Vol 27, No 2 (2023)

The aim was to assess the loading of large-size elements of machine structures using versatile strain gauges. A strain gauge was developed using a system analysis of failures and deficiencies in the manufacture and operation of large-scale structures, strain gauging, strength of materials methods, as well as the theory of elasticity of ring elastic elements. The ANSIS software package was used to calculate rational sensor parameters. The conducted study of ring elastic deformation (determination of stiffness and stress-strain state) allowed the authors to propose that the ring shape should be replaced by an octahedral polygon. This form is suitable for mounting strain gauges for simultaneous measurement of tension and compression, as well as bending and torsion, i.e., forces arising in a machine structural element or in the manufacture of large-size surfaces. The obtained results were used to derive dependences to determine the measurement error of the gauge under study. A comparative analysis of ring and octahedral gauges identified unique features of the latter, consisting in the possibility of assessing the measured values along the three coordinate axes with a high degree of accuracy. The conducted research shows that the proposed strain gauges are capable of registering the magnitude and fluctuations of loads with a high measurement accuracy. The proposed scheme of gauge placement makes it possible to determine the vertical and horizontal components of the forces arising in a structural element and to assess deviations in the process of measurement. In addition, the proposed measuring scheme minimizes the error of mutual influence of sensors. The developed force meter is a versatile device that can be used for registering static and dynamic impacts, as well as for digital control of force parameters in the range of up to 5 mm.

The aim was to develop, manufacture and test a technically simple dynamometer for monitoring the cutting process during boring and turning. An S20R-SSSCR09 right-hand cutter was selected as a research object. To register the cutting force and vibration movements of the cutter tip in tangential and radial directions, the cutter was equipped with four KF5P1-10-400-A-12 strain gauges mounted according to a half-bridge scheme. The bending stiffness of the cutter in two directions was measured by a DOU-3-01 compression dynamometer and a DDP-10A dial indicator. The cutter natural frequency was determined by a vibrogram of damped bending vibrations. The dynamometric boring tool was tested on a DMG NEF 400 turning machine by turning a workpiece made of 20X steel, 79 mm in diameter with a 200 mm extension, at a spindle rotational frequency of 600 r/min, a cutting depth of 0.8 mm and a longitudinal feed of 0.103 mm/turn. According to the conducted review of modern turning dynamometers and their designs, strain gauging of cutting tools is the simplest technical solution when carrying out boring procedures. The bending stiffness of the cutter in tangential and radial directions comprised 0.6 and 1.058 N/μm, respectively. The conversion coefficients for displacements in these directions were 3.5 and 4.2 μm/V, respectively. The mutual influence of registration of radial on tangential and tangential on radial displacements was 7.7% and 2.8%, respectively. The obtained vibrograms showed that the turning process under the given machining conditions is accompanied by distinct auto-oscillations of the cutter with a frequency of 561 Hz. Therefore, strain gauging of cutting tools provides information in the form of vibrograms about the two most important parameters of the cutting process dynamics – force and vibration displacements. The main advantages of the presented dynamometric cutting tool include its design simplicity, possibility of manufacturing in laboratory conditions, low cost and insensitivity to temperature and axial feed force variations.

In this paper, we investigate the possibility of using a solid fuel mixture based on lignite from the Bolshesyrsky coal mine and birch wood waste in power plants, taking synergistic interactions between the mixture components into account. Simultaneous thermal analysis was used to determine the main combustion characteristics of lignite, biomass and their mixtures. Non-isothermal heating was performed at a rate of 20°C/min across the temperature range of 25–800°C under the air flow of 50 ml/min. The sample weight was about 6 mg. Proximate and elemental analyses of lignite and biomass samples were performed according to conventional methods. The advantages and disadvantages of converting power plants operated on solid fossil fuels to a solid fuel mixture of lignite and biomass are discussed. The main combustion characteristics of lignite, biomass and their mixtures were defined. The ignition temperature of the coke residue and biomass was found to comprise 365 and 299°C, respectively. The temperature of combustion completion for lignite and biomass was 551 and 464°C, respectively. In comparison with lignite, biomass burns at lower temperatures due to the high content of volatile substances. The addition of biomass to lignite was found to reduce both the ignition temperature of the coke residue and that of combustion completion. An analysis of the combustion process of volatile substances and coke residue established the presence of both positive and negative synergistic interactions between lignite and biomass particles, affecting the maximum combustion rate and the mixture reactivity. The results obtained can be applied when designing power plants operated on solid fuel mixtures of lignite and biomass.

This paper is aimed at developing a versatile approach to selecting an optimal cable brand for overhead transmission lines for use in design practice, adapted to conventional and new-generation cable types. To implement multi-criterion evaluation of external factors and limitations when selecting a cable type, the methods of systems, hierarchy and comparative analysis were used. A method for selecting an optimal cable brand based on hierarchy analysis was developed along with an algorithm for its implementation when designing new or modernizing existing overheadlines. The developed approach is demonstrated on the example of construction and modernization of 220 kV overhead lines with the conventional AC cable and such new-generation domestic brands, as АСВТ, АСВП, АСк2у and АСТ. In the considered examples, the technical feasibility of the construction of a new overhead line was limited by the value of the sag. For the modernization project, the specific weight of the cable was of greater importance. The selection criteria included the span length, cable cost and admissible continuous current. The АСВП and АСТ cable brands showed the greatest compliance with the selection criteria (27.5% and 55.9%, respectively). Therefore, at minimum capital investments, the АСВП brand ensures the optimum span length in the construction of a new overhead line, whereas the ACT brand ensures the maximum capacity in the modernization of an existing line. The conducted verification calculations confirmed the feasibility and versatility of the proposed method for selecting a cable brand.

The aim was to study the effect of switching modes on the power of supply transformers in electrical networks up to 1000 V on the multiplicity of switching overvoltages, as well as to develop recommendations for their reduction. The study was carried out during switching of supply transformers in networks up to 1000 V. Vacuum contactors were used to study overvoltages arising during switching of supply transformers. Overvoltages were recorded using an RDN-1000 active divider and a Tektronix TDS2024B digital oscilloscope. The RC circuit capacitance was measured by a Mastech MY6243 digital LC-meter. To limit switching overvoltages, RC quenchers based on RC circuits were used, reducing not only the switching pulse amplitude, but also the rate of the switching pulse voltage rise. In addition, RC quenchers lack fading zones under high-frequency switching pulses. The capacitance of the primary winding of the transformers under study was measured. An increase in the transformer power was found to lead to a decrease in the multiplicity of switching overvoltages, when the transformer is disconnected from the mains. Under a 1.5-fold increase in the power of the transformer, its inductance and wave impedance decreases. As a result, when the same capacitance is connected to the transformer terminals, the wave resistance in more powerful transformers will be reduced to a larger extent (by 3 to 6 times), thus providing a more effective overvoltage limitation. The conducted experimental studies confirmed the effectiveness of RC circuits in limiting switching overvoltages.