Model tests for two individual Pelton turbines and a storage pump have been successfully completed for the Ritom pumped storage plant in Switzerland, confirming guaranteed values and expectations.

At its research and development center, the Brunnenmühle in Heidenheim, Voith technology group successfully completed three fully homologous model acceptance tests on a 5- and 6-nozzle Pelton turbine and a storage pump.

The Voith experts determined the efficiency, maximal output, runaway speed and the hydraulic forces of the machines on the basis of the fully homologous models. The specialists also controlled the cavitation behaviour at different operating points. As a result, the subsequent behaviour of the machines were analysed and the guaranteed parameters verified. The contractually assured guarantees were confirmed by the measurements and in some cases exceeded.

Even before the model acceptance tests were carried out, the electromechanical parts of the new machines were examined with detailed simulation models and optimized with regard to all requirements, said Voith, with its team initially starting testing on the two-stage storage pump.

"The results of the model acceptance tests for the storage pump were very positive. We were able to achieve parameters that exceeded the contractually guaranteed performance," said Christian Matten, Project Manager at Voith Hydro.

Afterwards the model acceptance tests of the two Pelton turbines were carried out. Despite the high efficiency guarantees, the parallel development of two completely different Pelton turbines and numerous conversions on the test stand, the Voith team was able to achieve the guaranteed parameters and thus successfully complete the model acceptance tests.

"Currently, the engineering of all components of the hydraulic and electric machines is in progress. The components from earlier construction phases, for example, the turbine housing and the distribution piping, are already in production. If everything goes according to schedule, these components can be installed on site in May 2021," explained Matten.

The four Pelton turbines with a total rated output of 44MW used in the existing Ritom storage power plan will be replaced by significantly more powerful machine groups in the new power plant. Voith will supply two Pelton turbines, each up to 60MW capacity and with a 60MW storage pump.

The first machine unit will supply power for the 16.7-Hz-grid of the Swiss Federal Railways and for operating its trains. The second machine unit will feed electricity into the public 50-Hz-grid. In conjunction with the turbine, the storage pump can provide control power for rapid grid regulation and stabilization with maximum flexibility.

The new hydropower plant will provide a control band from 60MW of feed-in to 60MW of power consumption for the Swiss 50-Hz-grid. In addition, the storage pump can be accelerated and synchronized with the grid using the 50-Hz-Pelton group by means of back-to-back startup.