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Abstract

The paper presents the microscopic and mechanoacoustic study of degradation processes of the porcelain material C 130 type.

This kind of material is used in the production of the most durable and reliable electrotechnical elements. Raw material composition of the studied porcelain was modified. This had an impact on the inner properties, cohesion and – in consequence – on operational properties of the material.

Using mechanical-acoustic and microscopic methods of testing of small-size samples that were subjected to compression, it was possible to distinguish successive stages of degradation of the porcelain structure. These stages were generally typical of the porcelain materials. In the authors’ opinion, they are connected to the ageing process happening over many years of work under operating conditions.

Optimization of composition and technological properties – important during technological processes – resulted in a slight decrease in inner cohesion of the porcelain. When compared to the reference material – typical domestic C 130 material, mechanical strength was somewhat lower. Carried out investigations proved that resistance of the investigated material to the ageing degradation process – during long term operation – also decreased. The improvement of technological parameters and the reduction in the number of defective elements occurred simultaneously with some decrease in the operational parameters of the material. To restore their initial high level, further work is needed to optimize the raw material composition of the porcelain.

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Authors and Affiliations

P. Ranachowski
Z. Ranachowski
K. Wieczorek
M. Jaroszewski
S. Kudela Jr
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Abstract

Two types of composites, consisting of pure magnesium matrix reinforced with two commercially used carbon fibers, were systematically studied in this paper. The composites fabricated by the pressure infiltration method, were subjected to quasistatic and dynamic compression tests. Morphology of fiber strands was observed using scanning electron microscope (SEM). The application of carbon fibre reinforcement led to the stiffening of tested materials, resulting in the limitation of the possible compression to approx. 2.5%. The performed tests revealed the remarkable difference in compression strength of investigated compositions. The cause of that effect was that GRANOC fiber reinforced composite exhibited insufficient bond quality between the brittle fibers and the ductile matrix. T300 reinforced composite presented good connection between reinforcement and matrix resulting in increased mechanical properties. Investigated composites demonstrated higher mechanical strength during deformation at high strain rates. Microscopic observations also proved that the latter fibers with regular shape and dense packaging within the filaments are proper reinforcement when designing the lightweight composite material.

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Authors and Affiliations

Z. Ranachowski
ORCID: ORCID
P. Ranachowski
A. Brodecki
M. Kopeć
S. Kudela Jr
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Abstract

The paper presents results of investigation of microstructure and micro-hardness for material of ZnO varistors applied to 110 kV surge arrester and surge arrester counter. The research combined two pairs of varistors, each consisted of one varistor subjected before to operation, while the other one was brand new unit and constituted a reference. All varistors were made of the same material by the reputable manufacture. The tests revealed a different degree of the material degradation for varistors subjected before to operation. This also refers to different degradation mechanism observed for the material of these varistors, if typical effects of degradation of aged ZnO varistors were considered as a reference. Physical state of spinel in the microstructure had a significant impact on the material degradation, however a considerable loosening of the microstructure associated with bismuth oxide was observed too. It was surprising, since the precipitates of the bismuth oxide phase most often showed very good binding to the ZnO matrix and high resistance to associated electrical, thermal and mechanical effects. The degradation effects in the ZnO matrix proved to be limited only.

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Authors and Affiliations

P. Papliński
J. Wańkowicz
H. Śmietanka
P. Ranachowski
Z. Ranachowski
ORCID: ORCID
S. Kudela Jr
M. Aleksiejuk
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Abstract

This paper presents the results of testing samples of shield-centering elements from medium-voltage surge arresters. The elements were made of TSE glass textolite. The elements have been dismantled from different operated surge arresters, which were subjected to discharge currents (short-circuit currents) of different intensity and duration. The discharge currents led to degradation of the tested elements with various degrees of advancement. The degradation was investigated using microscopic methods and energy-dispersive X-ray spectroscopy (EDS). Changes in the content of elements of the surface of textolite materials – as the degradation progresses – were documented.
It was found that high discharge current flows resulted in melting of the organic binder, epoxy resin, especially its surface layer. Partial charring and even burning of the resin was noticeable. Furthermore, it was found that with increasing degradation on the surface of the TSE laminate, the carbon and oxygen content, which are part of the organic resin, decreases. Simultaneously the amount of silicon, calcium and aluminium, which are present in the glass fibres, increases. The charring effect of the resin and the formation of conductive paths result in a decrease in the performance of surge arresters and their subsequent failure.
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Authors and Affiliations

P. Papliński
1
H. Śmietanka
1
P. Ranachowski
2
Z. Ranachowski
2
ORCID: ORCID
K. Wieczorek
3
S. Kudela Jr
4

  1. Institute of Power Engineering – Research Institute, 8 Mory Str., 01-330 Warsaw, Poland
  2. Institute of Fundamental Technological Research PAS, 5b Pawińskiego Str., 02-106 Warsaw, Poland
  3. Wrocław University of Science And Technology, Faculty of Electrical Engineering, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
  4. Institute of Materials and Machine Mechanics Slovak Academy of Sciences, Dúbravská Cesta 9/6319, 845 13 Bratislava, Slovakia

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