The Francis turbine is a type of water turbine. It is an inward-flow reaction turbine that combines radial and axial flow concepts. Francis turbines are the most common water turbine in use, and can achieve over 95% efficiency.
The process of arriving at the modern Francis runner design took from 1848 to approximately 1920. It became known as the Francis turbine around 1920, named after British-American engineer James B. Francis who in 1848 created a new turbine design.
The Studen Kladenets Reservoir (Bulgarian: язовир „Студен кладенец“, meaning "cold well") is the third largest reservoir by volume in Bulgaria after Iskar Dam and Kardzhali Dam. It is situated on the river Arda, and is created behind the Studen Kladenets dam, 30 km south-east of the town of Kardzhali. There are another two dams of the Arda - Kardzhali Dam to the west (upstream) and Ivaylovgrad Dam to the east (downstream). The dam is operated by the Bulgarian National Electric Company, NEK EAD.
The reservoir has a total volume of 388 million m and a drainage basin of 3,706 km and is 29 km long. It is situated at an average 227 m above sea level, its dam being 338 m long and 67.5 m high. The top of the dam consists of nine spillways, each one being 10.5 by 5 m."Studen Kladenets" Hydroelectric Power Plant is situated appr. 1 km downstream of the dam. Initially the HPP had four Francis-type turbines, 15 MW each. А project for reconstruction and upgrading the HPP with another 16 MW turbine and a smaller eco-turbine underwent and after the completion, the total output reached 85 MW with annual production of 165 GWh of electricity.
This article lists the largest power stations in the world, the ten overall and the five of each type, in terms of installed electrical capacity. Non-renewable power stations are those that run on coal, fuel oils, nuclear fuel, natural gas, oil shale and peat, while renewable power stations run on fuel sources such as biomass, geothermal, hydroelectric, solar, and wind. Only the most significant fuel source is listed for power stations that run on multiple sources.
As of 2025, the largest power generating facility ever built is the Three Gorges Dam in China, completed in 2012. The facility generates power by utilizing 32 Francis turbines for a total capacity of 22,500 MW. The eight largest power stations are also hydroelectric dams, beginning with Baihetan Dam, at 16,000 MW, also in China. The largest natural gas plant is Jebel Ali, UAE (8,695 MW) and the largest coal plant is Tuoketuo, China (6,720 MW). The largest nuclear plant is Kori, South Korea (7,489 MW) following the 2011 suspension of Kashiwazaki-Kariwa, Japan (7,965 MW).
The Kaplan turbine is a propeller-type water turbine which has adjustable blades. It was developed in 1913 by Austrian professor Viktor Kaplan, who combined automatically adjusted propeller blades with automatically adjusted wicket gates to achieve efficiency over a wide range of flow and water level.
The Kaplan turbine was an evolution of the Francis turbine. Its invention allowed efficient power production in low-head applications which was not possible with Francis turbines. The head ranges from 10 to 70 metres (33 to 230 ft) and the output ranges from 5 to 200 MW. Runner diameters are between 2 and 11 metres (6 ft 7 in and 36 ft 1 in). Turbines rotate at a constant rate, which varies from facility to facility. That rate ranges from as low as 54.5 rpm (Albeni Falls Dam) to 450 rpm.