The long-operating hydropower plant on the Sokolsky peninsula in Budweis, Czech Republic, was renovated, modernized and provided with state-of-the-art hydropower technology in a comprehensive project last year.

In December 2012 the three almost 80-year-old turbines were replaced with modern vertical Kaplan turbines from Andritz Hydro’s Standard Compact program. These turbines are now driving high-performance synchronous generators manufactured by TES Vsetin. With the successful renovation of the plant the total output has been doubled to 1,320 kW.

In the early 1930s the provincial government of Bohemia built a hydropower plant on the well-known Sokolsky island, where the Malse and the Vltava River join. The plant was put into operation in 1933 to produce electricity for the city of Budweis and its trams. In the beginning three Francis turbines had been installed, but these machine units were replaced after only a few years, in 1936. One of the Francis turbines was replaced with a Kaplan turbine of a higher performance, manufactured by Storek. The total output of the three turbines (210 kW, 250 kW and 300 kW) at that stage was 760 kW.
A significant element of this long-established power plant in South Bohemia is its weir plant. Exceptional features of the plant are the two approximately 28 meters long cylinders with a diameter of about three meters, designed to close the two-span weir. The log flume was constructed orographically on the left side, while the powerhouse was positioned on the right.

OLD PARTS CIRCULATING A HUGE OIL FLOW
German Schmatz GmbH acquired the power plant in the 1990s. “At that point, the power plant was out-dated, as we had expected it to be. The machine units from the 1930s were, of course, operating with an enormous oil circulation. However, there was an automatic system installed, which operated the old machine ensemble more or less automatically,” says Sigi Dietl, managing director of Bodenmais-based Schmatz GmbH. Aqua Energie, the official operator of the plant, did not hesitate to modernize it. The old centrifugal governors as well as other controlling devices were replaced with hydraulically regulated control systems 15 years ago. A modern automatization system made it possible to operate the power plant with the newest technology available. ISATS delivered the software and hardware for this system.

MORE HEAD THROUGH BED DEGREDATION
Originally the turbines were designed for a water amount of 10.2 m³/s and 11.5 m³/s, respectively, and a gross head of 3.4 meters. This all changed within the last decade when the Czech government launched a new project. The aim of the project was to improve flood control and shipping. A shipping service from Prague to Budweis was planned. The head was increased to 4.9 meters by lowering the bed in the tailwater. Adjusting the power plant to the new conditions presented a complex challenge. “Together with river management company POVODI VLTAVY and the University of Prague, Department of Hydraulic Structures, we had worked intensively on the ideal adaptation of the power plant since 2008. At the Department of Hydraulic Structures the team of Professor Fosumpaur constructed a model plant and proved that our reconstruction plans were not interfering with the state’s project for improvement of the shipping sector. On the contrary, we showed that ships were better able to make turns through the new design of the outlet. An expert opinion with a trial run in the model was compiled in 2009. The technical know-how of Professor Fosumpaur and his team was a huge support for us,” says Sigi Dietl. He adds: “Meanwhile smaller passenger liners steer close to our power plant where they can turn in a special turning basin.”

AMBITIONS TIME SCHEDULE
Thanks to the excellent cooperation with POVODI VLTAVY and the University of Prague the reconstruction project was finally approved. On October 5, 2010 the authorities gave the project the green light. After the following public invitation to tender the contract was awarded to construction company VHS Vodospodarske stavby s.r.o. Andritz Hydro won the contract for the electromechanical equipment of the plant. The contract comprised three vertical, double regulated Kaplan turbines with a diameter of the runner of 1,450 mm. Furthermore it included the appropriate oil hydraulic power unit, installation surveillance, commissioning and training.
The reconstruction works started in August and it soon became clear to all participants that the timetable was scheduled rather ambitiously and optimistically. For the installation of the turbines, for instance, the draft tubes had to be adjusted and reset in concrete. The existing concrete volute casings, however, could be used for the new turbines.

CRUCIAL POINT: BUILDING STATICS
“There were two main challenges with this project: first we had to deal with the tight schedule along with the difficulties of conducting the installation works at temperatures below zero and, second, we had to deal with the building statics. Assigned structural designer Mr. Krug from CDM Bingen did an excellent job and supported the construction company very well. Mr. Reisser of Andritz Hydro and I planned the machine units together, while the construction management was handled by the Czech company manager, Mr. Prasnicka, and me. ISATS was again responsible for the entire control technology and the electrical engineering works,” says Sigi Dietl.
The installation team and the supplier of the electrical engineering had to face Arctic temperatures last winter, which were constantly between minus 10 and minus 20 degrees. The works could finally be completed in February this year.
As the operator put it: “We had extreme frost and two meters of ice in the river this February. Still we managed to put the machine units into operation.”
Efficient Ensemble of Machines
Thanks to the lowering of the tailwater level and the subsequent increase of the head the operator was able to install machine units of considerably higher performance and efficiency. The three double regulated Kaplan turbines manufactured by Andritz Hydro are designed for an output of 440 kW each. The total installed machine capacity is now 1,320 kW, which is almost twice as much as the output of the original machine unit. In addition to the new and efficient high-performance turbines, the operator is now also using high-quality synchronous generators by TES Vsetin. The machine units of TES Vsetin stand for generous design, robust constructional components by renowned manufacturers and great know-how. The brushless synchronous generators for hydropower use are the Czech company’s flagship products. Today the Vsetin-based company produces generators of an output of 30 to up to 15,000 kVA.
The three generators operating in the Budweis Sokolsky power plant have a nominal apparent output of 430 kVA. They are driven at a nominal rotation speed of 230.77 rpm.

THE TECHNICAL JEWEL STEPS INTO A NEW HYDRO POWER ERA
Although the capacity of the turbines has been reduced marginally to 10 m³/s, the increase in output and production is striking. Sigi Dietl and his company manager expect a production of approximately 7 m kWh in an average year. This makes the power plant one of the five biggest hydropower plants in South Bohemia – just like at its commissioning 80 years ago. It is not under monument protection but it is regarded as a technical jewel in Budweis and beyond. The power plant has made a momentous transition to a new hydropower era with its new equipment.