Abstract Mineral insulating oil (MIO) and natural ester insulating (NEI) oil are used in power transformers as an insulating fluid, while elastomeric seals are usually composed of nitrile rubber (NBR). The proprieties of these seals can change in contact with insulating oil. Variation in sealant properties is undesirable in power transformers. In this work, the variation of some elastomer properties was evaluated before and after accelerated aging in MIO and NEI. The developed elastomeric compositions showed variation in the stress and strain at break after the aging test. It also appeared that MIO penetrated the samples and that dioctylphthalate (DOP) migrated or was extracted into MIO and NEI. The samples vulcanized with peroxide showed better results than those vulcanized with sulfur.

ABSTRACT Power transformers are essential equipment in the electric energy generation and distribution processes and are usually chosen with paper and insulating fluids. Insulating fluids have a dual function of insulation and heat exchange. Proper sealing of this equipment is essential to prevent leaks of the insulating fluid, which can cause a reduction in the life of the transformer, as well as environmental problems. Different compositions were formulated in nitrile rubber (NBR) compatible with those used as seals in power transformers, with different acrylonitrile contents (35 and 44%) and dicumyl peroxide (6.0 / 8.0 and 10.0 phr). The aging tests were conducted systematically under three conditions: insulating mineral oil (IMO), insulating natural ester (INE) soy and corn, traditionally used as insulating fluid in power transformers. The effects of the thermal aging of nitrile rubber on IMO and ENI, as well as the effects of the cross-linking content of the chains were studied using characterization methods such as oscillating disk rheometry, swelling, variation in mass, volume and Shore A hardness. The density of crosslinks and the average molar mass between the links were also determined by the Flory-Rehner theory. Changes in physical properties during the aging process were analyzed and compared. It was possible to observe a different behavior in the sealing elastomers when aged in IMO and ENI influenced by the crosslinks and acrylonitrile contents in the samples.

RESUMO Os transformadores de potência são equipamentos essenciais nos processos de geração e distribuição de energia elétrica, e são, normalmente, isolados com papel e fluidos isolantes. Os fluidos isolantes têm dupla função: isolamento elétrico do sistema refrigeração por troca térmica. A vedação adequada desse equipamento é fundamental para que não ocorra vazamento do fluido isolante, que pode causar redução do tempo de vida útil do transformador, bem como problemas ambientais. Neste artigo são apresentados resultados obtidos para formulações de borracha nitrílica (NBR) preparadas com diferentes concentrações de peróxido de dicumila 40% em Carbonato de cálcio (6,0/ 8,0 e 10,0 phr) e teores de acrilonitrila (35 e 44%). Os ensaios de envelhecimento foram conduzidos sistematicamente sob três condições: óleo mineral isolante (OMI), éster natural isolante (ENI) soja e milho, tradicionalmente empregados como fluido isolante nos transformadores de potência. Os efeitos do envelhecimento térmico da NBR em OMI e ENI, bem como os efeitos na formação das ligações cruzadas das cadeias foram estudados usando métodos de caracterização como reometria de disco oscilatório, inchamento em solvente, variação de massa, volume e dureza Shore A. Também foi determinada a densidade de ligações cruzadas e a massa molar média entre as ligações pela teoria de Flory-Rehner. Foi possível observar um comportamento diferente nos elastômeros de vedação quando envelhecidas em OMI e ENI influenciado pelo teor de ligações cruzadas e de acrilonitrila das amostras.

There are many processes capable of decontamination of polychlorinated biphenyls in several matrixes. The set of inputs, materials, operation conditions and efficiencies are wide. The base catalyzed dechlorination process shows application potential in great scale, mainly due mild chemical reaction conditions and low cost raw materials. The KPEG is a familiar process of base catalyzed dechlorination. This decontamination treatment was developed mainly on mineral insulating oil. Few information is found related to process residues, usually in reaction sludge means, limited to inform that its destination must fulfill specific territorial laws. In these work KPEG treatment process was performed on decontamination of mineral insulating oils containing between 200 and 330 ppm of polychlorinated biphenyls to evaluation of reaction residues and of the decontamination percentage. Chemical characterization of these residual material allows achievement of important information to explore procedures for recovery, regeneration and/or right disposal. The analysis performed on the residues showed the presence of reaction products containing unsaturation, absents on neat polyethylene glycol, possible organic complexes products with alkali metal as also the presence of chloride ions. In oil was verified the presence of less chlorinated biphenyls, probably formed by partial dechlorination of highly chlorinated biphenyls.

Hexagonal boron nitride (h-BN), graphite analogous structure, has many interesting applications due to its excellent thermal, electrical and mechanical properties. In this study, different routes of liquid exfoliation using solvent and ultrasound were used to obtain two-dimensional (2D) nanosheets of h-BN. The efficiency of the exfoliative routes was evaluated by Transmission electron microscopy (TEM) and UV-Vis spectroscopy. Results demonstrated that the technique was effective in the exfoliation of h-BN bulk and that the solvent's choice, considering an optimum surface tension of the solvent-solute system, and the rotation of the centrifugation in the selection of the exfoliated nanosheets, are crucial for the performance of the technique. The most promising exfoliation route has been found to be the dispersion of h-BN in solvent mixture (20% IPA in water) for 3 h on ultrasound, followed by centrifugation at 1500 or 3000 rpm.

Abstract Insulating paper holds significant importance in the insulation system of power transformers, and thus, its degradation is the subject of many studies. A successful evaluation of the degradation rate of such paper contributes to reducing downtime and avoiding equipment failure. In this work, samples of thermally upgraded paper were thermally aged in insulating natural ester (INE) and insulating mineral oil (IMO) and were evaluated by degree of polymerization (DP) and FTIR-ATR. It was possible to identify characteristic bands of dicyandiamide, an inhibitory compound of the thermal degradation of the paper, and to establish a correlation between the decrease in DP and the consumption of dicyandiamide during aging, which was observed to develop in three distinct steps for both IMO and INE.

Polychlorinated biphenyls (PCBs) were widely used between 1940 and 1970 as an insulating fluid for transformers and capacitors. However, they are bioaccumulative and potentially carcinogenic and, according to the 2001 Stockholm Convention, must be eliminated by 2025. In Brazil, they have been gradually eliminated but contaminated equipment remains. The Brazilian official standard for PCBs content in oil analysis is the ABNT NBR 13882 and there is also the IEC 61619 International Standard, both based on GC-ECD quantification. This work identified the inefficiency of these analytical methods and highlights potential failures which generated discrepancies on quantification of these contaminants. It was observed that the IEC 61619 is superior to ABNT NBR 13882 in analytical criteria, but has problems with the inefficiency of the adsorbent material used in pretreatments for removal of oxidation products from oil where these adsorbents adsorbed some PCBs molecules, causing errors in quantification.

Thermal and spectroscopic analyses of essential oil extracted from Siparuna guianensis Aublet, an aromatic plant belonging to medicinal ethnobotany family Siparunaceae, were carried out. The plant is known throughout the North and Northeast of Brazil by the name negramina and has wide application as a natural insect repellent. Thermogravimetric analyses were correlated with the Arrhenius Equation to provide kinetic parameters of evaporation, including activation energy and frequency factor. Differential scanning calorimetric analysis showed the presence of an exothermic oxidation peak, probably as a result of transformations and decomposition of the solid structure before melting.

A borracha natural é muito empregada na confecção de equipamentos de proteção individual e coletiva para o setor elétrico devido à sua excelente flexibilidade e isolamento elétrico. Para garantir a segurança dos eletricistas, os equipamentos são testados periodicamente, por ensaios elétricos. Durante esses ensaios ocorrem descargas corona que ionizam o ar, gerando ozônio, que pode reagir com a borracha natural mudando suas características iniciais. Neste trabalho são apresentadas as alterações provocadas pela exposição ao ozônio, em concentração medida durante os ensaios elétricos, nos equipamentos confeccionados em borracha natural. As amostras foram testadas com e sem tensão mecânica e avaliadas por microscopia e ensaios mecânicos. Foi observada alteração superficial nas amostras sem tensão mecânica, para as amostras tensionadas houve aparecimento de fissuras macroscópicas e decréscimo na resistência mecânica.

Natural rubber is used to manufacture line-life equipment due to its insulating and flexibility characteristics. In order to provide safety to lineman, these pieces of equipment are periodically submitted to electrical maintenance tests. During these tests, corona discharges occur generating ozone gas which can react with natural rubber, thus ageing it and affecting its initial characteristics. This study shows changes caused by ozone exposure with concentrations prevailing during electrical tests in equipment made of natural rubber. The samples were tested with and without mechanical deformation and evaluated by microscopy and mechanical properties. Superficial changes were observed in samples which were not exposed to mechanical stress, while for mechanically stressed samples there were macroscopic cracks and decrease in the mechanical properties.

No setor elétrico, a borracha natural (BN) tem sido amplamente utilizada na confecção de ferramentas isolantes. Esses são itens essenciais para a segurança e proteção de trabalhadores da área de manutenção de redes de distribuição de energia elétrica. A boa conservação dessas ferramentas deve ser assegurada com o objetivo de garantir o isolamento elétrico e resistência mecânica adequados, portanto a avaliação dos processos de degradação se torna importante. Neste trabalho duas formulações de borracha natural comerciais, utilizadas na confecção de equipamentos de proteção coletiva (EPC's), foram caracterizadas por envelhecimento térmico, ensaios mecânicos, termogravimétricos, análise termo-dinâmico mecânica, inchamento e extração.

Electrical engineering sector make use of natural rubber to manufacture line-life equipment, utilized to promote safety and protection for those who work in the electrical networks maintenance. A good conservation of the equipment must be assured in order to guarantee the necessary insulation. Thus, the assessment of the degradation processes becomes important. In this study two commercial types of natural rubber commonly employed to produce collective protective equipment (CPE), were evaluated using artificial thermal ageing through mechanical, swelling tests, thermogravimetric analysis, dynamic mechanical thermal analysis and solvent extraction.