Grand'Maison is a pumped storage hydropower plant featuring twelve 150 MW units, consisting of four Pelton turbines and eight reversible pump-turbines.

During the XFLEX HYDRO demonstration one Pelton turbine is being operated in Hydraulic Short Circuit (HSC) mode to offer a new option of frequency control in pumping mode. For this purpose, new turbine runners and updated controls developed by EDF, have been implemented for efficiency and flexibility improvements.

In parallel, computational fluid dynamics (CFD) investigations in the junctions for different flow configurations in HSC operating mode have been carried out by HES-SO. These have assessed the increase in head losses as well as the development of hydrodynamic instabilities. The additional head losses represent less than one per cent of the gross head and no hydrodynamic instability in the bifurcations has been noticed, which helped EDF to give the green light for on-site tests.

Computational fluid dynamics (CFD) in a bifurcation of Grand'Maison. Image credit to HES-SO.

Additionally, a 1D hydraulic transient analysis was performed by PVE in collaboration with EDF. To this end, a 1D SIMSEN simulation model was elaborated on by PVE and dully validated against site measurements performed by EDF for both turbine and pump mode operation. The results of the extensive 1D transient analysis performed for the HSC operation confirmed that the maximum and minimum pressures along the waterway and the extreme surge tank water levels both remain within the allowable limits. This demonstrated that the HSC operation is safe from the hydraulic transient perspectives. The 1D SIMSEN model developed and validated will serve as the backbone of the Hydro-Clone hydraulic transient monitoring system, which is currently under deployment at Grand'Maison.

Two on-site test campaigns were performed in May 2021. Key mechanical components of rotating units as well as waterways flow were investigated with excellent results. The operation of the units in HSC were monitored from minimum to full power in the most critical configurations, to assess as much as possible the full range of flexibility.

This led to a successful trial of the demonstration for two weeks in June 2021, when half of the time spent in pumping mode was in HSC operation, showing its undeniable added value to electricity grid balancing. The official demonstration phase started in September 2021. The demonstrator is operated daily according to grid flexibility needs.

Further work is now taking place including CFD simulations of the trifurcation and the development of the Smart Power Plant Supervisor, together with EPFL, to provide the plant with full HSC capacity.

View the latest Grand'Maison video.