The article is a continuation of the study of operational reliability level of electric networks (EN) of PJSC Rosseti Lenenergo in 2014 – 2021. The classification of causes of damage in the EN and identification of predominant among them in the Company's EN during the operation period are considered in detail. The purpose of the article is defined as the study of cause-and-effect relationships that determine the accident rate, for which a number of tasks are formulated to be considered. The input data are the results of annual reports on the number of failures, broken down by months from 2014 to 2021 in the Leningrad region (LO) and St. Petersburg (SP) electrical networks. As research methods, numerical methods for evaluating the study results and the MATLAB graphic editor technology were used to visualize the analysis results of the studied indicators. Methods of mathematical statistics and artificial neural networks were used as preventive damage assessment methods.
To approximate the series of emergency outages, programming algorithms developed by the authors were used, which enabled the visualization of the studied characteristics. It is established that the most appropriate solution is to use statistical methods based on the least squares method. With their application, it is possible to study trend-seasonal models that allow to assess the influence of the seasonal component on the number of failures of electric grid elements.
As a result of the study, the main causes of failures of elements of electrical networks have been identified. For the networks of the LO, the main damage cause is the fall of trees (41%), for the SP networks — the impact of unauthorized persons and organizations (48%). Trend and trend-seasonal models have been constructed that allow obtaining short-term forecasts of emergency outages. At the same time, the assessment of the seasonal component reflects the dependence of the number of accidents on the month in which they occurred. For a more detailed analysis, it is planned to consider the influence of climatic parameters on the studied indicator.

Reliable operation of high-voltage oil-filled equipment directly depends on the condition of the insulation. One of the main components of the insulation system is transformer oil, which has been used for more than 120 years. However, in the light of modern requirements for insulating materials, oil is significantly inferior to synthetic esters in terms of such properties as chemical stability, environmental safety and high fire resistance. At present, the mixing of synthetic ester and transformer oil can be considered as one of the ways to improve the properties of the latter. A change in the chemical properties of an insulating liquid during its aging, and, consequently, the formation of various impurities and a change in the structure of its component composition will also affect the electrical insulating characteristics of the liquid dielectric. And the more the liquid is oxidized, the more significantly the electrophysical parameters worsen, including the main parameter — electrical strength (or breakdown voltage).
This paper presents the results of a study of the chemical properties of mixtures of oil and synthetic ester during prolonged exposure to elevated temperatures. The assessment of the quality of insulating mixtures was carried out by changing such indicators as optical turbidity, acid value, ester value, peroxide value, surface tension and corrosiveness. Fluid testing results in this study indicate that blending of synthetic ester with aromatic oil at 10% and 20% (v/v) results in mixtures that show signs of a colloidal system. This is evidenced by atypical trends in the diagrams indicating the change in peroxide value, acid value and optical turbidity during their aging at a temperature of 110ºС with free access of air to the surface of the mixture. Increasing the proportion of ester in the mixture to 30% and above leads to stabilization or slowdown of chemical reactions occurring due to thermal-oxidative effects. Under thermal exposure (without air access), the addition of synthetic ester to the aromatic oil in a volume of 30% or more significantly reduces the likelihood of sediment formation due to the destruction and polycondensation of aromatic hydrocarbons in mineral oil.

The paper shows an energy-saving effect based on on the organic Rankine cycle (ORC) when using thermal secondary energy resources (SER) for the production of non-concentrated nitric acid (NNA).
The production of non-concentrated nitric acid in the Russian Federation is carried out on two types of aggregates: UKL-7 and AK-72. Each unit currently has upgraded versions: UKL-7M and AK-72M, in which the design production capacity has been increased. Nitric acid production at the UKL-7 unit is carried out at a uniform pressure of 0.716MPa at the stages of ammonia conversion and absorption of nitrous gases by water. Acid production on the AK-72 unit is carried out at different pressures at the stages of ammonia conversion and absorption. Ammonia conversion on the AK-72 unit proceeds at a pressure of 0.42 MPa, whereas the absorption process is carried out at a pressure of 1.1 MPa. In this paper, by way of example, the UKL-7 unit is considered.
A useful use of SER based on the ORC is to use the heat of compressed air after the axial compressor, which is released into the environment. In this case, the heat of compressed air is used for heating and evaporation of freon in the evaporator of the cycle, heating feed water in front of the deaerator in order to reduce steam consumption. It is also proposed to use the heat of condensation of freon after the turboexpander to evaporate ammonia, which also leads to a reduction in steam consumption. It is proposed to use freon R600a in the ORC.
The calculation results show that when using the heat of compressed air and the heat released in the EGU condenser, it is possible to generate about 2,613,600 kWh/ year of electricity, as well as save 39,630 tons of steam per year.

The use of reversible hydraulic machines is often the most cost-effective option in most pumped storage configurations. At the same time, among reversible machines, radial-axial pump-turbines are most often used. This is due to the fact that such hydraulic turbines are capable of operating at high pressures, which are used in pumped storage power plants. The impellers of such reversible machines have a rigid-blade system, that is, they are not able to change their position, like the blades of axial and diagonal rotary-blade hydraulic turbines. What makes the problem in the design of pump-turbines is that, due to the different influence of hydraulic resistances, the optimum in pumping and turbine modes is different. This is taken into account in the design and determines both geometric and operational parameters. As a result, the maximum impeller diameter calculated for the pumping mode does not correspond to the optimal turbine geometry. At the same time, it is the turbine mode that should have the maximum efficiency, since the cost of peak electricity is higher than the cost of energy during the hours of dips in the daily load schedule corresponding to the pumping mode. In order to design the impeller-pump of the turbine optimally for the turbine mode, it is necessary for the same impeller to develop a greater pressure in the pumping mode of operation. To increase the pressure in the pumping mode, multi-tiered paddle grids can be used. This paper discusses the effect of additional tiers of hydrodynamic grids on the turbine regime and the prospects for their modernization in conjunction with other well-known technical solutions to increase the pressure and expand the operating area of HPP hydroelectric units.

The article is dedicated to the study of the feasibility of increasing the efficiency, reliability and manufacturability of existing gas turbine power plants with additive technologies that allow creating recuperators with regeneration degrees of 90...95%. The characteristics are presented for the following gas turbine power plants: TEEDA (Iran) 3.13 MW, ODK Perm Motors GTU-4P (Russia) 4.13 MW, Siemens SGT-100 (Germany) 5.1 MW, Solar Turbines Taurus 60 (USA) 5.67 MW. The research was carried out using the methods and programs of the Higher School of Power Engineering for the calculation of thermal circuits of GTPP. The dependences of effective efficiency, work ratio, effective specific work and specific consumption of conventional fuel of GTPPs under examination on compressor pressure ratio and regeneration factor are obtained. Solving the problem of increasing the regeneration factor in GTPP (above 0.9) requires the development of special designs of heat exchanger matrices of the recuperator, which is only possible with the use of additive technologies and new heat-resistant materials. Promising recuperators have a more complex design of heat exchange matrices, which ensures their being very compact. Such technical solutions can ensure the development and creation of fundamentally new designs of GTPP heat exchangers and significantly improve their technical characteristics.

A structural diagram of calculation of reliability of hydraulic turbines is proposed taking into account control of arameters of state of system elements, based on data of the map of setpoints of automation and process protection of hydroturbine of HPP. Failure-free operation of hydraulic unit systems and assemblies was analyzed for reliability indicators. The main elements of the system are identified. The safety of HPP operation largely depends on the reliability of the main generating equipment. Hydroturbine equipment of a hydroelectric power plant is designed for specific operating conditions characteristic for each type of hydroelectric power plant. This allows for each type of turbine to efficiently obtain the greatest amount of hydraulic power if they operate under proper conditions. Therefore, when evaluating reliability indicators, it is proposed to take into account weighting factors reflecting the degree of influence of a particular parameter on the reliability of the system. The obtained results were compared according to the proposed model and according to the regulatory methodology for assessing the probability of system failure-free operation in a generalized form. Based on the results, a model is proposed that takes into account the failures of the hydraulic unit elements to predict the probability of trouble-free operation in order to ensure the reliability of equipment operation beyond the design service life and reduce operating costs.

Various variations of reducing the aerodynamic resistance of devices with a complex configuration of the flow path are considered. About 50% of power plants in the Russian Federation operate on coal, while two-stage cleaning is used in the ash collection process. Modern coarse ash collectors can achieve an efficiency of 55 – 80%, depending on the period of their work. It is advisable to reduce the number of purification stages by upgrading with the use of modern cleaning devices, which allow achieving high efficiency in cleaning a dusty flow and less subjecting this treatment complex to repair work. The inertial-vacuum ash collector (IVAC) provides trapping of a wide range of studied particles (1 – 100 microns) with an efficiency of up to 99%. This device was tested at the combined heat and power plant of the city of Omsk, and in addition to high efficiency, increased aerodynamic resistance was established. The aim of this work was to achieve an aerodynamic resistance of 660 Pa (resistance of the cyclone apparatus, so that the apparatus can be used as the first, and consequently as two stages of cleaning) while maintaining the efficiency of the apparatus. To achieve this goal, the IVAC uses the method of perforating holes along the divider for the subsequent decrease in speed in the confuser channel and a general decrease in resistance on the device. Perforation is carried out at three different heights, the distance between which is 1 meter. The study used the analysis of a numerical experiment in ANSYS CFX using a k-ε mathematical model (mass ash content 70 g/kg; One-way Coupling). Recommendations for further prospects for the study of the IVAC are proposed.

At present, process monitoring by comparing the current parameters against a specified setpoint is widespread at thermal power plants. This approach does not allow diagnosing the emergence of a trend leading to an emergency mode at early stages. On the other hand, the analysis of time series of parameters by means of methods of statistical process monitoring allows detecting deviations from normal mode of equipment operation before emergency conditions appear. The purpose of this work is to analyze existing works in the field of application of statistical methods of monitoring. A systematic literature review (SLR) method was used in the analysis. The research process included clarifying research questions, searching for articles in databases, and forming article evaluation criteria. The specifics of the process at TPPs, which impose restrictions on the application of individual methods of statistical monitoring, were formulated. The study resulted in 64 publications, which were filtered and classified into rating groups. The highest ranked articles were used to determine the most effective statistical monitoring methods to be used on thermal power equipment. The answer to the questions posed in the study also reveals the existing problems of applying statistical methods of monitoring. The results of the study will help to identify the most applicable statistical methods for thermal power industry. It is concluded that the most suitable methods for application on thermal power equipment are methods of control charts (both Shewhart charts and Hotelling charts) based on either process parameters or generalized variance, as well as the use of autocorrelation models.