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1

Degradation Processes in Shield-Centring Elements of Surge Arresters

Papliński P., Śmietanka H., Ranachowski P., Ranachowski Zbigniew, Wieczorek K., Kudela S. jr.

Archives of Metallurgy and Materials

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2023

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Vol. 68, iss. 1

237--242

EN

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.

2

Quasi-Static and Dynamic Testing of Carbon Fiber Reinforced Magnesium Composites

Ranachowski Z., Ranachowski P., Brodecki A., Kopeć M., Kudela S. jr.

Archives of Metallurgy and Materials

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2020

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Vol. 65, iss. 2

893--899

EN

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.

3

Comparative Studies on Degradation of Varistors Subjected to Operation in Surge Arresters and Surge Arrester Counters

Papliński P., Wańkowicz J., Śmietanka H., Ranachowski P., Ranachowski Z., Kudela S. jr., Aleksiejuk M.

Archives of Metallurgy and Materials

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2020

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Vol. 65, iss. 1

367--374

EN

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.

4

Study of Modified Aluminous Porcelain Subjected to Mechanoacoustic Tests

Ranachowski P., Ranachowski Z., Wieczorek K., Jaroszewski M., Kudela S. jr.

Archives of Metallurgy and Materials

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2018

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Vol. 63, iss. 4

1821--1826

EN

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.

5

Statistical Assessment of the Microstructure of Barite Aggregate from Different Deposits Using X-Ray Microtomography and Optical Microscopy

Żołek N., Ranachowski Z., Ranachowski P., Jóźwiak-Niedźwiedzka D., Kudela S. jr., Dvorak T.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 2A

697--702

EN

Two different barite ore (barium sulfate BaSO4) specimens from different localizations were tested and described in this paper. Analysis of the microstructure was performed on polished sections, and on thin sections using X-ray microtomography (micro-CT), and optical microscopy (MO). Microtomography allowed obtaining three-dimensional images of the barite aggregate specimens. In the tomograms, the spatial distribution of the other polluting phases, empty space as well as cracks, pores, and voids – that exceeded ten micrometers of diameter-were possible to visualize. Also, the micro-CT allowed distinguishing between minerals of different density, like SiO2 and BaSO4. Images obtained and analyzed on thin sections with various methods using the optical microscopy in transmitted light delivered additional information on the aggregate microstructure, i.e. allow for estimation of the different kinds of inclusions (like the different density of the minerals) in the investigated specimens. Above methods, which were used in the tests, completed each another in order to supply a set of information on inclusions’ distribution and to present the important differences of the barite aggregate specimens microstructure.

6

Application of X-Ray Microtomography and Optical Microscopy to Determine the Microstructure of Concrete Penetrated by Carbon Dioxide

Ranachowski Z., Jóźwiak-Niedźwiedzka D., Ranachowski P., Rejmund F., Dąbrowski M., Kudela S. jr., Dvorak T.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 4

1441--1447

EN

In the paper two advanced methods for testing cement based composites are described and compared. These are X-ray microtomography and optical microscopy. Microtomography supplies three-dimensional images of small concrete specimens. In the tomograms all cracks, pores and other voids and inclusions, that exceed a few micrometers, are shown. Such visualisation can become a valuable tool for analysis of the basic material properties. Images obtained on thin sections and analysed with various methods on optical microscopes supply additional information on material microstructure that cannot be obtained in tomograms. For example it is relatively easy to determine zone penetrated by CO2 ingress. These two methods, presented on examples of tests, complete each another in order to supply a set of information on composition and defects of tested composite materials.

PL

W artykule przedstawiono dwie nowoczesne metody analizy struktury materiałów kompozytowych ze spoiwem na bazie cementu. Są to mikrotomografia komputerowa oraz optyczna analiza cienkich szlifów. Mikrotomografia pozwala na uzyskanie trójwymiarowych obrazów niewielkich próbek betonowych. Na tomogramach widoczne są układy rys, porów i innych pustek, których wymiary przekraczają kilka mikrometrów. Przestawienie tych obiektów w przestrzeni jest ważnym narzędziem do analizy podstawowych właściwosci materiału. Obrazy uzyskane na cienkich szlifach w mikroskopie optycznym, analizowane następnie różnymi metodami, dostarczają dodatkowych informacji o mikrostrukturze materiału, które nie mogą być dostrzeżone na tomogramach. Stosunkowo łatwo jest np. uzyskac obrazy stref skarbonatyzowanej matrycy cementowej. Obie przedstawione metody uzupełniają się wzajemnie i pozwalają na otrzymanie zbioru informacji o składzie i defektach badanych materiałów kompozytowych.

7

Materials Degradation Research on the Basis of Mechanoacoustic and Microscopic Methods

Ranachowski P., Rejmund F., Ranachowski Z., Pawełek A., Piątkowski A., Kudela S. jr.

Archives of Metallurgy and Materials

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2009

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Vol. 54, iss. 4

1035-1043

EN

The paper presents the concept of mechanoacoustic testing of degradation processes of ceramic electrotechnical materials. Samples of small dimensions are subjected to slowly increasing compressive loading with simultaneous recording of acoustic emission descriptors. The process is continued to the destruction or is stopped at various stages of degradation of the material structure. Microscopic analysis of samples enables determining the effects of stress action.

PL

W pracy została przedstawiona koncepcja mechaniczno-akustycznych badan procesów degradacji ceramicznych tworzyw elektrotechnicznych. Małogabarytowe próbki poddawane sa wolno narastajacemu obciazeniu sciskajacemu z jednoczesna rejestracja deskryptorów emisji akustycznej. Proces prowadzi sie do zniszczenia lub zatrzymuje na różnych etapach degradacji struktury. Analiza mikroskopowa próbek pozwala określić efekty oddziaływania naprężeń.

8

Acoustic emission and strain mechanisms during compression at elevated temperature of Β-phase Mg-Li-Al composites reinforced with ceramic fibres

Pawełek A., Ranachowski Z., Piątkowski A., Kudela S., Jasieński Z., Kudela S. jr.

Archives of Metallurgy and Materials

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2007

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Vol. 52, iss. 1

41-48

EN

The object of investigations was the behaviour of acoustic emission (AE) during channel-die compression at room and elevated (140°C) temperatures of the composites based on Mg12Li3Al and Mg12Li5Al alloys containing the Β phase as well as of the composites based on Mg8Li3Al and Mg8Li5Al alloys also containing the phase. The results of AE measurements at room temperature show that the effect of anisotropy of the fibres distribution with respect to compression axis occurs also in composites based on Mg8Li3Al alloys. However, the results of AE measurements at 140°C show that the course of AE activity was a two-range character and that the level of the rate of AE events is higher than that at room temperature. These effects are attributed to the thermal weakening of the fibres strength at 140°C. Moreover, using an AE analyser of new generation, the investigations of the composites based on Mg8Li5Al and Mg12Li3Al alloys have been carried out at room temperature. On the basis of the constructed acoustograms and spectral characteristics the preliminary wavelet analysis of AE signals generated in the microcracking process of ceramic fibres has been carried out. The results obtained using the old and the new AE analysers are compared and discussed also on the basis of scanning microstructure observations and on the basis of the dislocation mechanisms of deformation and microcracking processes in the composites containing the Β phase of Mg-Li system.

PL

Badania dotyczyły zachowania się emisji akustycznej (EA) podczas testów nieswobodnego ściskania w temperaturze otoczenia i podwyższonej (140°C) kompozytów na osnowie stopów Mg12Li3Al oraz Mg12Li5Al, zawierających faze Β, a także kompozytów na osnowie stopów Mg8Li3Al i Mg8Li5Al, również zawierających fazę Β. Wyniki pomiarów EA w temperaturze pokojowej wskazują, że efekt anizotropii rozkładu włókien względem osi ściskania występuje również w kompozytach na osnowie stopów Mg8Li3Al. Natomiast wyniki pomiarów EA w temperaturze 140°C wskazują na dwuzakresowy przebieg aktywnosci EA oraz większy poziom tempa zdarzeń EA niż w temperaturze pokojowej. Wytłumaczono to osłabieniem termicznym wytrzymałości włókien w 140°C. Ponadto, wykorzystując analizator EA nowej generacji, wykonano badania w temperaturze pokojowej kompozytów na osnowie stopów Mg8Li5Al i Mg12Li3Al. Przeprowadzono analizę porównawczą wyników uzyskanych przy użyciu nowego i dotychczas stosowanego analizatora EA. W oparciu o skonstruowane akustogramy i charakterystyki widmowe, przeprowadzono analizż falkową sygnałów EA generowanych w procesie mikropękania włókien ceramicznych. Wyniki przedyskutowano również w oparciu o obserwacje mikrostruktur skaningowych oraz w oparciu o dyslokacyjne mechanizmy odkształcenia i mechanizmy mikropękania w kompozytach zawierających fazę Β układu Mg-Li.