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 methods of modelling of power system modes and of testing of relay protection devices with the aid the simulation complexes in real time and with the help of computer software systems that enables the simulation of virtual time scale are considered. Information input protection signals in the simulation of the virtual model time are being obtained in the computational experiment, whereas the tests of protective devices are carried out with the help of hardware and software test systems with the use of estimated input signals. Study of power system stability when modes of generating and consuming electrical equipment and conditions of devices of relay protection are being changed requires testing with the use of digital simulators in a mode of a closed loop. Herewith feedbacks between a model of the power system operating in a real time and external devices or their models must be determined (modelled). Modelling in real time and the analysis of international experience in the use of digital simulation power systems for real-time simulation (RTDS simulator) have been fulfilled. Examples are given of the use of RTDS systems by foreign energy companies to test relay protection systems and control, to test the equipment and devices of automatic control, analysis of cyber security and evaluation of the operation of energy systems under different scenarios of occurrence of emergency situations. Some quantitative data on the distribution of RTDS in different countries and Russia are presented. It is noted that the leading energy universities of Russia use the real-time simulation not only to solve scientific and technical problems, but also to conduct training and laboratory classes on modelling of electric networks and anti-emergency automatic equipment with the students. In order to check serviceability of devices of relay protection without taking into account the reaction of the power system tests can be performed in an open loop mode with the use of hardware and software test systems. Testing methods for relay protection and their models in open-loop mode have been proposed.

Lightning voltage impulse due to the waves of storm surge rolling out the high voltage line to a substation causes current to flow in the buses that, due to magnetic effect, induces overvoltage in the secondary circuit. Overvoltage in the system “wire – ground” is considered as obstructions which are hazard in relation to the possibility of electrical damage of the devices of relay protection and automation of substations. With the use of the inverse Laplace transformation, the solution of the problem the magnetic influence of the primary circuits to secondary circuits in the time domain depending on time of transition, which always occurs during the distribution of the voltage impulse in the buses, has been obtained. Estimation of the level of overvol tage in the system “wire – ground” for the case of failure of a bus nonlinear surges and arresters when lightning impulse of voltage is distributed on the buses along their length without deformation has been fulfilled. Solutions are obtained for overvoltage in the secondary circuits, according to which the levels of overvoltage can be estimated as “extremely stepped-up”, “lowered” and “averagely stepped-up” levels. With a method of computational experiment the levels of overvol tage for distribution substations with voltage 110 and 220 kV were assessed. The results are compared with the normalized values of the interference voltage. The suggested method of calculation of impulse magnetic influence of the primary circuits on the secondary circuits of substations while lightning impulse voltage is being distributed in high voltage buses for the case of failure of a nonlinear surge and arresters at the stage of design and operation of substations can be used as a test method for estimation of electrical durability of relay protection and automatic equipment from lightning and switching overvoltage.

The solution of the problem of reliable functioning of an electric power system (EPS) in steady-state and transient regimes, prevention of EPS transition into asynchronous regime, maintenance and restoration of stability of post-emergency processes is based on formation and realization of mathematical models of an EPS processes. During the functioning of electric power system in asynchronous regime, besides the main frequencies, the currents and voltages include harmonic components, the frequencies of which are multiple of the difference of main frequencies. At the two-frequency asynchronous regime the electric power system is being made equivalent in a form of a two-machine system, functioning for a generalized load. In the article mathematical models of transient process of a two-machine system in natural form and in d–q coordinate system are presented. The mathematical model of two-machine system is considered in case of two windings of excitement at the rotors. Also, in the article varieties of mathematical models of EPS transient regimes (trivial, simple, complete) are presented. Transient process of a synchronous two-machine system is described by the complete model. The quality of transient processes of a synchronous machine depends on the number of rotor excitation windings. When there are two excitation windings on the rotor (dual system of excitation), the mathematical model of electromagnetic transient processes of a synchronous machine is represented in a complex form, i.e. in coordinate system d, q, the current of rotor being represented by a generalized vector. In asynchronous operation of a synchronous two-machine system with two excitation windings on the rotor the current and voltage systems include only harmonics of two frequencies. The mathematical model of synchronous steady-state process of a two-machine system is also provided, and the steady-state regimes with different structures of initial information are considered.

The article focuses on a new method of calculating heat transfer coefficient of bimetallic finned tubes of air coolers taking into account external operational pollution. In contrast to wellknown methods that use the assumption of a uniform distribution of operational contamination layer with a constant thickness over the entire surface of the fins in the present method being introduced it is assumed that the thickness of the pollution layer during long-term operation is changed irregularly. Under such conditions the thickness of the pollution layer at the base of the fins becomes much greater than at the rest of the finned surface. The suggested method is based on a mathematical model developed with the use of the method of electrothermal analogy, whereby the heat flow through the wall of the finned tube is considered as divided into two components, viz. through the annular layer of outside contamination adjacent to the base of the ribs, and through the remaining part of the external ribbed surface covered with a thin layer of pollution. Within the framework of the developed methodology a new method for determining the thermal resistance of the pollution layer, which is based on analytical solution of two dimensional problem of heat conduction in the annular layer has been created. With the use of this technique the influence of the degree of contamination of the intercostal space of the industrially manufactured bimetallic finned tubes on the heat transfer coefficient has been studied taking into account the intensity of heat transfer of air and the properties and composition of the pollutant for industrial manufactured bimetallic finned tubes. It is established that a layer thickness of the pollutant at the base of the ribs has the greatest influence on the heat transfer coefficient. This is due primarily to the change of actual coefficient of the fins. It is demonstrated that the heat conductivity of the external pollutant has a significant impact on the heat transfer coefficient when the heat exchanger functions in the mode of forced convection of air.

Evaluation of energy consumption economy due to implementation of the principle of cold regeneration is a formidable problem of exergy analysis of cryogenic systems. A method or evaluation of power consumption economy due to the presence of heat exchangers in the scheme of cryogenic plant is suggested in the present article. The calculations of the economy for the refrigeration and liquefaction regimes of cryogenic nitrogen plant operating in accordance with a simple throttle cycle have been carried out. The approximate method for evaluation of power consumption economy demonstrated that for a simple throttle cycle the use of the heat exchanger enables to reduce power costs by about 30 % regardless of the mode of operation. The use of a heat exchanger makes it possible to avoid the problems associated with the use of work produced in the expander. The analysis of the results of the performed calculations demonstrated that the economy is practically independent on the operating regime. For the analyzed systems the minimal pressures of the working fluid after compressor that are needed to obtain a specified quantity of a product of required quality have been determined. The calculations made for Linde cycle demonstrated that this value depends on the mode of operation, but it is significantly less than the pressure in the cycle. The presented approach to determining the economy of energy consumption in low-temperature systems is applicable to power plants due to the presence of heat exchangers in its design. For such an application one need to override the purpose of these devices and to alter the equations exergy balances in accordance with it.

Magnetic fluids are promising lubricating material, in particular, in sliding bearings. With the aid of the magnetic system the magnetic fluid is held in the gap of friction that simplifies the design of the lubrication system sufficiently. It is known that when conventional lubricants (mineral oil, water) flow, with increasing of speed of rotation of the inner cylinder the transition of laminar flow in a vortex takes place. This dramatically increases the viscous friction losses. The friction losses in a wide range of speeds and possibilities of their decrease due to the vortex flow of the magnetic fluid in the gap between the cylinders are experimentally studied. It is revealed that when the dimensionless speed – number of Taylor equal to 41.2 – is reached, the slope of the curve of friction torque sharply increases, viscous losses also increase, i. e. there is a change laminar flow to a vortex one. The average temperature in the layer of the magnetic fluid reaches 60 оC. This factor leads to increased evaporation of the carrier liquid (water, mineral oil), which reduces the service life of the lubricant i.e. the magnetic fluid. In order to reduce viscous friction when a vortex flow of magnetic fluids takes place, carbon nanotubes, which are cylinders with a diameter of 5.0 nm and a length of about 0.1 mm, are brought into the magnetic fluid. Carbon nanotubes demonstrate elasticity under transverse bending: they curve under the impact of load, and after its removal they restore their original shape. They are also able to elongate along the axis by 16 % and to return to its original position after removal of the load. The effect of reducing friction (about 30 %) with a vortex flow of magnetic fluid by the introduction of carbon nanotubes in a magnetic fluid is experimentally obtained. The likely mechanism of friction reduction is the ability of nanotubes to deform under the influence of pressure pulsations and the velocity of the swirling flow, and to absorb partially a part of their energy. As it was experimentally demonstrated, there is an optimum weight concentration of the additive of nanotubes in the magnetic fluid (~10–4) that is associated with the maximum effect of reducing friction by 30 %. Thus, the insertion of carbon nanotubes in the lubricant (magnetic fluid) makes it possible to reduce the viscous friction and, consequently, to increase the range of operating speeds, to strengthen the online lubricant site.

This article deals with the issue of function regulation of customer’s plants that burn traditional types of fuel. Its aim was to develop certain measures for reducing customer’s plants influence on the Belarusian power supply system as their activity has unfavorable economic consequences. The following methods were used in the present research: the system analysis, the method of analogies and expenses calculation. The article presents the comparative characteristics of the power production during the typical working day of the heating period in the years 2013 and 2014 in terms of condensation power plants, central heating and power plants and customer’s plants. The potential damage caused by the customer’s plants to the power supply system has been calculated, the restrictions for the customer’s plants activity existing in the Republic of Belarus nowadays has been analyzed. The author has developed a number of measures within the framework of regulation policy of the activity of customer’s plants that burn traditional types of fuel: the fee for the spinning reserve necessary for the power supply system in case of the customer’s plants breakdown; the fee for the supervisory control; the fee for the service of transfer and distribution. The introduction of the proposed measures is supposed to bring the following advantages: high-quality growth of energy efficiency of the power industry; prime cost reduction of power energy in the power supply system as a whole; stimulation of market elements implementation in the power industry; the ability to react fairly fast to the alterations of economic conditions.