STEAM TURBINE DEVELOPMENT | COVER STORY
Above: HPCs eight steam generators will drive the two giant Arabelle turbines at the plant
tests are required. For the new 75in (1.905m) last stages of the HInkley Point C LP module, a scale turbine model was manufactured, and a thorough testing campaign was undertaken across the whole operating map. Even at conditions well beyond typical applications, the measured amplitudes were significantly below the dynamic stress limits imposed by the design rules. The tests were used to confirm the applicability of the last stage blade protection diagram, which is used by the operator to ensure that the last stage blade is operating within the correct regime.
A new blade for a new generation Efficient cost-effective turbines for very large nuclear applications require very large last stage blades. For the Hinkley Point C development, the size of the last stage blade, and the requirement for a relatively low blade weight posed a great challenge for almost all aspects of the design and development process. Unlike typical design projects, these constraints led to the development of new development processes and tools. In summary, the following aspects played a key role in
the development process: ● Improvement of the design system: Enabled the aero designer to implement the frequency and stress layout strategy from the mechanical integrity designer, with less iteration and enabling the achievement of higher performance. The consistency in geometrical modelling between the mechanical design, aerodynamics and
mechanical integrity analysis avoided errors and the requirement for additional design iterations.
● Frequency layout process: The complex tuning process of the mode shapes of the last stage blade was facilitated by changes to the design system, as well as the consistency of the geometry in the different disciplines and analyses.
● Design for manufacturing: Detailed understanding through measurement feedback of the geometrical variations in the manufacturing of the blade airfoil allowed adaptation of the manufacturing process, the milling machine, the tolerance scheme, and the geometry itself to achieve the requirements in terms of mode shape frequency layout and stresses.
● Validation: Scaled turbine testing over the whole operating map of the turbine ensured that the last stage blade can be operated even in off design conditions, as no aeromechanical issues were identified.
The development and application of the design tools and new manufacturing processes led to the creation of a high-performance last stage which could be manufactured at moderate cost. The increase in exhaust area of the last stage compared to the previous 69in (1.7526m) design has enabled a significant increase in the power plant output of the Arabelle steam turbine train, with the first units currently being deployed at the Hinkley Point C power plant, in the UK. ■
www.neimagazine.com | October 2024 | 29
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