Przemysław Rogalski

Structural analysis of multilayer metal nitride films CrN/MoN using electron backscatter diffraction (EBSD)

The electron backscatter diffraction (EBSD) analysis method was used for studying structure and properties of multilayer nitride CrN/MoN coatings fabricated by cathode arc physical vapour deposition (Arc-PVD). Samples were deposited on steel substrate with different single layer thickness from tens nanometers to 1 micron and with total thickness of coatings up to 8-13 μm. Colour grains mapping, grain size distribution profiles, pole figures and texture analyses were the main research instruments. Studying of obtained coatings was performed on specially prepared polished cross-section samples. The dependence between single layer thickness and grain size of materials, which is also changing through depth profile of the coating, was observed. In addition, it was possible to study phase composition, prevailing crystals orientation, dominant texture and grains growth. Studying of grains size, as well as other indicated parameters, is a very important task because it gives an information about grains interfaces volume, which causes changes in mechanical properties of material. Obtained results were cross-checked by X-ray diffraction analysis (XRD) where it was possible.

Statistical analysis of oil percolation through pressboard measured by optical recording

The paper presents a measuring station used to measure the percolation of transformer oil by electrotechnical pressboard. Nytro Taurus insulating oil manufactured by Nynas company percolation rate by the Pucaro company pressboard investigation was made. Approximately 60 samples of Pucaro made pressboard, widely used for insulation of power transformers, was measured. Statistical analysis of oil percolation times were performed. The measurements made it possible to determine the distribution of capillary diameters occurring in the pressboard.

Research of insulating oil percolation in electrical pressboard using optical registration

The paper presents developed and built measuring system for oil percolation through electrical pressboard speed measurements. The system by using automatically controlled camera records the time of percolation. The rate of insulating oil Nytro Taurus, produced by Nynas company, penetration across electrical pressboard, produced by Weidman company, was investigated. The time dependence of insulating oil percolation on sample thickness has been designated. New method of pressboard capillaries radius determining on the basis of oil percolation speed experimental measurements has been developed. It was found that electrical pressboard capillary radius is from 45 nm to over 100 nm.

Optical registration of transformer oil absorption processes in electrical pressboard nano-capillaries

The paper presents designed and built measurement system for measuring electrical pressboard oil absorption speed. During measurements the test bench allows for automatic record of oil level, time, temperature, humidity and atmospheric pressure. Measurements of Nytro Taurus oil, produced by Nynas company, absorption by pressboard, produced by Weidman company, were made. It has been observed, that the absorption of oil takes place in three stages, duration of which are respectively τ1≈0,66 h, τ2≈109 h and τ3≈524 h. It was established that the time required to complete the oil absorption process takes more than 46 days. This means that at least as much time should take oil impregnation process of pressboard samples made for electrical measurements.

Nonlinear phenomena in the constant electric field in insulation pressboard

The paper presents the results of DC conductivity dependence of a transformer oil impregnated pressboard, with moisture content of 2.9% by weight, measured for temperature from 20 °C to 80 °C and a field strength from 10 kV/m to 1000 kV/m. It was found that the non-linear phenomena, which presence cannot be explained by the theory of ion conduction of oil-paper insulation, is intensifying with increase of the electric field strength.

Determination of nanocapillaries radii statistical distribution in electrotechnical pressboard

The article presents research on the percolation time of oil through the electrotechnical pressboard, which results in determining the statistical distribution of capillary radii, involved in the process of impregnation of paper-oil insulation. On the basis of the conducted research, a positive effect of pressboard calendering on its operation was detected.

Modeling of dielectric to metal conduction transition in nanocomposites by using high voltage discharge

Paper presents method of the percolation phenomenon visualization through modeling metal-dielectric type nanocomposite. Model was based on high voltage discharge in air between metallic discs modeling the metallic phase. A research station for visualization and simultaneous registration of percolation process was developed and built. Models have been executed in 2 dimension plane of randomly arranged metallic discs. The quantity of metal rings models different value of metal nanoparticles concentration. For different concentration of nanoparticles relationship of discharge voltage to metal concentration was determined.

Visualization of the percolation phenomenon in two-dimensional arrangement of metallic spherical particles

The paper presented the method of visualization the phenomenon of percolation in the model of nanocomposite type metaldielectric, based on the occurrence of high voltage jumps in the air between metallic discs modeling the metallic nanoparticles. A research station for visualization and registration of the percolation process was developed and built. The models were made from metallic discs, randomly arranged on a plane for different values of „nanoparticles” concentration. The dependence of the jump voltage from the concentration was established. Visual images of percolation for different „nanoparticles” concentration were registered.

Optical registration of the vacuum impregnation process of electrotechnical pressboard by transformer oil

The paper presents a research stand developed to measure the kinetics of the vacuum impregnation process of electrotechnical pressboard with transformer oil. The object of the research was electrical pressboard made by Pucaro company impregnated by Nynas company Nytro Taurus oil. Studies were carried out in a vacuum chamber under reduced pressure. The results of the experiments allowed to determine the influence of reduced pressure on the impregnation process kinetics and to determine the diameter of the capillaries present in the electrotechnical pressboard.

Statistical analysis of transformer oil penetration speed through electrotechnical pressboard

The paper presents a measuring stand used to measure oil penetration times of capillaries present in electrotechnical pressboard. Based on the measurements, the statistical distribution of capillaries occurring in cellulose insulation was determined. Based on the analysis of the obtained results, the presence of randomly distributed areas with reduced density was detected.