Maciej Jaroszewski

Acoustic investigations of long-rod insulators and their material properties

The paper presents a nondestructive ultrasonic method of investigating long-rod insulators used on overhead power lines and in substations. A correlation between the degree of degradation of porcelain C 120 and the ultrasonic wave propagation and attenuation parameters was established. The ultrasonic method was used to analyze the quality of groups of line and post insulators after many years of service. Also a new mechanoacoustic method of investigating the stages in the degradation of insulator porcelain was applied. As a result of the investigations carried out on samples of porcelain C 130 the successive stages in the degradation of ceramic insulators during their service life were determined.

Composites Made of Polypropylene Nonwoven Fabric with Plasmas Layers

Engineering of materials used for shielding from electromagnetic fields is currently one of the most extensively developing field of applications of composite materials (Bula et al., 2006; Jaroszewski & Ziaja, 2010; Koprowska et al., 2004, 2008; Sarto et al. 2003, 2005; Wei et al., 2006; Ziaja et al., 2008, 2009, 2010). The choice of suitable materials for the shields and their appropriate arrangement have an essential meaning. Development of lightweight and resistant to environmental exposure shielding materials is possible by using substrates of polypropylene and plasma technology (Ziaja&Jaroszewski, 2011).

Mechanoacoustic research method of degradation processes in electroceramics materials

The paper presents the concept of mechanoacoustic testing of degradation processes of ceramic materials, which is applied to diagnose high voltage insulators in operation. The method depends on the application of slowly increasing compressive loading acting on the sample, with simultaneous recording of acoustic emission (AE) descriptors. The process of loading is continued to the destruction or stopped at different stresses, and the samples are subjected to microscopic examination. Microscopic analysis of the samples enables determining the effects of stress action. The results were compared with the images of similar materials obtained from the insulators after different periods of operation. On this basis, there were distinguished consecutive stages of ageing of electrotechnical porcelain materials and corresponding effects of their structure degradation. Using slowly increasing quasi-static compressive loading in a relatively short-term mechanoacoustic test makes it possible to get results similar to those of long lasting degradation effects in operated electroinsulating objects. Using this method there is possible to describe the factors which affect short and long-term mechanical strength of the tested materials. There is also possible assessment of the validity and application of the theories explaining the strength of porcelains. There was presented research of the influence of the mullite phase on the short- and long-term mechanical strength of electrotechnical porcelain of different types.

Dielectric characterization of electromagnetic composite barrier materials with plasma layers on nonwoven fabrics

Composite materials are becoming more widely used in the technique of shielding electromagnetic field. Among these materials, textile materials with modified surfaces are of growing importance. Among them we can distinguish nonwoven fabrics coated with conductive plasma layers which are responsible for the phenomenon of reflection and attenuation of electromagnetic wave. These phenomena are related to the dielectric properties of composite material and its structure, in particular with the phenomena on the surfaces of interphase. In the paper, dielectric properties of plasma layer-polypropylene nonwoven fabric composite is reported. To determine these properties, measurements of transient and conduction currents were used. Dielectric response of the composite to an electric field is complicated, and is a function of both the physical structure of nonwoven and applied layer. Current measurements indicate the existence of build-in charge. Electrical conductivity is nonohmic but is controlled by several mechanisms, which include ion hopping, Schottky emission, space charge limited current, and Poole-Frenkel mechanism. The dielectric parameters vary depending on the morphology of substrate surface and on parameters of the plasma generating process.