A method of increasing the reliability of determining the zone of short-circuit at the current step protection of the lines of 6–35 kV with unilateral power, aimed at improvement of their technical perfection, is presented in the paper. Having taken the relative simpleness of the current protection into account the authors consider the unilateral remote method of accounting the parameters of the emergency mode and the type of fault to be the most suitable for the implementation of the algorithm of its functioning as compared with the existing methods of fault location. The major factors affecting the accuracy of determining the short circuit zone based on the remote method are noted. With the use of the method of computational experiment the influence of the load currents and contact resistances of various levels on the magnitude and character of changes of errors of determination of the calculated distance of the point of fault from the protection installation location taking into account the errors of measuring transformers. It is demonstrated that in many cases of arc short circuit in a loaded line in order to define the zone of short-circuit with fair accuracy correction of the estimated distance to the fault as calculated by the parameters of the damaged loop (loops) is required. According to the results of numerical experiments corrective expressions on the basis of two relative asymmetry currents determined by the current values of the differences of the phase currents of the line for detecting a type of a short circuit have been obtained. The assessment of the efficiency of the proposed method has been performed. It is shown that the application of the proposed correction method makes it possible to increase the accuracy of fault zone detection. The dynamic properties of the proposed method applied to different modes of the line functioning have been studied. It is determined that in the worst case the definition of the fault zone for a maximum duration of 26 μsec is provided.

The issues of prospective operation of the city electric networks in the conditions of the MART GRID, which will be quite different as compared to the traditional understanding and approaches, are under consideration. This requires the selection and application of appropriate analytical criteria and approaches to assessment, analysis and control of the networks. With this regard the following criteria are recommended: in a particular case – the optimal (minimal) technological electric power consumption (losses), while in general – economically reasonable (minimal) cost value of electric power transmission. It should be also borne in mind that contemporary urban networks are actively saturated with distributed sources of small generation that have radically changed the structure of electrical networks; therefore, account for such sources is an absolutely necessary objective of management regimes of urban electric networks, both traditional and in associated with the SMART GRID. A case of the analysis and control of urban electric 10 kV networks with distributed small sources of generation has been developed and presented according to the theoretical criterion of minimum relative active power losses in the circuit as a control case. The conducted research makes it possible to determine the magnitude of the tolerance network mode from the point of the theoretical minimum. 

The main directions of increase of efficiency of production, transmission and distribution of electric energy have been formulated. The relation between the values of electricity losses during transmission via power grids of different countries and the level of the economies of these countries characterized by the value of gross domestic product at purchasing power parity per capita has been established. In the countries with a gross domestic product at purchasing power parity per capita less than 20 thousand US dollars electricity losses during its transmission via power grids are 1.5–2.5 times more than the ones transmitted via power grids of the industrialized countries where the specified purchasing power parity is in the range of 30.4–54.5 thousand US dollars. In the countries with more developed economies the technical culture of production, transmission and distribution of electricity is higher; the modern control systems of operation modes of electrical networks are used as well as of monitoring and accounting of electricity; also there are solvent and disciplined consumers in such countries as well as clear regulatory framework and tariff regulation system. However, the process of transmission and distribution of electricity is effective if not only low relative losses take place, but the normal (contractual) requirements for carrying capacity, quality and reliability of electricity supply are provided. The possibility of analytical determination of the optimum value of reserve capacity of power plants providing the required level of reliability of the power system has been considered.

The analysis of existing methods of diagnostics test of the windings of asynchronous motors demonstrated that a large error of measurement of diagnostic parameters is due primarily to the instability of the measuring equipment. Sole increasing the sensitivity of the measuring instrument increases the probability of a false conclusion on the faulty winding and can only be used in conjunction with other methods of ensuring high signal-to-noise ratio. During the research fulfillment it was found out that direct way of suppressing uninformative spectral components and distortions caused by the instability of parameters of the testing signal is complex and most difficult to be implemented. Thus, more appropriate is the selection of individual characteristic frequency components of the signal, which has high sensitivity to change of informative parameter of the measuring signal (for example, the time delay between two periodic sequences of pulses) and low sensitivity to random deviations in the signal due to instability in the functioning of the elements of the measuring circuits (for example, to deviation of the phase of the signal). Moreover, adjusting the amplitude, repetition period, pulse duration and delay time pulse sequences it is possible to implement a mathematically justifiable control of the parameters of the spectrum (to move the position of the zeros of the amplitude spectrum, to change the amplitude of the spectral components). The use of the dynamics of the spectra by controlling their parameters will ensure a high sensitivity to change of the informative parameter of the measuring signal, characterizing the degree of development of defects in the windings of asynchronous motors.

Fulfillment of the activities aimed to an increase of the thermal resistance of enclosing structures requires the determination of their thermophysical characteristics with the use of the determination method based on the solution of problems of heat conduction, establishing the con- nection between the spatial and temporal temperature changes under the effect of heat source. This work uses the solution of the problem under nonstationary heating of the enclosing structure in the form of unrestricted plate with boundary conditions of the III kind. According to the known relations and graphs alterations in surface temperature depending on warm-up time, on thermal resistance of constructions and on arguments of Fo and Bi, i. e. initial and boundary conditions are determined. The graphic dependencies that have been obtained show that the surface temperature depends on the thermal resistance, while the temperature at the opposite surface during heat expo- sure remains practically unchanged during t = 5 h. Thus, if the outside air temperature is altered, then the rate of change of surface temperature or relative temperature q make it possible to deter- mine the thermophysical characteristics by solving the inverse problem of thermal conductivity with the use of the converted ratio to determine R as a function R = f(q, t). If the constructed graphic dependencies R = f(q, t) are used at different heat transfer coefficients, then according to the measured temperatures at different time intervals it is possible to determine thermal resistance in the same time intervals and, according to their average value, determine the required resistance to heat transfer R. The estimated ratio of analytical and graphic dependencies that we have obtained demonstrate the adequacy of the conducted full-scale measurements, if the areas with homogeneous temperature field and temperature history are chosen, and they can be used in determining the heat resistance of the enclosing structure in the form of unrestricted plate with boundary conditions of the III kind.

The problems of energy, environment protection and ecology play a major role in the development of economy strategy in any country. Most of the traditional power stations operating on organic fuels have a negative impact on the environment. Furthermore, there is a depletion of natural resources due to human activities. One of the ways to solve the problem of environmentally friendly energy production is to use alternative sources of energy. Based on the foregoing, the development of the strategy for the development of traditional and alternative energy must consider environmental and economic factors in a specific country. In the present work it was evaluated the environmental and economic efficiency of application of traditional and alternative energy with regard to the conditions of the Islamic Republic of Iran. The program packages RETScreen which is one of the most effective tools to accomplish the task was used. Calculations of cumulative cash flow from the operation of power plants using different types of primary energy are carried out using models of package RETScreen for assessing the input efficiency of various types of energy sources aiming to cover the intending growth in electricity demands and the environmental assessment with reference to different countries. The results of the study showed that the planning prospects of the development of energy systems in relation to the Islamic Republic of Iran to cover the expected growth in electricity demands it is advisable to use the alternative energy sources, and, first of all, the generating capacity based on solar and wind energy.

The results of experimental research of heat exchange under the nucleate boiling of refrigerants R404a, R407c and R410a on the tubes with capillary-porous coating are presented. Experimental studies were carried out with the aid of an experimental installation in conditions of a large volume at pressures of saturation pн = 0.9–1.4 MPa and densities of the heat flux q = 5–35 kW/m2. For the first time the criterion equation for the calculation of the intensity of heat transfer during evaporation of ozone safe refrigerants on surfaces with high thermal conductivity sintered capillary-porous coating was obtained. Experimental data are summarized satisfactorily in a wide range of parameters of the porous layer, i.e. the pressure (pн = 0.9–1.4 MPa) and heat loads (q = 5–35 kW/m2). The ratio makes us possible to calculate the heat transfer coefficients within ±20 %. The dependence can be used in engineering calculations of the characteristics of the heat exchangers of the evaporative type. The coefficient of heat transfer during boiling of refrigerants on the investigated surfaces with the sintered capillary-porous coating, 4 times higher than on a smooth one and 1.5 times higher than on the finned surface, that allows us to come to a conclusion about the advantage of porous coatings. Boiling in capillary-porous coating leads to a decrease in weight and size of the installations due to the heat exchange intensification and the size of the tubes smaller as compared to the size of the finned ones.

During the operation of water wells, their specific production rate is reduced as a result of mechanical, biological and chemical colmatage. The extraction of the mudding element from the filter is complicated by the fact that the deposits cover not only the well filter, but also gravel package and are not completely removed by the treatment. An installation is proposed for reversereagent regeneration of water wells, consisting of a compressor, hoses and submersible device in the form of a two-chamber pneumatic displacement pump. The advantage of the unit is the absence of a circulating pump in its composition and the possibility of efficient processing of the limited filter interval. The downhole submersible device does not contain moving parts except for two floating check valves. In order to describe the process of dissolution of deposits by the method of reverse-reagent water well regeneration, a system of equations is used: the combined equation of motion and mass conservation and the generalized equation of kinetics. By integrating the kinetics equation, an analytical dependence is obtained to calculate the operating time of the unit for reverse-reagent filter regeneration, followed by the reducing of the specific volume of the colmatizing deposits in the gravel package to a predetermined level. According to the formulas obtained, a computer program was compiled, which allows calculating the number of operating cycles of the device, the duration of cleaning and the degree of removal of the colmatant at each stage of the work. With the aid of the developed computer program, the operation of the unit for reverse-reagent filter regeneration is considered on behalf of a water well using two different reagents: hydrochloric acid and sodium dithionite. The procedure for calculating the amount of reagent needed to restore water well productivity is presented.