Kravchenko S. Ensuring power increase and substantiation of long-term operation at above-design modes of turbogenerators of thermal power plants

The thesis is purposed to the topical issue of ensuring power increase and substantiation of long-term operation at above-design modes of high-capacity turbogenerators by developing new methods of three-dimensional computation of mechanical stresses in units and design elements of turbogenerators. The computation of refined reserves of strength of resource units of turbogenerators was performed to substantiate the provision of reliable operation of turbogenerators under conditions of supercritical loads. The goal of the thesis is the development of methods for studying the stress-strain state of units and design elements of high-capacity turbogenerators when operating at rated and above-design modes with the solution of a set of thermoelasticity and thermal conductivity problems in three-dimensional settings using finite element method for the coupled problem of thermoelasticity in the part of specifying the boundary conditions of the III-rd kind. The first section of the thesis is purposed to the analysis of the current state of generating equipment of thermal and nuclear power plants in Ukraine due to the periodically arising need to operate in supercritical modes. The general review of the design of turbogenerators and regulatory and technical requirements for their operating conditions was performed. The second section of the thesis is purposed to the development of methods and the algorithm for calculating the stress-strain state of turbogenerator designs in a three-dimensional setting. The geometry requirements were determined and the three-dimensional modeling of the computation units was performed. The third section presents the results of mechanical computations of the turbogenerator stator core fastening system using the developed three-dimensional modeling method, in which, unlike the existing ones, the strength calculation in the part of the thermoelastic problem is performed with the addition of actual contacts and taking into account the design and technological features of the parts. The fourth section presents the results of mechanical calculations of turbogenerator boxes (shields) by the developed method of calculating the strength of units and design elements of turbogenerators with the solution of a set of thermoelasticity and thermal conductivity problems in three-dimensional settings using the finite element method for the coupled problem of thermoelasticity in the part of specifying the boundary conditions of the III-rd kind, which is a feature of this method. The fifth section of the thesis is purposed to the analysis and correlation of the results of the stress-strain state study of units and design elements of turbogenerators. Scientific novelty of the work: 1. Existing engineering methods for determining strength based on the classical theory of resistance of materials and the theory of heat-mass exchange in a two-dimensional setting have been enhanced in terms of specifying strength reserves based on careful mathematical modeling of the physical state of the structure and correlation with methods of destructive control of the physical properties of materials. 2. The new method of calculating the strength of units and design elements of turbogenerators was created with the solution of a set of thermoelasticity and thermal conductivity problems in three-dimensional settings using the finite element method for the coupled problem of thermoelasticity in the part of specifying the boundary conditions of the III-rd kind. 3. The new method of calculating the strength of units and design elements of turbogenerators in terms of the thermoelastic problem was created with the addition of actual contacts of their elements and comparison with the design and technological features of the parts. 4. The algorithm for assigning boundary and initial conditions for three-dimensional models of design components of power equipment has been improved in the part of the detailed description of the design, taking into account its different stiffness and the peculiarities of the technological connection of parts based on three-dimensional modeling. Practical significance of the obtained results: 1. The methodology for calculating strength margins for units and parts of turbogenerators and similar power equipment has been developed, the use of which ensures reliable operation of turbogenerators at rated modes for at least 27,000 hours. The methodology is based on three-dimensional modeling methods developed in the work. 2. The rationale for ensuring power increase and long-term operation at above-design modes of turbogenerators of turbogenerators of thermal power plants is provided. 3. The regularities of the deformation of units and design elements of turbogenerator stators and similar power equipment under the influence of thermal, mechanical and vibrational factors for actually selected welds hav been established.