Pump start instability on a low head pump turbine and testing with partial deaeration

Abstract Since 2019 Iberdrola has had an interest in enabling pump operation of the Valparaiso hydropower plant. Iberdrola contacted Andritz, the original manufacturer of the machines, and a collaboration for that purpose was started. This powerplant was equipped with two pump turbine units in the 1980ies but pump operation has not been possible since strong vibrations occurred during pump commissioning in 1995. Therefore, the units had only been operated in turbine mode since then. In 2020 Iberdrola and Andritz performed a renewed pump start test with a fully rewatered machine. This again led to high vibrations during the initial phase of guide vane opening. Subsequently, guide vane flutter (self-excitation) was investigated as a potential cause of the vibrations but could not be established as the cause. Instead, it was found, that due to a transient effect, the machine entered the unstable part of the pump characteristic. Partial deaeration before guide vane opening during pump start was then considered as a solution and successfully tested in 2021.