The  6–35  kV  power-grid  current  protection  serves  to  protect  the  transmission  lines against phase-to-phase short-circuits. The major disadvantage of it lies in the relatively large time delays of the last stages especially in the main sections of the grid owing to the stepped relay characteristics as well as a large number of the steps. A full-fledged protection of the 6–35 kV lines against inter-phase short circuits can be provided by the two-stage current protection: the first stage being the current cutoff without any time delay and the second stage – the maximum current protection where the time delay is linear contingent on the distance between the protection placement and the fault-point location. The article introduces the rating formulae for the time delays of the second-stage and their exemplary graphic presentation. The authors offer a variant for solving the problem with computation of the second-stage time delays in those instances where several feeders diverge from the bus bars of the substation located in the end of the protected line.

Improving current protections for the 6–35 kV transmission lines with one-end power supply against interphase short-circuits can be based on the collective application of the following principles: accounting for the type and location of the short-circuit which provides for the high-performance cutoff zone instantaneous expansion and its independence on the mode of failure and the grid operation mode. It also allows increase of the last stage sensitiveness towards asymmetrical short-circuits; detection of the short-circuit location only on the results of fault currents measurement which simplifies the protection implementation; realization of the last (second) protection stage with linear-dependent time delay which ensures potentiality of its operation speed increase.

The article proposes a method for selecting the rated capacity of oil-immersed power transformers adjusted for a more accurate calculation of their load-carrying capability. A more precise method to determine load-carrying capability of oil-immersed power transformers, which is admissible with valid technological normative documents, is offered and reasoned. The major attention focuses on the analysis of the requirements of the technological normative documents on selecting the rated capacity of oil-immersed power transformers. The authors present the critical analysis of the well-established and extremely simplified method for ratedcapacity selection of power transformers and justify its inconsistence.

The paper shows that all the methods for selecting power-transformers rated capacity are the simplifications of the transformers load-capability assessment method based on thermal transient-processes computations. It is reasoned that the requirements of any transformer  operational-mode acceptability can be most precisely expressed in the form of critical-point allowable temperatures and the allowable overload-factors used in most applied methods are only indirectly calculated values. Allowable-temperature critical points regimented by the technological normative documents are cited.   The authors point to possible errors of the simplified selection-methods for rated capacity of oil-immersed transformers and adduce the computation results of the mathematical modeling of the thermal transient-processes under simplified conditions assumption to illustrate the  possible errors. The thermal transient-processes computation results for a transformer with   a 168-hour random electrical-load list demonstrate the performance capabilities of the offered  method.

The current-carrying cores of the electrical power cables should be resistant to effects of short-circuit currents whose values depend on the material of the core, its cross-sectional area, cable insulation properties, environment temperature, and the duration of the short-circuit current flow (1 and 3–4 sec. when tested for thermal endurance and mechanical bracing). The facilities for testing the 10 kV aluminum core cables with short-circuit current shall provide mechanical-bracing current 56,82 kA and thermal endurance current 11,16 kA. Although capacitors provide such values of the testing currents to the best advantage, utilizing conventional capacitor-units will involve large expenditures for erecting and  running a separate building. It is expedient to apply super-capacitors qua the electric power supply for testing facilities, as they are capacitors with double-electrical layer and involve the current values of tens of kilo-amperes.

The insulation voltage during short-circuit current testing being not-standardized, it is not banned to apply voltages less than 10 kV when performing short-circuit thermal endurance and mechanical bracing tests for electrical power cables of 10 kV. The super-capacitor voltage variation-in-time graph consists of two regions: capacitive and resistive. The capacitive part corresponds to the voltage change consequent on the energy change in the super-capacitors. The resistive part shows the voltage variation due to the active resistance presence in the super-capacitor.

The author offers the algorithm determining the number of super capacitors requisite for testing 10 kV-electrical power cables with short-circuit currents for thermal endurance and mechanical bracing. The paper shows that installation of super-capacitors in the facilities testing the cables with short-circuit currents reduces the area needed for the super-capacitors in comparison with conventional capacitors more than by one order of magnitude.

The article analyzes the methods affecting autonomous operation regimes of the powergrid sections with distributed electric-power sources (distributed generation) whose connection to the electric-power grid is realized by means of special distributed generation inverters. The authors evidentiate the reasons for which autonomous operation is undesirable; examine consequences of the autonomous asynchronous operation of the grid-sections during islanding. These problems are innate for the modern Smart Grid networks. Islanding detection methods include passive and active ones. The passive methods rely only on observation of the voltage and/or frequency at the point of common coupling (PCC) disconnecting the inverter if the  measured  values  are  outside  the  specified  limits.  Despite  their  simplicity,  passive methods cannot assure reliable islanding detection, especially in the cases when distributed generation power equals the power of loads in the potential grid-island. The active methods assume the inverter affecting the grid with the view of detecting deviation from the standard regime parameters in the PCC. Although these methods have much better islanding detection ability, their utilization reduces the power-grid operation quality.

The paper holds that the grid-sections autonomous regime detection without virtually no failure-to-detect zone is only possible with employment of effective anti-islanding schemes such as connecting capacitor batteries to the disconnected power-grid sector. If appropriate providing enhanced survivability and continuity of power supply, the authors recommend providing islanding detection lock option in the inverters of the distributed generation sources.

The quality of water-level regulation in the boiler-shells of heat-power and nuclear-power plants largely determines reliable and economical operation. The latter can be accomplished by means of massive reduction of the actuation-mechanism running time which depends directly on the regulator performance.

The paper examines some foreign methods of PID-regulator adjusting in the cascade system of boiler-shell water-level automatic regulation. The authors derive an invariant cascade system of automatic regulation in which they offer not to measure external disturbance, the steam rate for instance, but to realize a concurrent model of the real inertial section of the controlled member. The disparity between the current value of the water-level in the shell and the output from the inertial section of the controlled-member model is fed to the input of the external-disturbance equivalent compensating device. This allows employing the compensating device in closed circuit, and consequently, the regulation quality improves under the influence of any external disturbances. The comparative analysis of the modeling results of the Cascade-System Automatic Regulation (CSAR) with PID-regulator adjusted according to the foreign  methods  and  of  the  proposed  invariant  system  shows  considerable  improvement in regulation quality of the latter, viz. : system performance grows 2,5 times when working through the task jump, the peak value of overcorrection lowers from 42,5 to 10,0 %; while working through the internal disturbance, the regulating time reduces by 33 %, the maximum dynamic error of the regulation lowers by 65 %; the time of external combustion disturbance workout completion reduces two times, the maximum dynamic error of regulating – by 63 %; the maximum dynamic error of regulation while working through external disturbance with overheated steam rate diminishes by 71 %, the regulating time reduces by 1,5 times.

Rise in comfort and inhabitation safety is one of the main requirements of the general maintenance, reconstruction of the old and construction of the new residential houses. One of the essential factors of it is substitution in the household hot-water preparing sources: from the individual domestic gas  water-heaters to  the common  entire-building hot-water supply at the expense of the centralized heat supply. Extremely erratic hot-water daily consumption by tenants leads to the necessity of sharp increase in central heat-supply level during a few hours of the day, which requires a significant increase of the source heat-power. On that score, the authors propose to direct a significant part (up to 50 %) of the centralized heating and ventilation heat power-consumption to the hot water preparation during the period of short-term hot water consumption peak.

Substitution  of  the  individual  domestic  gas  water-heaters  with  the  common  entirebuilding hot-water supply releases a huge amount of natural gas which can be utilized not only for production of the necessary heat power but as well for electric power producing. This substitution is especially advantageous if heat-power is delivered to the residential area from a НРС where significant part of heat especially in a relatively warm season of the year is thrown out into the air. The content of the article is based on several patents received earlier.

The author presents analysis of renovation variants for 300 MW oil-gas power blocks: substitution of the steam-power energy blocks by those with gas-steam cycle units, technical re-equipment of the energy blocks by means of reconstruction or modernization of the steam turbine, substitution implementation of the steam turbine with an analogous new one, prolongation of the operation life of the equipment in service. Renovation variants for the power blocks of the specified type in the TPPs of Russia can be chosen based on various engineering solutions concluded on the following grounds: mediumand long-term perspectives of their fuel balance structure (natural gas, synthetic gas fuel-oil residual, pulverized coal fuel including clean-coal and coal-benefication production wastes); the demands laid by JSC the JI UES on the participation of power blocks in frequency regulation and node inter-flow; development in the country of the distributed generation and the perspectives associated with it of the reconstructed TPPs installed capacity utilization in corresponding power-grid nodes; the development of related industries of the country’s economy; the speed of mastering the eco-friendly homegrown steam-gas and coal technologies; creation of the competitive national element base of microelectronics.

Introduction of foreign steam-gas generators in this country requires development of the repair-and-service maintenance, provokes elevated risks and tangible costs, conduces to level decrease in the energy and national safety of the state. Orientation of the country’s power engineers to foreign gas-turbines of large single-unit capacity does not contribute to domestic power-plant industry development. With the view of reduction in value of the TPP-equipment by 12–15 %, it is prudent for power engineers to form a perspective manufacturing order for the period after 2016. In light of emerging political and economic situation in the world, technical re-equipment of the TPPs in the countries of the East-European region in the medium term is going to follow the way of reconstruction/modernization of the 300 MW-capacity power-block equipment and prolongation of the specified operation life.

The effective transmutation of radioactive isotopes into the stable ones with the use of neutrons requires the neutron high-flux and the spectra with significant part of fast and resonance neutrons. It is advisable to alternate a range of specified-duration irradiation sessions with revamping the composition of waste. The depleted fuel of the commercial reactor comprises near 1 % of such isotopes of their individual mass in the batch loading which amounts to several tens of kilograms. The article considers a perspective nuclear reactor for radioactive waste transmutation as regards its design, thermal physics and hydrodynamics. Mobile microparticles of the fuel build up the active zone of the reactor and form a steady dense ringshaped layer. The layer rotates within immovable vortex chamber using the energy of the coolant, i.e. water. The micro particles cool down with the coolant unmediated.

The  formulaic  valuation  of  the  device  capacity  with  water  under  pressure  comes to 1–5 MW per 1 liter of the layer. The condition of avoided boiling sets the most restrictive limitations  to  the  capacity.  The  bulk  of  the  layer  constricts  to  tens  of  liters  inasmuch as enlarging the chamber dimensions reduces the rotary acceleration and the force confining the fuel micro-particles on the free surface of the layer. The author offers and substantiates with calculations the active zone composed of several layers or a layer with a large ratio of the volume to the surface area for achieving criticality of nuclear fuel load with limitations on enrichment. The vortex chambers in case of the active zone of several layers can have the joint coolant exscapes along the axis. Implementation of the chambers with reverse vortices in composite active zones with joint escapes allows reducing the flow rotation below the vortex reactor along the coolant course.

Jet pumps are widely used in the power industry as well as in many others. Their main disadvantage is low operating efficiency which aggravates when the jet pump is working with a low ejection coefficient. Such modes are sometimes unavoidable being conditioned by the character of technological process. The article considers methods of improving the operation of central ejectors at small ejection coefficients.

The authors use mathematical simulation approach to study the particularities of kinematic structure of the flow in the mixing chamber of the central ejector operating with low ejection coefficients. They utilize Solid Works Cosmos Flo application-program package for the mathematical simulation. The study shows that areas of reverse flows appear alongside the walls of the mixing chamber under the above conditions which reduces the efficiency of the jet apparatus. The more is the extent of the discovered areas the more is the loss of energy. The study detects the regime zones where detached flows areas appear. The authors propose to replace such areas with solid surface (substitution bodies) for preventing them from emerging. The  mathematical  simulation  results  determine  the  geometric  parameters  of the  substitution bodies for the central ejectors with different modules and ejection coefficients and yield mathematical description of their shape. Mathematical and physical simulation of the centralejector operation with the substitution bodies shows the increase in pressure-head and efficiency coefficients in such apparatuses as compared to ejectors of the conventional form. Efficiency increase is the case in quite a wide range of operating modes.

The proposed method of the efficiency increase for the central ejectors is rather straightforward and does not require substantial financial expenditures for its implementation.

The article examines the main aspects of commercial realization of wind-power projects as application part of wind-power industry with the view of evaluating viability and financial feasibility of the specified projects. The paper presents the results of 10 years’ commercial service experience of two wind-farms accomplished on the basis of three wind turbines (WT) – NORDEX N54, 1.0 MW capacity each, 60 m tower height, located in settlements Uzava and Alsunga on the coast of the Baltic Sea in the Republic of Latvia. The results were obtained by the way of collation of the site-location wind conditions and the major economic factors of the WT operation in the considered wind farms. The collation included the following estimated figures: annual electricity production, average annual income received during the period under review, electricity prime cost. The WT-site location wind conditions and the site-distance from the coastal line have an effect on the WT-performance economic factors that provide an integral insight into the viability and financial feasibility of the wind energy projects.

Based on the analysis of the obtained data, the authors show that the relative produced energy value decreases 10 % with each kilometer wind-farm site distance from the coastal line of the Baltic Sea. They also indicate the effect the surrounding-area wind conditions and the TW-location site remoteness from the costal line have on the prime cost of the electricity generated by the wind farms. There is a good reason to utilize the presented results in the future for the wind-energy potential valuation of a particular region and a wind-farm location choice as well as for making particular managerial decisions in the way of realizing commercial wind-energy projects.