Skuteczna ochrona (wzmocnienie obudowy) skrzyżowania ściana–chodnik zapewnia ciągłość cyklu produkcyjnego, a mianowicie szybkie przesunięcie przenośnika ścianowego do czoła ściany. Stosowanie niskiego bądź wysokiego kotwienia jako elementu wzmacniającego obudowę podporową skrzyżowania ściana-chodnik, pozwala na wyeliminowanie tradycyjnych sposobów utrzymania skrzyżowania ściana–chodnik, a tym samym pozwala na efektywne wykorzystanie wysokiej wydajności nowoczesnych kompleksów ścianowych. W artykule przedstawiono długoletnie doświadczenia dołowe kopalni Knurów–Szczygłowice w zakresie stosowania, dla skutecznego utrzymania skrzyżowania ściana-chodnik, obudowy przykotwionej do górotworu przy pomocy dwóch par kotwi, wykazując pełną przydatność techniczną i ekonomiczną takiego sposobu wzmocnienia obudowy. W artykule zwrócono również uwagę na bezpieczeństwo pracy oraz na coraz powszechniejsze wykorzystanie badań endoskopowych przy określeniu zasięgu strefy spękań rzutujące bezpośrednio na właściwy dobór odpowiedniej liczby, nośności oraz długości stosowanych kotew. Przeprowadzone badania dołowe zasięgu strefy spękań i rozwarstwień stropu (endoskopowe i przy pomocy rozwarstwieniomierzy linkowych) przed frontem czynnej ściany, a także przeprowadzone badania laboratoryjne (stanowiskowe) pozwoliły określić współczynnik bezpieczeństwa utrzymania skrzyżowania ściana–chodnik rzutujący bezpośrednio na konieczność zabudowy dodatkowego wzmocnienia. Wartość współczynnika bezpieczeństwa Sbść-ch większa od 1 jest korzystna i bezpieczna, a wartość mniejsza lub równa 1 może prowadzić do znacznego pogorszenia warunków utrzymania skrzyżowania w obudowie podporowej przykotwionej.
Power systems that are highly loaded, especially by a stochastic supply of renewables and the presence of storages, require dynamic measurements for their optimal control. Phasor measurement units (PMUs) can be used to capture electrical parameters of a power system. Standards on the PMU dynamic performance have been modified to incorporate their new dynamic mode of operation. This paper examines the PMU dynamic performance and proposes essential algorithms for measurement accuracy verification. Measurements of dynamic input signals, which vary in amplitude or frequency, were taken during automated tests of two PMUs. The test results are presented and expounded with further recommendation for the performance requirements. This paper also presents and examines applied testing procedures with relevance to the specifications of the IEEE Standard for Synchrophasor C37.118.1™-2011 and its amendment C37.118.1a™-2014.
This paper presents accuracy characteristics of determining the position of corners of building structures with RTN GNSS surveying, using indirect methods of measurement. The studies included the following methods: a point on a straight line, intersection of straight lines and distance-distance intersection. The research experiment analyzed the coordinates of the corners of building structures obtained from the surveys and the mean errors of their position as well as mutual relationships of check measurements, or tie distances. The accuracy analysis also took into account base errors deter- mined in real time. Statistical analysis of these parameters was carried out, as a result of which a distance-distance intersection method was very well rated. For other methods, the results were diversified. The article also emphasizes a need to search for other solutions to modernize the indirect methods of measurement in such a way that their use in RTN GNSS surveys would give results most probable when compared to the real ones.
Both the growing number of dispersed generation plants and storage systems and the new roles and functions on the demand side (e.g. demand side management) are making the operation (monitoring and control) of electrical grids more complex, especially in distribution. This paper demonstrates how to integrate phasor measurements so that state estimation in a distribution grid profits optimally from the high accuracy of PMUs. Different measurement configurations consisting of conventional and synchronous mea- surement units, each with different fault tolerances for the quality of the calculated system state achieved, are analyzed and compared. Weighted least squares (WLS) algorithms for conventional, linear and hybrid state estimation provide the mathematical method used in this paper. A case study of an 18-bus test grid with real measured PMU data from a 110 kV distribution grid demonstrates the improving of the system’s state variable’s quality by using synchrophasors. The increased requirements, which are the prerequisite for the use of PMUs in the distribution grid, are identified by extensively analyzing the inaccuracy of measurement and subsequently employed to weight the measured quantities.
The presented paper describes the results of an experiment determining the instantaneous values of velocity vector components of the air stream at selected spots of the boundary layer formed at the sidewalls of the mine heading in the ŁP type steel arch support. The experiment was carried out in a mine heading in an active hard coal mine. A 3-axis thermoanemometric probe was used to obtain three-dimensional distributions of the velocity and turbulent values, such as turbulence intensity and turbulent kinetic energy of the flowing ventilation air stream. The analysis of the measurement results was aided by a numerical solution of the discussed case of flow. The research results presented in this paper provide a basis for extensive studies of the description of velocity distribution and other turbulent quantities within the near-sidewall structures of a mine heading. The objective of these tasks is to improve the accuracy and reliability of numerical calculations relating to air flow in mine headings.
The three-dimensional (3D) coordinate measurement of radio frequency identification (RFID) multi-tag networks is one of the important issues in the field of RFID, which affects the reading performance of RFID multi-tag networks. In this paper, a novel method for 3D coordinate measurement of RFID multitag networks is proposed. A dual-CCD system (vertical and horizontal cameras) is used to obtain images of RFID multi-tag networks from different angles. The iterative threshold segmentation and the morphological filtering method are used to process the images. The template matching method is respectively used to determine the two-dimensional (2D) coordinate and the vertical coordinate of each tag. After that, the 3D coordinate of each tag is obtained. Finally, a back-propagation (BP) neural network is used to model the nonlinear relationship between the RFID multi-tag network and the corresponding reading distance. The BP neural network can predict the reading distances of unknown tag groups and find out the optimal distribution structure of the tag groups corresponding to the maximum reading distance. In the future work, the corresponding in-depth research on the neural network to adjust the distribution of tags will be done.
The phase jitter enables to assess quality of signals transmitted in a bi-directional, long-distance fibre optic link dedicated for dissemination of the time and frequency signals. In the paper, we are considering measurements of jitter using a phase detector the detected frequency signal and the reference signal are supplied to. To cover the wideband jitter spectrum the detected signal frequency is divided and – because of the aliasing process – higher spectral components are shifted down. We are also examining the influence of a residual jitter that occurs in the reference signal generated by filtering the jitter occurring in the same signal, whose phase fluctuations we intend to measure. Then, we are discussing the evaluation results, which were obtained by using the target fibre optic time and frequency transfer system.
The contribution summarises the results of oxygen activity determinations, which were measured and registered continuously in castings from cast irons with various types of graphite. The results were used to find the relationship between two variables: natural logarithm of oxygen activities and reverse value of thermodynamic temperature 1 /T. Obtained regression lines were used to calculate oxygen activity at different temperatures, to calculate Gibbs free energy ΔG at the different temperatures and to calculate the single ΔG value for significant temperature of the graphite solidification. The results were processed by a statistical analysis of data files for the different types of graphite with flake, vermicular and spheroidal graphite. Each material has its proper typical oxygen activities range and individual temperature function of Gibbs free energy for analysing and governing casting quality.