The article presents the results concerning the use of clustering methods to identify signals of acoustic emission (AE) generated by partial discharge (PD) in oil-paper insulation. The conducted testing featured qualitative analysis of the following clustering methods: single linkage, complete linkage, average linkage, centroid linkage and Ward linkage. The purpose of the analysis was to search the tested series of AE signal measurements, deriving from three various PD forms, for elements of grouping (clusters), which are most similar to one another and maximally different than in other groups in terms of a specific feature or adopted criteria. Then, the conducted clustering was used as a basis for attempting to assess the effectiveness of identification of particular PD forms that modelled exemplary defects of the power transformer’s oil-paper insulation system. The relevant analyses and simulations were conducted using the Matlab estimation environment and the clustering procedures available in it. The conducted tests featured analyses of the results of the series of measurements of acoustic emissions generated by the basic PD forms, which were obtained in laboratory conditions using spark gap systems that modelled the defects of the power transformer’s oil-paper insulation.
The paper relates to the problem of adaptation of V-block methods to waviness measurements of cylindrical surfaces. It presents the fundamentals of V-block methods and the principle of their application. The V-block methods can be successfully used to measure the roundness and waviness deviations of large cylinders used in paper industry, shipping industry, or in metallurgy. The concept of adaptation of the V-block method to waviness measurements of cylindrical surfaces was verified using computer simulations and experimental work. The computer simulation was carried out in order to check whether the proposed mathematical model and V-block method parameters are correct. Based on the simulation results, a model of measuring device ROL-2 for V-block waviness measurements was developed. Next, experimental research was carried out consisting in evaluation of waviness deviation, initially using a standard non-reference measuring device, and then using the tested device based on the V-block method. Finally, accuracy of the V-block experimental method was calculated.