Thermal lifetime of transformer electroinsulating oils (original) (raw)
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A comparative study of impact of electrical stress and thermal aging on transformer oil
2014 IEEE 11th International Multi-Conference on Systems, Signals & Devices (SSD14), 2014
There is a general agreement that in service conditions the quality of insulating fluids gradually deteriorates under the impact of electrical, thermal and chemical stresses. The object of this contribution is to compare the variation of transformer oil parameters in different aging tests: thermal aging, electrical aging and the combination of both. The effects of the three different types of aging on the physicochemical and electrical properties of transformer oil have been examined, with the aim of investigating the stress which strongly affects the gassing tendency and physicochemical properties of oil under the service conditions. In this regard, various scenarios were considered. The study was carried on mineral oil under: electrical stress, thermal aging and a combination of both stresses. The ASTM methods are used to monitor the deterioration of liquid insulation step by step. The results obtained using laboratorygrade equipments indicate that the rate of increase or decrease in parameters is different from aging type for other and the electrical field accelerate strongly the degradation of new and aged oil. The study is made on a naphthenic commercial-based mineral oil.
Influence of Transformer Oil Decay Products on its Thermal Conductivity
The fluid inside transformer must function as an insulating medium and heat transfer agent. During service, there is a gradual deterioration of the fluid that eventually compromises the unit's reliability. In this contribution, the physicochemical and thermal properties of aged oil are studied. It is shown that with the production of oxidative aging by-products, the physicochemical properties along with the thermal conductivity and viscosity of oil are affected. From the obtained results, it seems that the decay products increase slightly the thermal conductivity of oil. The cinematic viscosity as aging time progressed may be directly correlated to the turbidity and dissolved decay products results. Measuring the amount of insoluble/soluble suspensions therefore appears to be very important, since these by-products clearly affect the insulating oil physicochemical properties.
Corresponding Author: Aging Study and Lifetime Estimation of Transformer Mineral Oil
Problem statement: Power transformer is the most expensive equipment in electrical network; and the mineral oil has the main roles of insulating and cooling in it. Oil is subjected to the degradation because of the ageing, high temperature and chemical reactions such as the oxidation. Then the oil condition has to be checked regularly and reclaimed or replaced when necessary, to avoid the sudden failure of the transformer. It will be very desirable also if we can predict the transformer oil remaining lifetime, from time to time. Approach: An experimental study was accomplished on the used oil specimens coming from several power transformers of various ages, working in Iranian power network, to recognize the correlation between the real age of the oil and the rate of its different characteristics and to know the most appropriate property which can represent its ageing. Accelerated aging experiments were accomplished on oil specimens at different temperatures. Furthermore a method for estimation of the remaining lifetime of the oil, using Arrhenius law, was employed. Results: According to our experiments, it was verified that, by using Celsius degrees and natural logarithm, the Arrhenius law can be applied properly to the thermal degradation phenomena of the oil. Conclusion: It was shown that the presented method can be used to study the degradation of transformer mineral oil and to estimate its remaining lifetime.
An Experimental Study to Determine the Life Time of Naturally Aged Transformer Oil
Journal of King Abdulaziz University-Engineering Sciences, 2005
Several efforts have been made over the past years to study the electrical, physical and chemicals properties of insulating oils. Among those efforts there is a property of natural aged oils (real oil samples corresponding to the scale of industrial transformers). This is investigated in this paper to determine the lifetime of naturally aged oil with different applied electric field and different shapes. This paper presents an experimental work to study the lifetime of transformer oil as a function of conduction current. In this paper, the electrification current in the tested oil is measured for different temperatures. Finally, tests have been carried out on oil samples under testing with different services period to determine the relation between breakdown voltage and the oil lifetime under uniform and nonuniform fields.
Investigations of thermal degradation and spectral response of transformer oil
Acta Scientiarum. Technology, 2013
In order to maintain continuous power supply in the electrical system, condition monitoring of the sensitivity equipments in power system is very essential. Among those equipment in which more concentration required is Power transformer. To determine the performance of transformer, it is necessary to have investigations on ageing of transformer oil due to thermal degradation. In this work an effort has been made to analyze various critical parameters like acidity, Breakdown Voltage (BDV), viscosity, volume resistivity, loss tangent, dielectric constant and spectral response for different range of thermal degradation of transformer oil with various compositions of materials like pressboard and Kraft paper. As initiative an exclusive Thermal-UltraViolet (UV) analysis has been carried out to investigate the spectral response of transformer oil. By estimating the condition of oil, the unexpected failure of transformer and power outages can be prevented.
Analysis of Factors Influencing the Intensity of Transformer Oil Ageing in Long-Term Operation
Bulletin of the National Technical University "KhPI". Series: Energy: Reliability and Energy Efficiency, 2021
The results of the analysis of influence of operational factors and peculiarities of transformer design on intensity of oxidative reactions of transformer oils in the tanks of 110 kV high-voltage power transformers are presented. As a result of two-way analysis of variance it was found that with increasing operating time there is a statistically significant increase in the value of the organic acid content in the oil. At the same time the rate of increase in the organic acids content in the transformer oil, operated under different conditions, significantly differs, which indicates a significant influence of operating conditions on the intensity of oxidative reactions. The results of two-way analysis of variance also show that the effects of changes in factor levels are not additive, that is, the effect of a change in the level of influence of one factor leads to a change in the effect of the level of influence of another. In other words, the process of oil oxidation is cumulative a...
Energies
The effect of thermal aging on the electrical properties of the insulating oil used for transformers has been explored in this experimental work. In particular the dielectric dissipation factor, the resistivity and the breakdown voltage have been measured and correlated. The numerical results predicted by mathematical model and those measured in the laboratory have been compared by using a regression analysis. Experiments on thermal aging were performed on insulating oil (Borak 22, Nynas, Austria) during a period of time of 5000-h at three different temperatures. First, the transformer oil’s dielectric dissipation factor, the resistivity and the breakdown voltage are measured after every 500 h of aging. Then, polynomial and exponential regression expressions are proposed for modelling the oil’s electrical parameters variations with thermal ageing at different aging temperatures and periods. The results show that after thermal aging, the resistivity and the breakdown voltage decrease...
Parameters affecting the electrical and thermal properties of transformer oils
2010 Annual Report Conference on Electrical Insulation and Dielectic Phenomena, 2010
Transformer oil is expected to function as an insulating medium and heat transfer agent. In this contribution, contaminants that mostly influence the electrical and thermal properties of transformer oil are addressed. To access the influence of the type of impurities on oil properties, various scenarios were considered. Investigations were therefore performed on new oil, new oil submitted to electrical stress, service-aged oil, reclaimed (by Fuller's Earth) service-aged oil, dehumidified service-aged oil, dehumidified and degassed service-aged oil. The influence of each type of "contaminant" is emphasized and discussed. The results obtained from the measurements show that electrical discharge by-products (charges carriers), mostly affect oil insulating properties, and influence the conduction phenomena which in turn increases the dissipation factor. It is also shown that colloidal suspensions in oil affect the heat transfer capability of this later, as assessed by viscosity.
Quantifying the Effect of Catalysts on the Lifetime of Transformer Oil
Applied Sciences, 2020
The effect of catalysts in the form of a transformer copper winding with Kraft paper insulation on the lifetime of transformer oil was studied via ultraviolet-visible (UV-Vis) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The tested naphthenic mineral oil was exposed to accelerated thermo-oxidative aging with limited access to air at temperatures of 110, 120, and 130 °C for times ranging from 24 to 2424 h in the presence and absence of catalysts. The UV-Vis technique focused on assessing the change in the color of the oil and quantified a 35%–45% reduction in oil lifetime, depending on the aging temperature, due to the influence of catalysts. The FT-IR analysis focused on the decrease in the spectral band at 3650 cm−1, which corresponds to the low-temperature antioxidant present in the oil, and quantified the 35% reduction in the oil lifetime independent of the aging temperature. This high rate of reduction in the transformer oil lifetime points to the dominant c...
Effect of Copper on Ageing Behavior and Breakdown Voltage Properties of Transformer Oil
Transactions on Electrical and Electronic Materials, 2020
In this paper, the "Breakdown Strength" of ester base liquid MIDEL 7131(MIDEL Ltd), Mineral Transformer oil (Grosvenor Oil Service), Diala D (Shell Ltd) and THESO insulating oil (Tetra Corp) that are subjected to three different ageing conditions is examined. The breakdown strength of thermally aged insulating oils with copper and without copper has also been tested. Therefore the effect of copper as a catalyst in ageing of insulating liquids was also examined. After analyzing the effect of copper on ageing indicated that, copper had a huge influence on darkening all the insulating oils except MIDEL 7131 and thereby accelerating the ageing process. The breakdown mechanism of oils has changed due to ageing with copper. In this paper, breakdown comparison of transformer oils are analyzed with different insulating oils like un-aged and aged. Transformer oils breakdown voltage test under 0.9 mm gap spacing and the average breakdown voltage behaviour, field behaviour, maximum field at the needle tip transformer oils are also investigated.