726 research outputs found
Phototherapy of Renal Pruritus and of Pruritus Associated with HIV Infection
Introdução e Objectivos: A fototerapia (UVB isolados ou em combinação aos UVA) tem-se revelado eficaz no tratamento do prurido grave que complica, frequentemente, a doença renal crónica (DRC) ou a infecção pelo
vÃrus da imunodeficiência humana (VIH). Pretendemos neste estudo avaliar a eficácia e segurança das radiações UVA e UVB de banda-larga, combinadas, no tratamento do prurido refractário associado à DRC e à infecção pelo VIH.
Material e métodos: Para tal foi efectuado um estudo retrospectivo e descritivo de 83 doentes (55 com prurido renal e 28 com infecção pelo VIH), que efectuaram 3 sessões/semana de UVAB. Os UVB foram administrados na dose inicial de 20 a 30mJ/cm2 (70% da DEM), aumentados em 30mJ/cm2 por sessão, na ausência de eritema, até à regressão do prurido. As doses iniciais e subsequentes de UVA foram calculadas de acordo com o fototipo, não se ultrapassando a dose máxima de 6J/cm2. Resultados: Os doentes com prurido renal (33 homens e 22 mulheres) tinham em média
57,7 anos de idade, duração da DRC de 8,7 anos e do prurido de 27,8 meses; realizaram, em média 11,1 sessões de fototerapia com doses cumulativas de UVA de 22,9J/cm2 e de UVB de 1900mJ/cm2; verificou-se melhoria do prurido após 5 sessões e alivio completo no final do ciclo; todos os doentes continuavam assintomáticos após perÃodo médio de 11,2 meses. Os doentes com infecção VIH (18 homens e 10 mulheres) apresentavam, em média, idade de 40,8 anos, seropositividade conhecida há 2,5 anos, prurido generalizado com duração de 13,4 meses e contagem de CD4 de 177 células/μL; efectuaram, em média, 12,1 sessões de fototerapia, 24,3J/cm2 de UVA e 2000mJ/cm2 de UVB; em 21 doentes constatou-se diminuição do prurido após 5 sessões de UVAB e regressão completa no final do ciclo, permanecendo assintomáticos após perÃodo médio de 13,4 meses. Não ocorreram efeitos secundários, excepto
pigmentação moderada e eritema ligeiro e transitório. Nos doentes com infecção pelo VIH não se detectou agravamento da imunossupressão. Conclusão: Estes resultados apoiam a eficácia e segurança da fototerapia combinada no controlo do prurido associado à DRC e à infecção pelo VIH, podendo o tratamento de um maior número de doentes
confirmar as suas potenciais vantagens em relação aos UVA ou UVB utilizados isoladamente
Condition monitoring and diagnostics of power transformers
This paper addresses the subject of condition monitoring and diagnostics of power transformers. The main
results of two reliability surveys, carried out under the auspices of CIGRE and IEEE in order to assemble objective data
on the performance of transformers in service, are presented, providing useful information on the main causes of
transformer failures, the most likely affected components and the related outages times. A survey of the most important
methods, actually in use, for condition monitoring and diagnostics of power transformers is also given, which stresses
the need for the development of new diagnostic methods, that can be applied without taking the transformers out of
service, and that can also provide a fault severity criteria, in particular for determining transformers windings integrity.
Preliminary results, concerning the on-going research activity on the development of a new approach for inter-turn
winding fault diagnosis in three-phase transformers, are also reported in the paper
Modelling and simulation of three-phase power transformers
This paper presents the development and implementation
of a digital simulation model of a three-phase,
three-leg, power transformer. The proposed model, implemented
in MATLAB environment, is based on the physical
concept of representing windings as mutually coupled coils,
and it is intended to study its adequacy to incorporate, at a
later stage, the influences of the occurrence of windings inter-
turn short-circuits. Both simulation and laboratory tests
results, obtained so far, for a three-phase, 6 kVA transformer,
demonstrate the adequacy of the model under normal operating
conditions
A permeance-based transformer model and its application to winding interturn arcing fault studies
This paper investigates the behavior of power transformers under the occurrence of permanent or intermittent winding insulation faults
Incipient turn-to-turn winding fault diagnosis of power transformers by the on-load exciting current Extended Park`s Vector Approach
This paper presents the application of the
on-load exciting current Extended Park's Vector
Approach for diagnosing incipient turn-to-turn
winding faults in operating power transformers.
Experimental and simulated test results demonstrate
the effectiveness of the proposed technique, which is
based on the spectral analysis of the AC component of
the on-load exciting current Park's Vector modulus
On-line diagnostics of transformer winding insulation failures, by Park's Vector Approach
This paper presents a non-invasive approach for diagnosing winding insulation failures in three-phase transformers, which is based on the on-line monitoring of the
primary and secondary current Park's Vector. Experimental and simulated results demonstrate the
effectiveness of the proposed technique, for detecting
winding inter-turn insulation faults in operating three-phase transformers
A coupled electromagnetic transformer model for the analysis of winding inter-turn short-circuits
This paper presents the development and implementation of a coupled electromagnetic transformer model
for the simulation of three-phase power and distribution
transformers affected by the presence of winding inter-turn
short-circuits. Generically, the coupled electromagnetic
transformer model is based on the simultaneous consideration of both magnetic and electric equivalent circuits. To incorporate the internal faults in this model a suitable equivalent
circuit of the faulty winding is proposed. Both simulation and
laboratory tests results are presented in the paper, which
demonstrate the adequacy of the proposed model
Power transformers' fault diagnostics by Park’s Vector Approach
The electricity market was, for a long time, dominated by national or regional monopolies.
During the last decades, this picture has changed drastically, particularly in Europe and
in the United States. The trend toward free competition and privatization with the related
demands on return on investments results in a cost consciousness among utilities. In this
context, monitoring and on-site diagnostics are seen as a possible way of optimizing existing
assets. The main driving forces are to reduce maintenance costs, to prevent forced
outages with the related consequential costs, and to work existing equipment harder and longer [1]. Transformers constitute the largest single component of the transmission and distribution equipment market
Detection of trasformer intermittent winding faults by the on-load exciting current Park`s vector approach
This paper presents the application of the on-load exciting current Park's Vector Approach for diagnosing
permanent and intermittent turn-to-turn winding faults in operating power transformers. First, an
experimental investigation of the behaviour of the transformer under the occurrence of both permanent
and intermittent winding faults is presented. Finally, experimental test results demonstrate the
effectiveness of the proposed diagnostic technique, which is based on the on-line monitoring of the
on-load exciting current Park's Vector patterns
Diagnóstico de avarias em transformadores trifásicos em serviço através da análise do Vector de Park das correntes de excitação em carga
Devido ao seu custo e importância estratégica, os transformadores de potência constituem
um componente vital dos sistemas de produção, transmissão e distribuição de energia
eléctrica. A sua fiabilidade constitui assim um factor crucial no funcionamento dos sistemas
eléctricos de energia. Não admira, pois, que sobre estes equipamentos recaiam grandes
preocupações relativamente à sua manutenção e, consequentemente, ao desenvolvimento de
métodos capazes de fornecerem um diagnóstico completo e fiável do seu estado de
funcionamento. Para o efeito, torna-se porém indispensável possuir um conhecimento
detalhado acerca das avarias susceptÃveis de ocorrerem nos transformadores, bem como dos
mecanismos especÃficos que lhe estão subjacentes
- …