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 object of this study is the thermal and hydraulic characteristics of the oil coolers in a thrust bearing and guide bearing cooling system of hydrogenerators. The study addresses the task to improve the efficiency of the cooling system of the supporting elements of hydrogenerators while maintaining mass and dimension indicators. The main problems in this case are the unbalanced flow of oil within the typical cooling system and different stiffness of the thrust bearing segment supports. The main result is the design of a cooling system structure that ensures effective heat removal from the oil. According to calculations, an oil cooler for a hydrogenerator with a capacity of 56 MW provides removal of 250 kW of losses with a heat transfer margin of 26.2%, for a hydrogenerator with a capacity of 96 MW – 150 kW and 31.8%, respectively. The results are explained by the use of new antifriction materials for supporting elements (fluoroplastic-4) and a higher strength group material for the thrust bearing disk. The designed structure of the cooling system enables operation with preservation of isotropy of cooling liquids and does not have "dead" zones of these liquids flow. A feature of the proposed method for calculating oil coolers is the addition to existing criterion equations of an experimental coefficient B, which takes into account the peculiarity of the geometry of the structure in addition to the nature of the oil flow and gas-dynamic parameters. The action of three-dimensional forces, temperatures, and pressures within the base metal and cooling liquids were comprehensively taken into account. The proposed structures of the thrust bearing and guide bearing, as well as their cooling systems, could be implemented in the design and modernization of medium and high-power hydrogenerators

Представлена робота присвячена методології визначення натягів бандажних кілець методом розрахунку напружень в деталях бандажного вузла ротора. Були проведені: статичний розрахунок центруючого кільця у стані спокою, статичний розрахунок центруючого кільця при номінальній частоті обертання та статичний розрахунок центруючого кільця при угонній частоти обертання. Ці розрахунки вперше були виконані в тривимірній постановці за методом математичного моделювання.

The jumpers of rotor pole-to-pole connections are highly stressed elements in a hydraulic generator structure. These assemblies often fail due to deformation that exceeds the size of an air gap. Existing methods do not take into account the thermal component and attempts to improve the design are not based on mathematical models that make it possible to perform calculations with an accuracy of more than 50 %. The method devised in this work makes it possible to obtain boundary conditions of the third kind on the basis of three-dimensional mathematical modeling of the ventilation system of the hydraulic unit without simplifications. The method accuracy is explained by taking into account the spatial thermal component. The heat transfer coefficient determined by this method in the pole-to-pole connections area was ~250 W/(m2·K). Using FEM, mathematical modeling of the thermal stress state of pole-to-pole connections was carried out, taking into account mechanical and thermal factors. This made it possible to design the improved connection structure with additional fastening elements, which make it possible to reduce the displacement to 0.03 mm, and the stress to 53 MPa at the rotor rotation frequency of 880 rpm. This design makes it possible to enable reliable operation of the hydraulic unit under the condition of increasing the rotor rotation frequency to overspeed with disconnected combinatorial dependence, provided that the actual stresses are 0.95 % of the material yield strength. The convergence of the values obtained by the proposed method and by the HSS method exceeded 99 %. The practical result is the proposals for the hydraulic generator design modernization

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.