Strength Margin Research Articles

The influence of the cyclic performance of paulownia wood semi-finished products on the strength indicators of corrugated paper

Corrugated paper is a component of corrugated cardboard, which plays an important role in the formation of strength indicators, and its production in the last decade is one of the most developed sectors of the world pulp and paper industry. The article scientifically substantiates the differences between primary and reprocessed fibers and explains the essence of “irreversible keratinization” of the fiber. The paper examines the use of leafy semi-finished products obtained from paulownia wood by alkaline-sulfite and sodium methods for the production of corrugated paper with the study of the potential of its repeated processing. Patterns of decreasing paper strength indicators with increasing recycling cycles were obtained, which is explained by irreversible keratinization. It is shown that the use of semi-finished products obtained by the alkaline-sulfite method in the paper provides strength values for all indicators for the B-2 and B-3 grades after four times processing these fibers. It should be emphasized that in terms of absolute resistance to paper crushing, the obtained values meet the standards of the highest grade B-0 after a three-fold recycling cycle. The obtained data on the repeated processing of paper from natron SFP show that the greatest decrease in mechanical strength indicators is observed after the first cycle of processing, especially the absolute resistance to pressing. However, after the second cycle of processing, according to this indicator, a margin of strength is preserved, which is enough for the norms of the B-2 and B-3 grades. After five times of recycling such paper, the strength indicators remain at almost 50 % of the initial ones, in contrast to alkaline-sulfite paper – after four times of recycling, the potential is approximately one-third. Microphotographs of the paper surface and changes in fiber structure depending on the number of processing cycles confirmed the patterns obtained during the study.

Wind load simulation for the analysis of the antenna dual-purpose poles aerodynamics

Introduction. In addition to the location of cellular communication equipment, dual-purpose poles perform the function of a lighting pole. Since dual-purpose pole are located on the central streets of the city, they have strength margins and minimum dimensions. The growing number of urban dual-purpose poles makes the correct calculation very relevant for ensuring their safe operation.Aim. Analysis of the change in the wind load on the dual-purpose pole with panel antennas and its effect on the strength of the dual-purpose pole structure. In order to achieve this, the following tasks were formulated: to deter-mine the dependence of the aerodynamic coefficient and the magnitude of the wind load on the dimensions of panel antennas and their location; to formulate recommendations for the installation of panel antennas on the upper dual-purpose pole section with a diameter of 114 mm.Materials and methods. An analysis of changes in the wind load and aerodynamic coefficient of the dual-purpose pole section, 114 mm in diameter, with panel antennas, installed thereon, depending on the dimensions of antennas and their location.Results. The aerodynamic coefficient was established to decrease at an increase in the projection of the panel antennas beyond the pipe rack, regardless of their dimensions. The more the panel antennas are pressed against the pipe rack, the closer they are to the neighboring antennas, thereby making it difficult to blow the cross-section in the center. Despite the fact that the aerodynamic coefficient decreases with an increase in the projection beyond the pipe rack, the value of the wind load remains almost constant.Conclusions. Panel antennas on a pipe rack with a diameter of 114 mm must be designed taking into account the cross-section dimensions of panel antennas. If the panel antenna width and thickness exceed 350 and 150 mm, respectively, the installation of such panel antennas should be as close as possible to the considered pipe rack in order to reduce the wind load on the dual-purpose pole. In other cases, the projection of panel antennas will have no significant effect on the change in the wind load.

Optimization and verification of mechanical design for small total reflection optics

Mechanical performance assurance is one of the key concerns in the design of small total reflection optics. This article addresses the issue of insufficient strength margin in the design of a total reflection optics for a space photoelectric sensor. Firstly, structural design optimization research was conducted on the optics, and the effectiveness of structural improvement was verified through finite element analysis; Secondly, a concave analysis was conducted under mechanical test conditions to further reduce the risk; Afterwards, the accuracy of the simulation results was verified by comparing the simulation with the experiment through small-scale random vibration tests; Finally, sine vibration tests, random vibration tests, shock tests, acceleration tests were conducted on the entire machine, and optical tests were conducted before and after the tests. The experimental and testing results indicate that the entire machine has passed the mechanical test assessment at the appraisal level and maintained good optical performance. The total reflection optics optimized by mechanical design meets the requirements of engineering applications.

An atmospheric pressure plasma device with multiple ring electrodes for decontamination of flexible tubing with variable scales

AbstractPlasma bacteria decontamination devices for the inner surface of medical tubes have to consider more practical application problems, such as the processing compatibility for medical tubes of variable scales, a reasonable and effective design model for plasma electrode parameters, and so on. This paper proposes a novel multisegment‐casing ring‐ring jet (MSC‐RRJ) without embedding the electrode into the target tube, obtaining the variable tube length processing capability. And through establishing an effective design model based on electric field distribution properties, ensuring the electric field strength margin in each segment of MSC‐RRJ to achieve the processing capability of variable tube diameters. A prototype device is developed based on the proposed MSC‐RRJ electrode and design method being verified by killing Staphylococcus aureus and Escherichia coli.

Efficient mix design method for lightweight high strength concrete: A machine learning approach

The application of lightweight high strength concrete (LWHSC) is becoming popular due to its superior mechanical properties and lighter weight nature. As a result, it offers advantages in terms of faster construction and cost effectiveness. However, achieving both high strength and lightweight is quite challenging as LWHSC possesses unique characteristics that require different mix design methods compared to conventional concrete. Additionally, the lack of appropriate mix design guidelines limits the usage of LWHSC. Therefore, appropriate tools are necessary to develop effective mix design methods for LWHSC, especially when aiming for high strength. In this study, four machine learning (ML) algorithms, namely support vector regressor (SVR), multilayer perceptron (MLP), gradient boosting regressor (GBR), and extreme gradient boosting (XGB), were applied to comprehensively analyse LWHSC mixes and provide effective prediction models to carry out mix design. To focus on the upper high strength margin of lightweight concrete (LWC), an experimental database consisting of 403 datasets with 28-day compressive strengths greater than 60 MPa and oven dry densities less than 2000 kg/m3 was developed from an extensive literature survey to predict the compressive and splitting tensile strength of LWHSC. The results demonstrated that all ML models predicted LWHSC strengths well with optimum hyperparameter combinations. Among them, GBR outperformed the other three models with an accuracy of less than 5% and 10% in predicting the average compressive and splitting tensile strengths, respectively. Furthermore, partial dependence plots (PDP) and individual conditional expectation (ICE) plots were provided to visualise the correlation between mix compositions and LWHSC strengths.

ПРОБЛЕМА БІДНОСТІ В УМОВАХ ЗБРОЙНОГО КОНФЛІКТУ: ПРИКЛАД УКРАЇНИ

The article examines the problem of poverty in Ukraine under the conditions of the Russian invasion. By the invasion of Russia, the author understands the large-scale war that has covered the entire territory of Ukraine since February 2022, since hostilities on the territory of Ukraine have been ongoing since 2014. The problem of poverty is especially relevant today, because in the conditions of armed conflicts, impoverishment affects the absolute majority of people. In the case of Ukraine, even people who, according to their social and economic characteristics, were confidently in the middle class, became poor. The article emphasizes that at the time of the beginning of the invasion, the Ukrainian economy did not have the necessary «strength margin». The standard of living in Ukraine throughout the period of independence has remained relatively low, which is proven by statistical data. So, Ukrainians had rather small amounts of savings, which adversely affected their lives after the beginning of the Russian invasion. A number of consequences of the armed conflict were identified, which directly or indirectly affected the level of poverty. Thus, the destruction of housing, by definition, determines the transition of a person to the category of citizens who are in a state of poverty. Given the number of people whose homes have been destroyed or significantly damaged, quick recovery is impossible given Ukrainian realities. The destruction of industrial facilities, road infrastructure, shopping areas, etc. is significant. Accordingly, citizens were left without work and the means of livelihood. A significant reduction in the territory controlled by Ukraine led to the loss of a significant part of the coastline and the complete loss of access to the Sea of Azov. It is emphasized that Russia gained control over a significant part of Ukraine’s natural resources. Special attention is paid in this article to Russia’s appropriation and smuggling of grain from Ukraine. Loss of life, health of citizens, mass evacuation and mobilization negatively affected the economic situation, which is discussed in detail in the work. The claim is made that evacuated citizens pay taxes, buy goods and services in host countries, supporting the economies of other countries. It has been proven that a decline in the level of education can have a long-term impact on economic development and the level of poverty. Peculiarities of the impact of the Russian invasion on the development of human capital in Ukraine have been studied. The thesis is expressed that the state and business bear an obligation to observe social responsibility. Special attention is paid to the impact of the war on the energy infrastructure. It has been demonstrated that Russia’s targeted attacks on the Ukrainian electricity industry are significantly harming the country’s economy. The list of consequences of Russia’s armed aggression against Ukraine given in the article is not complete. Moreover, a complete list with an exhaustive classification cannot be created by definition, because a significant number of facts have not yet become known. In addition, some effects will manifest only after a certain time. But it is already possible to state the need to involve the entire civilized world in order to restore the economy of Ukraine. The article uses the achievements of economic, political, sociological, psychological and other sciences, taking into account the interdisciplinary synthesis and pluralism of approaches. Modern trends in the interpretation of the consequences of Russia’s invasion of Ukraine are analyzed.

The Role of State in Managing the Wind Energy Projects: Risk Assessment and Justification of the Economic Efficiency

Our paper focuses on assessing the role of state funding in supporting wind energy projects with a focus on economic efficiency and risk assessment. In particular, we analyze the new program aimed at supporting Russian renewable energy (RE) projects envisaged for the period from 2024–2035 that involves a reduction in investments in such projects and the introduction of large fines for non-compliance with regulatory requirements for localization and export. These strict rules imposed by the regulatory authorities, as well as the withdrawal by foreign manufacturers of equipment for renewable energy from the domestic energy market, put into doubt the economic feasibility of the participation of sector players in state-supported programs. Our paper assesses the economic justification for the practicality of the Russian energy market to implement renewable energy projects under the influence of negative environmental factors and the reduction of state support programs. We employ a case study of wind energy projects carried out in 2018–2020 as a part of the first sector support program. Our methodology is based on the calculations of the classical indicators of economic efficiency of projects (NPV, IRR, and DPP). Our own approach reveals that these indicators are supplemented by taking into account the cost of specific political, environmental, and economic risks of wind energy projects. Our results reveal that, at the moment, Russian wind energy projects in various scenarios retain a sufficient margin of financial strength and are able to withstand a reduction in the amount of financial support from the state. Our findings allow the formulation of some practical recommendations for reducing the share of governmental support for wind energy projects on the local energy market as a measure of cutting costs and increasing overall economic efficiency.

Multi-objective holistic optimization method for CR SRPS based on cross-scale failure simulation of composite to improve oil recovery benefits

A carbon/glass hybrid fiber continuous sucker rod (CR) with lower specific gravity, better corrosion resistance and higher strength was developed to replace the steel rod in oil production. This paper proposes a multi-objective holistic optimization method of sucker rod pumping system (SRPS) using CR for improving oil recovery benefits. Firstly, based on the cross-scale failure criterion and finite element simulation, a judgment index for fatigue damage of CR and their joints under multiple loads, namely fatigue strength margin (FSM), is constructed, and used as a life characterization parameter of SRPS. After it is verified with liner correlation between the production cycle and FSM of realistic SRPS, FSM in addition to energy consumption and the production rate are included in the optimization objectives. Then, a multi-objective optimization model with the holistic parameters of CR SRPS as the decision variables is established. To improve the efficiency of solving the model, a hierarchical enumeration algorithm with the strategy of reducing the optimization space repeatedly by weakened constraints is presented. Finally, the proposed method was applied to the design of CR SRPS for realistic oil wells, its effectiveness and superiority are verified by the application effect and comparison results with current methods.

RESEARCH ON IMPACT LOADING OF A MOBILE TRACKED PLATFORM WITH AN AUTONOMOUS STABILIZATION SYSTEM

The work presents a developed 3D model of a mobile robotic platform with an autonomous stabilization system for reconnaissance operations. Mobile robotic platforms have been found to be widely used in intelligence because they can help gather information from dangerous and hard-to-reach places and reduce the risk to the lives of intelligence personnel. Unmanned aerial vehicles and mobile robotic platforms with tracks are mainly used in reconnaissance. An important distinguishing quality of tracked mobile robots is their maneuverability. Having an independent drive for each of the tracks separately, the mobile robot can easily change the direction of its own movement. A study on shock loads (external influences on the system that can cause deformation, damage or destruction) of a mobile tracked platform with an autonomous stabilization system was conducted and the obtained results were described. The SOLIDWORKS software environment was used to model the design of the mobile platform. For numerical studies on impact loads, it is advisable to use linear elastic isotropic materials and bilinear Mises plastic materials. The results of the simulation of the movement of the mobile platform of the developed structure and the stresses in the collision with different speeds of 1, 5, 10, 25 m/s and the platform material carbon steel and rubber are presented. It was established that when a mobile platform collides with speeds of up to 25 m/s, the maximum stresses do not exceed 1.85 MPa, which gives a sufficient margin of strength in the event of impact loads for the selected material of the mobile platform. The use of steel inserts allows you to reduce the value of the maximum contact stresses under impact load, but increases the cost of the mobile platform, increases the total weight and, accordingly, reduces the operating time from the installed power batteries.

Designing of Aircraft Reinforced Carbon- Composite Torsion Boxes

At the initial design stage, there is a problem of determining the thicknesses of the load-bearing elements of an aircraft structure made of composite materials. The paper presents the intelligent design of the composite caisson structural strength. Intelligent design is based on the finite element method. The task of optimization used the objective function of minimum mass and setting some constraints including no types of buckling al-lowed. In optimization, the parameter is the thickness of the element, which changes in the process of minimizing the objective function for elements made of PCM by an amount equal to the thickness of the package. The results show the strength margins of spar webs and rib webs of the caisson of vertical empennage torsion box satisfy the safety factor design.

An innovative method of assessing yield strength of floater hull for semi-submersible floating wind turbine in whole life period

The concepts of external and internal corrosion damage of materials have been proposed, and the improved corrosion damage models considering marine corrosion zone have been established. Then, a new method of assessing yield strength of floater hull for semi-submersible floating wind turbine considering the effect of corrosion damage in whole life period is proposed based on the equivalent design wave and structural quasi-static analysis method. Taking the OC4 floating wind turbine foundation for example, this new assessment method has been conducted. The results show that the stresses and displacements of structures will be increased under the influence of corrosion damage in whole life period and the risk of structural failure is also increased due to the corrosion damage. The structures which locate in the high stress level region will up to the yield failure critical point (yield strength margin is close to zero) by the end of service period if just considering the external corrosion damage, and these structures may fail due to yield after 18–22 years of service if considering the external and internal corrosion damage simultaneously. Therefore, the corrosion damages (especially the internal corrosion damage) have produced an important effect on the structural yield strength. In addition, the value of material factor γm = 1.1 (given by DNVGL-ST-0119) is small, and the suggested value is 1.25–1.3 for the structures in high stress level region.

Strength Calculation of the Coupling of the Floor Slab and the Monolithic Reinforced Concrete Frame Column by the Finite Element Method

This study aims at developing the concept of fragmentation of the frame to assess the load-bearing capacity of the floors. As a rule, a frame-rod design scheme is used under the finite elementmodeling of high-rise buildings made of monolithic reinforced concrete. Numerical experiments using volume-rod and volume-plate models of a repeating structural fragment were performed on a test example of a six-span three-storey monolithic reinforced concrete frame. Practical recommendations have been developed for the refined strength calcula-tion of the floors of monolithic reinforced concrete frames of multistorey buildings. Materials and Methods. Computational experiments were performed using the ANSYS Mechanical software package, in which the finite element method was implemented in the form of a displacement method. A plate-rod ensemble of finite elements was used to simulate the stress-strain state of a monolithic reinforced concrete frame. The refined calculation of the coupling zone of the floor slab and column under static loading was performed using solid, beam, truss and plate elements. Results. An engineering technique has been developed for numerical analysis of the stress-strain state of the coupling of the floor and the column of the reinforced concrete monolithic frame under static loading. The most accurate result was provided by a finite element model constructed using beam finite elements as reinforcing rods. Discussion and Conclusions. The developed technique of numerical modeling of the coupling of the floor and the column made it possible to estimate the real strength margin of this node, taking into account the real geometry of reinforcing grids, as well as to clarify the bearing capacity of a monolithic reinforced concrete frame under various loading scenarios.

Теоретичні та прикладні аспекти формування механізму управління адаптивним розвитком промислових підприємств в умовах трансформації економіки

The article discusses both the theoretical and the applied aspects of the formation of a mechanism for managing the adaptive development of industrial enterprises in the context of transformation of the economy. An analysis of the factors of influence has been carried out, the main of which is found to be the level of market prices for iron ore products, significantly depending on fluctuations in exchange rates. Taking into account the need to adapt the totality of operations in the foreign and domestic markets of iron ore products to fluctuations in the exchange rate, the principle of proportionality of income from exported iron ore products and those consumed in the domestic market is proposed. It is determined that the introduction of elements of scientific and technological progress in the activities of iron ore enterprises is a prerequisite for their successful functioning in today’s crisis conditions of economic management. The urgency of introducing elements of scientific and technological progress in the formation of investment and innovation potential, margin of financial strength, level of labor productivity, etc., of an iron ore enterprise has been proved, and the importance of the sales potential of economic entities under modern conditions has been shown. Among the numerous methods and techniques for mathematical calculation of optimized indicators, the most expedient appears the use of modeling through iterative variation of the exchange rate to optimize the volume of exports and domestic consumption of iron ore products. It is specified that, taking into account the need for a margin of financial strength and balance of production and economic programs, this approach is the most appropriate in determining the directions for improving the efficiency of using the resource and production potential of an iron ore enterprise. A model for maximizing income from the sale of products of an iron ore enterprise in the foreign and domestic markets has been proposed, on the basis of which modeling of the value of exports and domestic consumption of iron ore products has been carried out.

БЮДЖЕТИРОВАНИЕ КАК ИНСТРУМЕНТ УПРАВЛЕНЧЕСКОГО УЧЁТА И ЕГО СВЯЗЬ С ВНУТРЕННИМ КОНТРОЛЕМ В АГРАРНЫХ ФОРМИРОВАНИЯХ

The article discusses the author's approach to the organization of budgeting in agrarian formations. Budgeting in the agrarian formation is aimed at improving the efficiency and effectiveness of the costs incurred by linking the budget of the organization and the results that it provides, through the use of systematic information on efficiency (indicators, estimates, costs). Results management helps you prioritize costs and improve production efficiency. This mechanism will help the leaders of agrarian formations to be more flexible in the use of resources, especially in the choice of resources for the production of finished products. The purpose of the research is to study budgeting as a tool for management accounting and to establish its connection with internal control on the example of agrarian formations. The choice of scientific methods and approaches was carried out by the authors on the basis of the principle of reliability, reasonable sufficiency, relevance and feasibility. This made it possible to provide the necessary level of validity and in-depth study of the set goal and the range of tasks. The application of this approach makes it possible to consider that the study was carried out systematically, scientifically and objectively. Results. The authors calculated the tactical and strategic sales volume according to pilot organizations. The volume of production of finished products is determined, which is able to ensure the implementation of the sales budget. The types of products that have the largest margin of financial strength for the organizations under study are identified. The scheme of functioning of the budget process is presented. Conclusions. In the course of the study of the budgeting process in the pilot organizations, it was found that quite close attention is paid to this budget. This applies both to the determination of sales volumes, the structure of products sold, and to the quality of products. The forecast selling price then depends on the quality of the products, which, in turn, determines all the financial indicators of the economic entity.

ТЕНДЕНЦИИ ДЕЙСТВУЮЩИХ МЕТОДОВ САНАЦИИ КАК ПЕРСПЕКТИВЫ РАЗВИТИЯ МЕХАНИЗМА ПРЕДУПРЕЖДЕНИЯ БАНКРОТСТВА БАНКОВ

In recent years, the activities of Russian commercial banks have been influenced by a complex of external and internal factors, which requires strengthening the adaptation of banking models to the conditions of an unstable economic environment and creating a margin of financial strength for its continuation. At the same time, the ability to identify negative trends in the bankruptcy prevention mechanism will make it possible to take preventive measures to prevent it both by the regulator and the credit institution itself, which is a trigger for the development of the banking sector. It is important to pay close attention to identifying negative trends in the banking sector in order to reduce the mass revocation of licenses of credit institutions due to the deterioration of the financial position of banks, which may further worsen the state of the banking sector. These circumstances determined the relevance of the study.

ОСОБЕННОСТИ ВЛИЯНИЯ ФОРМ ОПЛАТЫ ТРУДА НА ЗАПАС ФИНАНСОВОЙ ПРОЧНОСТИ БИЗНЕСА

A financial model has been developed that takes into account the impact of forms of remuneration on the margin of financial strength and allows you to manage its value

Numerical analysis of the thermal-elastic-plastic state of electrical contact gasket made from dispersion-reinforced composite materials using the fusioned deposition modeling method

The article presents the results of a theoretical study on determining the suitability of using electrical contact gaskets (ECG) in industrial conditions (Castner direct graphitization furnaces), made of coke-pitch composite using additive technologies based on the Fused Deposition Modeling (FDM) method.
 Numerical analysis of the physical state of ECG under the conditions of industrial application was performed on the basis of the mathematical statement of the thermo-elastic-plasticity problem and the algorithm of implicit inverse mapping of its solution based on the finite element method in the Mathcad programming environment. To construct the geometry and tetraid mesh of the ECG model, a freely open program code was used - the Gmsh CAD system for grid generation, and for the visualization of the results of physical field calculations, the free open program code ParaView was used.
 The study of the thermo-elastic-plastic state of ECG under the conditions of the graphitization process in Castner furnaces was carried out in the temperature range up to 900 °С, at which the thermoplastic properties of the material are manifested. At the same time, such physical fields of ECG were analyzed as temperature distribution, resulting displacements, equivalent elastic stresses according to Mises, equivalent total, elastic and plastic deformations according to Mises, and the volume fraction of ECG material in a plastic state, depending on the temperature level and radial gradient temperatures (radial temperature difference) of electrical contact gaskets.
 Numerical simulation of the thermo-elastic-plastic state of the ECG was carried out under the conditions of force loading by external pressure on the lateral surface of the gasket of 2.5 MPa and different values ​​of the radial temperature difference in the range of 15–90 °C in the temperature range up to 900 °C. It was established that: at the stages of formation of semi-coke and coke in the material of the coke-pitch composite ECG under the thermomechanical conditions of operation of the Kastner furnace, a margin of strength of not less than unity was obtained; with the subsequent increase in the temperature level in the Castner furnace to 3000 °C and above, the raw material of ECG, as a result of thermal destruction, has already turned into coke and, therefore, its mechanical properties have become close to the mechanical properties of electrode blanks in columns that are subjected to graphitization. This gives reason to assert that the ECGs will not be mechanically destroyed during the entire graphitization campaign of the Castner furnace.
 On the basis of the analysis of the results of numerical simulation, the possibility of using ECGs made from dispersion-reinforced composite materials (coke-pitch mixtures) by the FDM method in the technology of graphitizing electrode products according to the Сastner method is substantiated.

Asymmetric Method of Heat Transfer Intensification in Radial Channels of Gas Turbine Blades

Loop and semi-loop cooling schemes are widely used for the high-temperature gas turbine blades. In such schemes, the mid-chord airfoil parts are traditionally cooled by radial channels with ribbed walls. The blades with a small specific span, or “short” blades, have different heat flux amounts on pressure and suction sides, which results in a temperature difference in these sides of 100–150 °K. This difference causes thermal stresses and reduces the long-term strength margins. This paper presents a new method of heat transfer intensification in the ribbed radial cooling channels. The method is based on air streams’ injection through holes in the ribs that split channels. The streams are directed along the walls into the stagnation zones behind the ribs. The results of a 3D coolant flow simulation with ANSYS CFX code show the influence of the geometry parameters upon the channel heat transfer asymmetry. In the Reynolds number within a range of 6000–20,000, the method provides the heat transfer augmentation difference by up to 40% on the opposite channel walls. Test results presented in the criteria relations form allow for the calculation of mean the heat transfer coefficient along the channel length.

Обзор методов измерения механической прочности тонких плёнок

This review article discusses methods for measuring the main mechanical properties of thin films: tensile testing, indentation, evaluation of the mechanical strength margin for the curvature of the plate-thin film system, bulge method and research using a deformed and resonant cantilever. In the process of critical analysis of domestic and foreign literary sources, the advantages and disadvantages of the methods were revealed; the authors' motivation for conducting such studies was explained. In addition to the existing widely used methods, an original and relatively new technique is given - the use of electric current as a controlled means of applying thermo mechanical stresses to electrical conductors to characterize their fatigue behavior. Approaches for increasing the mechanical strength of thin films are also indicated.

Diagnostics of Power Transformer Main Insulation According to the Oil Dielectric Strength Statistical Criterion

Improvement of methods for assessing the technical condition of power transformers continues to be among urgent operation problems at power companies. A set of studies and calculations of the power transformer main insulation electrical strength has been carried out based on determining the transformer oil electrical strength statistical parameters with taking into account regulatory procedures and the newly developed method of statistical characteristics. The results obtained from calculations of the variation coefficient and the average breakdown voltage of operating oils for the transformers under study are considered and analyzed taking into account the requirements of regulatory documents in force in the power industry. An oil electric strength statistical criterion is determined based on the standard and by the method of statistical characteristics using the Gnedenko–Weibull distribution. A dependence of the oil electric strength statistical criterion limiting values on the power transformer power is obtained. An approach to diagnosing the power transformers’ main insulation electrical strength according to the oil electrical strength statistical criterion is proposed. The distribution histograms of the oil electrical strength statistical criterion and the oil breakdown voltages lower limit are shown. A positive correlation has been established between the oil electric strength statistical criterion and the variation coefficient based on a comparison of the statistical parameters obtained using the conventional diagnostic method and the one proposed in the ongoing study. The values of the operational transformer oil electrical strength statistical criterion for operating transformers are compared with the calculated limit values of this parameter. It has been found from the study results that with decreasing the electrical strength margin, the number of transformers that meet the electrical strength statistical criterion requirements decreases for all values of the transformer nominal capacity.