Eliminating vortices in the charge pumps of Forces Motrices Hongrin-Léman SA (FMHL)
The PSA charge pump on Veytaux 1 in unit no. 2 was being severely disrupted by a vortex forming at its suction cone. In collaboration with the HES-SO University of Applied Sciences and Arts – Western Switzerland, this hydraulic phenomenon was simulated and eliminated.
The HYDRO team working on the FMHL Veytaux 1 structure had to find a solution to a vortex problem. The four main pumps lift water from Lake Geneva into the Hongrin dam. As these are above the level of the tailrace (Lake Geneva), they each need to be supplied with water by a 1.5 MW PSA charge pump.
For some time, the PSA pump on unit no. 2 had been suffering from strong vibrations and cavitation wear, requiring extensive monitoring and maintenance interventions.
Diagnosis confirmed by camera
Following analysis of the vibration, the only plausible explanation was a stationary disturbance the four blades of the pump impeller were passing through. Installing a camera in the pump pit confirmed this hypothesis and revealed a magnificent vortex.
A solution to eliminate this phenomenon had to be found. It was occurring at the bottom of an inaccessible pit eight metres below the surface of the lake. A digital simulation of the flow was carried out by the HES-SO to identify the best solution. In order to run the digital model, it was necessary to model the entire suction pit as well as the feeding pump. This enabled the vortex to be reproduced digitally and various solutions tested.
Installing an anti-vortex screen
In the end, it was decided to install an anti-vortex screen, a solution that required no major intervention and reduced the pump’s downtime. The screen was manufactured and installed on unit no. 2 in three weeks by the hydraulic operations group Riviera-Chablais.
Following this modification, the amplitude of the vibrations of the PSA pump went down from 30 to 6 mm/s, confirming the efficiency of the intervention and the elimination of the vortex.
