This study's object is the aerodynamic characteristics of the compressor diffusers in hydrogen-cooled turbogenerators. This paper reports a solution to the task of improving the efficiency of a cooling system discharge unit. This issue relates to enabling the necessary gas consumption while reducing the number of diffuser blades. The problem was solved by introducing a seal with improved technological control capabilities and step-by-step optimization of the diffuser flow part. Another issue is the thermal loads on the power components of the diffuser unit due to the action of circulating currents and temperature gradients. The problem was solved by introducing dielectric and non-magnetic elements into the structure, by additional finning and multi-component design for the diffuser strength circuits. The main result is the designed multi-component diffuser structure with a number of blades of 20 while enabling a head of Hst = 978 mm H2O. The adopted duct opening angle was 20°. Other necessary geometric parameters were determined. The introduction of a multilayer seal made it possible to reduce the gap between the impeller and the diffuser to 0.9 mm. The proposed design was tested on the bench at a manufacturing enterprise. The results of the study are attributed to the use of non-magnetic and dielectric materials (AISI 321 steel and fiberglass), as well as the introduction of additional strength decoupling elements. A special feature of the proposed method is the application of mathematical models based on the basic equations of gas dynamics, taking into account the composition principles of engineering alloys and synthetic materials. This could be achieved via a step-by-step optimization of the design. The proposed structure could be implemented when designing and modernizing hydrogen-cooled turbogenerators

Gas coolers are critical elements of turbogenerator cooling systems, which ensure the reliability and stability of the thermal mode of high-power electric machines. The aim of this research is to improve the accuracy of thermal calculations of gas coolers by combining analytical methods with numerical CFD-modeling (Computation Fluid Dynamics). The cooler’s total cooling capacity is approximately 3.8 MW, distributed across three identical sections.An analytical calculation of heat transfer for a hydrogen-water gas cooler with finned tubes was performed, using classical dependencies to determine the heat transfer coefficients and pressure losses. The results were verified using three-dimensional CFD-modeling of the hydrogen flow through the cooler using the standard k-ε (k-epsilon) turbulence model. The discrepancy between the results of analytical and numerical calculations is less than 10%. The temperature of the cooled hydrogen at the outlet meets the design requirements (+40 °C); however, areas of uneven temperature distribution were identified that require further design optimization. The study introduces, for the first time, a combined approach using analytical calculations and CFD by thoroughly evaluating the heat exchange between the cooling tube fins and hydrogen. This scientific solution enabled the simulation of hydrogen flow within the multi-stage cooler system. The proposed method has proven to be reliable and can be applied both at the design stage and for the analysis of upgraded cooling systems of turbogenerators.

The reliability of a high-power turbogenerator largely depends on its cooling system. The trouble-free and efficient operation of this system, in particular the gas cooler, is a problem that has not been fully resolved as of now. A modernized design of a gas cooler for a 325 MW turbogenerator, featuring high-finned bimetallic tubes, is proposed in the paper. To substantiate the efficiency of such a design and determine the heat transfer reserve of the gas cooler, its thermal state was calculated. The obtained results showed that the water overheating in the gas cooler is 5 °C. At the same time, one section of the gas cooler provides heat loss removal of 1266 kW at a hydrogen flow rate of 6.66 m3/s and a cooling water flow rate of 200 m3/s, which meets the requirements for this gas cooler.

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.