№ 112(8), October, 2015
Public date: 30.10.2015
Archive of journal: Articles count 151, 381 kb
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PROSPECTS OF SMALL HYDROPOWER PLANTS IN THE PIEDMONT AND MOUNTAIN STREAMS
DescriptionThe article reveals the advantages of low energy in comparison with other renewable energy sources. It is shown that broad prospects are visible for small (100 - 1000 kW) and micro hydropower plants (up to 100 kW) when used in the foothill and mountain areas. At the same time, the construction of hydropower plants of sleeve-type has improved the operational and technical characteristics, among other types of small-scale power plants. The article presents main analytical expressions for calculating hydroelectric power generator and it has built graphic dependences for the power generator of pressure and water flow. To improve the performance of small hydroelectric power plants we have proposed using unregulated water turbine and non-contact induction generator in their construction, thus, we could stabilize voltage and frequency directly by the frequency converter. Depending on the requirements of consumers to power supply reliability and electricity quality, we have offered several options for structural and circuit solutions of autonomous systems of electrosupply, made using small hydroelectric power plants. Thus, we can greatly enhance the efficiency of such systems if they are used with other types of renewable sources, such as windfarms or solar power plants
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THE CHOICE OF THE GENERATOR AND ELECTRICITY STABILIZATION FOR SMALL HYDROPOWER PLANTS
DescriptionThe article analyzes the main characteristics of the electricity generators to use them as a part of small hydroelectric power plants. It is shown, that contactless asynchronous generators in comparison with synchronous generators and DC generators have improved their operational and technical characteristics, and above all, their reliability and performance efficiency. We have shown graphic dependences of the cost and the weight of power generators. It is proposed using direct frequency converter as a stabilizer of parameters of asynchronous generator of electricity, used as a source of electricity for small hydropower plants. The article explains the features of the work and the choice of parameters for generators, working together with the direct frequency converters. The authors have revealed some aspects of the work of direct frequency converters with natural commutation and with adjustable phase angle, including their advantages and disadvantages. The article also presents block diagrams for small hydroelectric power plants, made with the help of asynchronous generators and direct frequency converters
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WAYS OF STABILIZATION THE ENERGY OF SMALL HYDROPOWER PLANTS
DescriptionThe article deals with the basic methods of stabilizing voltage generators for small hydroelectric power plants. It shows a block diagram of the implementation and analysis of the characteristics of the work; it reveals the advantages and disadvantages. The authors explain the features of the work of the functional circuits voltage regulators with discrete ballast, with phase control and management of the load current. It is shown, that to improve the performance of small hydroelectric power plants considerably we have to use contactless generators in their construction: asynchronous generators with capacitive excitation and synchronous generators with permanent magnets. The functional scheme of the voltage regulator, the construction of which has an additional field winding, simplifies the system voltage stabilization of the synchronous generator with permanent magnets, as well as a functional scheme of an asynchronous generator voltage regulator, made using step-up transformers, which significantly reduces the weight of the capacitors providing excitation of the generator and compensation of reactive power load. We have discussed the methods and devices for stabilization of voltage generators which will improve the effectiveness of pre-design work on the creation of new devices of stabilization of parameters of electric power generators for small hydroelectric power plants with improved operational and technical specifications
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FEATURES OF CALCULATION OF THE NONCONTACT ELECTRIC POWER GENERATORS
DescriptionThe article shows that to improve the performance of autonomous systems we need new methods and principles of their design, associated with both the use of renewable sources and the application of new technical solutions of electromechanical generators and static stabilizers and inverters electric power settings. We have disclosed modern requirements for generators of electric power, as well as features of calculating the parameters of contactless electrical power generators: asynchronous generators capacitive excitation and asynchronous generators with permanent magnets. The article presents some analytical expressions for calculating the electrical losses and the efficiency of the generators, specific weight and power. It is shown, that expedient to designing contactless electrical power generators to carry out as part of the autonomous electricity supply systems, as it is sometimes advantageous to understate the main criteria of efficiency of generators, in order to improve, for example, weight and overall dimensions of static converters. The conclusion is made that in order to improve the efficiency of designing contactless electrical power generators in the early stages of designing it is necessary to carry out a preliminary assessment of the main criteria of efficiency of contactless electrical machines. We have also discussed analytical expressions, which might be used for preliminary evaluation of application features for various types of contactless generators in the stand-alone electricity supply systems taking into account the conditions of use
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AUTONOMOUS WIND POWER INSTALLATIONS AND SYSTEMS
DescriptionThe article shows the main advantages and disadvantages of renewable energy sources. It is shown, that in general, the use of renewable energy in the world has acquired real momentum and stable growth trend. An interesting fact is that the greatest application was currently the most mutable and unstable form of energy - wind. The total global installed capacity of large wind turbines, according to various estimates, is approximately 20 GW. This is because the specific investment in wind power is lower than with most other forms of renewable energy. The article presents features of the design and operation of modern wind power stations. It is shown that when choosing wind power plants and stations we must take into account the following main parameters and factors: the average value of amount of electricity consumed by power consumers on a monthly basis; power generator; uptime in the absence wind or when weak wind. The study shows block-circuit solutions of different options of energy systems made using wind power plants. We have also disclosed prospects of development wind energy and considered the advantages and the features of the choice of the main functional units of wind power stations which will increase the effectiveness of predesign work on the creation of high-performance systems of electrosupply with combined power supply systems based on renewable energy sources
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SERVICE LIFE OF THE SUPPORT ROLLERS OF TRACKED TIMBER HARVESTING MACHINES
DescriptionDue to strict economical factors, determining a service life of the structural components of a tracked timber-harvesting machine (TTHM), including the support rollers becomes a key issue for the manufacturers and customers. With that, optimum relationship between the original cost of the support rollers and their life cycle cost for maintenance and repair during the entire service life shall be observed. The timber harvesting machines are operated under severe environmental and production conditions. In the course of operation, they meet variable obstacle, including stubs, stones, fallen trees, etc., which in their turn affect negatively the service life of the support rollers. This article offers a research of the service life of the tracked timber harvesting machine support rollers. It describes main defects of the support rollers, including operational, mechanical and thermal ones, as well as embedded flaws and dynamic defects. It also presents the factors affecting the support rollers' wear. The article presents a service life-determining model where the following principle can be generally applied. Service life of a support roller is determined by its admissible operational wear-out divided by actual factor for this support roller and operational conditions
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THEORETICAL INVESTIGATIONS OF STRAW PARTICLES MOTION WHEN LEVELING HAY ROLLS
DescriptionOne can see some density irregularity within the roll in the baler with a chamber of constant volume. We have found out that the maximum density of hay roll width (the baler width) is observed in the middle part. This is due to the shape of the hay roll entering the baler. To even the hay rolls they have mounted some rotating disks having some inclined spring pins above the baler. To improve the roller distribution the disks above the baler have been pushed forward forming a tapering gap. The evening discs rotating above the moving roll will cause some relative motion of hay particles. The interaction of the evening disks with the hay roll in the vertical plane will be determined by the elasticity of the hay roll and the weight of the frame with the disks. We have studied the trajectories of hay particles motion with the help of MathCad program. We have had the following initial parameters: the degree of compaction (decrease of the roll height when evening), the friction coefficient, the angle rate of the evening disks, the number of pins and the speed of the hay roll. As a result we have got the trajectories of the hay particles motion when the evening disks functioning. The analysis of the trajectories has allowed to establish some basic parameters of the evening device such as the distance of 0.15…0.2 m between the pins; the degree of compression while evening 20...25 %, the angle rate of the evening discs 23...30 rad / s and the diameter of the evening disc 0.74 m. The application of the evening device in the form of the disks with pins provides a uniform distribution of hay particles edgewise of the baler ensuring preliminary hay roll seal press before passing to the baler pressure chamber that contributes to getting the rolls with larger mass and a uniform distribution of hay density inside the roll
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PROPERTIES OF THE FINE-GRAINED CONCRETE RECEIVED AT NEGATIVE TEMPERATURES
DescriptionResearches of fine-grained concrete testify the possibility of using mineral mechanically activated and nano-additives in a complex with the anti-frost additives providing the organization of production of concrete works at negative air temperatures that is especially important for the Arctic regions
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MATHEMATICAL MODEL OF DECISIONMAKING SYSTEM INTEGRATION IN THE MULTIPLE CHOICE ALTERNATIVES
DescriptionThe article deals with the models and the methods of the market of the proposed sub-systems and equipment, based on the analysis of the requirements for security to choose the best solution for the synthesis of the integrated security system
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Description
The NP-problem of discrete optimization of consumption of non-renewable resources is considered in the article. It is offered to use transitions of NP-system conditions on the complete graph with number of vertexes, equal to quantity of discrete resources, for the problem decision. The purpose of such system is construction of a chain of the predetermined length and the minimum weight on the complete graph. The length of a chain defines quantity of the consumed resources. The problem factor is factorial growth of number of variants of chains on graph at linear growth of quantity of resources. The main idea consists in a finding of statistical regularities of ranks of transitions of NP-system at construction of chains with the minimum weight on graphs of the small size. Use of ranks allows to abstract from concrete weights of transitions, which are variables for each problem of optimization, and to find the patrimonial feature of all optimum decisions. It is offered to use the found regularities to solve the problems of the big dimension. As a result of researches, it has been defined that probabilities of ranks of transitions are described by geometric distribution. In the article, the algorithm of definition of parameter of geometrical distribution for a rank of each transition depending on the initial and consumed quantity of resources is presented. Realization of a method of generating of suboptimum chains is based on use of generators of the pseudo-random numbers setting values of each rank of transition of NP-system according to geometrical distribution of probabilities. It is offered two variants of generators of ranks of chains to use. Computer experiment has shown useful effect of an offered method at the decision of problems of small and average dimension