Volume XV Issue 4
The Volkhov hydro power plant in Russia was built according to state plans for electrification of the country more than 70 years ago. At this time the hydro power plant was the most powerful in the country.
Eight hydro units, each rating 8.6MW, were installed there under a head of Hp = 10.5m. The turbines were equipped with radial-axial (Francis) runners, 4.5m in diameter, which were manufactured by the Swedish Company Verkstaden Kristinenhamn. The runners have 12 steel blades cast in hub and a rim made of cast iron. The runner blades are of constant profile and are 30mm thick, with the exception of the inlet and outlet edges which are 16mm thick.
The main peculiarity of these turbines is the positioning of guide vanes close to the runner, a feature which is not typical in modern turbines. The diameter of the guide vanes is DO = 1,11D1 while modern turbines have DO = 1,2D1. As a result the edges of the guide vanes (24 pieces) overhang the runner blades.
The Volkhov turbines became obsolete a long time ago. During 1994-1996 three turbines were replaced by new ones with higher rated capacity. These turbines were 6% more efficient and give 20% more generated power at the same Head (HP = 10.5m). Replacing all the remaining turbines at Volkhov is seen as a necessity but all reconstruction works have been suspended due to the unstable economic situation in Russia. As replacement was not possible, the alternative option to deal with the deteriorating condition of the turbines involved increasing the generated power of old turbines and upgrading the existing blade system.
This involved increasing of maximum turbine rated capacity (by 5-10% depending on the head) as well as aggregate working efficiency, particularly when functioning at high opening angles of guide vanes ( the most frequent regime).
The first step was to select the optimum variant of modernisation. The applied theoretical methods with special programmes allowed efficiency and flow values, capacity, loading and cavitation characteristics of the turbines to be determined.
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