Breakdown Voltage Of Oil Research Articles

Dielectric properties of mixed mineral and synthetic ester oil

The dielectric properties of 20% synthetic ester oil mixed with mineral oil were studied for its potential applications as an insulator in transformers. The corona inception voltage of mixed oil under AC and DC voltages was measured by the ultra-high frequency (UHF) technique. A statistical study of the breakdown voltage of mixed oil under AC, DC and standard lightning impulse voltages was carried out to obtain a database which would be useful for designing transformer insulation. Further, the mixture was subjected to continuous breakdown studies under AC voltage with lightning impulse voltages, at regular intervals and characterised through measurement of interfacial tension, flash point, ionic mobility as well as UV–vis spectroscopy and frequency-domain spectroscopy studies to understand the liquid's chemical stability. The results of the study have shown that the mixture was stable even after several breakdowns. The ionic mobility and polarisation current have increased, indicating higher losses in the oil. UHF signal energy analysis and phase-resolved partial discharge analysis have revealed a reduction in discharge activity with mixed oils.

Breakdown characteristics of transformer oil with cellulose particles in a non-uniform field under lightning impulse voltage

This study presents experimental results on the influence of cellulose particles on the breakdown characteristics of transformer oil in a highly non-uniform field under lightning impulse voltage. The experimental results show that as the particle content increases, the breakdown voltage reduces with little change in the breakdown time lag. At the same cellulose particle content, the oil breakdown voltage under oscillating lightning impulse (OLI) is lower than that under standard lightning impulse (SLI) and the breakdown time lag under OLI is longer than that under SLI. The impulse wave oscillation has a large effect on the accumulation of particles around the high voltage electrode and cellulose particles affect the development of the streamer process. At mid to high particle content the accumulation of particles around the high voltage electrode causes a decrease in the conductivity of the surrounding oil. This work contributes to the understanding of the effect of cellulose particles in oil and breakdown and on oscillating waveforms and provides guidance for lightning impulse tests on oil-immersed power transformers in the field.

Role of air bubbles in the breakdown of flowing transformer oil

In this paper, a liquid circulation system is constructed whereby gas bubble dynamics and electrical signal evolution preceding the oil gap breakdown are registered in stationary and flowing transformer oil. Based on a number of repetitive tests, two types of breakdown are classified: one takes place after bubble growth and originates in the bubble or the mixture of liquid and gas when the applied voltage is in the negative half-cycle; the other follows streamers resulting from the protrusion of bubble tip in the positive half-cycle. For each type of breakdown, partial discharge (PD) pulse is captured preceding the breakdown. As the oil flow rate varies, bubble dynamics change but the characteristics of each breakdown remain. In addition, it is found that oil breakdown voltage is improved as the flow rate increases. In terms of PD occurrence and bubble growth, the role of gas bubble in oil breakdown initiation, as well as the effect of oil flow on breakdown, is discussed.

The effect of antioxidants on the physical and chemical properties of rice oil, corn oil, peanut oil and Kraft paper

This paper presents an experimental study on the physicochemical properties of rice oil, peanut oil, corn oil and Kraft paper immersed in these oils in the presence of antioxidants (butylated hydroxytoluene, tertiary butyl hydroquinone and Naugalube¯ 750). The experiments are performed on new and aged conditions. Ageing of oils is carried at 115 °C for 96 hours while Kraft paper is aged in oils at 130 °C for 164 hours. Both closed and open cup methods are used for ageing. The results show that ageing insignificantly affects the breakdown voltage, but markedly increases the acid number and the viscosity of the vegetable oils. The combination of tertiary butyl hydroquinone and either butylated hydroxytoluene or Naugalube¯ 750 slightly increases the breakdown voltage, but significantly raises the oxidation stability of the vegetable oils. This results in a reduction in the viscosity and the acid number of the vegetable oils. Moisture significantly affects the breakdown voltage of both vegetable and mineral oil. High moisture content results in low breakdown voltage. The results also show that ageing insignificantly affects the breakdown voltage, but markedly decreases the tensile strength of oil-impregnated paper. Although the presence of antioxidants does not increase the breakdown voltage of aged paper, these additives slow down the ageing process. This results in an increase in tensile strength of the paper.

Effect of surfactants on the lightning breakdown voltage of palm oil and coconut oil based Al2O3 nanofluids

In this paper, the effect of different types of surfactants on the lightning breakdown voltages of palm oil (PO) and coconut oil (CO) based aluminium oxide (Al2O3) nanofluids is investigated. Three different types of surfactants were used in this study known as cationic (cetyl trimethyl ammonium bromide (CTAB)), anionic (sodium dodecyl sulfate (SDS)) and non-ionic (oleic acid (OA)). The volume percentage concentrations of Al2O3 dispersed into PO and CO were varied from 0.001% to 0.05%. The ratio of surfactant to the nanoparticles was set to 50% from the volume concentration of nanoparticles which equivalent to 1:2. In total, two types of refined, bleached and deodorized palm oil (RBDPO) and one type of CO were examined for lightning breakdown voltage. The test was carried out based on needle-sphere electrodes configuration with 25 mm gap distance. The presence of Al2O3 improves both positive and negative lightning breakdown voltages of RBDPO and CO. Under the positive and negative polarities, the CTAB does provide further improvements on the lightning breakdown voltages of RBDPOA (1st type of samples) and CO at most of the volume of concentration of Al2O3. SDS and OA could also further improve the lightning breakdown voltage of CO at certain volume concentration of Al2O3. On the other hand, the lightning breakdown voltage of RBDPOB based Al2O3 nanofluid (2nd type of samples) does not further improve with the introduction of surfactants. At most of the volume concentration of Al2O3, the introduction of CTAB further increases the times to breakdown and decrease the average streamer velocities of RBDPOA under both polarities. The same finding is observed for CO under positive polarity with CTAB and SDS as well as under negative polarity in the presence of all surfactants. The streamer velocities and times to breakdown patterns of RBDPOB based Al2O3 nanofluid are inconsistent in the presence of all surfactants. It is found that RBDPO and CO based Al2O3 nanofluids have second mode of streamer whereby the streamer velocities are from 1 km s−1 to 1.63 km s−1 regardless with or without surfactants.

High $Q$ Microwave Microfluidic Sensor Using a Central Gap Ring Resonator

In this article, a highly sensitive and compact microwave sensor with quality factor (Q ≈3000) is proposed for identifying and sensing liquid samples using a central gap ring resonator (CGRR). The high Q is a result of surface current redistribution. Our sensor is designed to operate at 2.5 GHz with an active gap region, where the sample flows, in which the electric field is at its maximum amplitude. The sensor was simulated, fabricated, and tested for a new application to identify the condition of oil used as a coolant and an insulating material in high-voltage transformers. The efficiency of oil in this application depends on its insulation capability and water content. Since both of these factors correlated with the oil's dielectric constant, the CGRR sensor showed very good sensitivity for detecting the ratio of water in oil from the measurements of Q change (and its link to the oil's breakdown voltage) involving fresh and used oil samples.

Investigation of the Lightning Impulse Breakdown Voltage of Mineral Oil based Fe3O4 Nanofluids

The recent interest in the development of nanomaterials has led researchers to the study of their electrical properties and the applications that they may have as insulating materials. One of these applications is the use of nanofluids as electrical insulation of power transformers. It has been reported that the dielectric properties of insulating liquids in which small amounts of nanoparticles have been dispersed are, in some cases, superior to those of the base fluids. Although these materials are promising, and their application could lead to advantages for the transformer design and reliability in the future, more research is necessary to evaluate different combination of materials under a wider range of experimental conditions. In this paper, a research on the lightning impulse breakdown voltage of mineral oil and several Fe3O4-based nanofluids is presented. Fluids prepared with different concentrations of nanoparticles were subjected to impulse lightning voltages considering both positive and negative polarities. As shown in this work the positive impulse breakdown voltage of the liquids showed improvements of up to 50%; in the case of the negative impulses not significant improvements were obtained.

Dielectric properties of mineral oil‐based nanofluids under temperature variations

The aim of this research is to improve the electrical properties of dielectric liquids. An examination of the dielectric properties of mineral oil-based nanofluids was carried out, using three different nanoparticle types: titanium dioxide, zinc oxide, and barium titanate, each with a mean diameter not exceeding 100 nm. The test samples were divided into two groups, including mineral oil mixed with nanoparticles at a concentration of 0.01 and 0.03% volume fraction, respectively. Determination of the AC breakdown voltage of the unmodified mineral oil and the nanofluid samples was performed through testing at temperatures varying within the range of 35-90°C in accordance with the standards of IEC 60156. Furthermore, testing was also performed to determine the dielectric dissipation factor (tan δ ) for each of the liquid samples according to IEC 60247. From the study, it was shown that the performance of nanofluid was significantly affected by increasing the temperature. It could be observed from the findings that the use of nanoparticles in creating mineral oil-based nanofluids had potential to bring a number of advantages in terms of dielectric applications.

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.

A STUDY ON BREAKDOWN PROPERTIES OF COCONUT OIL

This paper presents the results of electric breakdown properties of coconut oil with AC voltage. Experimental results show that breakdown voltage of new coconut oil is comparable to that of mineral oil. Ageing was seen to significantly affect the breakdown voltage of both coconut oil and mineral oil. However, influence extent of ageing on the breakdown voltage was higher for mineral oil. The antioxidant was seen to reduce the breakdown voltage of new coconut oil, but raised the breakdown voltage of aged coconut oil. The V-t characteristic of coconut oil is not as good as that of mineral oil.

Impact of Fe3O4, CuO and Al2O3 on the AC Breakdown Voltage of Palm Oil and Coconut Oil in the Presence of CTAB

This paper presents an experimental study on the AC breakdown voltages of Refined, Bleached and Deodorized Palm Oil (RBDPO) Olein and Coconut Oil (CO) in the presence of conductive (Iron (II,III) Oxide, Fe3O4), semi-conductive (Copper (II) Oxide, CuO) and insulative (Aluminium Oxide, Al2O3) nanoparticles without and with surfactant. The type of surfactant used in this study was Cetyl Trimethyl Ammonium Bromide (CTAB). The volume concentrations range of Fe3O4, CuO and Al2O3 was varied from 0.001% to 0.05%. Transmission Electron Microscope (TEM) was used to characterize the nanoparticles in RBDPO and CO. AC breakdown voltage tests were carried out for RBDPO and CO of which the AC breakdown voltage at 1% probability was determined based on Weibull distribution. It is found that only Al2O3 can improve the average AC breakdown voltage of RBDPO and CO. The AC breakdown voltages at 1% probability for RBDPO and CO can be improved through introduction of Fe3O4, CuO and Al2O3 at certain volume concentrations. Al2O3 provides the highest enhancement of AC breakdown voltages at 1% probability for RBDPO and CO with the highest percentage of improvement can be up to 52%. CTAB has no clear effect on the improvement of AC breakdown voltages of RBDPO and CO based Fe3O4, CuO and Al2O3 nanofluids.

The Impact of TiO2 Nanoparticle Concentration Levels on Impulse Breakdown Performance of Mineral Oil-Based Nanofluids.

The insulation of mineral oil-based nanofluids was found to vary with different concentration level of nanoparticles. However, the mechanisms behind this research finding are not well studied. In this paper, mineral oil-based nanofluids were prepared by suspending TiO2 nanoparticles with weight percentages ranging from 0.0057% to 0.0681%. The breakdown voltage and chop time of nanofluids were observed under standard lightning impulse waveform. The experimental results show that the presence of TiO2 nanoparticles increases the breakdown voltage of mineral oil under positive polarity. The enhancement of breakdown strength tends to saturate when the concentration of nanoparticle exceeds 0.0227 wt%. Electronic traps formed at the interfacial region of nanoparticles, which could capture fast electrons in bulk oil and reduce the net density of space charge in front of prebreakdown streamers, are responsible for the breakdown strength enhancement. When the particle concentration level is higher, the overlap of Gouy–Chapman diffusion layers results in the saturation of trap density in nanofluids. Consequently, the breakdown strength of nanofluids is saturated. Under negative polarity, the electrons are likely to be scattered by the nanoparticles on the way towards the anode, resulting in enhanced electric fields near the streamer tip and the decrement of breakdown voltage.

Feasibility study of waste vegetable oil as an alternative cooling medium in transformers

Vegetable oils due to their unique properties of availability and biodegradability can be considered as a reliable substitute for petroleum-based oils in transformer cooling system. Therefore, the performance of waste cooking vegetable oil after transesterification process for application in electrical transformers has been evaluated. The important properties of this oil such as density, heat capacity, viscosity, thermal conductivity, breakdown voltage and flash point have been measured and compared with those of mineral oil. Furthermore, the thermal behavior of the cooling system of an actual transformer was numerically simulated using the measured properties. Based on these measured data, the breakdown voltage and thermal conductivity of the vegetable oil as the two main indexes of transformer oil are, respectively, 48% and 33%, higher than those of the mineral oil, while its viscosity is considerably lower. Furthermore, the transformer hotspot temperature with vegetable oil is 3 °C lower than the mineral oil and the transformer experiences considerably lower temperature in the thermally critical region. Present study proposed the waste cooking vegetable oil not only as an alternative cooling medium for liquid-filled transformers but also as a sustainable way of using the waste resources, decreasing the environmental pollution and promoting environmental and economic benefits.

Analysis of Life Cycle Characteristics of Power Transformer Based on Linear Regression

How to determine the insulation status of transformers reasonably which is very important for the life management of transformers. Electrical data, oil Chromatograph data and oil test data are important parameters for measuring the insulation state of transformer. In this paper, the relationship between electrical, chromatographic and oil test data and transformer operating years in production operation is analyzed by means of regression analysis and hypothesis testing. The results show that the relationship between the absorption ratio, oil breakdown voltage and hydrogen hydrocarbon content is very weak between the operation years of the transformer and the CO and CO2 gas content is strictly related to the operation years of the transformer. The former mainly reflects the insulation performance of transformer oil, and can effectively identify the integral fault of transformer, but it cannot effectively reflect the residual life of transformer by the influence of filter oil and oil transfer. The latter reflects the state of transformer solid insulation and is an old characteristic of transformer life prediction. An example verifies the validity of the above conclusion.

Study of Breakdown Voltage of Vegetables oil with SiO2 Nanoparticle Additive

<p>This paper investigates the suitability of vegetable oils to replace mineral oil based on its AC breakdown voltage, partial discharge and viscosity. The purpose of the study is to analyze the effect of the nanofluids containing SiO<sub>2</sub> nanoparticle in vegetables oils; namely, Coconut oil and Palm oil. A nanofluid is a fluid containing nanoparticles. However, the precise effects on the electrical properties is still uncertain. For decades, transformers use petroleum-based mineral oil because of its good dielectric properties and cooling capability. Coconut oil (CO) and Palm oil (PO) are thought to be suitable alternatives to replace mineral oil as transformer oil as they are sustainable and available in plenty as natural resources. It was obtained in this study that the breakdown voltages of these raw oils have fulfilled the standard specifications of good insulating liquid. However, the addition of SiO<sub>2</sub> did not improve the AC breakdown voltage and viscosity of coconut oil and palm oil at different temperatures. However, the addition of SiO<sub>2</sub> gave positive results in the values of partial discharges in which the presence of the nanoparticles has greatly reduced the mean volume of partial discharges for both coconut oil and palm oil.</p>

Impact of wavefront time of microsecond impulse on the breakdown voltage of oil impregnated paper: Mechanism analysis

Breakdown in dielectrics, the mechanism of which is still not yet fully revealed, exhibits very complicated test phenomena and characteristics. The breakdown voltage of a dielectric is believed to be related not only to the dielectric properties but also to the waveform of the applied voltage. For most dielectrics, the impulse breakdown voltage decreases with increasing wavefront time. However, we found for oil-impregnated paper (OIP) used in power transformers, increasing wavefront time in lightning impulses (at microsecond timescales) may lead to a significant increase in breakdown voltage. In contrast, the variation in the wavetail time produces very little effect on breakdown voltage. Combined with our previous test results on the space charge distributions in OIP, we tried to provide two explanations regarding this interesting phenomenon: First, the wavefront time of the applied impulse voltage affects the movement process of the positive particles in the oil-filled micro cavities in OIP, which is strongly related to the local electric field in the oil filled micro cavities and the breakdown voltage of the OIP. Moreover, the wavefront time is closely related to the trapping and detrapping process of the dielectrics. Therefore the effects of the traps in dielectric on the breakdown characteristics are different when the wavefront time varies.

Prediction of insulating transformer oils breakdown voltage considering barrier effect based on artificial neural networks

The insulating oil performance could be enhanced in high-voltage apparatus using barriers. The importance of the barrier in increasing the dielectric strength of the insulating oils in order to reduce the oil failure stresses had not been sufficiently studied. In this paper, the effects of the barrier variables on the insulation performance of the transformer oil for point-plate and plate-plate gaps were demonstrated. These variables are: gap space (d), the barrier location relative to the high-voltage electrode (a / d) %, barrier diameter (D), barrier thickness (e), electrode configurations (EC), the presence of contaminating particles, the weight of the contaminating particles (W) and the temperature of the insulating oil (T). The statistical t test was used to explain whether the effect of these parameters was significant or not. Furthermore, the above-mentioned variables were used as training variables to construct the prediction model of oil breakdown voltage considering barrier effect based on the artificial neural networks (ANN). The ANN model was developed based on the results from experimental works. Therefore, 784 samples were used as training data set and other 25 samples were taken as testing and validating samples. The results explained that the prediction ANN model had a high ability to expect the breakdown voltage for other different experiment cases. The average errors of the training and testing samples were 1.6%, and 2.66%, respectively. Therefore, the prediction accuracy could be considered as 98.4% for training and 97.34% for testing.

Influence of ultrasound on the electrical breakdown of transformer oil

When the transformer oil is exposed to low power ultrasonic waves (< 2 W/cm2) at initial moment the breakdown voltage of transformer oil is reduced relative to the breakdown voltage of pure oil due to degassing and the occurrence of cavitation bubbles. With the increase of sonication time the breakdown voltage also increases, nonlinearly. The experimental data indicate the possibility of using ultrasonic waves of low power for degassing of transformer oil.

Influence of Copper Particles on Breakdown Voltage and Frequency-Dependent Dielectric Property of Vegetable Insulating Oil

The insulating performance of oil is vulnerable to particles especially the conductive particles. This paper investigated the influence of copper particles of micrometer size on the breakdown strength and frequency-dependent properties of vegetable oil. The AC breakdown voltage of contaminated vegetable oil with copper particles of different numbers (ranging from 103 to 106) was measured. The frequency-dependent dielectric properties including volume resistivity, relative permittivity and dissipation factor of the contaminated vegetable oil with copper particles of various volumetric concentrations (0.011%, 0.056% and 0.112%) were measured. Identical experiments were conducted with mineral oil for comparison. Results show that the AC breakdown voltage of vegetable oil decreases with the increase of copper particle concentration. The mineral oil exhibits a similar trend, but the influence of copper particles on the AC breakdown voltage of vegetable oil is less significant than that on mineral oil because of its greater viscosity. The relative permittivity and dissipation factor increase with increasing copper volumetric concentration while the volume resistivity decreases. The influence of copper particles on them is significant at low frequencies and this influence becomes inconspicuous as the frequency increases. Similar results were observed for mineral oil.

Moisture effect on conductivity of kraft paper immersed in power transformer vegetable‐based insulation oils

Vegetable insulation oils in transformers have become a reality. However, they are inherently hydrophilic and can absorb much moisture. Existence of moisture in transformer insulation will generally lower the breakdown voltage of oil. Moisture will also accelerate cellulose deterioration by increasing its dc conductivity. Both oil and cellulose are components of the transformer insulation system. It is therefore important to understand how this class of oils retains their dielectric strength and their relationship with kraft paper (KP) after absorbing so much moisture. This study presents effect of moisture increase in three samples of vegetable oil and its effect on dc conductivity of KP samples immersed in the oils. The dc conductivity of the samples is calculated based on dielectric response polarisation and depolarisation current measured. The result shows that KP in vegetable insulation oil performs better when the oil samples are wetter and drying the vegetable insulation oil accelerates KP degradation. The finding will help to understand of the deterioration of cellulose when immersed in the oil.