Project parameters
Located in the picturesque mountains of the Czech Republic, the pumped-storage hydroelectric power plant (PSPP) Dlouhé Stráně is an engineering marvel. Originally equipped with massive pump turbines installed in 1996, the plant operates under extreme high-head conditions and serves as a critical asset for grid stability.
However, to meet evolving energy demands and ensure long-term reliability, the plant's owner and operator, ČEZ, initiated a critical uprating project od units. Litostroj Power and Litostroj Engineering stepped up to deliver a comprehensive modernization.
The Challenge: dynamic loads and operational demands
After nearly two decades of rigorous operation, the original turbine runner at Dlouhé Stráně faced significant challenges that required immediate engineering intervention.
- The original runner was approaching its lifetime expiration, a direct consequence of the incredibly high dynamic loads experienced during frequent pump-turbine operations.
- ČEZ required a much wider operational range for the machine, particularly when operating in generating mode.
- The client also demanded an overall improvement in the total efficiency of the entire pump-turbine cycle.
Engineering a heavyweight solution
To resolve these challenges, Litostroj's hydraulic and mechanical designers collaborated to develop a completely new runner design to replace the existing one. The engineering phase leveraged cutting-edge diagnostic and testing methods to guarantee reliability and performance.
- Extensive hydraulic research was conducted using Computational Fluid Dynamics (CFD) to optimize the turbine's shape and improve efficiency levels in both turbine and pump modes.
- To ensure the new runner could withstand the severe dynamic loads, engineers utilized Finite Element Method (FEM) simulations to to evaluate natural frequencies, vibration modes, and the structural response to dynamic excitation.
- Manufacturing the massive runner, with a diameter of 4,540 mm, was a monumental task. It took approximately 14 months to complete the entire process, making it one of the largest Francis runners Litostroj has produced in more than 70 years.
- To minimize the risk of weld-related defects in highly stressed areas, Litostroj developed an innovative welding concept that relocates critical welds to the flow channel, where stresses are significantly lower. Litostroj was the first company in the hydro industry to successfully implement this technology.
Conclusion
The installation of the new runner transformed the operational capabilities of unit TG2 at Dlouhé Stráně. The newly engineered hydraulic design dramatically extended the turbine's operating range, allowing it to safely generate power from an extremely low output of 5 MW all the way up to a maximum of 328 MW.
By successfully increasing efficiency in both operational modes and delivering the heart of the largest single pump-turbine unit operating in Europe, Litostroj firmly confirmed its position among the world's premier hydro turbine manufacturers.
