Electrical ageing studies of polymeric insulation for power cables (estudo do envelhecimento eléctrico do isolante polimérico de cabos eléctricos

Dissertação apresentada para obtenção do Grau de Doutor em Engenharia Física - Física Aplicada pela Universidade Nova de Lisboa, Faculdade de Ciências e Tecnologia

Ação adsorvente da bauxita sobre óleo isolante novo

Samples of new insulating mineral oil, after contact with bauxite, were analyzed by visible spectrophotometry, impedance spectroscopy and their total acidity index was measured. The results of these analyses were compared to samples of new insulating mineral oil, which had not been in contact with bauxite. The comparison demonstrated that the bauxite didn't reduce the insulating capacity of the mineral oil and thus could be used to treat the oil in situ during the operation of an electric transformer.

Determinação de ascarel em óleo isolante de transformadores

The contamination level of silicon oil used as insulation liquid in high-voltage transformers by ascarel (PCBs) is above those permitted by the Brazilian law. Thus new techniques able to detect ascarel, with low operational costs, are very attractive. The present work proposes an analysis of the contamination levels of silicon oil using the following techniques: naphthalene anion radical reaction for ascarel dechlorination; and potentiometry with an ion-selective electrode for chloride ion determination. The data obtained with the proposed methodology agree well with those from the official methodology, (method IEC 61619).

Caracterização de bauxita ativada antes e depois da saturação com óleo mineral isolante

A characterization of activated bauxite and of activated bauxite impregnated with insulating mineral oil was made. The activated bauxite is used as adsorbent material in percolators during the regeneration of insulating mineral oil. After regeneration an insulating mineral oil is obtained with physical and chemical characteristics similar to those of the new oil. Moreover, saturated activated bauxite impregnated with insulating mineral oil is also produced. It is a dangerous residue according to NBR 10004 (Class I) and, thus, harmful to the environment. An alternative use of this waste in the ceramic industry is discussed.

Avaliação de diferentes métodos para a determinação de cobre em óleo mineral isolante por espectrometria de absorção atômica com forno de grafite

This aim of this work was to compare two methods for copper determination in insulating oils from power transformers by GFAAS. The first method was extraction induced by emulsion breaking, which determined the preconcentration of copper in an aqueous solution and exhibited a limit of quantification of 0.27 µg L-1. Also, a second method based on the direct introduction of samples into GFAAS in the form of detergent emulsions, prepared with Triton X-114 and HNO3, was investigated. In this case, the limit of quantification was 1.7 µg L-1. Seven samples of used oils were successfully analyzed by both methods.

AVALIAÇÃO DAS NORMAS DE ENSAIO APLICADAS NA QUANTIFICAÇÃO DE PCBs EM ÓLEO ISOLANTE

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.

Sistema de sensoriamento eletromagnético utilizado para detecção da contaminação do óleo isolante do motor no método de elevação artificial do tipo bombeio centrífugo submerso

In the artificial lift method by Electrical Submersible Pump (ESP), the energy is transmitted for the well´s deep through a flat electric handle, where it is converted into mechanical energy through an engine of sub-surface, which is connected to a centrifugal pump. This transmits energy to the fluid under the pressure form, bringing it to the surface In this method the subsurface equipment is basically divided into: pump, seal and motor. The main function of the seal is the protect the motor, avoiding the motor´s oil be contaminated by oil production and the consequent burning of it. Over time, the seal will be wearing and initiates a contamination of motor oil, causing it to lose its insulating characteristics. This work presents a design of a magnetic sensor capable of detecting contamination of insulating oil used in the artificial lift method of oil-type Electrical Submersible Pump (ESP). The objective of this sensor is to generate alarm signal just the moment when the contamination in the isolated oil is present, enabling the implementation of a predictive maintenance. The prototype was designed to work in harsh conditions to reach a depth of 2000m and temperatures up to 150°C. It was used a simulator software to defined the mechanical and electromagnetic variables. Results of field experiments were performed to validate the prototype. The final results performed in an ESP system with a 62HP motor showed a good reliability and fast response of the prototype.

Fibras de sisal (Agave sisalana) como isolante térmico de tubulações

In the last decades there was a significant increasing of the numbers of researchers that joint efforts to find alternatives to improve the development of low environmental impact technology. Materials based on renewable resources have enormous potentials of applications and are seen as alternatives for the sustainable development. Within other parameters, the sustainability depends on the energetic efficiency, which depends on the thermal insulation. Alternative materials, including vegetal fibers, can be applied to thermal insulation, where its first goal is to minimize the loss of energy. In the present research, it was experimentally analyzed the thermal behavior of fiber blankets of sisal (Agave sisalana) with and without surface treatment with oxide hidroxide (NaOH). Blankets with two densities (1100/1200 and 1300/1400 g/m2) were submitted to three rates of heat transfer (22.5 W, 40 W and 62.5 W). The analysis of the results allowed comparing the blankets treated and untreated in each situation. Others experiments were carried out to obtain the thermal conductivity (k), heat capacity (C) and the thermal diffusivity (α) of the blankets. Thermo gravimetric analyses were made to the verification of the thermal stability. Based on the results it was possible to relate qualitatively the effect of the heat transfer through the sisal blankets subjected to three heat transfer rates, corresponding to three temperature values (77 °C, 112 °C e 155 °C). To the first and second values of temperature it was verified a considerable reduction on the rate of heat transfer; nevertheless, to the third value of temperature, the surface of the blankets (treated and untreated) in contact with the heated surface of the tube were carbonized. It was also verified, through the analyses of the results of the measurements of k, C e α, that the blankets treated and untreated have values near to the conventional isolating materials, as glass wool and rock wool. It could be concluded that is technically possible the use of sisal blankets as constitutive material of thermal isolation systems in applications where the temperature do not reach values greater than 112 ºC

Estudo de um isolante térmico para tubos fabricado em material compósito

It presents a new type of insulation for ductwork hot water, which can be used in solar systems for heating water, which consists of a composite of different compositions based on plaster, cement and EPS ground, palm and water. This composite has as its main features easy assembly and manufacturing processes and low cost. Comparative results will be presented on the tests of materials and thermal tubes proposed. Four formulations were used to manufacture tubes with three diameters 70, 65 and 42mm. It was also tested conventionally used for elastomeric foam insulation to 110 ° C, for a comparative analysis with the composite pipe insulator proposed. It will demonstrate that the cost of manufacturing of such tubes is competitive with alternative elastomeric foam tested, but results of the composite tube to the temperature range studied, are lower. Another drawback of the composite insulator tube is its large mass. It would be important to test such a composite for greater levels of temperature to a diagnostic technique competitive with conventionally used insulators. A positive factor of using the proposed composite-tube would be the recycling of EPS so damaging to the environment, representing an environmentally friendly application of science

Efeito da rampa isolante na insensibilização de frangos de corte e seus reflexos sobre o bem-estar e qualidade da carcaça

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Monitoramento da degradação térmica de óleo mineral isolante de transformador utilizando espectroscopia de absorção e fluorescência UV-Vis

Pós-graduação em Engenharia Elétrica - FEIS

Análise do enxofre corrosivo em óleo mineral isolante e remoção do dibenzil dissulfeto com nanotubos de carbono baseados em matriz metálica

Falhas inesperadas em transformadores levaram a identificação da formação de sulfeto de cobre, depositado sobre os condutores, avaliando-se da presença qualitativa de enxofre corrosivo resultando na alteração da norma brasileira ABNT NBR 10505, que avalia a presença de enxofre corrosivo em óleo mineral, alterando-se o tempo e a temperatura de ensaio para 150 °C por 48 horas. Realizando-se a especiação química de compostos organosulfurados via cromatografia gasosa acoplada a espectrometria de massas, onde foram encontrados 13 compostos sulfurados no óleo Nynas e 9 compostos no óleo da Petrobras, sendo o dibenzil dissulfeto (DBDS) o de maior concentração, encontrado apenas no óleo Nynas. Para realizar a determinação da presença do DBDS em óleo mineral isolante foi desenvolvido um método através de cromatografia gasosa acoplada a espectrometria de massas, e por este método foi possível quantificar o teor de DBDS em amostras de OMI oriundas de transformadores de potência. Foi avaliado o processo de passivação do cobre por benzotriazol e tolutriazol, utilizados como aditivos anticorrosivos no núcleo dos equipamentos elétricos, verificando-se que o efeito da adição agente de passivação torna-se ineficaz com o passar do tempo. A solução para a remoção de DBDS em óleo mineral foi a utilização de nanotubo de carbono baseado em matriz metálica (NTC/Al) como agente de remoção do DBDS. Verificou-se que o agente de adsorção foi capaz de efetuar a remoção total do DBDS do OMI até um volume de 4000 mL de óleo contaminado com DBDS.

Investigação da transição isolante-metal do CDM via algoritmos computacionais e estudo de nano-dispositivos orgânicos

Apresentamos neste trabalho um estudo teórico sobre polímeros orgânicos conjugados. É conhecido que estes sistemas, em geral semicondutores ou isolantes, sob dopagem química podem vir a adquirir propriedades elétricas de material condutor. E ainda, sob ação de campo elétrico, pequenos oligômeros podem apresentar comportamento equivalente ao de dispositivos usuais, mas com inúmeras vantagens como, por exemplo, tamanho extremamente reduzido (alguns nanômetros). Dessa forma no primeiro capítulo faremos uma breve introdução sobre polímeros orgânicos conjugados mostrando alguns resultados experimentais obtidos para o polímero 4-dicianometileno-4,4-ciclopenta [2,1-b: 3,4b’] ditiofeno – CDM, que é o objeto central de estudo desta dissertação. O capítulo 2 trata dos métodos quânticos utilizados. Citaremos a Teoria de Hartre-Fock (HF) e suas derivações semi-empíricas. A técnica de Interação de configuração (CI) e a Teoria do Funcional da Densidade (DFT) também serão tratadas neste capítulo. O capítulo 3 é dedicado a descrever as características de alguns dispositivos usuais como diodos e transistores. Aqui o fundamental é entender a composição, o funcionamento e principalmente, como se comportam suas curvas características corrente versus voltagem (IxV). Citaremos ainda alguns dispositivos eletrônicos extremamente pequenos. No capítulo 4 começa nossos resultados e discussões referentes a análise da transição isolante-metal em CDM sob ação de dopagem. Primeiramente a nível semiempírico, obtivemos a caracterização ótica de oligômeros de CDM neutro e na presença de defeitos conformacionais do tipo bipólarons negativo e positivo. Partindo de geometrias otimizadas via métodos AM1 e PM3 obtivemos o espectro de absorção para sistemas com e sem carga. A nível Hartree-Fock calculamos a Estrutura de Bandas e a Densidade de Estados (DOS) para o PCDM no estado neutro e dopado. O cálculo da DOS e da Dispersão foram realizados através de programas computacionais desenvolvidos aqui no Grupo de Física de Materiais da Amazônia (GFMA). Apresentamos ainda neste capítulo o espectro de absorção teórico para oligômeros de CDM com diversas configurações com geometrias totalmente otimizadas pelo DFT. No capítulo 5 temos os resultados relativos à análise de nanodispositivos baseados em tetrâmeros de CDM com e sem carga. As curvas do deslocamento de carga versus voltagem apresentam características de curvas de dispositivos usuais. Analisamos também o espectro de absorção teórico dos nanodispositivos para valores de tensão nula e em pontos de saturação de corrente nas regiões direta e reversa.

Estudo da interação entre camadas de super-redes supercondutor/isolante/ferromagneto

Pós-graduação em Ciência e Tecnologia de Materiais - FC