Power Engineering Problems Research Articles

Analysis of Temperature Conditions Influence on Cables Insulation Operation Life

Electrical equipment fault current interruptions reduce is one of the most important problems of electrical power engineering and diagnostics. Power cables operation life is one of the parameters mostly affecting fault current interruptions on cables. The paper describes the research on thermal degradation of low voltage cables insulating materials and its influence on insulation operation life. The known mathematical models of the insulation aging depending on its temperature are considered. Low voltage cables have an insignificant electrical aging influence, so it is assumed that such cables aging mostly caused by their thermal operating conditions. Experimental research of cables insulation temperature monitoring is performed. Seven weeks of the experiment showed a temperature change between 17˚C and 27˚C. The mean temperature was 21.9˚C. Assuming that cable has normal operation life with an average temperature of 20˚C and accounting thermal conditions cable insulation operation life is reduced for about 20%. Such operation life reduce is significant and shows a considerable influence of insulating material thermal deterioration.

Проблемы ядерно-лазерной энергетики и способы их решения

Проблемы ядерно-лазерной энергетики и способы их решения

Nanocomposites Based on Magnesium for Hydrogen Storage: Achievements and Prospects (A Survey)

We describe three fundamental problems of hydrogen power engineering, namely, the problems of efficient production, storage, and use of hydrogen. We present a survey of recent works devoted to the investigation of various types of materials used for hydrogen accumulation and, in particular, of magnesium-based nanocomposites as the most promising materials. Our main attention is given to the analysis of the sizes of particles of the components of composite materials and the effect of catalytic admixtures on the parameters of hydrogen sorption and desorption. We present a brief overview of our results on the mechanochemical synthesis of MgH2, as well as of the new results obtained for Mg-based composites with nano-Ti admixtures, including the synthesis and properties of composites produced from Ukrainian raw materials. The prospects of application of magnesium-based hydride composites are also demonstrated.

Optimizing Insertions in a Constraint Routing Problem with Complicated Cost Functions

An iterative method for solving routing problems subject to constraints and possible dependence of the cost functions on the list of tasks that have not been accomplished is considered. Such statements occur in some problems of nuclear power engineering and in developing optimizing programs for sheet cutting on programmable numerically controlled machines (in the first case, the dependence on the list of tasks can occur due to sequential dismantling of radiation sources, and in the second case it can be due to taking into account technological constraints using penalties). It is assumed that the problems under examination are large, which calls for the use of heuristic methods. The approach proposed in the paper makes it possible to design an iterative procedure based on optimizing insertions that use widely interpreted dynamic programming. The proposed algorithm is implemented on a multicore personal computer.

Direct and Inverse Problems of Thermomechanics Concerning the Optimization and Identification of the Thermal Stressed State of Deformed Solids

We describe the main stages of the development of investigations originated by Prof. Vihak in the fields of the theory and methods of optimal control over the thermal processes and thermal stressed state of deformed solids, theory of inverse problems of heat conduction and thermomechanics, and the mathematical methods in the mechanics of deformable solids. We indicate the existence of close relationship between the obtained theoretical results and the applied problems of thermal power engineering motivating investigations of this kind. We describe a significant contribution made by the researchers of the Pidstryhach Institute for Applied Problems in Mechanics and Mathematics of the Ukrainian National Academy of Sciences to the development of investigations in these fields. The prospects of further development of these studies are analyzed and some facts from the life and creative activity of Prof. V. М. Vihak are presented.

Автоматизована система розрахунку коригувальних мас і прогнозування залишкової вібрації при динамічному балансуванні турбоагрегатів

In Ukraine, 47,7 % of electricity production falls on nuclear power plants. An important and time-consuming process in the NPP is the monitoring of the level of vibration and dynamic balancing of turbines. Nowadays in our country we have only a partial automation of it. Therefore, solving of technical problems in power engineering based on modern information technologies is actual and in demand. Analysis of existing solutions shows that there is practically no single algorithm for dynamic balancing and the method of selecting one optimal load for a set of bearings to eliminate the calculated vibration. The goal of the work is to create unified software that could not only compute the corrective loads, but also immediately offer an engineer the most optimal solution how to eliminate the vibration. Actually, to create such functionality, it is necessary to combine the numerical and vector methods of determining the vibration and to improve them for the possibility of choosing the best value. Our main tasks: to find the optimal mass of test load and optimal place to put it; find the optimum mass and the optimal location of the correcting load during repair and under load in order to get the minimum values of vibration at all monitored points, without exceeding their normal values; to analyze and predict how the direction of the vibration vector would change; to visualize the results on the selected direction; to improve a technology of calculation corrective load for each bearing to obtain more accurate and quick results. Sometimes the calculated values of the expected vibration do not coincide with real values when a turbine unit is operating at high power. Therefore, one of the solutions to the problem is to create a knowledge base for the system and an algorithm to select corrective loads based on conclusions and attempts that system made earlier.

The International Conference “Problems of Thermal Physics and Power Engineering” (PTPPE-2017)

Editor Alexey V. DedovOrganizersThe Ministry of Education and Science of the Russian FederationThe Russian Academy of SciencesNational Committee for Heat and Mass TransferNational Research University “Moscow Power Engineering Institute”The Institute of Thermophysics SB RAS named S.S. KutateladzeConference sponsorsRussian Foundation for Basic ResearchComsolGazEcosInterenergoIntroductionThe International Conference “Problems of Thermal Physics and Power Engineering” (PTPPE-2017) held at Moscow, Russia on October 9-11, 2017. The conference will take place in the National Research University “Moscow Power Engineering Institute” (NRU “MPEI”)Lists of Scientific and Organizing Committee members are available in this pdf.

Applications of wavelet transform on power engineering problems — A brief review

The main scope of this paper is about the applications of wavelet transform (WT) on power engineering research. This review paper deals with the summary of applications of WT to different power system problems including transmission line faults detection, power quality issues, power forecasting, power measurements and power system stability. Different types of wavelet are used for the solution of various power engineering issues, and the selection of suitable wavelet for specific problems is also discussed in this paper with the support of literature.

PowSysGUI: A new educational software package for power system stability studies using MATLAB/Simulink

Graphical user interfaces have been progressively used in the classrooms to provide users of computer simulations with a friendly and visual approach to specify all input parameters with enhanced configuration flexibility. In this paper, an educational software package called PowSysGUI (Power System GUI), which runs on MATLAB and uses graphical user interfaces, has been developed for analysis and simulation of small to large size electric power systems. PowSysGUI is open-source software and anyone can see the inner structure of the program to figure out how to code a power engineering problem. It is designed as a simulation tool for researchers and educators, as it is simple to use and modify. PowSysGUI has algorithms for solving power flow, small signal stability analysis, and time-domain simulation. In the case studies, IEEE 16-machine 68-bus test system is given to show the features of the developed software tool. Moreover, classroom experience has shown that the developed software package helps in consolidating a better understanding of power system stability phenomena.

Multiobjective and multiattribute decision making in a fuzzy environment and their power engineering applications

This work presents and generalizes our experience in the use of fuzzy set theory, including its combination with another branch of mathematics of uncertainty, in developing general approaches and methods for optimization and decision making with considering the uncertainty and multicriteria factors in problems of the design, planning, operation, and control of complex systems. Two major classes of situations that require the use of a multicriteria approach are identified. In accordance with this, two general classes of models related to multiobjective (〈X, F〉 models) and multiattribute (〈X, R〉 models) problems, respectively, are considered. Methods for their analysis based on the use of the Bellman–Zadeh approach to decision making in a fuzzy environment and fuzzy preference modeling techniques, respectively, are considered. Although, the use of 〈X, F〉 and 〈X, R〉 models is of an independent character, they also serve as parts of a general scheme for multicriteria decision making under conditions of uncertainty. This scheme is associated with the use of a generalization of the classic approach to considering the uncertainty of information to multicriteria problems, based on analyzing special aggregations of payoff matrices. The authors' experience in the use of the results indicated above for solving diverse classes of power system planning and operation problems is described. This experience convincingly demonstrates diverse advantages of applying fuzzy mathematics in optimization and decision making problems of power engineering.

Routization Problem Complicated by the Dependence of Costs Functions and «Current» Restrictions From the Tasks List

The problem of a routization of the movements complicated by the restrictions of different type (preceding conditions, the restrictions on the attainability of states by each movement and others) is considered. A multivariance at the movement step is permitted, it is naturally resulted in the problem about the visiting of megalopolises. The costs of movements and jobs executed when visiting megalopolises may depend on the list of tacks. This list may correspond to performed or unperformed tasks. ”Current” restrictions (on movements) may depend on the aforementioned list of tasks. The considered setting is oriented to the application with regard to a nuclear power engineering problems (the problem of decreasing irradiation of the nuclear power station staff when executing a complex of tasks under high radiation intensity) and the machine building. In the second case, which consists in controling a machine for the sheet cutting of details by the numerical program control machines, ”current” restrictions on movements may be conditioned by temperature tolerance relative to the fragments of sheet which have already been ”visited” by the cutting machine. The scheme of constructing the optimal solution based on the widely understood dynamic programming is considered in this article. The used algorithm is realized on a personal computer; the results of its application are illustrated by the modelling examples.

Problemy atomnoyi enerhetyky: istoriya ta suchasnist'

Problemy atomnoyi enerhetyky: istoriya ta suchasnist'

Degenerate optimization problems of economy and power engineering

Optimization of large economy and power engineering systems leads to degenerate solutions of a high dimensionality. This is a very strong mathematical complication. It however allows the future evolution of power engineering to be considered both as based on joint operation of nuclear power plants (NPP), coal-fired power plants (PP) and gas-fired PPs, and based on only NPPs. This requires a system optimization of the NPP parameters.Computational studies on optimal high-dimensionality systems have led to the degenerate space of admissible economy and power engineering solutions to be understood as a set of points on a lunar surface with a finite number of craters. Such degenerate space may be referred to as “non-convex, non-concave”.In other words, an N-dimensional degenerate “non-convex, non-concave” space of a high-dimensionality optimization problem (N≥10,000) looks like a “lunar surface” with craters of different depths. Craters form the neighborhood of locally optimal plans, and the locally optimal plan as such is on the bottom of a crater. The crater depth defines the value of the functional being optimized. Occasionally, the deepest but different craters include equally deep craters, that is, craters with equal values of the locally optimal plan functionals. The local optimum (local plan) in different craters may differ structurally, and the optimization problem functionals for these points may be equal in value.Calculations show that equally sized craters (with equal values of economy and power engineering development locally optimal plan functionals) occasionally include craters with locally optimal plans of economy and power engineering evolution (in a diversity of the potential combinations of economy and energy technology states) based only on coal- or gas-fired PPs, or on coal-/gas-fired and nuclear PPs, or on NPPs. By weighing the values of the locally optimal plan functionals in different craters, one can find an optimal solution – a locally optimal plan with the best functional value (e.g., in the event of the functional minimization, with the minimum objective functional value out of the entire number of the considered craters).

Using the Interior Point Method to Find Normal Solutions to a System of Linear Algebraic Equations with Bilateral Constraints on Variables*

The authors consider primal interior point algorithms to find normal solutions to systems of linear equations with bilateral constraints on variables. Analyzing this problem and the methods of its solution is important to develop the theory of mathematical modeling (in particular, to solve power engineering problems) and to create efficient computational algorithms. The paper contains the results of experimental analysis of the algorithms using test problems and identifies the ways to accelerate the computational process.

A new approach for the column apparatuses modeling in chemical and power engineering

The column apparatuses are main devices for solution of technological and ecological problems in chemical and power engineering. A new approach of the column apparatuses modeling on the base of the physical approximations of the mechanics of continua, using two steps models: convection-diffusion type of model (for qualitative analysis) and average concentration model (for quantitative analysis), is presented. The convection-diffusion type of models describe chemical and mass transfer processes in column apparatuses in the cases of one, two ore three phases systems, where the solid phase is reagent, catalytic or packed bad. A qualitative analysis of these models, using generalized (dimensionless) variables, where the characteristic (inherent) scales are the maximal or average values of the variables, is presented. The using of the convection-diffusion type of models for quantitative analysis of the processes in column apparatuses is not possible because the velocity function in the convection-diffusion equation is unknown. The problem can be avoided if the average values of the velocity and concentration over the cross-sectional area of the column are used. The average concentration models permit to analyze the effect of the radial nonuniformities of the velocity and the concentration on the process efficiency in the column and to solve the scale-up problem. The convection-diffusion type of models are presented as a base for to be created convection and diffusion type of models.

Generalized Algorithms of Discrete Optimization and Their Power Engineering Applications

Generalized algorithms for solving problems of discrete, integer, and Boolean programming are discussed. These algorithms are associated with the method of normalized functions and are based on a combination of formal and heuristic procedures. This allows one to obtain quasi-optimal solutions after a small number of steps, overcoming the NP-completeness of discrete optimization problems. Questions of constructing so-called “duplicate” algorithms are considered to improve the quality of discrete problem solutions. An approach to solving discrete problems with fuzzy coefficients in objective functions and constraints on the basis of modifying the generalized algorithms is considered. Questions of applying the generalized algorithms to solve multicriteria discrete problems are also discussed. The results of the paper are of a universal character and can be applied to the design, planning, operation, and control of systems and processes of different purposes. The results of the paper are already being used to solve power engineering problems.

Computer Simulation of Hydrogen Thermodesorption

In the context of problems of hydrogen and thermonuclear power engineering intensive research is being conducted into ways to protect construction materials against hydrogen corrosion, chemical reactor design, materials suitable for hydrogen storage and transporting. Mathematical models help to specify physical-chemical ideas about the interaction of hydrogen and its isotopes with solids, to discover the limiting factors and to significantly reduce the expenses of experimental research by means of numerical simulation for different parameters and experimental conditions (including extreme ones). Classical diffusion models are often insufficient. The paper is devoted to the model and numerical solution of the boundary-value problems of hydrogen thermo desorption taking into account nonlinear sorption-desorption dynamics on the surface and its reversible capture in the bulk. Computational algorithms based on difference approximations and the results of computer simulation of the hydrogen thermo desorption flux from a structural material sample are presented. KeywordsHydrogen Interaction with Solids; Surface Processes; Thermo Desorption Method; Nonlinear Dynamical Boundary-value Problems; Finite-difference Schemes; Computer Simulation

Obszarowe zarządzanie dużą generacją wiatrową w kontekście zapewnienia bezpiecznej pracy sieci

The paper presents a new approach to the problem of optimizing wind generation distribution in cases of overloads in the grid caused by high level of wind generation. The approach is based on a modified and enhanced version of a genetic algorithm presented at the previous “Aktualne Problemy w Elektroenergetyce” (APE) [Present-Day Problems of Power Engineering] conference in 2011. The idea of coherent a grid nodes is introduced in order to optimize generation levels for groups of wind farms instead of individual wind farms, enabling grid operators to distribute power reduction among wind farms in a more equal manner, which can result in enabling larger wind generation penetration in grid with low transmission capacities. The test results as well as results obtained using the algorithm for a real-life, large-scale case are also presented.

An Anisotropic Geomechanical Model for Jointed Rock Masses at Taishan Nuclear Power Station, Southern China

Abstract:An anisotropic geomechanical model for jointed rock mass is presented. Simultaneously with deriving the orthotropic anisotropy elastic parameters along the positive axis, the equivalent compliance matrix for the deflection axis orthotropic anisotropy was derived through a three‐dimensional coordinate transformation. In addition, Singh's analysis of the stress concentration effects of intermittent joints was adopted, based on two groups of intermittent joints and a set of cross‐cutting joints in the jointed rock mass. The stress concentration effects caused by intermittent joints and the coupling effect of cross‐cutting joints along the deflection‐axis are also considered. The proposed anisotropic mechanics parameters method is applied to determine the deformation parameters of jointed granite at the Taishan Nuclear Power Station. Combined with the deterministic mechanical parameters of rock blocks and joints, the deformation parameters and their variability in jointed rock masses are estimated quantitatively. The computed results show that jointed granite at the Taishan Nuclear Power Station exhibits typical anisotropic mechanical characteristics; the elastic moduli in the two horizontal directions were similar, but the elastic modulus in the vertical direction was much greater. Jointed rock elastic moduli in the two horizontal and vertical directions were respectively about 24% and 37% of the core of rock, showing weakly orthotropic anisotropy; the ratio of elastic moduli in the vertical and horizontal directions was 1.53, clearly indicating the transversely isotropic rock mass mechanical characteristics. The method can be popularized to solve other rock mechanics problems in nuclear power engineering.

Fuzzy Set Based Models and Methods of Decision Making and Power Engineering Problems

The results of research into the use of fuzzy set based models and methods of multicriteria decision making for solving power engineering problems are presented. Two general classes of models related to multiobjective (X，M> models) and multiattribute (X，R> models) problems are considered. The analysisX，M> of models is based on the use of the Bellman-Zadeh approach to decision making in a fuzzy environment. Its application conforms to the principle of guaranteed result and provides constructive lines in obtaining harmonious solutions on the basis of analyzing associated maxmin problems. Several techniques based on fuzzy preference modeling are considered for the analysis of X，R> models. A review of the authors’ results associated with the application of these models and methods for solving diverse types of problems of power system and subsystems planning and operation is presented. The recent results on the use ofX，M> andX，R> models and methods of their analysis for the allocation of reactive power sources in distribution systems and for the prioritization in maintenance planning in distribution systems, respectively, are considered.