The need to decarbonise our energy system push us toward the use of different clean renewable energy sources, such as solar, wind and hydroelectric energy. It is well known that some of these renewable energy sources suffer of intermittence, which requires the conventional dispatchable power plants to become more flexible to respond to any power change to ensure a stable electrical grid. For this specific purpose, the European project XFLEX HYDRO is focusing on the hydropower sector, with seven demonstrators in three different countries to demonstrate the possibility to enhance the flexibility, one option being to use the variable-speed technology combined with smart digital control. Among these seven demonstrators, one is the Alto Lindoso hydropower plant owned by EDP and located in North-West of Portugal. It consists of two fixed-speed vertical Francis turbines with a high head of approximately 275 m and a rated power of 317 MW. The objective of this demonstrator is to assess the potential of a variable speed using the Doubly Fed Induction Machine (DFIM) technology to increase the flexibility of the power and the lifetime of the turbine. Therefore, this paper explores numerically the hydraulic behaviour of the model runner when operated at a selected part load conditions (60% BEP) with the rotational speed changed by ±10%. Second, a FEM analysis is carried out to evaluate the runner blades damage rate. This preliminary study showed that in term of wear and tear, the variable speed technology would bring in an advantage.