JOURNAL / ISSUES               ISSN 2310-6697 / ISSN-L 2310-6697
open transactions on independent scientific-engineering research


Attribution 4.0 International License CC BY 4.0
# Electrical Engineering - Expérimentation
Interfaces in High Voltage Engineering: A Most
Important Question for Conventional Solid Insulating
Materials as well as for Nanocomposite Polymers
M. G. Danikas, R. Sarathi
Interfaces consist a most important part of conventional insulating systems at high voltages. They are considered to be problem areas which have to be dealt with. Numerous publications have contributed in rendering the mechanisms of interfaces understandable. On the other hand, interfaces in nanocomposite polymers seem to function in an entirely different manner from that in conventional insulating systems. The present paper reviews past work on both the conventional insulations and in nanocomposites. Differences regarding the interfaces are mentioned and discussed. Whereas interfaces in conventional insulating systems are to be avoided, interfaces in nanocomposite polymers seem to be desirable – at least - up to a certain percentage of nanoparticles in the base polymer. Although things are better understood in conventional insulating materials, more work has to be performed in order to clarify several aspects, such as space charges and electrical trees emanating from enclosed cavities. Needless to say that much more work has to be done in nanocomposites w.r.t. their modeling and possible explanations of the surprising performance of interfaces, a performance that deviates strongly from the performance in classical insulating materials.
# Applied Electromagnetics - Théorie
Spherical Beltrami Fields in Chiral Media:
Reciprocity and General Theorems
N. M. Berketis
The Beltrami fields are extremely important for the description of time-harmonic electromagnetic fields in chiral media. This paper introduces the spherical Beltrami fields in chiral media, extending the corresponding known results for plane electromagnetic waves. Two key theorems are given for the scattering of spherical electromagnetic waves in chiral environment from a perfect conductor: the Reciprocity and the General Scattering theorems.
# Telecommunications Engineering - Applications
Self-Standing End-Fed Geometrically Uniform
Linear Arrays: Analysis, Design,
Construction, Measurements and FLOSS
K. Th. Kondylis, N. I. Yannopoulou, P. E. Zimourtopoulos
The array factor of a both geometrically and electrically uniform array is the simple formula for the complex geometric progression sum. This fact, although results in the simplest of all possible analytical designs, obviously does not in the least simplify the complicated practical problem of feeding the array elements using multiple driving points. In order to begin the examination of uniform linear arrays with a single driving point, this paper presents a compact study of the end-fed space arrays with application to geometrically uniform, self-standing linear arrays of parallel dipoles. A number of test array models were simulated, constructed and their radiation pattern was then measured. The experimental and computational results were found to be in good agreement. The developed software applications are available through the Internet as FLOSS Free Libre Open Source Software.
# Electrical Engineering - Expérimentation
Parameters Affecting the Lifetime of Transformer Oil
in Distribution Transformers: Parameter Monitoring
of 50 Transformers from the Athens Area
M. G. Danikas, E. Rapti, I. Liapis, A. B. B. Abd. Ghani
The aim of this paper is the study of various parameters affecting the ageing of transformer oil in distribution transformers of 20/0.4 kV. Fifty (50) samples of oil were taken from such transformers. The transformers function in the major Athens area, Greece. Parameters, such as breakdown strength, oil color, humidity, interfacial tension and tanδ were taken into account. Transformer ageing and lifetime are strictly related to the rate of ageing of the whole insulating system, and mainly of the oil. Absence of transpiring system with silica gel has as a result the increase of oil humidity. The lengthy use of transformers under heavy load, and consequently under high temperatures, is a main factor for oil ageing and oxidation. Especially in the last few years, the increased loads required by the transformers which have to do also with the climatic changes, have as a result the additional stressing of the oil. Various arcs, resulting from short circuits in the network, have as a consequence the production of gases and sludge. Such gases and sludge influence in a negative way the insulating properties of the oil as well as its rate of ageing. The role of silica gel is stressed.