Insulating Mineral Oil Research Articles

Fluid-thermal analysis of the cooling capacity of a commercial natural ester in a power transformer

The low fire safety and high environmental impact of the mineral oil of the power transformers are two factors that have a negative influence in the goals of maximizing the return on investment and lowering the total costs associated with power system operation. Thus, many studies about alternative liquids (natural and synthetic esters, silicon oil) are being developed worldwide. This paper studies the cooling characteristics of a commercial natural ester in comparison with a traditional insulating mineral oil. A fluid-thermal simulation is done in a 3D-model of a partial cross-section of a single phase of a three-phase power transformer. The comparison of temperatures, velocities and dimensionless numbers (Re and Pr) of both fluids allows concluding that the direct substitution of the traditional liquid by the new one is not possible since the cooling characteristics of the latter one is quite worse than the first one.

Enhancing gas formation theory assessment in power transformers by using decision tree transparency and new guess into decomposition temperatures of insulating mineral oil

Enhancing gas formation theory assessment in power transformers by using decision tree transparency and new guess into decomposition temperatures of insulating mineral oil

Room-temperature SnO2-based sensor with Pd-nanoparticles for real-time detection of CO dissolved gas in transformer oil

SnO2 and Pd nanoparticles (NPs) were synthesized by hydrothermal method and sol-gel, respectively. A paste formed by tin dioxide NP and PVDF was deposited as thick film on alumina substrates through screen printing method and decorated with Pd on surface. The morphology and structure of the samples were investigated by Scanning Electronic Microscopy (SEM), X-Ray Diffraction (XRD) and Raman Spectroscopy. The SEM images show SnO2 nanoparticles with rod shapes and 10–15 nm of diameter size and Pd spherical nanograins with 15–35 nm of diameter. XRD analysis identifies rutile structure for SnO2 powder and cubic structure for Pd NP. To investigate the gas sensing property of the SnO2:Pd nanostructured composite, the electrodes were immersed in an insulating mineral oil, in a closed system where different gas concentration of monoxide carbon (CO) were injected into the headspace and then dissolved into oil, according to Ostwald coefficient. All measurements were carried out at room temperature using a concentration range from 50 to 500 ppm (in headspace). The electric characterization showed that our SnO2-based sensor had change its resistance in a lower concentration of dissolved gas, ∼13.3 ppm of CO, into the mineral oil, indicating its potential use for real time monitoring of transformers.

Variability of the Acoustic Emission Signals Generated by Partial Discharges in Mineral Oil

The main purpose of the presented research is to investigate the partial discharge (PD) phenomenon variability under long-term AC voltage with particular consideration of the selected physical quantities changes while measured and registered by acoustic emission method (AE). During the research a PD model source generating surface discharges is immersed in the brand new insulation mineral oil. Acoustic signals generated by the continuously occurred PDs within 168 hours are registered. Several qualitative and quantitative indicators are assigned to describe the PD variability in time. Furthermore some long-term characteristics of the applied PD model source in mineral oil, are also presented according to acoustic signals emitted by the PD. Finally various statistical tools are applied for the results analysis and presentation. Despite there are numerous contemporary research papers dealing with long-term PD analysis, such complementary and multiparametric approach has not been presented so far, regarding the presented research. According to the presented research from among all assigned indicators there are discriminated descriptors that could depend on PD long-term duration. On the grounds of the regression models analysis there are discovered trends that potentially allow to apply the results for modeling of the PD variability in time using acoustic emission method. Subsequently such an approach may potentially support the development and extend the abilities of the diagnostic tools and maintenance policy in electrical power industry.

Stratifying transformer defects through modelling and simulation of thermal decomposition of insulating mineral oil

The current work aims to propose an adequate thermodynamic model, in addition to proposing and evaluating two composite models for the thermal decomposition of insulating mineral oil (IMO), considering that the models based on classical diagnostic methods do not have the ability to satisfactorily reproduce empirical data. The simulation results obtained using the proposed model showed better agreement with the presented data than the results obtained using classical models. The proposed model was also used in the development of a phenomenological based diagnostic method. The characteristics of this new phenomenological proposal and the classical diagnostic methods of dissolved gas analysis are compared and discussed; the proposed method showed better performance when compared to Rogers, Doernenburg, or IEC and equivalent performance to Duval triangle method commonly used in this field of knowledge. The general procedure for applying the new diagnostic method is also described. In order to account for the event's dynamics, the suggested model in particular made it feasible to replicate intermediate scenes of equilibrium C(s). Compared to the findings from the classical models found in the literature, the two-dimensional simulation results generated with this model demonstrated a better agreement with the actual data.

Effective Electrical Properties and Fault Diagnosis of Insulating Oil Using the 2D Cell Method and NSGA-II Genetic Algorithm.

In this paper, an experimental analysis of the quality of electrical insulating oils is performed using a combination of dielectric loss and capacitance measurement tests. The transformer oil corresponds to a fresh oil sample. The paper follows the ASTM D 924-15 standard (standard test method for dissipation factor and relative permittivity of electrical insulating liquids). Effective electrical parameters, including the tan δ of the oil, were obtained in this non-destructive test. Subsequently, a numerical method is proposed to accurately determine the effective electrical resistivity, σ, and effective electrical permittivity, ε, of an insulating mineral oil from the data obtained in the experimental analysis. These two parameters are not obtained in the ASTM standard. We used the cell method and the multi-objective non-dominated sorting in genetic algorithm II (NSGA-II) for this purpose. In this paper, a new numerical tool to accurately obtain the effective electrical parameters of transformer insulating oils is therefore provided for fault detection and diagnosis. The results show improved accuracy compared to the existing analytical equations. In addition, as the experimental data are collected in a high-voltage domain, wireless sensors are used to measure, transmit, and monitor the electrical and thermal quantities.

Partial Discharge Detection in Pressboards Immersed in Mineral Insulation Oil With Quantum Well Hall Effect Magnetic Field Sensors

Insulation degradation may cause inefficient and faulty operation of transformers. The insulation failures in transformers mostly start with a Partial Discharge (PD) event. For both operational and cost reasons to ensure the best performance and functionality of transformers, early detection of PD events is of great importance. In this paper presents a novel PD detection technique by using a highly sensitive Quantum Well Hall Effect (QWHE) magnetic field sensor and compare the findings with an off-the-shelf silicon magnetic field transducer. The investigation of the QWHE for high voltage engineering problem such as PD detection is given first time in this paper. The aim of the study is to detect PD activity in pressboards immersed in mineral insulation oil experimentally using a new QWHE sensor. The measured experimental data from both sensors are decomposed by Empirical Mode Decomposition (EMD) and Wavelet Decomposition (WD) methods, and PD signals are analyzed comparatively. The results show that QWHE sensors provide more accurate and noise free measurements allowing early and more accurate PD detections.

Rešavanje problema eksploatacije transformatora sa korozivnim sumporom desulfurizacijom ulja primenom jake neorganske baze i organskog rastvarača

Most power transformer failures are associated with the presence of corrosive sulfur compounds in mineral insulating oil, of which dibenzyl disulfide (DBDS) is the best known and most widespread corrosive sulfur compound. The oil of failed transformers usually contained DBDS, a compound with a pronounced affinity for the formation of copper (I) sulfide (Cu2S). Copper (I) sulfide is a compound that does not dissolve in oil, conducts electricity, and can be deposited on the paper insulation or copper conductor of the transformer. Created conductive paths between the windings can initiate turn-to-turn breakdown and failure of the transformer. Several technological procedures have been developed as a solution to oil corrosivity. The application of desulfurization technology developed by the Electrical Engineering Institute "Nikola Tesla" enables the efficient removal of DBDS and aging products from mineral insulation oils.

Partial Discharge Detection in Pressboards Immersed in Mineral Insulation Oil with Quantum Well Hall Effect Magnetic Field Sensors

Partial Discharge Detection in Pressboards Immersed in Mineral Insulation Oil with Quantum Well Hall Effect Magnetic Field Sensors

Analysis of Polarization and Depolarization Currents of Samples of NOMEX®910 Cellulose–Aramid Insulation Impregnated with Mineral Oil

The article presents results of laboratory tests performed on samples of NOMEX®910 cellulose–aramid insulation impregnated with Nynas Nytro 10× inhibited insulating mineral oil using the polarization and depolarization current analysis method (PDC Method). In the course of the tests, the insulation samples were subjected to a process of accelerated thermal degradation of cellulose macromolecules, as well as weight-controlled dampening, thereby simulating the ageing processes occurring when using the insulation in power transformers. The effects of temperature in the ranges typical of normal transformer operation were also taken into account. On the basis of the obtained data, the activation energy was then fixed together with dominant time constants of cellulose–aramid insulation relaxation processes with respect to the temperature and degree of moisture, as well as thermal degradation of cellulose macromolecules. It was found that the greatest and predictable changes in the activation energy value were caused by the temperature and the degree of moisture in the samples. A similar conclusion applies to the dominant time constant of the relaxation process of cellulose fibers. Degree of thermal degradation samples was of marginal importance for the described parameters. The final outcome of the test results and analyses presented in the article are regression functions for the activation energy and the dominant time constants depending on the earlier listed parameters of the experiment, which may be used in the future diagnostics of the degree of technical wear of cellulose–aramid insulation performed using the PDC method.

Simulação matemática do transporte de óleo mineral isolante na zona vadosa considerando a constante dielétrica e o índice de plasticidade

Acidentes ou falhas em equipamentos elétricos em subestações de energia podem resultar em vazamentos de óleo mineral isolante (OMI), ocasionando contaminação do solo e da água subterrânea. A modelagem matemática é uma importante ferramenta para a previsão dos impactos destes vazamentos e para a determinação do tempo de resposta das ações emergenciais. Um dos simuladores mais utilizados neste processo é o Hydrocarbon Spill Screening Model (HSSM), distribuído pela U.S.EPA. Contudo, esse e outros modelos baseados na equação de Nutting (1934), não consideram o efeito da constante dielétrica na determinação da mobilidade dos contaminantes. O objetivo deste estudo contemplou a avaliação da influência da constante dielétrica na modelagem matemática de OMI e analisou a simulação de derramamento de OMI em cinco subestações de energia elétrica com o simulador Hydrocarbon Spill Screening Model (HSSM). Os resultados indicaram que em solos constituídos de argilas expansivas, a inclusão da constante dielétrica na modelagem matemática do transporte na zona vadosa pode representar um acréscimo de até três ordens de grandeza à condutividade hidráulica ao OMI, influenciando as ações de contingenciamento ambiental ponderadas sobre essas estimativas.

A relevant condition monitoring of corrosive sulphur deposition on the windings of oil-filled electrical transformers

The purpose of this study is to determine whether the currently applied condition monitoring (CM) techniques are sufficient and effective for early detection of copper corrosion fault in transformers and to establish a more relevant CM technique for early detection of such fault. In this study, experimental work is carried out by applying appropriate methods on different commercial insulating mineral oils for the detection and identification of additional related by-products of copper corrosion process, if any. The major finding of this experimental investigation includes identification of additional by-products, which could be useful to establish a more effective CM technique. Furthermore, the role of sulphur compounds in copper corrosion fault is considered, and a relevant reaction mechanism of formation CSD is developed based on the findings of the related by-products. It is concluded that, the application of a relevant CM technique is necessary for establishing a cost-effective condition based maintenance (CBM) to minimize the economic losses, hazardous effects on human life and the environment.

Analysis of the application of Insulating Vegetable Oil in electric power distribution transformers


 
 
 Distribution transformers are present in large quantities in the electrical system, in addition to being essential equipment for delivering quality and reliable energy to consumers. This distribution transformers have a dielectric insulation and refrigeration system, with Insulating Mineral Oil (IMO) being the most used. However, the large-scale use of IMO entails a very high environmental risk, because in addition to its fossil origin (petroleum), it also has low biodegradability and is highly toxic and polluting to the environment. In view of this, substitution alternatives for the IMO began to be sought, where, over the years and with technological advances, Insulating Vegetable Oil (IVO) with characteristics similar to the IMO emerged, in addition to being highly biodegradable and providing an alternative sustainable development for the construction of transformers. Thus, the objective of this work is to carry out an analytical study about the characteristics and benefits of using the vegetable fluid for the equipment and for the environment, in addition to comparing the efficiency and cost parameters of IVO and IMO according to current standards. As a contribution, this paper seeks to provide a broad theoretical foundation on IVO and IMO in order to provide conceptualization to agroenergy researchers.
 
 

ANÁLISE DE DESEMPENHO DO TRANSFORMADOR DE POTÊNCIA ISOLADO A ÓLEO VEGETAL EM RELAÇÃO AO TRANSFORMADOR DE POTÊNCIA ISOLADO A ÓLEO MINERAL

A utilização dos transformadores de potência é imprescindível para a continuidade de operação do sistema elétrico. Um dos componentes importantes do transformador é o óleo isolante, responsável por seu isolamento elétrico interno e sua refrigeração. Com a crescente preocupação ambiental, viu-se a necessidade de buscar novas alternativas para o sistema de isolamento dos transformadores, uma vez que o óleo mineral isolante é proveniente do petróleo, considerado tóxico, nocivo ao ambiente e de baixa biodegradabilidade. Pesquisas atuais mostraram que o óleo vegetal isolante é uma alternativa a ser considerada por empresas do setor elétrico, por ser um fluido biodegradável, com ponto de fulgor e combustão elevados, sendo caracterizado como um fluido com maior segurança. Este trabalho analisa as vantagens técnicas e operacionais da utilização do óleo vegetal isolante comparado com o óleo mineral isolante. São verificadas suas características físico-químicas, implicações ambientais em caso de derramamento, bem como implicações de segurança quanto ao ambiente de instalação. Conclui-se que o óleo vegetal apresenta vantagens na maioria dos aspectos operacionais e ambientais e também nos requisitos de instalação para segurança e confiabilidade operacionais.

Streaming Electrification Phenomenon of Electrical Insulating Oils for Power Transformers

The subject matter of this study was the problem of the ECT (electrostatic charging tendency) of mineral insulation oils during their flow. The electrostatic charges generated may lead to partial discharges, and as a consequence, to the breakdown of a power transformer insulation system. In this study, the results of the ECT of mineral oils used in transformers were compared. The method of streaming electrification of insulation liquids using a flow-through system was used. The influence of flow speed, temperature, and the pipe material on the values of the electrification current and volume charge density qw were analyzed. The results obtained in this study should be taken into account regarding the operation of power transformers.

Streamer evolution arrest governed amplified AC breakdown strength of graphene and CNT colloids

The present paper explores the concept of improving the AC dielectric breakdown strength of insulating mineral oils by the addition of graphene or carbon nanotubes (CNTs) to form stable dispersions. Experimental observations of graphene and CNT nano-oils show that not only improved average breakdown voltage, but also significantly improved reliability and survival probabilities of the oils under AC high voltage stressing is achieved. Improvement of the tune of ∼70–80% in the AC breakdown voltage of the oils has been obtained. The study examines the reliability of such nano-colloids using a two-parameter Weibull distribution and the oils show greatly augmented electric field bearing capacity. The fundamental mechanism responsible for such observed outcomes is reasoned to be delayed streamer development and reduced streamer growth rates due to effective electron scavenging. A mathematical model based on the principles of electron scavenging is proposed to quantify the amount of electrons scavenged by the nanostructures.

Study of frequency domain dielectric properties of vegetable oil and mineral oil transformer

To study the properties of vegetable oil transformer, the mineral and vegetable insulation oil two transformers with the same parameters are studied using the frequency domain spectroscopy (FDS) method. The complex capacitance and the dielectric loss factor are tested by the insulation diagnostic equipment IDAX300, these parameters can reflect the insulation properties of the transformer. The experimental results show that properties of vegetable oil transformer are different to the mineral. The complex capacitance and the dielectric loss factor tanδ of vegetable oil transformer are higher than those of mineral oil transformer, and the moisture content in vegetable oil is higher than that in mineral oil. The test results are also emphatically analysed, which ultimately laid a theoretical foundation for large-scale operation of vegetable oil transformers.

Polyurethane Foams Derived from Vegetable Oil Used in the Adsorption of Polychlorinated Biphenyls Present in Insulating Mineral Oil

PCBs, polychlorinated biphenyls (polychlorinated biphenyls), are the generic names given to the class of organochlorine compounds resulting from the reaction of the biphenyl group with anhydrous chlorine in the presence of a catalyst. They are toxic, persistent, bioaccumulative and pose the risk of causing harm to human health and the environment. Large quantities of PCBs were produced in several countries between 1927 and 1977. In the United States the prohibition occurred in 1977. Due to high toxicity, production and marketing of PCBs have been banned worldwide since 1980. It was carried out at the Chemistry Institute of Sao Carlos—University of Sao Paulo, and developed a procedure for decontamination of mineral insulating oil containing PCBs values above 50 mg/kg. In the procedure, the contaminated oil was passed by percolation in a column containing polyurethane foam derived from vegetable oil, produced by the Laboratory of Analytical Chemistry and Polymer Technology (GQATP), thus obtaining a 55% reduction in the levels of PCBs.

Разработка и опробование методики идентификации элементного состава осадков, образующихся в изоляционных минеральных маслах при эксплуатации высоковольтного оборудования

Разработка и опробование методики идентификации элементного состава осадков, образующихся в изоляционных минеральных маслах при эксплуатации высоковольтного оборудования

Application of Mathematical Interpolation Technique in Nano Based Insulating Mineral Oil

In general, insulating oil serves as an insulation and cooling medium of power transformers and different High Voltage (HV) application. The properties of insulating oil like breakdown voltage (BDV), viscosity, flash point and fire point are enhanced by adding of different additives in an optimal way. In this work, a mathematical model has been developed by using Lagrange interpolation technique for predicting the critical properties values in different volume concentrations (in Vol %). The predicted critical properties are compared with the set of measured data. Based on this approach, accuracy of predicted value has been obtained in between the two available measured data in two known different volume concentrations. From the volume concentrations (0-0.01%), the error seems to be negligible. Hence, Lagrange interpolation technique is considered as a reliable technique for predicting the intermediate value for different concentrations of nano powder doped insulating oil used in different HV power apparatus.