The magnetizing current inrush appears in electrical power units equipped with transformers in case of no-load energizing of the power transformers and in a number of other cases. This phenomenon could cause a false triggering of the current protection. To prevent incorrect actions of the current protection during the magnetizing current inrush a protection blocking is carrying out. The blocking principle operation is based on the fact that in a three-phase system in normal mode and in case of symmetrical short circuit the first harmonics contained in the phase currents of electrical installations form a direct sequence and the second ones – the negative sequences. In case of an asymmetric mode, including an asymmetric short circuit, the negative sequence appears, formed by the first harmonics that are part of the phase currents of the specified system. In magnetizing current inrush modes, second harmonics of significant magnitude are present in phase currents, which form the negative sequence. Based on the analysis of the information parameters of the specified sequences currents, identification of the magnetizing current inrush and short-circuit modes is performed with the implementation of the protection blocking if necessary. The study of the current protection blocking functioning was performed using computational experiment by analyzing the calculated changes of blocking parameter compared with the threshold setpoint. The specified researching is done by using the digital model that is implemented in the dynamic modeling environment MatLab-Simulink. As a result of the performed calculations, the principal operability of the proposed current protection blocking was confirmed that provides a fairly reliable identification of the magnetizing current inrush and short-circuits modes, regardless of the degree of saturation of current transformers. It was found that the proposed principle of the current protection blocking has a higher sensitivity in comparison with the classical one based on the estimation of the ratio of the second and first harmonics of the phase currents. In short-circuit modes in an electrical power units the proposed blocking causes a current protection operation delay that can be reduced by digital filters performance improvement.

 

The linear wind load on the wires and cables acting perpendicular to the wire depends on the angle between the direction of the wind and the axis of the overhead line. In the methodology of mechanical calculation of wires and cables, it is recommended to take the wind directed at an angle of 90° to the axis of span and it is not specified which side the wind blows from. For spans of air, this is not so much significant as for switchgear spans, where the deviations of the wires depend on the direction of action of the taps to the electrical apparatus. The article discusses various options for the location of taps and their effect on the wire, as well as changing the direction of the wind. An algorithm for calculating the horizontal deviation of a flexible wire and its increase coefficients in the presence of horizontal concentrated loads due to the action of windon spacers, barriers, taps to electrical apparatuses and other structural elements of substations and overhead lines is given. In the absence of wind, horizontal concentrated loads and deviations occur when an arrangement of the taps is non-keel. The formulas for calculating the horizontal component of the load coefficient to solve the equation of state in the presence of horizontal concentrated forces acting in any direction have been derived. The results of the mechanical calculation are obtained for the cases of one and two horizontal concentrated forces, differently oriented with respect to the distributed wind load. In design practice it is recommended to take the wind flow in the direction of the action of horizontal concentrated forces, since in this case the greatest horizontal deviations and load factors are obtained. The reduction in the coefficients of the horizontal load occurs when the current lead is unloaded because of the opposite directions of the wind and horizontal concentrated forces. In the absence of wind, it is proposed to use the formulas for calculating horizontal deviations and load after finding the product of the coefficient of increase in horizontal deviations and the horizontal component of the coefficient of load per linear load.

The relevance of research is caused by the increase of the number of photovoltaic power plants in the Republic of Belarus and, accordingly, the need to solve problems of diagnostics of photovoltaic modules. A new Simulink model of a photovoltaic module focused on using the standard SimPowerSystems library of power supply system elements (a part of the MatLab/Simulink) is proposed. The model allows altering solar irradiation values for each solar cell of the module. The use of the model also makes it possible to obtain calculated values of voltages and currents at the photovoltic module output. In addition, the model provides the simulation of individual solar cells shading in the module. The developed Simulink model operates on the base of a well-known exponential dependence describing the volt-ampere characteristic of a photovoltaic module, and also takes into account the real circuit of the module with bypass diodes. The series resistance of the photovoltaic module is calculated by the subtraction between its experimental and theoretical volt-ampere characteristics for conditions that are close to normal. The Simulink model of the SF-P672300 module contains 72 nonlinear elements implemented on the basis of controlled current sources and connected in series. The model solved the problems of the algorithm stability for calculating algebraic cycles by introducing constraint the current and the voltage parameters. Experimental studies for the fully illuminated and partially shaded SF-P672300 module have demonstrated that the maximum relative error of the developed Simulink model does not exceed 15 %. Experimental and theoretical current-voltage characteristics of the SF-P672300 module under full illumination and partial shading are presented. The presented Simulink model may be used both at the design stage and at the operation stage of photovoltaic power plants in order to simulate and analyze the factors that affect the operation of them.

When industrial waste flows (mixtures of different substances) are burned, thermal energy is generated in the combustion chambers of the heat generating plants. In this case, the energy contribution of the chemical compounds included in their composition is different. The article considers the enthalpies of combustion of the most characteristic chemicals, formulates the energy balance equations while simultaneously burning several mass flows of fuels, taking into account their calorific value. The general mechanisms of heat transfer to the walls of the combustion chamber are investigated. An analysis is made of the contribution of convection and the radiation mechanism to the total amount of heat transferred to the heat generator, depending on the process temperature. It is demonstrated that the heat transfer by radiation between the combustion chamber and the boiler tubes depends on the thermal radiation properties of ash deposition. In this case, the emissivity of the resulting ash deposition decreases with increasing temperature. The dependence of the maximum flame radiation on the C/H ratio by weight is considered using the example of the initial combustible chemicals that are part of solid, liquid and gaseous wastes of industrial technologies. The main pollutants which emerge during the combustion of industrial waste are determined. The mechanisms of formation of nitrogen oxides (NO_x), particulate matter, sulfur oxides (SO_x), halogen acids, polymers, soot, volatile organic compounds and ash are considered in detail. The distribution of various processes of formation of nitrogen oxides depending on the value inverse to the coefficient of excess air (φ = 1/α) is determined. A physical scheme and a system of chemical equations of the mechanism of soot formation which includes the most important stages of the formation of polycyclic aromatic hydrocarbons are presented. The stages of the separation of reactive ash-forming elements are considered. It is demonstrated that ash deposits pose serious problems in the operation of heat generators, especially those that have such a developed heat exchange surface, such as boiler plants. In this regard, the forms and conditions of the processes of ash deposition are also considered separately. The combustion conditions affecting the state, size and distribution of solid particles and the condensed phase of ash are determined.

Improving the operational efficiency (OE) of thermal power plants is one of the most important problems of electric power systems (EPS). According to modern concepts, efficiency is the simultaneous consideration of three properties of objects, viz. economy, reliability and safety. The methodology of their joint assessment assumes that the service life of the main equipment does not exceed the standard value, but this condition is now met by less than half of the production enterprises of a lot of EPS. In order to increase OE, it is necessary, first of all, to learn how to objectively compare the performance of objects both of the same type – in a given time interval, and unique ones – in adjacent intervals. Existing methods for calculating integrated performance indicators do not fully take into account the random nature of technical and economic indicators (TEI). The article presents a new method for comparing the OE of EPS objects, the essence of which is to switch from joint consideration of TEI to analysis of their relative changes in comparison with the factory default value (nominal value). Relative values of indicators characterize the amount of wear or residual life. In this case, for example, the arithmetic mean of the relative values of the TEI determines the average wear of the object. This physical representation enlivens integral indicators, and their comparison and ranking ceases to be science-intensive. It is proposed to take into account also the degree of variation of relative deviations (wear), which is adequate to the object’s misalignment. It manifests itself in a significant change (deterioration) of one or (less often) two relative values of the TEI in the calculated time interval (month) and is characterized by such statistical indicators as the geometric mean and the coefficient of variation of relative deviations. Herewith, if the arithmetic mean value of the object’s wear is restored during major repairs, then the misalignment is eliminated much faster – during current repairs. A necessary condition for the feasibility of using these or those integral indicators is their functional and statistical independence. The results of the studies performed using the simulation method made it possible to establish that the smallest correlation occurs between the integral indicator calculated as the arithmetic mean of random variables and the integral indicator calculated as the coefficient of variation of the same random variables. Comparison of correlation fields clearly confirms these conclusions.

The article considers 46 low-boiling working media (LBWM) with zero potential for ozone layer destruction. Out of them, 14 ones are single-component hydrofluorocarbon refrigerants, 28 ones are multi-component mixtures of hydrofluorocarbon refrigerants, and the four ones are native refrigerants. Thermodynamic analysis of working media based on the classical turbo-expander scheme with a heat exchanger designed to cool the superheated LBWM that has left the turbo-expander has been performed. For this scheme, a cycle is constructed in T–s-coordinates. The LBWM was compared using the exergetic coefficient of efficiency (KE). In the course of the study, it was found that for some LBWM, the sequence of location of the exergetic efficiencydependences on temperature at thermodynamically optimal working medium pressures is preserved over the entire temperature range under study (from 100 to 300 ^оC). In other words,if the working medium has the highest exergetic efficiency coefficient, then this property is inherent in it at any temperature in a given interval. It is proposed to perform the analysis of the LBWM for exergetic efficiency at an arbitrarily selected temperature (250 ^оC). The study demonstrated that the highest exergetic efficiency of natural refrigerants is R600A (50.25 %), among single component hydrofluorocarbon refrigerants – R245FA (50.00 %), R1233ZD(E) (49.91 %), R236EA (49.59 %), among multi-component mixtures of hydrofluorocarbon refrigerants – R429A (47.92 %), R430A (47.49 %) and R423A (47.47 %). Out of the all examined refrigerants, the following ones have the highest exergetic efficiency of all the considered LBWM: R600A, R245FA, R1233ZD(E), R236EA, R1234ZE(Z), R236FA. They belong to both natural refrigerants (hydrocarbons) and single-component hydrofluorocarbons. It should be noted that each of these working media has its drawbacks: some have a high potential for global warming, others are explosive, and others have a high cost.

Borehole water intakes of underground water are widely used for water supply of agricultural towns, urban settlements, small and large cities and megacities. The number of consumers in these localities determines the number of water intakes, the number of wells, their productivity, location and connection to the prefabricated water conduits. Due to the increase in the use of underground water, the existing water intakes are being reconstructed and expanded. These works are accompanied by grouting of failed wells, their re-drilling, drilling of additional wells, re-laying of old and laying of new prefabricated water conduits. All this causes the complexity of the configuration of prefabricated water conduits due to the construction of jumpers and rings, the emergence of new wells with connection lines. Under the new conditions, in order to properly develop water intake operating modes which meet the minimum energy consumption for lifting and delivering a required volume of water to the collection-and-control tanks, to accurately choose the appropriate water lifting equipment in wells, to develop measures for intensifying water intake alongside with a forecast of their efficiency and to optimize the operation of the water intake, it is necessary to create its mathematical model that allows performing complex calculations. Water intakes with ramified prefabricated water conduits, as well as with an area scheme of the location of wells and a ring scheme of the connection of prefabricated water conduits are the most difficult object for mathematical modeling. The methods of calculating such water intakes are not sufficiently reflected in the literature, and there are no specific examples of calculation. The present article aims to clarify the methodology for calculating borehole water intakes with ramified prefabricated water conduits and with a ring scheme of their connection.