The development and implementation of a digital current measurement element for proper operation during current transformer (CT) magnetic core severe saturation are considered. CT transient performance is often accompanied by primary current transformation to secondary one with great errors. In this case the secondary CT current which is an input signal of the digital measurement element differs from the ideally transformed CT current both in shape and magnitude. This causes impermissible signal settling time at the standard digital measurement element output. As a result, main requirements to the protection devices such as reliability and fast operation are violated, that in some cases makes the high-speed protection device ineffective. To solve this problem, it is proposed to form the output signal of the digital current measurement element in depending on the input signal total harmonic distortion (THD) coefficient value. Moreover, it is worthwhile to form the output signal so that for a low CT saturation conditions this output signal slightly differs from the secondary current RMS value, and for a severe CT saturation conditions it exceeds this value. Digital current measurement element model has been developed and implemented in the MatLab-Simulink environment using the following blocks: a digital filter block responsible for the input signal fundamental frequency component magnitude calculation; a digital filter block responsible for the input signal RMS value calculation; and, also, a standard blocks for basic mathematical calculations needed for proper functioning of the proposed measurement element. The functional testing of the proposed digital current measurement element model was carried out using the signal, that was similar in form to the waveform of the secondary current of the severe saturated CT. The tests that had been performed confirmed that the proposed digital current measurement element in comparison with the standard current measurement element ensures stable functioning and enhanced operation time during transients.

Operational control of parameters of electrolytes (first of all–of specific electric conductivity), is an important electrochemical technology. The methods of measurement of electric conductivity of electrolytes is a subject of permanent discussions because of complexity of physical-and-chemical processes accompanying ion transport and of electrolyte polarization near surfaces of electrodes and of electrochemical processes on the electrodes surfaces. Actual highand low-frequency conductometric methods require relatively expensive equipment and are not free of methodological flaws. In this paper a new method of electric resistance of liquid electrolytes is described and substantiated. It is based on automatic performance of a series of measurements of electrolyte resistance at DC, data processing and extrapolation of an appropriate dependence to threshold voltage at measurement cell plates. The character of functions approximating resistance-applied voltage dependence and method of resistance determination are substantiated. The measurements of specific resistance of some electrolytes were performed. The advantages of the proposed method and measuring device are their simplicity, cheapness, reliability and, consequently, wider possibility to utilize it at technological lines and processes, even at such sites of production processes where such a control was impractical earlier. The method can be widely used for express-diagnostics of electrolytes in such areas as electrochemical energy storage, medicine, agriculture, chemical industry, food production.

The variable speed electrical drives for industrial mechanisms with a constant static torque usually operate in a large range of speeds and loads. Along with this, for any speed of a given range the electrical drive motor is to provide a continuous permissible torque without overheating. Mostly the electrical motors have self-ventilation; the ventilator being located on the motor shaft. In such motors heat dissipation depends on a motor speed. The permissible continuous motor torque is determined out of a heat balance equation where power losses being converted into heat must be transferred in the ambient space and the motor temperature must not be over a permitted level for a given class of winding insulation under the certain ambient temperature. A heat balance equation is usually obtained on a basis of a one-mass motor heat model, i. e. the model that was used in this research. But even the one-mass heat model gives a non-linear heat balance equation. In order to get convenient analytical expressions out of the motor heat balance equation, it is necessary to take some justified assumptions; the latter was also implemented in this research. As a result, formulas have been obtained by which the long-term permissible motor torque can be calculated as a function of the relative speed of the rotor at a given ambient temperature. For the examples presented in the articles we chose (20 and 40 °С as a standard temperature for the thermal calculation of electrical machines). Dependences of a relative permissible continuous motor torque m on a relative frequency value (or relative rotor speed) are presented for three synchronous motors with permanent magnets and rated power of 3; 25 and 250 kW.

The paper presents a fragment of on-going investigations directed on creation of optimum data environment that ensures an access to world scientific journals and other publications which are necessary for qualitative implementation of works on priority directions of R&D in the field of road-construction industry in the period of 2016–2020. A citation analysis has been applied while using data of Journal Citation Reports for selection of world scientific serial publiccations which are necessary for execution of investigations on heat and mass transfer in road dressings. The road dressings are considered as open heterogeneous thermodynamic systems. Their deformations occur under various climatic conditions due to heat and mass transfer processes and interaction of transport flows and road surface. Crack formation takes place in depth of the road dressings and on road surfaces as a result of temperature, mass transfer processes. As it is known material structure of constructive layers especially which are created with the help of technogenic wastes (asphalt-concrete, concrete, reinforced concrete scrap and products of its recycling, brick rubble, various wastes of production etc.) influence on heat and mass transfer. The paper presents results of investigations on heat flows, boundary layers according to air viscosity, velocity of geometric permeability characteristics, capillary pressures in road pavements.

The article presents and analyzes the results of an experimental study of the aerodynamics of the flow in the working volume of cyclone chambers of a large relative length, significantly exceeding the length of the chambers that were used in the previous studies. Air supply to the chamber swirler was carried out tangentially from diametrically opposite sides by two inlet channels. The air discharge from the working volume of the chamber was made from the opposite end of the chamber through a round axisymmetric hole. The values of the area of the inlet channels and the diameter of the outlet were varied with replaceable incrustations and clamps. The experiments were performed with the use of laser Doppler anemometry. As a result, previously unknown features of flow formation in the working volume of relatively long cyclone chambers have been determined. The main characteristic values of the working volume flow have determined as well. In particular, the determining influence of the flow core characteristics on its structure in relatively long cyclone chambers has been discovered. The calculated ratios have been chosen to determine these values depending on the geometrical characteristics of the chamber under study. The boundary of the near-wall flow region, in which favorable conditions for the flow instability are created, is determined. Numerical simulation of the flow in the ANSYS Fluent software has been performed. Based on its results, a comparison of the results of numerical simulation, calculated dependencies and experimental data is presented. A comparison of the results demonstrated a completely satisfactory coincidence. Data obtained in the process of research and calculated ratios can be used in engineering practice and are of an interest from the point of view of further study of aerodynamics in a highly swirled flow of cyclone devices in order of to improving the methods of their thermal and aerodynamic calculations.

The article deals with the problem of parametric optimization of automatic control systems for power units of 300 MW of Lukoml’skaya GRES in the mode of variable pressure of turbine inlet superheated steam. The modernization of automatic power control systems of all power units of Lukoml’skaya GRES was carried out in the nineties of XX century for the last time. At the moment, these systems no longer meet all the requirements of the new standard, which regulates the participation rates of thermal power units in the normalized primary frequency control and in automatic secondary control of frequency and active power flows. According to this standard, the time to achieve the half value of the required power change should be 10 seconds within the normal and emergency reserves; the time to achieve the full value of the required power change should be 30 seconds within the normal reserve and 2 minutes within the emergency one. The construction of the Belarusian NPP is also being completed; its first unit will be put into operation in 2019, and the second one–in 2020. After the launch of the NPP, the Lukoml’skaya GRES power units will be necessitated to operate in a wide range of load changes. It is for these reasons that it is necessary to improve the efficiency of power units in particular and of the entire power plant in general. This can be achieved with the help of the outlined method of parametric optimization of a typical system of automatic control of power units, which allows improving the quality of control of turbine inlet steam power and pressure. The results of computer simulation of transient processes in the system illustrate the technique described in this article and confirm its correctness and undoubted advantages over other methods of optimization of typical systems of automatic control of power units.

The article presents method and results of experimental study of the intensified heat transfer for the single-row bunch consisting of bimetallic pipes with spiral knurled ribs with the following parameters: outer diameter of a rib d = 56 mm; rib height h = 15 mm, rib pitch s = 2.5 mm, average thickness of a rib D = 0.5 mm; diameter of a rib at the bottom d0 = 26 mm, coefficient of fins j = 21. The pipes cross pitch S1 in a single-row bunch makes 58, 61, 64 and 70 mm. The intensification of a heat transfer has been arranged in a stream of heated air over an experimental bunch by means of two types of exhaust shaft i.e. the one with adjustable height and the one with the adjustable section through passage. The aim of the work was to perform an experimental study and to summarize the data of a heat transfer of the single-row bunches consisting of bimetallic finned tubes under the intensified (mixed) air convection and also to develop an engineering method of calculation of single-row recirculation air heaters. The results of experimental study of the intensified convective heat transfer of the single-row bunch consisting of bimetallic finned tubes in a stream of heated air are presented in the form of dependences of number of Nusselt on Grashof number and Reynolds number. As a result of generalization of experimental data, the generalized criteria equation for calculation of heat transfer of the single-row bunch consisting of bimetallic finned tubes when cross pitches of installation of tubes, the areas of exhaust outlets and heights of the exhaust shaft are various, has been obtained. The engineering technique for design calculation of the single-row recirculation air heater has also been developed.

New ways of experimental data processing by generalized complex variables that are characteristic of the drying process are presented. The authors presented the results of a study of heat and moisture exchange in the convective drying of thin flat moist capillary-porous materials. As a result of the processing of the experimental data, equations were obtained for determining the densities of heat fluxes, average integral temperatures, drying time and moisture evaporation rate in the second drying period. The relationship between the densities of heat fluxes in the first and second periods and the temperature change in the second period is revealed. The dependence for calculating the temperature of the material in the period of the falling drying rate taking into account the heat that is expended to heat the wet body is presented. The equations for determining the temperature in the second period by the temperature coefficient of drying, the rate of heating of the wet material and the rate of heating of the wet body are presented as well. An equation for determining the drying time by the value of the rate of loss of moisture content of the material is given. A mathematical expression for calculating the intensity of moisture evaporation in the first and second drying periods depending on the ratio of moisture content in the first period and the current in the second moisture content one is set. The conditions of a regular regime for heat and moisture exchange for a second drying period are adduced. The authors consider the possibility of determining the rate of heating of wet material by the heating rate using the graphical differentiation of the temperature function, which is described by the curve, as a function of time in the second drying period. The problems of using the methods of the theory of the regular regime for heating wet bodies during the investigation of the drying process are considered. The formulas for determining the rate of heating of the body and the rate of loss of moisture content are given. The accuracy of the experimental data processing and the reliability of the experimental equations obtained for all the materials under study are verified. As a result of the research, all the basic kinetic characteristics necessary for the calculation of heat and moisture exchange in the drying process have been determined.