Investigation of Microstructure of ZnO Varistors Taken From Surge Arrester Counters

The paper presents investigations of microstructure of varistors of damaged surge arrester counters. A similar ZnO varistor, not subjected before to operation, was a point of reference in this research. The results of investigations of the ZnO varistors show an untypical phase composition of their material, which was characterized by unsatisfying homogeneity and cohesion. The degradation processes of varistor material in the subsequent stages were recognized and described. A harmful impact of humidity inside the untight surge arrester counter on its operation and its ZnO varistors was proved. Some conclusions being the result of the operation checking of surge arrester counters were presented too

Microstructure and Degree of Degradation of ZnO Varistors in Surge Arresters Due to Operation

The paper presents the test results for the microstructure of ZnO varistors comprising high voltage gapless surge arresters. The tests were performed on varistors produced in different periods and by various manufacturers. The research was inspired by different characteristics of changes in values of current flowing through surge arresters as a function of changes in values of system voltage in a 220 kV substation, and the temperature in a multi-year cycle. Furthermore, the effects of varistor microstructure degradation following a failure of an unsealed surge arrester were investigated. The results provided the grounds for assessment of ZnO varistor microstructure parameters in terms of their durability and resistance to degradation processes

Mechaniczno-akustyczna metoda badań degradacji tworzyw porcelanowych

This paper presents the results of acoustic emission (AE) measurements of samples under slowly increasing compressive stress. Additional research, concerning structure and parameters of the material, was performed using microscopic method. The objects of investigation were samples of porcelain material C 120 and C 130 types. These aluminous porcelains find wide application in modern electrotechnical engineering. The aim of study was recognition of stages of degradation processes of the porcelain structure. The analysis of mechanical-acoustic characteristics pointed out diversified strength and complicated mechanism of material degradation. The effectiveness of structural reinforcement of aluminous porcelains was ascertained. On the basis of AE measurements of compressed samples the successive stages of structure degradation have been distinguished. Detailed microscopic analysis enabled to specify the processes of the gradual growth of microcracks and decohesion of the ceramic body.W pracy przedstawiono wyniki badań emisji akustycznej (EA) próbek poddanych wolno narastającemu naprężeniu ściskającemu. Uzupełniające badania strukturalne wykonane zostały metodą mikroskopii optycznej. Przedmiotem badań były próbki tworzyw porcelanowych rodzaju C 120 i C 130. Najważniejszym celem pracy było rozpoznanie etapów degradacji struktury tworzyw. Badania wykazały znaczne zróżnicowanie wytrzymałości próbek oraz złożony, kilkuetapowy mechanizm degradacji struktury porcelany. Opisane etapy niszczenia struktury próbek znajdują odniesienie w wieloletnich procesach starzeniowych tworzywa izolatorów w eksploatacji. Zastosowana mechaniczno-akustyczna metoda pozwoliła na wyróżnienie poszczególnych etapów degradacji badanych struktur. Udokumentowano proces powstawania, rozwoju i łączenia się pęknięć, które stopniowo doprowadzają do zniszczenia badanych próbek

Acoustic examination of epoxy-glass insulator material

Ultrasonic, microscopic and acoustic emission (AE) methods were applied to investigate the microstructure of composite rods, used as a carrying element of the medium voltage insulators. Such features of material structure as homogeneity level and the appearance of defects were discussed. The research was aimed at determining the influence of the technology of epoxy-glass fabrication on quality parameters of the insulator rods. The results of acoustic testing were compared with the effects of microscopic investigation

Aluminous porcelain degradation study using mechanoacoustic and microscopic methods

This experimental paper comprises the results of acoustic emission (AE), microscopic and ultrasonic measurements of samples subjected to slowly increasing compressive stress. On the basis of conducted measurements the successive stages of the material structural degradation have been recognized. The objects of study were samples made of C 120 aluminous porcelain. The investigated material has found at present the application in the fabrication of technical elements like overhead power line insulators. In the case of such objects, not only high mechanical strength, but especially elevated durability as well as operational reliability are required. The expected "life time" of net insulators during exploitation is about 40 years. The analysis of obtained mechanoacoustic dependences pointed out a complex mechanism of degradation of the material. Microscopic investigation of samples, which were stressed to different levels of load, enabled to specify the development of gradual growth of microcracks and successive crushing out of elements of the structure. These processes appear to be similar to the ageing processes occurring in the material during long period of exploitation under a working load. Three stages of the structure degradation were distinguished. The preliminary and subcritical ones show low or moderate intensity of AE signals and considerable variety for the particular samples. The critical stage directly precedes the destructtion of samples. Its range is relatively narrow and reveals the AE activity of high energy. The effectiveness of dispersive and fibrous reinforcement of modern aluminous porcelain C 120 type has been described. Structural strengthening by corundum grains and mullite needle shaped crystals improves mechanical parameters and distinguishes this material from typical aluminosilicate ceramics. The presented results enable drawing up the conclusions concerning the resistance of investigated material to the ageing degradation process development during long term operation

Examination of the Properties of Samples from Glass-Epoxy Core Rods for Composite Insulators Subjected to DC High Voltage

This article presents the results of an examination performed on a set of samples of glass-epoxy core rods used in composite insulators with silicone rubber housings. The goal of the examination was to test the aging resistance of the core material when exposed to Direct Current (DC) high voltage. Long term exposure of a glass-epoxy core rod to DC high voltage may lead to the gradual degradation of its mechanical properties due to the ion migrations. Electrolysis of the core material (glass fiber) may cause electrical breakdown of the insulators and consequently lead to a major failure. After being aged for 6000 hours under DC high voltage, the samples were subjected to microscopic analysis. Their chemical composition was also examined using Raman spectroscopy and their dielectric losses and conductance in the broad range of frequencies were tested using dielectric spectroscopy

Mechanical-Acoustic Examination of Ceramic Material

The paper presents a new mechanical-acoustic method of research of material degradation. As comparative method there was used microscopic technique (MO). Examinations were carried out on the samples of C 130 kind porcelain cut out from the rod of typical HV line insulator LP 75/31W. On the basis of acoustic emission (AE) measurements of slowly compressed samples, the successive stages of structural degradation have been registered

The Application of Neural Networks for Studying Phase Transformation by the Method of Acoustic Emission in Bearing Steel/ Zastosowanie Sieci Neuronowych Do Badania Przemian Fazowych W Stali Łożyskowej Metodą Emisji Akustycznej

The research was carried out on steel 100CrMnSi6-4 under isothermal austempering resulting in forming the duplex structure: martensitic and bainitic. The kinetics of transformation was controlled by the acoustic emission method. Complex phase transformations caused by segregation and carbide banding occur at the low-temperature heat treatment of bearing steel. At the temperature close to Ms, a certain temperature range occurs where an effect of the first product of prior athermal martensite on the bainitic transformation can be observed. In the registered signal about 15 million various events were registered. There were considered three types of acoustic emission events (of high, medium and low energy), with relatively wide sections and with different spectral characteristics. It was found that the method of acoustic emission complemented by the application of neural networks is a sensitive tool to identify the kinetics of bainitic transformation and to show the interaction between martensitic and bainitic transformations.Badania realizowano na stali 100CrMnSi6-4 poddanej hartowaniu izotermicznemu, prowadzacemu do utworzenia struktury duplex: martenzytyczno-bainitycznej. Kinetykę przemian kontrolowano metodą emisji akustycznej. Przy niskotemperaturowej obróbce cieplnej stali łożyskowej występują złożone przemiany fazowe spowodowane segregacją i pasmowością węglików. W temperaturze zbliżonej do Ms, występuje pewien zakres temperatury, gdzie zaznacza się oddziaływanie wcześniejszego produktu przemiany martenzytycznej na przemianę bainityczną. W zarejestrowanym sygnale zarejestrowano około 15 milionów różnych zdarzeń. Uwzgledniono trzy rodzaje zdarzeń emisji akustycznej (o wysokiej, średniej i niskiej energii) o względnie szerokich przedziałach, o różnej charakterystyce widmowej. Stwierdzono, że metoda emisji akustycznej uzupełniona o zastosowanie sieci neuronowych jest czułym narzędziem do identyfikacji kinetyki przemiany bainitycznej oraz oddziaływania przemiany martenzytycznej na przemianę bainityczną

Ultrasonic Non-Destructive Diagnostics of HV Insulators

The paper presents non-destructive ultrasonic method for investigations of long-rod insulators, operated on overhead power lines and stations. It was established correlation between the degree of C 120 porcelain material degradation and the parameters of ultrasonic wave propagation and attenuation. As example of application of the method there were presented ultrasonic examinations of two groups of insulators – 15 line and 49 station post. On the basis of the measurements advancement of ageing degradation of the material and the quality of the tested insulators were ascertained