Mavel has successfully installed, tested and commissioned the first of three units at the Stvanice hydroelectric plant on the river Vltava in Prague, the capital of the Czech Republic.
The output of the new double regulated Kaplan “S” turbine exceeded guaranteed values by more than 25 per cent, the Czech-based water-to-wire supplier announced on 8 August. Prior to refurbishment the maximum power per unit was 1.6 MW. Mavel’s contract mandated a guaranteed output of 1.75 MW. The new turbine reached 2.1 MW before output was reduced owing to the capacity limitations of the existing generator. Installation of the first unit began in January this year, with full commissioning in March and performance testing completed in July. Installation of the second unit is expected to be completed in September with the third and final unit to be commissioned in May 2019.
Mavel is carrying out the complete rehabilitation of the plant, including mechanical and hydraulic design, replacement of three horizontal turbines, refurbishment of generators, supply of a control system and all related civil work, under an engineering, procurement and construction (EPC) contract awarded by Czech water management authority Povodi Vltavy in August 2017 (see H&D Issue 3, 2017). Stvanice was commissioned in 1914 before being decommissioned in 1972. The plant was then renovated and brought back into operation in 1987 but the efficiency of three ‘S’ Kaplan turbines at the renovated plant, which operate with a flow capacity of 44 m3/s under an head of just less than four m, have since declined while the operator has seen increasing problems with the bearings. Using computational fluid dynamics (CFD) modelling, Mavel said it had found that reversing the rotational direction of the turbine would maximize the energy potential and minimize losses in the inlet and draft tube. Mavel developed a new hydraulic design for the turbine customized for the specific hydraulic parameters and requirements of the plant. The first of the new four-blade horizontal Kaplan turbines, with a runner diameter of 3400 mm, was installed with a counterclockwise rotational direction. The solution allowed for the use of the existing generators, which were refurbished and also adapted for the directional change.