Recently, there has been an increased interest in the use of artificial neural networks in various branches of the electric power industry including relay protection. The operation of the traditional microprocessor-based relay protection device is based on calculation the RMS values of the monitored current and voltage signals and its comparison with the predetermined thresholds. However, calculated RMS values often do not reflect the real processes occurring in the electrical equipment under protection due to, for example, current transformer saturation. In this case secondary current has a characteristic distorted waveform, which is significantly differs from its ideal (true) waveform. This causes underestimation of the calculated RMS value of the secondary current compared to its true value; also, it causes a trip time delay or even to a relay protection devices operation failure. In this regard, one of the perspective applications of the artificial neural network for the relay protection purposes is the current transformer distorted secondary current waveform restoration due to its saturation. The article describes in detail the stages of the practical implementation of the artificial neural networks in the MATLAB-Simulink environment by the example of its use to reconstruct the distorted secondary current waveform of the saturated current transformer. The functioning of the developed neural networks was verified in the MATLAB-Simulink environment; with the use of the SimPowerSystems component library a model was implemented which allow simulating the current transformer saturation, accompanied by the secondary current waveform distortion, and its further restoration using developed artificial neural networks. The obtained results confirmed the ability of the neural networks that had been developed to almost completely restore the distorted secondary current waveform. Thus, it seems promising to use pre-trained artificial neural networks in real relay protection devices, since such use will ensure the speed of real relay protection devices; their operation reliability will also increase.

. “Sticking” and vibrations of the stator of permanent magnet generators cause their increased wear, noise; also, their operation efficiency decreases. The article theoretically considers the possibility of eliminating the starting torque and oscillation of the rotation torque of the generator with permanent magnets without load due to mutual compensation of the interaction of coils with the field of permanent magnets at a certain symmetry of this field. The mentioned pheno-menon is called pi-resonance. For the specified class of model interaction potentials of the field of permanent magnets and coils, it has been shown that full compensation occurs with a certain number of coils (Ns) and magnets (Nr), while for other combinations of {Ns, Nr} the interaction is in the nature of oscillations. The corresponding tables for various classes of potentials are given which can serve as a basis for making design decisions when developing generators. Pi-resonance more probably takes place in the case of even number of stator coils and odd number of magnets, as well as with an increase in the number of stator coils. The cases of both one-sided and two-sided arrangement of the stator relative to the rotor are considered. Numerical modelling has shown that the pi-resonance is easily destroyed if the placement of magnets or coils is inaccurate, as well as by the magnet field potential symmetry breaking. An error in the angular arrangement of the coils of 1° can result in the appearance of a significant “cogging” of the rotor with energy of the order of the interaction energy of an isolated magnet – coil pair. A distortion of the symmetry of the potential yields a result similar in scale which is equivalent to the adding of a rump function with the amplitude of 10 % of the amplitude of the symmetric periodic potential. The patterns that have been discovered can be used in the design of efficient generators with reduced level of noise and vibration.

The problems of reactive power compensation and improving the quality of electrical energy in the power supply systems of industrial enterprises are inseparable. Their relevance is due to the widespread use of electric receivers that consume reactive power and distort the quality of electrical energy in the network, as well as the implementation of new technologies, systems and equipment into production that make increased demands on the quality of electrical energy consumed. An important characteristic of the quality of electrical energy rationed by GOST 32144–2013 is the non-sinusoidal voltage. The main reason for the non-sinusoidal voltage in the electrical networks of industrial enterprises is the use of electrical equipment with a nonlinear voltage characteristic, which is a source of conductive electromagnetic interference, in particular: adjustable DC and AC electric drives, uninterruptible power supplies of electric receivers, electric welding equipment, electric arc furnaces, induction heating installations, gas-discharge radiation sources. Due to the nonlinearity of the current-voltage characteristics, the above devices consume a non-sinusoidal current from the network, which causes harmonic distortion of the supply voltage, including the fundamental harmonic component and higher harmonic components that are multiples of the fundamental frequency. Non-sinusoidal voltage, in turn, causes additional losses of power and energy in the elements of the electrical network, causes overheating and accelerated aging of the insulation of electrical equipment, reducing its operational reliability and reducing service life, worsens the accuracy of electrical measurements, causes malfunctions in automation systems, telemechanics, relay protection, electronic systems and communications. Non-sinusoidal voltage significantly complicates the compensation of reactive power in the electrical network. Compensating devices are made on the basis of capacitors, whose electrical parameters (resistance, power, current) depend on both the magnitude of the supply voltage and its harmonic composition. The present article identifies problems and proposes solutions in terms of reactive power compensation and improving the quality of electrical energy in electrical networks containing thyristor voltage converters and frequency converters used in adjustable electric drive installations of industrial enterprises.

. The results of numerical studies carried out on the basis on a mathematical model developed by the authors of this paper devoted to the investigation of the influence of various factors on the characteristics of the process of heat treatment of composite products in industrial heat technology installations in the presence of internal heat emissions distributed over the volume of individual layers of the product are presented. The formulation of boundary conditions for this model is proposed, considering the multilayer structure of products and the peculiar properties of the organization of their heat treatment process in a heat technology installation. A detailed description of the mathematical model was presented in the previous works. In this study, the functions of temperature distribution and the coefficient (degree) of hydration in the spatial regions that make up the product have been studied as characteristics of the heat treatment process. Model composite products of the same shape and structure but of different volume, consisting of two layers of material in which an exothermic hydration reaction takes place separated by a layer of expanded polystyrene were considered. The temperature-time regime of heat treatment was assumed to be close to that used in industrial conditions in the production of three-layer external wall panels. The boundary and initial conditions corresponded to the conditions of heat treatment on flat stands with water heating and sheltering products from above. It has been determined that the presence of a thermal insulation layer in the core of the product separating the layers that have an internal heat source, changes the distribution of temperature values and the hydration coefficient in the upper and lower layers significantly. An increase in the characteristic volume of the product leads to an increase in the influence of internal volumetric heat release on the processes of heating and hydration, while heat release caused by the course of the hydration reaction begins to have a decisive influence on them.

The hydrogen removal system ensures hydrogen safety. At a VVER nuclear power plant, it consists of passive catalytic hydrogen recombiners. The calculation of devices is of great importance for safety justification, since the complex conditions of an accident at a power unit are not reproducible in experiments. The recombiner consists of a casing and a cassette with catalytic elements, the design of which ensures the passage of a gaseous medium through the device. Upon contact with the catalyst, a chemical reaction of hydrogen and oxygen compounds occurs, accompanied by the release of heat; as a result, the concentration of hydrogen under the shell decreases. The problem is starting from a cold state since the activity of the cold catalyst is low, and the thrust is not observed until the catalyst is heated and a column of warm gas is formed inside the device. The transition from the cold state to the working state takes a certain time, during which the recombiner performance is below nominal. The start-up time is a parameter that is important in terms of safety. The article calculates the start-up time of a hydrogen recombiner with a catalytic block in the form of equidistant parallel catalytic plates. Local cross-sectional averages and transmission coefficients are used, the latter taking into account the influence of free convection and chemical reaction. The gas velocity is determined by the balance of buoyant and resistance forces. The calculated data and the data known from the scientific and technical literature coincide satisfactorily. As a conservative estimate of the start-up time of the recombiner, it is recommended to use the value of 300 s. An increase in temperature practically does not affect the start of the recombiner with an active catalyst, an increase in the concentration of hydrogen accelerates the start, and a decrease in pressure slows it down. The results obtained in the study can be used in the justification of the safety of VVER nuclear power plants and the examination of reports on the justification of the safety of power units.

A program has been developed for the selection, calculation and thermodynamic analysis of turbine units based on the organic Rankine cycle, which makes it possible to determine the values of the optimal parameters of the working fluid, as well as to select the working fluid with the highest exergetic efficiency for cycles on superheated steam and with intermediate overheating. The structure of the developed mathematical model for thermodynamic analysis is presented. The studies were conducted at pressures up to 20 MPa and temperatures of the working fluid in front of the turbine up to 250 °C; the temperature of the working fluid at the outlet of the condenser was 25 °C, while the maximum temperature of the working fluid at the outlet of the intermediate superheater was 250 °C. The analysis of the results showed that the use of reheating in the organic Rankine cycle – as well as in the classical (i. e. steam turbine) one – led to higher exergic efficiency of the cycle. On average, for the studied working media, the increase in exergetic efficiency at optimal parameters of the working body was 4.28 %. However, some working media significantly exceeded this result (for example, 8.14 and 6.56 % for R717 and R32, respectively) due to their thermophysical properties. The error for all low-boiling working media did not exceed 2 % of the obtained result of exergetic efficiency. Grassmann – Shargut charts were made for the studied circuits using the example of the refrigerant R245FA. Exergetic analysis demonstrated that intermediate overheating at thermodynamically optimal parameters of the working media before the high and low pressure parts of the turbine causes a decrease in exergy losses in the heat recovery boiler, a significant increase in regeneration in the heat exchanger, an increase in exergy losses in the pump and their redistribution in the turbine unit, heat exchanger and condenser.

Aluminum radiators of various brands have become widespread on the market of heating equipment nowadays. It is possible to reduce the cost of manufacturing radiators by reducing the surface of the heat-emitting internal fins, while maintaining their appearance, and the heat transfer claimed by the manufacturer is being maintained high enough. Decree of the Government of the Russian Federation No 717 of June 17, 2017 introduced mandatory certification of all types of heating appliances. Deviations of the nominal thermal power of the section indicated in the device passport from the indicators established by the test results should not exceed the maximum permissible values (from –4 to +5 %). As a rule, no previous tests were carried out by the manufacturer. Thus, the study of the influence of the radiator connection mode with a reduced fin surface on its thermal characteristics is an urgent task. The article presents the results of the studies of a factory aluminum radiator with a reduced surface of STI Classic brand fins with a heat output of 1.92 kW under design conditions. The specified heat transfer of the device does not take into account its connection mode. The reduction of the inner and rear fins reduced its surface area by 28.8 %. As a result of the experiments carried out, it was found that the thermal power of the device is 22 % lower than the declared value when connected from top to bottom and 48 % lower when connected from bottom to top under design conditions. During the warmer period of the heating season, with a small temperature difference between the coolant and the indoor air, the average heat output of the radiator coincides with the declared value.