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Ageing of C4F7N and CO2-based insulating gas mixtures by free-burning arcs
Full text linkThis study examines the effects of arc-induced ageing in CO2/O2 (86.3%/13.7%),C4F7N/CO2/O2 (5%/82%/13%) and C4F7N/CO2 (5%/95%) mixtures at 5 bar absolute pressure. The gases were subjected to a series of free-burning arcs with a total energy dissipation relevant to high-voltage circuit breaker applications. The arc voltage remained similar across all mixtures with no significant variation due to ageing or the addition of C4F7N and O2. In addition, the influence of the insulating gas on the erosion of the arcing contacts (20% wt. Cu/80% wt. W) was analyzed. While the increase in average surface roughness was comparable across all mixtures, the contact mass loss was relatively higher in those containing C4F7N. Decomposition of the gas mixtures was examined through gas chromatography-mass spectrometry analyses. Solid byproducts generated during arcing were analyzed using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS)
Improving the production process of silicon nanoparticle and quartz microlens
Full text linkThis study presents a comprehensive investigation into advanced laser micro/nano machining techniques, utilising three distinct laser sources: a Q-switched Nd:YAG laser, a fibre laser, and a CO2 laser. Notably, the creation of remarkably stable silicon nanoparticles was achieved, opening up promising avenues for new applications. The potential of quartz sheets was exploited to produce spherical microlens arrays, thereby demonstrating the precision of optical element engineering. The distribution of surface and subsurface temperatures for both silicon and quartz materials during laser processing was determined through an in-depth thermal analysis facilitated by COMSOL software. Notably, peak temperatures of 5 700 K and 2 630 K were achieved for silicon and quartz, respectively, highlighting the effectiveness of the laser methodologies employed. Numerical optimisations were conducted using Design of Experiments (DOE) software to enhance silicon nanoparticle production, yielding nanoparticles with a remarkable stability parameter of 33.5 mV. Furthermore, notable outcomes were achieved in the production of quartz microlenses with a numerical aperture of 0.494 and a surface roughness of 4.5 nm. The controllable and precise nature of the laser micro/nano machining techniques enables applications in optoelectronics and advanced biological imaging. The exceptional properties of the engineered silicon nanoparticles and microlens arrays demonstrate their potential across various scientific and technological domains
Determination of mechanical properties of very thin 3D-printed specimens for numerical analysis of tensile strength and fracture toughness
Full text linkThis research deals with the influence of thickness on the mechanical properties of polyamide (PA12) samples produced by the SLS 3D technology. Experiments included fracture toughness and simple tensile tests on samples with thicknesses ranging from 0.50 mm to 2.00 mm. The experiment revealed that the thickness of the specimen significantly affected the tensile strength and Young’s modulus. The measured tensile strength (22–34 MPa) was notably lower than the 41 MPa reported by the manufacturer. As a result, a numerical analysis using ATENA software showed substantial discrepancies between the FEA predictions and the experimental data. This led to a modification of the material model and the determination of the effective Young’s modulus fit to thin polyamide samples, which improved the agreement of the numerical and experimental data
Direct current nanogrid providing energy for water pumping: a comparative study in a riverside community in the Amazon
Full text linkWater pumping systems are crucial for improving the quality of life for riverside communities. In the Amazon, most of these systems still rely on fossil fuels. However, new off-grid electrification structures using Direct Current Distribution Nanogrids (DCDN) offer better energy efficiency, resilience, cost savings, and reduced environmental impact. This article presents a comparative theoretical and experimental study of various water pumps in Ilha das Onças, Pará, Brazil, where an open structure DCDN with distributed photovoltaic generation and energy storage was implemented to power eight residences and a church. The case study monitored a residential pumping system, analysing the performance before and after installing the DCDN, focusing on various energy supply types (fossil fuel, AC via inverter, and DC connected to the grid), as well as the economic and environmental impacts associated with the energy supply on the island. The results show potential savings of up to $4.5 million in gasoline costs over 25 years, and the equivalent annual CO2 emission can be reduced by 123 tons annually, considering the replicability to other nearby residences, showcasing the benefits of the solution and positive technical, economic, and environmental impacts
Integration of STEM technologies into the professional training of transport engineers and expert education teachers
Full text linkThe article outlines a methodology for creating three-dimensional object models for a standardised approach to STEM (science, technology, engineering and mathematics) design. The study was conducted on the example of tightening the vertical levers of a freight wagon bogie. The features of the tightening design as well as the strength calculation for the rod system are described. Its loading under the action of an external force was simulated using the finite element method by means of the SolidWorks simulation software to determine the stress distribution and displacement fields in the tightening. A 3D-printing of the tightening prototype was carried out, which confirmed the accuracy of digital models and the effectiveness of additive technologies for their creation. The achieved results showed the potential for using 3D-printing to test and improve wagon brake systems. The presented methodology has practical significance for mechanical engineering, transport systems, and automation, as it can be used to reduce design and production cycles and increase the product competitiveness
Automation of small sample positioning for mechanical testing in hot cells
Full text linkThe main objective of this paper is to propose an improvement and automation of the current mechanical testing procedure of concrete and rock samples in hot cells, i.e. in laboratories designed for radioactive sample testing. The paper describes the effect of radiation on the different components of concrete and consequently on the concrete itself. To give a general idea of sample handling and hot cell operations, safety precautions are prescribed which significantly prolong and complicate the handling of a radioactive rock sample. Video recordings of the tests were used to analyse the progress of the tests. The main issues were the placement of samples off the axis of the compression test machine, sample curvature, compression test machine design and poor recording of sample deformation. New centring stops were introduced to improve the handling of the specimen when placed in the test machine. Additionally, the use of image processing was proposed to evaluate the correct placement of the sample in the test machine. These improvements should lead to easier sample handling and correct results which will serve as a good basis for subsequent numerical analyses
Experimental validation of MHD arc simulation in encapsulated horn gap arrangements
Full text linkThis work describes the use of experimental methods on model spark gaps for comparison with the simulation models (MHD) from the ignition of the impulse arc to the entry of the arc into the arc chamber, taking into account material effects and thermal reignitions of the arc, e.g. as a result of the gas flow within the encapsulated spark gap. Examples are provided to show that the simulation can accurately represent the experimental processes and improve the understanding of the complex processes
Investigation of detecting DC series arcs with short gaps to simulate failure conditions in actual low-voltage DC facilities
Full text linkDirect current (DC) facilities are increasing with the spread of renewable energy such as photovoltaic power generation. DC series arc may occur in poor contact or disconnecting in the facilities and cause fire incidents. This paper presents DC series arc generation experiments in air considering actual failure conditions, and Wavelet transformation analysis of the measured current waveform. Using the obtained results, a method of detection of arc generation in low-voltage DC facilities is proposed
Modelling of microdischarges in metal vapour of cadmium in comparison with electrical measurements
Full text linkMicrodischarges in cadmium vapour occur in a testing equipment for safety assessment of electric devices for explosion protection. In this work, a unified non-equilibrium model is employed to obtain the plasma properties for a current of 60 mA and gap lengths from 20 up to 160 µm corresponding to conducted experiments. The predicted voltage as a function of the discharge length agrees well with the measured values. The model provides the heat generation relevant to the ignition of a gas mixture
Electric breakdown in CO2/O2 gas mixture in weakly and strongly non-uniform electric field distributions at temperatures 300-4000K
Full text linkGas breakdown in weakly and strongly non-uniform electric fields at elevated temperatures, which can occur in gas circuit breakers after current interruption, is decisive for the performance of such devices. In a previous contribution [1], breakdown under such conditions was examined for the case of nearly uniform electric field distribution in a test setup. Results of an investigation of weakly to strongly uniform electric field distributions in axial and transverse gas flow will be shown in the present contribution. The pressure was typically in the range of 0.1 MPa to 0.4 MPa and temperatures were in the range of 300 K to 4000 K. The conditions for breakdown and their dependence on temperature and pressure will be discussed