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. It is noted that at present, 10 and 35 kV overhead power transmission lines are being laid outside the settlements of the Republic of Belarus on reinforced concrete vibrated (10 kV) and centrifuged (35 kV) poles that are characterized by low reliability and damaging the environment (on account of alienation of land for poles, the need to make a wide clearing for laying in the forest, obstructions by poles and wires of lines to the operation of agricultural machinery, the danger of electric shock to personnel and the public). It is possible to avoid these disadvantages if, instead of overhead lines, power transmission cables with cables insulated by cross-linked polyethylene are used which are characterized by a very low failure flow parameter. Contrary to the prevailing opinion about the higher cost of cable power transmission lines compared to overhead ones of the same rated voltage, it turned out that, taking into account reliability, the cost of electricity lost in the lines for a year, damage to the environment and to the power system caused by the need to perform more expensive emergency repairs (as compared to a planned one), laying cable lines with three-core and single-core cables of a voltage of 10 and 35 kV instead of overhead cables outside the populated area is fairly justified. In this connection, the laying of three-core cables is more preferable. It should be also borne in mind that with an increase in the length of cable lines, the capacitive earth fault current increases, to compensate for which additional devices are needed to be installed in power centers, viz. arc-extinguishing reactors or resistors, accounting for the cost of which (up to 22 % of the cost of one kilometer of cable line) does not significantly affect the conclusions we have drawn regarding the effectiveness of using 6–35 kV cable power lines in an unpopulated area instead of overhead ones, however.

The thermal impact of cable power lines and structural materials of cables on the environment has been considered. A quantitative evaluation of the thermal impact of electrical cables with cross-linked polyethylene insulation on the environment was carried out using the Elcut program. Analysis of the temperature field near the loaded cable line of 10 kV demonstrated high values of soil temperature that negatively affects its redox potential and living organisms. To evaluate the environmental impact of electrical cable materials, an approach has been developed that takes into account not only the toxicity of the materials but also their volumetric content in the cable. Cable lines with cables with traditional paper-oil insulation cause more damage to the environment than cable lines with cables, insulated with crosslinked polyethylene. The environment, in turn, also has an impact on the electrical cables: the values of long-term permissible load currents depend on the ambient temperature (when laying cables in the open air, in an earthen trench or in cable rooms). The impact of solar radiation on the thermal conditions of the electric cable is estimated. A comparative analysis of the complex environmental impact of electric cables with traditional insulation and insulation of crosslinked polyethylene demonstrated that unarmored cable with crosslinked polyethylene insulation at a voltage of 10 kV (regardless of the type of its shell) causes less damage to the environment than the same traditional cable throughout the considered temperature range on their surfaces.

It is found that the voltage at the lowest points of the wire or cable sag and at the points of their suspension on the pillars in the same span, determined in accordance with the properties of a perfectly flexible filament (similar to which the wires and cables are located in the span), differ slightly, and taking the difference of the mentioned values into account is only of methodologycal importance. The article presents the results of the calculation of wire and cable sag of large spans of power transmission line of 500 m or more length using both the traditional theory of the catenary line and the theory of equal resistance, when the cross-sectional area of a wire or cable, proportional to their tension, is considered variable in the span length, which provides the same probability of breaking them at any point of the span. When calculating the wires and cables in normal and emergency conditions, the largest sags are determined, which take place either at a higher ambient temperature or at a load of the wire with ice. The wire must be mounted in such a way as to ensure the normalized permissible dimensions to crossed engineering structures, water barriers or land, that are determined depending on the nominal voltage of the line. It is noted that the values of the wire and cable sags determined using the theory of the catenary line for the transition spans are less (although slightly) as compared to the data obtained on the basis of the theory of the equal resistance circuit. This must be taken into account in the design process.

The assessment of the suitability of cables of 6–110 kW with XLPE insulation in comparison with cables of the same voltage but possessing paper-oil insulation has been fulfilled on the basis of the method of multi-objective optimization that makes it possible to account not only the quantitative characteristics (of reduced costs), but also qualitative ones. As an indicator of the reliability of the cable line the maximum mean time to failure (the value inversely proportional to the parameter of succession of failures), which is an order more for cable lines with XLPE insulation than for cable lines with paper insulation, is adopted. A comprehensive assessment of the convenience of installation of cable lines revealed that the installation of cable with XLPE insulation features a 1.2–1.6 times easier installation as compared to three-wire (voltage 10 kW) and 1.4 times easier installation as compared to single-core oil-filled cables (voltage of 110 kW). The efficacy of the cables 6–110 kW with XLPE insulation is proved on the basis on the method of multi-objective optimization, that took into account as the costs for the construction and operation of cable lines and the reliability of its operation, ease of its installation and other quality indicators. If the goals taken into account are considered as equally important, the polyethylene-insulated cables for a voltage of 10–110 kW is more efficient as compared to three-wire (voltage 10 kW) and solid (110 kW) cables with paper insulation. Herewith, the cost of the cable with XLPE insulation may exceed the cost of cable with paper insulation up to two times. If the most important aim is to provide the minimum reduced costs for the construction and operation of the cable line, the use of cables with XLPE insulation for voltage of 10 kW is most advisable in individual cases.

The assessment of the suitability of cables of 6–110 kV with XLPE insulation in comparison with cables of the same voltage but possessing paper-oil insulation has been fulfilled on the basis of the criterion of reduced costs. Thus, the comparison was undertaken between cables of various design and material of insulation: three-core paper insulated ones vs. three-core XLPE insulated ones; three-core paper-insulated ones vs. solid wires with XLPE insulation; single-core oil-filled cables of 110 kV with paper insulation vs. solid wires of 110 kV with XLPE insulation. The increase in long-term permissible current loads for cables with XLPE insulation because of the larger permissible temperature of heating in comparison with cables with paper-oil insulation complies with as would increase in the cross-sectional area of cable cores (equal to 0.61 from the original) and therefore reduces the cost of the cable by reducing the cost of manufacture of conductors. The reduced costs of the construction and operation of cable lines with XLPE insulation (accounting the increase in the cost of a cable 1.2 and 2 times as compared with the cost of a cable with three-core insulation), despite the decline in the cost of manufacture of conductors and the reduced annual operating costs (9 % and 17 % respectively of cable lines of voltage of up to 35 kV and 110 kV), occurred to be more than the reduced costs of the construction and operation of cable lines with paper insulation. Currently the cost of one meter of cable with XLPE insulation is less than the cost of cables of AAB, CASB, AASv types of a voltage of 10 kV with aluminium cores, that ensures their undeniable efficacy.

The reliability of the main circuit of electrical connections at a nuclear electric power plant that has two units with a capacity of 1,200 MW each has been determined. Reliability, economical, maneuverable properties of the atomic power plant under study are largely determined by its main circuit, so the choice of the circuit for the design and its status in the process of operation occur to be critical objectives. Main electrical connection circuits in nuclear electric power plants are selected on the basis of the schematic networks of the energy system and the land attached to the plant. The circuit of the connection of a nuclear power plant to the grid in the original normal operating modes at all stages of the construction of such a plant should provide the outcome of the full added capacity of a nuclear power plant and the preservation of its stability in the power system without the influence of the emergency system automatics when any outgoing transmission line is disabled. When selecting the main circuit the individual capacity of the installed units and their number are taken into account as well as the order of development of the plant and power supply system; the voltage on which the power of a plant is delivered; a shortcircuit current for switchgear high voltage and the need for their limitation by circuit means; the most power that can be lost when damage to any switch. A model of reliability of the main circuit of electrical connections is designed to detect all types of accidents that are possible at the coincidence of failures of elements with the repair and operational modes that differs in composition and damageability of the equipment, as well as under conditions of the development of accidents due to failure of operation of devices of relay protection and automation.

The paper considers two schemes of the urban distributive electric network for supply of the second and third category consumers for whom indicators of reliability have been determined.As for a network scheme of the 2nd category it has been determined that while installing low-oil and vacuum switches at a distributive point the most remote transformer substation has the highest non-availability factor which is higher of the corresponding non-availability factor of the nearest transformer substation by 1,21–1,23 fold accordingly.As for a network scheme of the 3rd category consumers it has been obtained the data that reliability of consumers receiving supply from bus-bars of transformer substations with 0,38 kW voltage changes significantly (by 1,2–1,9-fold) while changing a breakpoint of the network with 10 kW voltage.

The paper considers four variants of inspection of overhead power transmission lines with 35 kV voltage and higher. Technical and economic indices for every inspection variant have been determined in the paper. The most rational inspection variant of the line having length up to 30 km is a scheme of line inspection by team of electricians within one day. Execution of overhead power transmission line inspection by one person being sent on an assignment trip is expedient when the line length is more than 30 km. In the case of inspection criteria equivalence (minimum cash expenditures on inspection, minimum inspection duration, maximum quality of work execution) a scheme presupposing to use a helicopter with a scanning device is considered as the most rational one.

The paper contains values of torque magnification ratio while shifting vertical loads due to horizontal wind forces affecting on supports of overhead transmission lines of 35 kV and higher. These values pertain to various types of unified reinforced concrete conic and cylindrical supports while changing climatic conditions. The values make it possible to exclude rather complicated calculations in respect of support deflection in the case when there is uncertainty in initial data.

The paper considers a methodology for forecasting electric load of power system in theRepublicofBelaruson the basis of an artificial neuron network method. A configuration of the neuron network has been developed and the process of its training has been considered in the paper. Forecasting of power system electric load has been prepared while using artificial neuron networks.

The paper considers conditions for selection of power supply of the unit which is used for testing samples of cable products by thermal and dynamic stability currents. It has been shown that while conducting testing by thermal and dynamic stability currents at nominal cable voltage it is more justifiable to use a percussive energy accumulator, and in the case when the voltage is low an inductive energy accumulator is used.

Calculations of phase capacity of two-circuit open-air electric power lines with voltage of 35 kV relative to the ground have been carried out. The paper gives values of capacities of open-air electric power lines with voltage of 35 kV which are located on two-circuit supports depending on the operational mode of the second circuit. The values of capacity of a two- circuit electric power line have been determined provided that circuits of various rated voltage are located on a line. Changes in capacity of an electric power line with voltage of 35 kV have been calculated in comparison with the capacity of an one-circuit line depending on a distance between axes and the operational mode of the second line, if the lines are parallel.

It is installed that hooking two lines and two transformers at scheme distributing device by voltage 330 sQ «transformers – a buses with joining line through two breakers» and three installed transformer on substations brings about reduction of the factor to unavailability in 18,2 times in contrast with scheme with two transformers. At connection of the third transformer through two breakers factor to unavailability practically does not change.At connection one of the transformer through two breakers, at one-and-a-half-breaker scheme RU 330 sQ factor to unavailability falls in 6,6 times to scheme RU 330 sQ «transformers – a buses with joining line through two breakers» under three transformers.