ASSESSMENT OF THE ELECTROMAGNETIC COUPLING BETWEEN LINES OF DIFFERENT VOLTAGES SHARING THE SAME STRUCTURES


Com a crescente demanda em áreas densamente povoadas e a consequente falta de espaço para corredores de linhas de transmissão exclusivas, o compatilhamento de estruturas entre linhas de transmissão e distribuição tornou-se uma solução comum especialmente em países emergentes. Essa prática causa a interação magnética entre essas linhas. Este artigo avalia o efeito da acoplamento eletromagnético entre uma linha convencional de 69kV e uma linha de distribuição aérea compacta(espaçador), avaliados em 11.4kV, compartilhando as mesmas estruturas. Simulações foram realizadas usando o software ATPDraw (Alternative Transient Program) considerando condições de estado estacionário, a ocorrência de falhas na linha de alta tensão e a energização da linha de transmissão.

Publicado em CIRED - 2017





MODELAGEM DE ALIMENTADOR E SUPRIMENTO DE REATIVO NA B.T. EM AMBIENTE SIMULINK®


Através de uma série de curvas de demanda aferidas para transformadores de distribuição, da implementação da estrutura física de um alimentador típico, da alocação de cargas e do cálculo dos elementos da rede, foi possível simular o comportamento dinâmico da tensão de fornecimento para com os consumidores e as características elétricas – tensão, corrente, potência ativa e reativa – do ramo principal do alimentador. Por fim, avaliou-se tecnicamente a implementação de compensação de reativo na baixa tensão.




SOFTWARE PARA ANÁLISE E DETECÇÃO DE FALHAS EM TRANSFORMADORES ATRAVÉS DE ENSAIOS DE IMPULSOS ATMOSFÉRICOS ESCALONADOS


O ensaios de descarga atmosférica em transformadores é de suma importância para avaliação da robustez do seu isolamento. Todavia, a análise dos resultados é objetivo de grandes discussões, entre fabricantes e clientes, frente a sua aprovação, ficando, com exceção dos casos de curto franco, a cargo do responsável técnico analisar as formas de onda.

Este artigo visa detectar a falha de isolamento em transformadores. Para isso realizou-se uma modelagem envolvendo um gerador de impulsos e um transformador em elementos distribuídos no software ATP®. Após isso, demonstrouse, através de simulações, que o curto circuito entre pequenos trechos da bobina geram consequências nos sinais adquiridos pelos instrumentos de medição e no fator de forma da onda. Por este motivo foi desenvolvido o software de análise promovendo, através de técnicas digitais, a acurácia no processo de avaliação dos resultados. Logo após a aquisição de dados através de osciloscópio é necessária uma sequência de procedimentos para obter o aumento da resolução vertical, redução de ruídos brancos além de cálculos dos parâmetros da forma de onda decorrente. De posse de um sinal mais fidedigno e com parametrizações bem definidas iniciou-se um processo de sincronismo dos impulsos reduzidos e plenos, modularizando as amplitudes e comparando ponto a ponto a deformação das ondas. Caso elas venham ocorrer, com consequências nos sinais de tensão e corrente simultaneamente, a probabilidade de falha de isolamento é elevada, provado pelo banco de ensaios realizados.

Publicado em SNPTEE - 2017





PROPOSITION OF AN ENGINEERING EQUIVALENT CIRCUIT FOR DISTRIBUTION TRANSFORMERS WIDEBAND MODELLING


Although they are major components on every distribution systems it is very difficult to model precisely medium voltage distribution transformers for transient studies. Considering that the design details of these transformers are only available to the manufacturers, which are the legal owners of the data, there is a strong lack of available data for the fulfillment of the most common recommended simulation models, some of them a kind of black box without any physical meaning.

The problem with models for general transient studies is that it is necessary to represent the equipment behavior for a wide frequency band. For this reason, it is necessary to the model to cover the nonlinear behavior of the iron-core, caused by magnetization and hysteresis and in some cases also to represent the frequency dependence of the leakage and magnetizing parameters. Very high-frequency transients require the accurate representation of all capacitances: to ground, between winding, intersection and even interturn.

The subject addressed in this paper is the determination of typical parameters for physically model medium voltage distribution transformers. Therefore, it is proposed an engineering equivalent circuit able to represent the transformer behavior for a large wide frequency band. Basically, the data for this model are based on the results of open, short circuit, lightning impulse and capacitance tests, carried out according to the precepts of the Brazilian National Standard NBR. As discussed, based on the results of the these tests, it is possible to assign values to each circuit component.

The model, introduced in this paper, is base on classic transformer lumped circuits, where the behavior of the all components try to represent a physical effect. The insertion of the leakage and self-capacitances considers the result of preliminary studies and an interactive method. The elements of the model considers values determined through testing, calculations and mathematical optimization methods. For a fast convergence of the results, these evaluation methods take into account initial values, based on the test results. For a large number of transformer constructive types, it is expected that the new model presents a larger band frequency fitness. The model validation was performed by the comparison of terminal impedance results obtained with the aid of FRANALYZER tests on transformers randomly chosen.

Publicado em ISH - 2017





RESTORATION OF OVERHEAD DISTRIBUTION NETWORKS BY MEANS OF TEMPORARY FAULT INDICATORS APPLICATION


This paper discusses a new methodology for restoration of overhead distribution networks based on the application of temporary fault indicators. Unlike the traditional fault indicators, these are installed on the network only after the occurrence of the fault. Placed in key points of the network after the disconnection of a feeder, for example, the temporary fault indicators can sense the fault current after the first manual reclosing attempt. Then, they send this information to a portable operation unit that helps to pinpoint the faulty branch of the network by showing the fault´s path in a map. All the devices communicate in a ZigBee mesh network and the fault indicators are georeferenced by GPS, which give their location in the network map.

Publicado em CIRED - 2017





ARTIFICIAL RAIN ACCELERATED AGING TEST OF HDPE PIN INSULATORS FOR MEDIUM VOLTAGE DISTRIBUTION IN BRAZIL


High density polyethylene (HDPE) is a polymer commodity widely used in manufacturing of polymer pin unsulators (PIN) for medium voltage distribution. The major problem to be faced in the use of HDPE by PIN manufacturers is their low resistence to oxidative degradation in the processing step and/or the prolonged exposure of HDPE-PIN to weathering and operation voltage for a long time. This work presents the experimental results on artificial ageing in Brazil. Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR/ATR) for chemical analysis. UV-visible diffuse reflectance spectroscopy (DRUV-Vis) for band-gap (Eg) evaluation, contact angle (CA) for determination of polar surface tension (γ^p) components and scanning electron microscopy (SEM) for morphological surface analysis were conducted on aged and unaged specimens. Chemical analysis results of ATR/FTIR confirmed the occurrence of oxidation reactions with significant increase of polar groups C=O at tested HDPE-PIN specimens. It was also observed a significantly increase on contribution of γ^p to the sufrace energy for all HDPE-PIN after 500 hours of accelerated aging time. The experimental values of Eg for aged commercial HDPE-PIN samples suggest that the accelerated aging test produces structural defects in commercial HDPE-PIN samples. The SEM micrographs reveal cracks, pinholes and degradation in the form of crustals and cavities after 3,500 hours of accelerated afing test in all HDPE-PIN specimens. The physicochemical performance of the aged commercial HDPE-PIN specimens analyzed in this work indicates that the HDPE resin was not formulated to be suitable for perfoming in tropical medium voltage environments.

Publicado em IEEE Transactions on Dielectrics and Electrical Insulation





METODOLOGIA DE DIAGNÓSTICO DE ISOLADORES DE PINO DE PORCELANA ATRAVÉS DA ANÁLISE DE CORRENTE DE FUGA


Este artigo aborda a investigação da correlação entre a corrente de fuga de isoladores de pino de porcelana classe 15 kV e importantes parâmetros relacionados à sua integridade, como nível de poluição, presença de lascas, trincas e perfurações. As características da corrente de fuga analisadas são: amplitude e fase de suas componentes resistiva e capacitiva, distorção harmônica e incidência de descargas superficiais. A correlação entre estas características e a integridade dos isoladores é realizada mediante ensaios de laboratório normalizados (ensaios de suportabilidade sob chuva e tensão disruptiva). O objetivo dessa investigação é obter uma metodologia de inspeção que possa indicar qual a situação dos isoladores instalados na rede através de ensaios em laboratório.

Publicado em CBQEE - 2015





DEVELOPMENT OF NEW METHODOLOGY FOR INSULATORS INSPECTIONS ON AERIAL DISTRIBUTION LINES BASED ON PARTIAL DISCHARGE DETECTION TOOLS


The necessity of improving the reliability of aerial distribution systems in Brazil has led to development and application of new techniques and tools aiming at prediction of problems related to transformers, insulators, cables and other major components of the network. In the case of insulators the traditional inspections consist of visual scans, however, have poor precision once they depend greatly on the ability and experience of the linemen workers. This paper discusses the partial results of the application of new tools to 15 kV class porcelain pin insulators in the ENERGISA distribution lines. These tools are based on the emission of infrared, ultraviolet, radio frequency and ultrasound by damaged insulators. Using these experimental tools a great amount of insulators were scanned and the suspicious units were removed from the structures. These insulators were submitted to visual inspection and evaluation through withstand and disruptive-discharge voltage tests. The results from these tests are compared with the results from the tools applied to the inspections in order to find out what are the more adequate tools for 15 kV porcelain pin insulator inspection. Additionally, the leakage current was analyzed in laboratory, having the RMS value and the waveform registered for further possible association with the insulators conditions.

Publicado em ICHVE - 2014





METHODOLOGY FOR FAST FAULT LOCATION IN OVERHEAD DISTRIBUTION NETWORKS BY THE APPLICATION OF TEMPORARY GEOREFERENCED FAULT INDICATORS


Most of the electricity distribution companies in Brazil, especially in rural areas, usually spend a long time to locate shunt faults in overhead lines. The major cause of the excessive time spent in the fault location process is the lack of appropriate tools. In spite of the existence of some tools that could be applied to aid the fault location, as permanent fault indicators, they are usually not installed by the companies because of the high cost and vandalism. In order to shorten this time, a new methodology has been developed aiming especially long networks in rural areas. This methodology consists in installing temporary georeferenced fault indicators in the branches after the fault occurrence. These devices communicate with a computer via mesh network, allowing a diagnostic software to indicate the path of the fault, and its location, in the overhead line map.

Publicado em ICHVE - 2016





RESTABELECIMENTO DE REDES DE DISTRUBUIÇÃO AÉREAS A PARTIR DA APLICAÇÃO DE INDICADORES DE FALTA TEMPORARIOS


No Brasil, o tempo despendido pelas equipes de manutenção no restabelecimento dos ramais de distribuição de energia pode ser elevado, em especial para aquelas que apresentam trechos longos que se estendem em áreas rurais. A maior causa para o tempo excessivo se dá pela falta de ferramentas adequadas e que, consequentemente, obrigam as equipes de manutenção a adotarem procedimentos demorados para a localização do defeito. Apesar da existência de algumas ferramentas que podem ser aplicadas para auxiliar a localização da falta, como projetos que envolvem a instalação permanente de indicadores de falta ao longo dos ramais, esta medida não é usualmente adotada pelas companhias de energia devido ao elevado custo do projeto e casos de vandalismo. Neste cenário, uma nova metodologia de restabelecimento está sendo desenvolvida com objetivo de diminuir o tempo de restabelecimento de ramais de grande extensão localizados em áreas rurais. Esta metodologia conta com a instalação de indicadores de falta temporários em pontos estratégicos da rede após a ocorrência da falta com a rede desernegizada devido à atuação de dispositivos de proteção. Reenergizando o sistema ainda com a presença do curto circuito, os indicadores de falta temporários são sensibilizados pela sobrecorrente, permitindo que a equipe de manutenção deduza o “caminho da falta” e, por conseguinte, restrinja a área de pesquisa do problema.

Publicado em ERIAC - 2017





CORRELATION OF EXTERNAL PARTIAL DISCHARGES AND VOLTAGE WITHSTANDING OF MEDIUM VOLTAGE PIN INSULATORS


This paper studies the correlations observed in the dry leakage current shape and the voltage withstanding of medium voltage pin insulators. The development was based on laboratory tests on roughly 1,500 insulators obtained from a field research aiming at detecting prone to failure insulators, in operation, in over head medium voltage lines, in four different regions of Brazil. Field inspection methods were applied for inspection of overhead medium voltage distribution lines, and according to this research, for medium voltage levels, the best approach considers the application of ultrasonic and radio frequency detectors (antennas). Detecting equipments based on infrared and ultraviolet techniques, at least for the voltage level of 15 kV, the range of the present research, were not effective. The meaning of effective, in this research, is the ratio of truly detected prone to failure insulator (faulty insulator) by the total number of possible prone to failure insulators, as detected by the field inspections. Faulty insulators were determined by a failure on only one of a set of laboratory tests or by means of visual inspections. Therefore, in the present research the insulators were inspected on field by radio frequency and ultrasound antennas, removed from the pole, sent to laboratory and tested. In laboratory the insulators were submitted to the dry leakage current, wet withstanding and wet sparkover voltage tests. The correlation between field detection results and test failures define a prone to failure, or even, a faulty insulator. During the dry leakage current determination, it was recorded the shape of the total leakage current. This paper presents a short view on the testing set up, the acquisition system for recording the leakage current, at first, in laboratory and the obtained statistical correlations. Finally, this technique can be useful for application in laboratory as a subsidiary tool, also a further development for field applications.

Publicado em ISH - 2015