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In the period of shelling of energy facilities of Ukraine by the enemy, emergency damage to the working blades of the rotors and stators of the turbines occurs. Papers related to the determination of the thermal and stress-strain states of power equipment elements, which have a significant impact in the conditions of the CHPP operation after its damage, are quite relevant. The authors determine the thermal and stress-strain states that occur after damage to the medium-pressure rotor (MPR) of the T-100/120-130 power unit of the CHPP under emergency damage conditions. When calculating the thermal and stress-strain states of the MPR, taking into account the technical audit data on damage, a geometric model of the MPR was created, which takes into account all existing emergency damage and changes in the frame compared to the design one. When starting from the cold state of the T-100/120-130 turbine MPR, the maximum intensities of conditional elastic stresses at the moment of time of 16800 s in the zone of the seal groove behind the third non-regulated stage of the MPR are equal to σі=127 MPa, and in the zone of the axial opening – σі=125 MPa. The maximum intensities of conditional elastic stresses at the moment of time of 18000 s in the zone of the seal groove behind the third non-regulated stage of MPR are equal to σі=123 MPa, and in the zone of the axial hole – σі=125 MPa when starting from an uncooled state. The maximum intensities of conditional elastic stresses during start-ups from the hot state of the T-100/120-130 turbine MPR at the moment of time of 6400 s (3000 rpm) in the zone of the first unregulated stage in the seal groove according to the MPR stage are equal to σі=201 MPa, and in zone of the axial opening they are equal to σі=161 MPa. The intensities of conditional elastic stresses at the moment of time of 7000 s (3000 rpm) in the zone of the first unregulated stage in the seal groove according to the degree of MPR σі=168 MPa and in the zone of the axial hole σі=161 MPa also are significant.

The paper is devoted to the study of temperature and stress distribution in the medium-pressure rotor of the K-200-130 turbine, which are of considerable interest when predicting the durability of this equipment and extending its operation beyond the service life. A geometric model of the most loaded part of the rotor – from the middle of the shaft neck in the thrust bearing area to the 5th stage disc – was developed. The study of the thermal and stress-strain state of the rotor during start-up from a cold state was performed in a two-dimensional formulation using the finite element method. The non-stationary problem of heat conduction during start-up was solved. The obtained results indicate a fairly uniform thermal state during variable operating conditions. The largest temperature gradient (1200–2200 K/m) is observed at the time points from the rotor push to the synchronization of the turbine generator with the power system. After the turbine generator is loaded with up to 30 MW of electric power, a decrease in the temperature field irregularity and its gradual stabilization are observed. It was found that when operating at the nominal steam parameters, the maximum metal temperature is 508 °C in the region of the control stage and decreases when the distance from it increases. The stress-strain state of the rotor was evaluated taking into account the unevenness of temperature fields during start-up, stresses from thermal expansion, and centrifugal forces. The highest stresses are characteristic of the moment when the turbine comes to idle in the area of thermal compensation grooves of the rotor and the control gate and amount to 440–472 MPa. It is noted that these areas are the most likely zones of ring crack nucleation during turbine start-up operations. Subsequently, the stress level gradually decreases as the turbine unit reaches its rated power. It has been established that the most stressed area of the rotor during stationary operation is the area of the axial bore under the control stage and its diaphragm seal (121–134 MPa)

Currently, when large-scale military actions are taking place on the territory of Ukraine, the inclusion of the domestic energy system in the European one is a reliable component of providing electricity to the country's energy market. However, according to experts, uninterrupted and safe operation of nuclear power plants is still considered a prerequisite for the stable operation of the energy sector of Ukraine. The purpose of the paper is to assess the damageability and individual resource of the rotor of high-pressure cylinder (HPC) of the K-1000-60/3000 turbine power unit of the LMZ after damage to the blades in order to prolong the operation of the power unit in the conditions of a stressed state of the power system. One of the most effective ways to partially solve the problem of replacement of generating capacities is to extend the operating periods of NPP power units after the end of the project operating period, provided that nuclear and radiation safety standards are met. The review of the previously established service life of the energy equipment of NPP power units involves the assessment of the residual resource of the energy equipment in accordance with the regulatory documents. After the accidental damage of the blades of the last stage of the HPC rotor of the K-1000-60/3000 turbine power unit of the LMZ, there was a need to study the cyclic and static damage, the individual residual resource of the HPC rotor. In the process of achieving the goal, studies were carried out for three design options: the original option (five stages of the HPC rotor), the option without the blades of the last stage and the option without the fifth stage (with four first stages). The calculation of the resource indicators of the rotor in the execution of the HPC without blades of the 5th stage shows that the static damage accumulated in the main metal is 52%, the cyclic damage is 5% when applying the standard strength reserves for the number of cycles and for deformations at the level of nN=10 and nε=1.5 according to the recommendations of SOU-N MEV 40.1-21677681-52:2011. Thus, the total damage to the base metal is 57%, which sets the residual resource of the HPC rotor at the level of 88.4 thousand hours. The calculation of the resource indicators of the rotor in the execution of the HPC without entire 5th stage shows that the static damage accumulated in the base metal is 52%, the cyclic damage is 6% when applying the standard strength reserves for the number of cycles and deformations at the above-mentioned level. The total damage to the base metal is 58%, which determines the residual resource of the HPC rotor at the level of 85.6 thousand hours.

In practice, during the operation of steam turbines, accidental damage to the blades of the rotors and stators of powerful steam turbines occurs. The main causes of emergency stops of steam turbines were vibration fatigue of the blades material, erosive damage to the blades body, and resonance problems during the power equipment operation. Based on this study, the assessment of changes in the thermal and stress-strain state of power equipment elements, which at nuclear power plants significantly affect the continued operation of the turbine after its damage, are quite relevant. Changes in the thermal and stress-strain state, which may occur after damage to the rotor of high-pressure cylinder (HPC rotor) of the K-1000-60/3000 turbine power unit of the LMZ in the station conditions, have been considered and analyzed and will provide an opportunity to assess the individual resource and continue the power unit operation. In the calculated assessment of changes in the thermal and stress-strain state of the HPC rotor, taking into account the data of the technical audit regarding damage, a geometric model of the rotor was created. Studies were conducted for three options of designs: the original option (five stages of the HPC rotor), the option without the blades of the last stage and the option without the fifth stage (with four first stages). For the project design, when working at the nominal parameters of the steam, the most stressed areas are the unloading holes of the 5th stage (σi=202.8 MPa), axial hole of the rotor in the area of the 5th stage (σi=195.2 MPa), as well as the 5th-degree welding fillet from the side of the end seals (σi=200.3 MPa) and unloading holes of the 4th and 3rd stages with a stress intensity of about 170–185 MPa. The high values of the stress intensity in the area of the 5th stage can be explained by the significant concentration of the mass of both the stage itself and its blades, which provoke significant centrifugal forces when working at the nominal rotation frequency. For a HPC rotor without blades of the 5th stage, there is a shift of the maximum stress intensity to the area of the unloading holes of the 4th and 3rd stages, as well as the axial hole of the shaft under the same stages. The maximum stress value is σi max=184.8 MPa. At the same time, the intensity of stresses in the area of unloading holes of the 5th degree decreased almost by half, to the level of 124 MPa.

In the regulatory documents of the Ministry of Energy and Coal Industry of Ukraine, the beyond-design operating life of the high-energy equipment of 220 MW power units is limited to the operating life of 220 thousand hours and 800 start-ups. To date, the high-temperature cast bodies of the control valves for the high- and intermediate-pressure cylinders of the K-200-130 200 MW steam turbines of DTEK Lugansk TPP have operated about 305–330 thousand hours with the total number of start-ups from 1438 to 1704, which exceeded the beyond-design service life characteristics. Therefore, it is necessary to assess the residual operating life of the control valve bodies of the high- and intermediate-pressure cylinders of K-200-130 steam turbines in order to determine the possibility of their further operation. These calculations were carried out on the basis of our earlier studies of the thermal and stress-strain states of cast turbine equipment. This paper establishes the values of stress intensity amplitudes, the values having been reduced to a symmetric loading cycle for the most typical variable operating modes. Using the experimental low-cycle fatigue curves for the 15Kh1M1FL steel, we established the values of the permissible number of start-ups and the cyclic damage accumulated in the base metal. We also determined the value of the static damage accumulated in the course of stationary operating modes according to our previously obtained experimental data on the long-term strength of the 15Kh1M1FL steel. The calculations showed that the total damage to the control valve bodies of the K-200-130 steam turbine of power unit 15 of DTEK Lugansk TPP is 97 and 98%. The residual operating life of the metal of the control valves of high-pressure cylinders is practically exhausted, being equal to 10 thousand hours. The residual life of the control valves of intermediate- pressure cylinders is 7 thousand hours, i.e. it is also practically exhausted, with safety factors for the number of cycles and strains at the level of 5 and 1.5, as well as the permissible 370,000 operating hours of the metal. With an increase in the permissible operating life of the metal to 470 thousand hours, according to experimental studies of Igor Sikorsky KPI, the total damage to the metal of cast valve bodies is reduced to 80%, and the residual metal life increases to 79,000 h and 75,000 h for the control valves of the high- and intermediate-pressure cylinders, respectively.

200 MW steam turbines of DTEK Lugansk TPP units have operated for about 305–330 thousand hours with a total number of starts from 1.438 to 1,704, as of the end of 2019. The term for extending the operation of high-temperature power equipment between scheduled preventive maintenances has expired. When extending the operation of cylinder bodies and rotors, one should also pay attention to steam distribution elements. A peculiarity of the re-extension of the operation of a 200 MW power unit is the beyond-design operating time of power equipment of more than 250 thousand hours and the operation of equipment in maneuverable modes (more than 1,700 starts from various thermal states), with covering peaks of the electrical load with the excess of the number of starts for certain types of equipment by two to three times. Such a significant number of variable operating modes negatively affects the life cycle of equipment and requires studying the influence of the main damage mechanisms on the metal of cast components. The paper presents a calculated study of the thermal and stress-strain states of high- pressure (HP) and intermediate-pressure (IP) control valves of a K-200-130 turbine. The calculations were carried out using three-dimensional geometric models, as well as taking into account real operating conditions. The geometric model of HP control-valve bodies was constructed taking into account the complex geometry during the transition from the inlet nozzles to the valve vapor volume with a subsequent narrowing of the outlet nozzle section to the control stage of the HP cylinder. Similarly, the geometric model of IP control-valve bodies was constructed taking into account the complex spatial geometry according to the drawings provided by the operating organization. A numerical study of the thermal and stress-strain states was carried out for typical operating modes, using the finite element method. Start-up modes were investigated in a non-stationary setting, while constant ones – in a stationary setting. The thermal states of HP and IP control valves were calculated for three variants of startup modes: cold-startup mode at an initial metal temperature of 100 °C, warm-startup mode at an initial metal temperature of 250 °C, and hot-startup mode at an initial metal temperature of 410 °C. The boundary conditions for thermal state calculations were determined using real and most representative startup schedules provided by the power plant. When calculating thermal states for different startup modes, the dynamics of changes in temperature gradients was taken into consideration. During the stress-strain state studies, the main zones of stress concentration in control valves of a K-200-130 steam turbine were established.

The reliable operation of nuclear power plants (NPPs) is a prerequisite for the constant development of Ukraine's energy sector. At the current stage of development, a considerable part of the NPP steam turbine equipment is reaching its end-of-design-life value. The continuation of the operation of NPPs beyond original design life requires that the remaining useful life of its main components be verified. A model for the estimation of the resource parameters of the high-pressure (HP) rotor of a K-1000-60/3000 steam turbine has been developed. On the basis of the three-dimensional spatial analogue, the calculation of the thermal and stress-strain states of the HP rotor has been performed for all typical operating modes. It has been established that the stress concentration zones are the fillets and relief holes in the first stages, as well as the axial relief holes in the fourth and fifth stages. The calculation of the rate of cyclic damage accumulation in the base metal has been performed using correlational low-cycle fatigue dependencies, since there are no experimental data on the resistance of steel grade 30KhN3M1FA, from which the rotor is made, in the literature. Permissible values of the number of startup cycles from different thermal states and the permissible operating time under steady-state operating modes have been calculated. The level of the accumulated cyclic and static damage has been estimated for the HP rotor of Rivne NPP (RNPP) Unit 3. The loss of long-term steel strength, as a mechanism of destruction, has been found to have a dominant influence on the resource performance of the rotor under study, compared to low-cycle fatigue. The static component, Dst, of the accumulated damage of the HP rotor of the K-1000-60/3000 turbine of RNPP Unit 3 is 77%, the cyclic one Dcy is 11%. The individual remaining useful life is 26,287 hours, which allows extending the HP rotor life by additional 25 thousand hours.