tested may be established over the entire range from a fraction of a microsecond to more than one minute.