In microprocessor current protection, instantaneous, amplitude, current, and average values can be used as current information parameters. They are determined as a result of the appropriate processing of the digital filter output signal. In unsteady modes, the specified parameters depend on the transient characteristic of the filter. Therefore, the behavior of the microprocessor current protection in case of damage is largely determined by the specified characteristic of the digital filter. Non-recursive Fourier filters and their varieties are most widely used in existing defenses. The main disadvantage of these filters is their relatively low speed. Based on them, filters with higher dynamic properties are implemented, in which frequency properties are preserved. Based on the similarity of the transient characteristic, the following varieties are distinguished: filters with a monotonic transient characteristic; filters with an aperiodic transient characteristic; filters with an oscillatory transient characteristic. The effect of these filters on the behavior of a micro-processor current protection containing the main high-speed and backup slow-acting stages has been investigated. As a result of the mentioned investigations, it has been shown that digital filters with a monotonous transient characteristic provide stable functioning and selective action of protection steps in case of damage in the main and adjacent sections. Filters with an aperiodic transient characteristic contribute to the non-selective action of the high-speed stage in case of short circuits at the beginning of the adjacent section. Filters with an oscillatory transient characteristic also contribute to the non-selective operation of the high-speed stage and can cause its unstable operation at short-circuit currents close in values to the operating and return currents. The slow-acting protection stage functions steadily and selectively for all types of transient characteristics of digital filters.

The asymmetry of power transmission mode parameters due to the induction current effect on structural elements of electrical equipment is investigated. Three-phase AC current produces a rotating magnetic field that affects the power transmission system symmetry, and when it is violated, the induction current appears that causes additional heating of the electrical equipment. To find the flux linkage with research object caused by uncompensated magnetic field, a calculation was performed using the Poisson equation for vector magnetic potential. The symmetrical components method is used to calculate power losses in the asymmetric mode, taking into account losses in the ground. There is proposed a parametric synthesis of energy balance in structural elements of outdoors electrical equipment to calculate and verify the induction heating, taking into account the processes of natural convection, radiation and thermal conductivity. There are shown the thermograms of power transformer and gantry pillars on guy rods to open the additional energy losses caused by induction currents. Calculation of power transmission via overhead line taking into account the mutual induction of supporting structure was carried out in a three-phase vector system and in a transformed system using the symmetrical component method for the case of longitudinal asymmetry. Accounting the earth's resistance leads to a change in the ratio of active and reactive components, i.e. active power losses increase, and reactive ones become smaller, and, correspondingly, the load angle decreases. There are proposed the solutions in above examples to reduce additional energy losses and a technical and economic benefits for overhead line is performed. The result of the work can be useful in the design and modification of power transformers and overhead power transmission lines.

The present article discusses the problem of the technical and economic efficiency of using materials with increased thermal conductivity when filling trenches of power cable lines. The specific thermal resistance of the soil significantly affects the permissible cable currents and, as a result, the choice of their cross-section. When the soil dries out or it is initially of high thermal resistance, the carrying capacity of the conductors decreases, which often forces the use of cables with a larger cross-section to provide the required load current. One of the ways to improve cooling conditions is to use a special backfill with lower thermal resistance values, which is more expensive than the ground one. This raises the question of the feasibility of such a solution, since more expensive materials may not pay off in some cases. An optimization technique is proposed based on the calculation of reduced costs, taking into account the cost of cable, line construction and operating costs. The model that has been developed takes into account the influence of both normal and post-emergency operation modes. It is shown that increasing the cable current capacity due to special backfilling can reduce the cable cross-section by one step and, thus, compensate for the cost of more expensive material. Otherwise, the use of special backfills becomes impractical. To solve the optimization problem, a genetic algorithm implemented in the MS Excel environment was used. The results of calculation examples are presented, showing that the proposed methodology and algorithm can be used for various voltage and laying conditions, allowing the designer to select effective parameters of the cable line design.

The article presents an experimental study of the dependence of the heat transfer rate of a six-row staggered bundle made of bimetallic ribbed tubes on the technological factors of manufacturing a cold-rolled ribbed aluminum shell on a supporting tube. The bundle was installed in a wind tunnel and washed by a forced perpendicular air flow. To measure heat transfer, a local thermal modeling method was applied using an electrode calorimeter tube of a fluidized type installed in the middle of the third and fifth transverse rows of the bundle. The experimental data were presented in the form of dependences of the Nusselt and Euler numbers on the Reynolds numbers. Also, thermal contact resistance (the inverse value of thermal conductivity during thermal contact) and the length of the air gap in the contact zone between the aluminum shell and the bearing tube of a bimetallic ribbed tube were experimentally studied. Due to experimental studies, it was found that the lubricating and cooling liquid on the surface of rolled aluminum ribs of bimetallic ribbed tubes does not worsen the rate of heat transfer and the aerodynamic resistance of the bundles of the heat exchange section of air-cooling units. The presence of additional crimping discs in cold rolling mills for ribbed tubes increases heat transfer by 8–13 %. At the same time, the extrusion force cannot be accepted as the main criterion for assessing the quality of connecting the shell of bimetallic ribbed tubes, as is customary in the industry at present. The value of the relative length of the air gap more objectively characterizes the state of contact between the main tube and the ribbed shell, but its use as a determining parameter in express quality control of bimetallic tubes is impossible due to the laboriousness of its calculation. In the contact zone of bimetallic ribbed tubes, any medium with a thermal conductivity coefficient greater than that of air reduces the thermal contact resistance and is an intensifying factor of heat transfer. Due to the thermal characteristics of bimetallic ribbed tubes of air-cooling units, it is impractical to remove presservative grease or other oil from the outer surface of the bearing tubes.

The main requirement for the functioning of a gas distribution system – starting from gas supply sources to end-users of gas – is to ensure its reliability, safety and operational efficiency while reducing the burden on the environment, from gas supply sources to end users of gas. At the same time, it is necessary to maintain all facilities of the gas distribution system in a technically sound condition, their constant updating and development. So, the aging and wear of the gas distribution system facilities in operation (gas distribution pipelines, gas control points, cabinet control points, electrochemical protection equipment for steel gas pipelines) is currently becoming an urgent problem. The article discusses the structure and growth dynamics of the length of steel underground gas pipelines operated in Minsk and the Minsk region, depending on the duration of operation. The results of laboratory studies of the actual state of steel pipes with different service lives are presented. The degree of degradation of the structure, mechanical properties and chemical composition of metal samples of steel underground gas pipelines with different service lives has been determined. The methods for assessing the actual state of the insulating coating of steel underground gas pipelines are presented. The analysis of the results of measurements of the electrical transient resistance of the insulating coating obtained in the field and laboratory conditions is carried out. The calculation of the residual life of an insulating protective coating is presented using the example of mastic bitumen insulation by determining the actual aging time constant, and a method for estimating changes in their activation energy of thermal and oxidative degradation as a method for determining the residual life of the insulating coating of steel underground gas pipelines is given, too. The values of the activation energy for mastic protective bitumen coatings of steel underground gas pipelines with different service life, including the limiting state, have been determined. A technique for technical diagnostics of steel underground gas pipelines is proposed, taking into account aggregated statistical data. A method for prioritizing gas distribution system facilities is described.

The issues of improving the environmental safety of energy facilities, in particular small hydroelectric power plants, which make it possible to effectively use local energy resources, including the ones for remote and autonomous consumers, are considered. With the increasing number of small hydroelectric power plants in the world, there is a need to ensure their biological safety in order to reduce the impact on the biological environment of reservoirs. Currently, a number of technical solutions are available, in particular for impellers of hydraulic turbines, which allow reducing possible negative consequences for the environment. However, these proposals are mainly aimed at combating the physical impact of a collision with the mouth, while matters related to energy efficiency and other types of negative impacts, such as barotrauma, remain open. The present article examines the effect of blade thickness on efficiency and biosafety when exposed to a pressure drop. The impeller of an axial hydraulic turbine was created and tested for the study. With the help of CFD and the BioPA technique, the dependences of survivability on different blade thicknesses were determined, and the dependence of the efficiency of a hydraulic turbine on survivability, calculated from the pressure drop, at different blade thicknesses was obtained. The obtained results show the importance of creating biologically safe impellers of hydraulic turbines, taking into account various quality indicators, in order to obtain both effective and safe solutions.