Analysis of start-retardation modes in high-power synchronous electric drives

The article analyzes the start-retardation modes of synchronous electric drives of high-power exhausters, which are accompanied by high starting currents, not only under a direct start, but also under control of electric energy flows from a semiconductor converter. A mathematical model of electric drive is proposed and substantiated for the analysis of transition processes of ac electric drives. This model has an electromechanical converter that constitutes the links with distributed parameters. A distinctive feature of the model is refinement of the magnetization characteristic of the magnetic-circuit steel, which was carried out during full-scale measurements of the variables of the synchronous electric drive with direct start of the exhauster. To check the adequacy of the mathematical model, the results of a full-scale test were compared with the simulation results by statistical methods using Student’s criterion. The computational results using the proposed model were compared with the calculations by the classical models with lumped parameters. It has been noted that, in the overload zone (for M > 1.5 MN) the calculated values differ considerably, with this being especially evident at low speeds. The obtained results can be recommended for selection of the parameters of semiconductor converters.     

Steam Condensation from a Moving Steam-Gas Mixture

To date, heat exchange has been studied to the greatest extent for the case of the condensation of pure still and moving steam as well as for the case of condensation from a still steam-gas mixture. There are hardly any papers available wherein a moving steam-gas mixture with a substantial content of noncondensable gases is considered. To investigate this process, an experimental workbench of the working section has been developed, which makes it possible to determine the local values of the heat transfer coefficient from the steam-gas mixture to the walls of cooled heat-exchange tubes at different parameters and velocities of the gas-steam mixture. In the first four rows of tubes of the working section, there is no cooling, and their function consists in a hydraulic stabilization of the flow. In the fifth and the sixth row of tubes, the wall temperature of the cooled heat-exchange tubes is measured for determining the heat transfer coefficients from the moving steam to the tube walls. The seventh row of tubes is also not under cooling. Measuring tubes with temperature sensors have been manufactured that make it possible to obtain the wall temperature for determining the heat transfer coefficient. The adopted scheme of steam motion and the measurement system make it possible to obtain correct results of the heat and mass transfer investigation in the course of steam condensation from a gas-steam mixture with a significant content of noncondensing gases. The studies on steam condensation from a moving steam-gas mixture have been carried out in the range of parameter ρw² = 9.5 ? 66 Pa and at a volume concentration of air in the steam amounting up to ν_air = 0.18. Convective heat transfer coefficient α values for the heat transfer from a moving steam-gas mixture to the wall of a cooling tube were obtained. At small values of parameter ρw² = 9.5 Pa and the volume fraction of the air content ν_air = 0.06 in the steam, the average heat transfer coefficient exhibits a decrease by a factor of two as compared with that inherent in the condensation of almost pure steam. At the values of parameter ρw² = 66 Pa and at ν_air = 0.06, the average heat transfer coefficient decreases by 1.3 times. The studies on almost pure steam are in good agreement with Berman’s dependence.     

Parametric optimization of a synchronous electric drive with improved mass and size parameters

This article describes a possible new synchronous drive with an active concentrated winding and a stator with a number of phases other than three, control laws, and nonsinusoidal phase currents. This drive is characterized by improvements in weight and size achieved by taking into account the interaction of the electric motor and the inverter. Using the criterion of maximum effort to volume ratio of the electric machine, we have carried out parametric geometry optimization of the stator and rotor backs and windings slots. We have listed recommendations on selection of the number of phases and main circuit connections of the electric power converter that feeds the electric machine. We have proven that, by means of intelligent selection of geometrical parameters for an electrical–mechanical converter slot, it becomes possible to improve the mass and size parameters by approximately 30% relative to conventional solutions.     

Synthesis of electric drives realizing limit operating regimes in terms of operation speed and overload capacity

A special class of machine electric drives, which have an increased range of variation of the load torque and speeds with harsh and extreme operating conditions, are considered. It is shown that expansion of these parameters without increasing the rated power of the electric drive provides a significantly improved quality of technological regimes without increasing the cost of the electric drive. The strategy of the synthesis (design) of electrotechnical complexes is formulated providing the limit characteristics and consisting of the following stages: synthesis of a generic mathematical model, determination of the limit capacity of the object of control, parameter optimization of the electrotechnical complex in order to provide the limit characteristics, selection of simplified mathematical models of an electric drive, synthesis of the structures and the control system, and the search for the phase path of motion of the electric drive–working body system realizing the extreme operating regime. A determination of the possibilities of each stage is given.     

Thermochemical processing of high-sulfur Israeli shale

The thermochemical processing of high-sulfur shale from the Mishor Rotem deposit (Israel) is studied in terms of the material balance, in a Fisher retort and a larger-scale laboratory system. The properties of the products (tar, char, and gas) are determined. The shale tar has a high sulfur content, on account of the presence of a wide range of thiophene derivatives. In the fractions of semicoking tar from Mishor Rotem shale that boil at temperatures up to 250°C, 236 compounds are quantitatively identified. The content of thiophene and its homologs with the substituents C₁–C₅ and of benzothiophene with alkyl substituents C₁–C₃ is determined.     

Nanotextures of composites based on the interaction between hydroxyapatite and cellulose Gluconacetobacter xylinus

Organic-inorganic composite materials with different nanotextures have been prepared using three methods based on two nanosized and biocompatible compounds—cellulose Gluconacetobacter xylinus (CGX) and hydroxyapatite Ca₅(PO₄)₃OH (HA). The structure of the initial components and their composites has been studied using the methods of X-ray diffraction, electron microscopy, and computer simulation. During the combined aggregation of aqueous HA and CGX suspensions, the phenomenon of their adsorption, in the process of which the axis c of HA crystals is oriented parallel to the plane (?110) of CGX microfibrillas, was observed. By varying the quantitative ratio of the components and the methods of introducing HA into composites, it is possible to obtain a wide spectrum of materials for medical practice.     

Liquid–Liquid Equilibrium in an Extraction System Based on Polyvinylpyrrolidone-3500 and Sodium Nitrate

Theoretical Foundations of Chemical Engineering - Liquid–liquid phase equilibrium for a new extraction system based on polyvinylpyrrolidone-3500 and sodium nitrate at 298.15, 313.15, and...     

Electrical resistance of copper under shock compression: Experimental data

The electrical resistance of copper foil under shock compression is measured. The electrical resistance and electrical conductivity are plotted as functions of the shock pressure in the interval up to 20 GPa. These dependences are monotonic and have no visible inflections or singularities. A qualitative dependence of the electrical resistance of the metal on the shock impedance of the material of the block containing the sample is found. A comparison of the data obtained in this study with results of other authors shows that it is important to take into account the block material, the shape and thickness of the sample, and the procedure of determining the state of the sample.     

Study of Adsorption of TiO Nanoclusters on a TiS 2 Single Layer via the ab initio Random Structure Searching

The adsorption of TiO nanoclusters onto a TiS2 single layer surface is investigated via the density functional theory in combination with random structure searching algorithms. The nanoclusters are Ti—O dipoles and their orientation in the electrostatic field is induced by S atoms near the TiS2 single layer surface. The binding energy of nanoclusters with a TiS2 single layer surface is found to be 4.713 eV. Another curious observation is the creation of a nanocluster with an S–S–S–O anionic tetrahedron by Ti atoms, where the O anion is located at the maximum distance from the surface.