Створення методу визначення запасів міцності елементів конструкцій бандажних вузлів турбогенераторів

The complexity of assessing the safety margins of design elements and assemblies of high-power turbogenerators under the influence of temperature and force loads is due to the need to solve a set of problems: gas-dynamic, temperature, and thermoelastic problems. When designing a turbogenerator rotor bandage assembly, the solution to this set of problems associated with determining the thermally stressed state of structures is complicated by the presence of pre-tensions, the influence of temperature fields that depend on the parameters of the ventilation systems, and many other factors. The use of high-alloy steels with high hardness and tensile strength as the main material of the band rings also requires an increase in tension, which can cause cracks to appear in the most stressed structural elements. Solving the problem of determining the stress-strain state of the bandage assembly elements with the required accuracy when using exclusively classical engineering methods is not advisable, since they do not allow for effective consideration of the entire set of factors due to the presence of their mutual complex influence. The proposed method allows for more accurate computation of safety margins and determination of necessary stresses by solving a set of thermoelasticity and thermal conductivity problems in a three-dimensional setting using the finite element method with the transfer of initial and boundary conditions between problems. The refined safety margin coefficients of the elements of the bandage assembly in a state of rest, at nominal speed, and overspeed were determined when conducting a study using the developed method. For the main design elements of the bandage assembly of a 200 MW turbogenerator, the minimum safety factor at the overspeed and maximum tension was 1.3. The maximum contact stresses (approximately 550 MPa) that arise in the centering ring at zero rotation speed are local and concentrated in the area of the stress concentrator– the hole. All stress modes do not exceed the permissible values. At the same time, the tensions cannot be changed to a smaller side because the minimum permissible safety factor for the design elements of the bandage assembly of a 200 MW turbogenerator is from 1.5 to 1.05 at the overspeed.