Ystradffin small hydro plant
Ystradffin is a medium head derivation small hydro power plant, located several kilometres downstream of the Llyn-Brianne reservoir on the Towy River in Wales. With a bottom type intake and a Tyrolean screen, it has an installed power capacity of 1900kW with operation parallel to the grid.
Work here focused on two turbine-generator units with different discharge output for better coverage of low flows. The horizontal Francis turbines were directly connected with a synchronous generator, using a unique space-saving turbine arrangement called Stroner’s arrangement – named after Hydropol‘s Chief Engineer Milan Stroner.
Burying the steel penstock, which had an average diameter of 1800mm and was 2.8km in length (including a 1.5km long inverted siphon), led to significant reductions in excavation works. A vacuum pump was also installed on the top of the siphon. Described as a challenging solution, Hydropol claims it is possibly one of the only hydro power plants in the world with such a sized inverted siphon.
Woolston weir
The Woolston Weir bypass is located on the Mersey River in England. Work on this 600kW, very low head small hydro power plant centered on a rare type of existing weir with a siphon. Part of the Manchester Ship Canal, it enables the transfer of large water flows with a small increase of upstream water level.
The plant is operated in line with Environment Agency requirements to limit abstraction from the river with levels of dissolved oxygen lower than 60%. An oxygen sensor was placed several kilometres downstream at Howley Weir. Construction works were executed under the protection of a temporary sheet-piled foundation pit, where some of the steel walls become permanent structures.
LAC project
The LAC project was built for electrification of one of the largest rubber plantations in Africa. This low head small hydro power plant, bypassing the natural waterfall of the Slo River in Liberia, has 1720kW of installed power with island operation.
Installed equipment included two turbine-generator units with different discharge output for better coverage of low flows, and vertical double-regulated Kaplan turbines directly connected with synchronous generators and large flywheels.
The plant supplies power to a rubber plantation over 11km away, where the rubber treatment factory is the main consumer. As there is no public electric network in this part of Liberia, it was described as being a challenging task to size turbine-generator-flywheel units to be able to accommodate 350kW of sudden load changes enforced by the factory machines.
Lavoreit small hydro
Reflecting on their experiences in Italy, Tošnar spoke about the 700kW project which is a medium head derivation small hydro power plant on the Chiarso River. Its sole vertical Francis turbine unit was directly connected with a synchronous generator. And to meet flood protection requirements, the powerhouse was fully underground and the 1400mm diameter, 1.8km long buried steel penstock with spherical joints enabled fast installation.
A shallow lateral intake, with a weir equipped with steel flap gates, enabled flushing of the upstream basin as the Chiarso River carries large sediment load. Tošnar says the very high load factor was unique as due to strict environmental protection a very low abstraction rate was permitted.
