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[en] A DIAGNOSTICS SYSTEM OF HIGH VOLTAGE POWER APPARATUS BASED IN PARTIAL DISCHARGES OCURRENCE / [pt] UM SISTEMA DE DIAGNÓSTICO DE EQUIPAMENTOS ELÉTRICOS DE ALTA TENSÃO COM BASE NA OCORRÊNCIA DE DESCARGAS PARCIAISHELIO DE PAIVA AMORIM JUNIOR 13 December 2001 (has links)
[pt] Os equipamentos elétricos de alta tensão são peças
fundamentais na produção industrial. Porém, os sistemas de
isolamento são os que mais apresentam problemas ao longo da
vida útil dos nossos equipamentos. Suas propriedades
dielétricas são alteradas ao longo do tempo e, desta forma
devem ser monitoradas. Dentre as principais anomalias
acometidas aos sistemas de isolamento, estão as Descargas
Parciais (DP).Elas são resultado do rompimento da rigidez
dieétrica do material isolante submetido a um intensivo
campo elétrico . Até alguns anos atrás, em virtude da
existência dos mecanismos de medição que possibilitassem o
armazernamento de dados, muito pouco se efetuava para o
acompanhamento das condições apresentadas pelos sistemas de
isolamento.Com advento de sistemas digitais,esta limitação
foi vencida. No entanto, a obtenção de dados reais e sua
posterior avaliação são mecanismos que ainda carecem de um
bom número de anos de experiência para sua elucidação. Esse
fato advém,principalmente, da dificuldade em obtê-los .Como
forma de contornar problema de falta de dados reais, foram
desenvolvidas as célualas que têm como características
simular os principais tipos de defeitos existentesnos
sistemas de isolamento de alta tensão.Essas células são
isoladas por materiais dielétricos idênticos ao que são
usados em equipamentos elétricos reais. Dessa forma, foi
possível a simulação de defeitos e a posterior aquisição,
através do método eletromagnético de medição de DP, de um
número suficiente de dados. Esses dados foram,então,
aplicados no ajuste do sistema de reconhecimento de padrões
de DP, onde se faz uso da teoria fractal, como um mecanismo
de compactação de dados, por meio das grandezas fractais
denominadas de dimensão fractal e lacunaridade, e também
das redes neurais artificiais, com a utilização de um
algoritmo supervisionado através do modo de treinamento
back-propagation.Essa etapa,denominada de laboratorial, foi
de fundamental importância para obtenção de conhecimento
experimental bastante útil para a aplicação em ambientes
reais.Outra fonte de informação também foi disponibilizada
e se refere aos níveis de gases encontrados nas amostras de
óleo colhidas junto aos transformadores de potência. Esta
análise, conhecida como análise cromatográfica,baseia-se na
existência de determinados tipos de gases para apontar o
tipo de anomalia acometida ao sistema de isolamento do
equipamento elétrico.Embora existam alguns métodos capazes
de realizar tal diagnóstico, a tese fez uso das
informações de um especialista.Essas afirmações foram
então empregadas em um sistema neuro-fuzzy hierárquico, que
tem como fundamento a extração de regras que relacionam os
níveis de gases obtidos pela cromatografia gasosa com o
tipo de anomalia existente no sistema de isolamento .Após
esse processo um conjunto de transformadores de potência
reais foi monitorado através de técnicas de cromatografia e
do método eletromagnético.As duas técnicas, portanto, são
usadas para estimar a ocorrência de DP nos sistemas de
isolamento e, cosequentemente, o nível de degradação dos
mesmos.Desta forma, a tese apresenta um sistema de
diagnóstico que se utilizada de dados internos ao sistema
de isolamento dos equipamentos elétricos baseados na
ocorrência de DP. Esse sistema indica, ao seu final, um
conceito sobre o atual estado operativo do mesmo, podendo
este ser utilizado em um planejamento mais adequado que
previna perdas intempestivas. A avaliação de desempenho do
modelo, tanto laboratorial quanto em campo, apresentou
ídices elevados, culminando em uma confirmação visual
interna de um equipamento real, que comprova a eficiência e
a importãncia do sistema. / [en] High voltage (HV) power apparatus are fundamental parts in
the industrial process. It is also well Known that
electrical insulation systems are the parts that present
more problems through the life cycle of an HV apparatus.
The dielectric properties of materials are altered during
operation time and for this reason they should be
monitored. Among the main anomalies that can affect the
insulation systems are the Partial Discharges (PD). They
are result of a partial failure of the dielectric rigidity
of the insulating material submitted to an intense electric
field.Until recently, probably due to the inexistence of
measurement mechanisms that made possible the storage of
data, very a little could be done to accompany the actual
condition of insulation systems. With the coming of digital
systems, this limitation was overcome.However, the
obtention of real data and their subsequent evaluation are
mechanisms that still will demand a good number of years
of experience to perfect . This fact occurs, mainly, due to
the difficulty in obtaining those data .As a way to the
problem of lack of real data, special cells development
with the purpose of simulating the principal types of
defects that occur in HV insulation equipment . In that
way, it was possible to do both the simulation of the
defects and the measurement and acquisition, through the
electromagnetic measurement method, of an expressive number
of data. Those data were used to adjust a system of pattern
recognition of PD, using artificial neural networks, where
it is also made use of the fractal theory, as a mechanism
of data compression, by measures of fractal dimension and
lacunarity. That stage, denomited laboratory, was of
fundamental importance to the obtention of experimental .
Knowledge very useful to the development of real operating
systems .Another source of information that was also
available refers to the levels of gases found in oil
samples from the interior of power transformers. This
analysis, known as analysis of dissolved gases or
chromatography, is based on the existence of certain types
of gases as an indication of the type of anomaly on the
electrical insulation system. Although some mehods exist,
capable of accomplishing such diagnosis, the thesis made
use of a specialist`s information. Those statements were
used then in a hierarchical neuro-fuzzy model, designed
method, with the type of anomaly existent in the
insulation system. After that process, a real sample of
operating HV power apparatus was monitored using the two
analysis techniques, the chromatography and the
electromagnetic method of PD measurement.Therefore these
two techniques, are used to estimate the PD activity in
the insulation systems and, consequently, their level of
degradation . In resume the thesis presents a diagnosis
system that makes use of internal data from the electrical
insulation system with base in the PD occurrence. That
system indicates, at the end, a concept of its current
operative state, being able to be used in a more
appropriate planning in order to prevent inopportune
losses. The evaluation of the model, as much of simulating
as in field, present high indexes and a visual confirmation
intern of a real equipment, that proves the efficiency and
the importance of system.
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Studies On Epoxy Nanocomposites As Electrical Insulation For High Voltage Power ApparatusPreetha, P 08 1900 (has links) (PDF)
High voltage rotating machines play a significant role in generation and use of electrical energy as the demand for power continues to increase. However, one of the main causes for down times in high voltage rotating machines is related to problems with the winding insulation. The utilities want to reduce costs through longer maintenance intervals and a higher lifetime of the machines. These demands create a challenge for the producers of winding insulations, the manufacturers of high voltage rotating machines and the utilities to develop new insulation materials which can improve the life of the equipment and reduce the maintenance cost.
The advent of nanotechnology in recent times has heralded a new era in materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials that exhibit unique combinations of physical, mechanical and thermal properties which are advantageous as compared to the traditional polymers or their composites. Even though they show tremendous promise for dielectric/electrical insulation applications, there are no studies relating to the long term performance as well as life estimation of the nanocomposites. Considering this, an attempt is made to generate an understanding on the feasibility of these nanocomposites for electrical insulation applications. An epoxy based nanocomposite system is chosen for this study along with alumina (Al2O3) and silica (SiO2) as the nanofillers.
The first and the foremost requirement for studies on polymer nanocomposites is to achieve a uniform dispersion of nanoparticles in the polymer matrix, as nanoparticles are known to agglomerate and form large particle sizes. A laboratory based direct dispersion method is used to process epoxy nanocomposites in order to get well dispersed samples. A detailed microscopy analysis of the filler dispersion using Scanning Electron Microscope (SEM) has been carried out to check the dispersion of the nanofiller in the polymer. An attempt is made to characterize and analyze the interaction dynamics at the interface regions in the epoxy nanocomposite by glass transition temperature (Tg) measurements and Fourier transform infrared (FTIR) spectroscopy studies. The values of Tg for the nanocomposites studied
decreases at 0.1 wt% filler loading and then starts to increase gradually with increase in filler loading. This Tg variation suggests that there is certainly an interaction between the epoxy chains and the nanoparticles. Also no new chemical bonds were observed in the spectra of epoxy nanocomposite as compared to unfilled epoxy. But changes were observed in the peak intensity and width of the –OH band in the spectrum of epoxy nanocomposite. This change was due to the formation of the hydrogen bonding between the epoxy and the nanofiller.
The thermal conductivity of the epoxy alumina and the epoxy silica nanocomposites increased even with the addition of 0.1 wt% of the filler. This increase in thermal conductivity is one of the factors that make these nanocomposites a better option for electrical insulation applications.
The dielectric properties of epoxy nanocomposites obtained in this investigation also reveal few interesting behaviors which are found to be unique and advantageous as compared to similar properties of unfilled materials. It is observed that the addition of fillers of certain loadings of nanoparticles to epoxy results in the nanocomposite permittivity value to be lower than that of the unfilled epoxy over the entire range of frequencies [10-2-106 Hz] considered in this study. This reduction has been attributed to the inhibition of polymer chain mobility caused by the addition of the nanoparticles. The tan values are almost the same or lower as compared to the unfilled epoxy for the different filler loadings considered. This behavior is probably due to the influence of the interface as the strong bonding at the interface will make the interface very stable with fewer defects apart from acting as charge trapping centres.
From a practical application point of view, the surface discharge resistant characteristics of the materials are very important and this property has also been evaluated. The resistance to surface discharge is measured in the form of roughness on the surface of the material caused by the discharges. A significant enhancement in the discharge resistance has been observed for nanocomposites as compared to unfilled epoxy/ microcomposites, especially at longer exposure durations. The partial discharge (PD) measurements were carried out at regular intervals of time and it is observed that the PD magnitude reduced with discharge duration in the case of epoxy alumina nanocomposites. An attempt was made to understand the chemical changes on the surface by conducting the FTIR studies on the aged surface.
For all electrical insulation applications, materials having higher values of dielectric strengths are always desired and necessary. So AC breakdown studies have also been conducted. The AC breakdown strength shows a decreasing trend up to a certain filler loading and then an increase at 5 wt% filler loading for epoxy alumina nanocomposites. It has been also observed that the type of filler as well as the thickness of the filler influences the breakdown strength. The AC dielectric strength of microcomposites are observed to be lower than the nanocomposites.
Extensive research by long term aging studies and life estimation are needed before these new nanocomposites can be put into useful service. So long term aging studies under combined electrical and thermal stresses have been carried out on unfilled epoxy and epoxy alumina nanocomposite samples of filler loading 5 wt%. The important dielectric parameters like pemittivity, tan and volume resistivity were measured before and after aging to understand the performance of the material under study. The leakage current was measured at regular intervals and tan values were calculated with duration of aging. It was observed that the tan values increased drastically for unfilled epoxy for the aging duration considered as compared to epoxy alumina nanocomposites. The life estimation of unfilled epoxy as well as epoxy nanocomposites were also performed by subjecting the samples to different stress levels of 6 kV/mm, 7 kV/mm and 8 kV/mm at 60 oC. It is observed that the epoxy alumina nanocomposite has an enhanced life which is nine times the life of the unfilled epoxy. These results obtained for the nanocomposites enable us to design a better material with improved dielectric strength, dielectric properties, thermal conductivity, resistance to surface discharge degradation and enhanced life without sacrificing the flexibility in the end product and the ease of processing. Dry type transformers and stator winding insulation need to be cast with the above material developed and tested before practically implementing these in the actual application.
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