The Austrian automation specialist Schubert Elektroanlagen GmbH carried out a comprehensive update of the Rusel power plants in Deggendorf in Lower Bavaria between August 2019 and February 2020.

The power plant network, consisting of a total of five turbines, two raised storage facilities and a lower reservoir, was brought up to modern standards in terms of electrical and control technology by the Lower Austrian company. Everything from auxiliary power distribution and machine automation to excitation and protection technology was comprehensively renewed and modernised in the storage and run-of-river power plants operated by Eurowatt GmbH. In addition to ensuring the black start and isolated operation of several machine units, which enables the network to be restored for the entire plant in the event of a blackout, a whole series of operational optimisations were achieved in the course of the revitalisation.

In the Lower Bavarian district town of Deggendorf, hydroelectric power generation has a long history. A storage power plant was built on the site of a former sawmill in the Maxhofen district as early as the 1920s. After the end of the Second World War, the existing power plant was successively supplemented with additional machines. Until the 1960s, the plant network, which was expanded over the years to include two pumped storage power plants as well as a steam and diesel plant, served as general supplier to the town of Deggendorf. The diesel plant was later to be shut down again, and the Oberberg pumped storage power plants 1 and 2 were sold to a new operator. The Rusel power plant network, consisting of the Bogenbach, Maxhofen-Oberberg, Höllbach, Hausturbine and Ausgleichswerk machine units, is today owned by Munich-based Eurowatt GmbH. The Bogenbach and Maxhofen-Oberberg power plants are supplied by the Sauloch upper reservoir, while the Höllbach and Hausturbine plants receive their works water from the Höllbach upper reservoir. After being processed at the machine units, which are housed in two connected buildings, the works water first returns to the stream bed and is then collected in the nearby Maxhofen lower reservoir. From the inlet area there, the water is led to Ausgleichswerk and flows back into Höllbach after being pumped through the turbine.

COMPREHENSIVE AUTOMATION
Although the hydroelectric power plants now cover only part of the electricity needs of the city with its population of around 37,000, the plants continue to play an important role as environmentally friendly energy suppliers. In order for the Rusel power plants can continue to produce at maximum efficiency in the future, Eurowatt GmbH recently invested in a comprehensive revitalisation programme. The core of the modernisation project comprised plant automation and the renewal of various electrical and control components. In addition, three of the five machine units were adapted to the turbines and the associated mechanical-hydraulic infrastructure. While the mechanical refurbishment was carried out by the Austrian turbine manufacturer Kössler, which has since been taken over by Voith Hydro, the contract for the electrical modernisation was awarded to Schubert Elektroanlagen GmbH, also from Lower Austria. Founded in 1965, the company has equipped more than 400 hydroelectric power plants in 25 different countries with its well thought-out solutions throughout its 55 years of existence. In addition, Schubert can also point to a large number of successful revitalisation projects, and the expertise gained in these projects was once again fully utilised in the Rusel power plant contract. The well-established planning office of Thomas Grimmer was commissioned with the overall planning of the revitalisation. The renowned industry expert, who operates several hydropower plants in Austria and Germany, was able to make a significant contribution to the success of the complex project with his many years of practical experience.

CONNECTING OLD AND NEW
The project encompassed all parts of the power plant network, from the machine units to the upper and lower reservoirs and the central control room. In order to keep generation losses to a minimum, the revitalisation of the individual plants was implemented step by step. In terms of time, the renewal operation between August 2019 and February 2020, which was precisely planned in consultation with the operator, took just over half a year. In conversation with zek HYDRO, Schubert project manager Markus Kerschner explains the challenges of the assignment: „As with any revitalisation project, the general challenge with the Rusel power plant project was in connecting old and new components. On average, the electrical systems were between 30 and 40 years old. From the start of the project, this required the collection of a wide range of data and circuit diagrams, which also had to be checked for accuracy.“ Kerschner goes on to say that the revitalisations primarily focused on auxiliary power distribution, protection technology, and automation. With the exception of Ausgleichswerk, where the entire electrical system and generator were replaced and a used transformer installed, the components that affected the 5 kV and 20 kV range remained essentially unchanged.

SYSTEMS CAPABLE OF ISOLATED OPERATION
The machine unit at Bogenbach power plant, consisting of a 2-nozzle Pelton turbine with a directly coupled 850 kVA synchronous generator, was given a mechanical refurbishment in addition to the electrotechnical update from Schubert. The turbine‘s two Pelton nozzles, which could only be opened and closed together before the rebuild, were fitted with new drive cylinders by Voith. In combination with a new hydraulic unit, the nozzles can now be moved independently. As with the other systems, Schubert provided for the automation of the automatic start-up and shut-down, speed control, synchronisation, and control in parallel operation. In addition to the renewal of grid and generator protection, the plant was converted to static excitation. Kerschner notes that the isolated operation of the Bogenbach power plant had to be maintained, which was quite a challenge given the now static excitation system. At the Höllbach power plant, which is also designed for isolated operation and whose machine unit consists of a single-nozzle Pelton turbine and a 1,750 kVA synchronous generator, the electrotechnical revitalisation included the same measures as at the Bogenbach plant. The switchgear used jointly by the two power plants for 400 V auxiliary power distribution and the 24 V battery system were also redesigned.

MAXHOFEN-OBERBERG AND HAUSTURBINE
The Maxhofen-Oberberg power plant uses a 2-nozzle Pelton machine with a directly coupled 1,750 kVA synchronous generator to generate electricity. However, the machine unit cannot be operated in isolated mode due to insufficient flywheel mass. Apart from this, the same revitalisation measures were implemented as for the Bogenbach and Höllbach plants. At the Hausturbine power plant, whose single-nozzle Pelton turbine with the 275 kVA synchronous generator forms the smallest machine unit of the Rusel power plants, the capability for black start and isolated operation had to be guaranteed in the course of the modernisation. In the event of a total blackout, the plant is used to rebuild the internal network and synchronise it with the other two plants capable of isolated operation. Both the Maxhofen-Oberberg and Hausturbine plants have been equipped with new 400 V auxiliary power distribution systems. The 24 V battery system for the Maxhofen-Oberberg plant also supplies the Hausturbine plant. The other revitalisation measures at the Hausturbine power station were identical to those at the other plants, and Voith also installed a new hydraulic unit.

VIDEO SURVEILLANCE INSTALLED
The same measures were also taken at the Sauloch and Höllbach upper reservoirs. The hydraulic pipe rupture protection and level measurement systems at both reservoirs were automated. For additional monitoring of the reservoirs, Schubert installed video cameras in dome design, which offer optimum visual control from afar with their pan, tilt, and zoom functions. The two reservoirs are connected to the network via SHDSL (single-pair high-speed digital subscriber line), which enables data transmission to the control room via Ethernet. At the Maxhofen reservoir, which feeds the Ausgleichswerk plant, two gates were automated, both for level control and overwater discharge. The hydraulically operated trash rack cleaner was also automated and integrated into the overall concept of the plant. Like the upper reservoirs, the Maxhofen reservoir was equipped with video surveillance, and data transmission was again realised with SHDSL. The pipe burst protection at the Ausgleichswerk plant was also automated, equipped with a new flow measurement system, and connected to the network via SHDSL.
The machine unit at the Ausgleichswerk plant consisting of two differently sized Francis spiral turbines was equipped with a new 400 kVA synchronous generator from Hitzinger in the course of the revitalisation. Voith carried out the mechanical installation of the generator, which was placed centrally between the Francis machines. In contrast to the other systems, the 20 kV switchgear was also replaced in the Ausgleichwerk plant, and Schubert also connected a transformer provided by the customer. The automation of the power plant, auxiliary power distribution, network and generator protection, video surveillance in the power house, and network connection via SHDSL were also newly implemented.

REVITALISATION IS BECOMING MORE IMPORTANT
All data and signals from the plant network are consolidated in the central control room in Deggendorf, where Schubert has installed two new PCs. The images from the video cameras are transmitted on one computer, while the other PC is used to control the plants. The control PC is based on the SIMATIC WinCC Professional process control system from Siemens, which is used worldwide in monitoring and control technology. Schubert‘s intuitive visualisation of the power plant control system provides the operating personnel with an optimum overview of the current status of the individual plants. The logging of the most important data as well as fault message and trend records are fully automated. Thanks to encrypted VPN access, authorised users can also access the control system remotely via mobile devices such as smartphones or tablets. A few months after final commissioning, Schubert project manager Markus Kerschner is very satisfied with the progress of the project: „The revitalisation of the Rusel power plants, which has been one of our larger revitalisation projects to date, was a very exciting and interesting contract. Thanks to the good communication with the customer representatives and the responsible parties at Voith right from the start, the implementation went according to plan. With the increasing number of hydroelectric power stations that are slowly getting on in years and in some cases only have very rudimentary automation systems, revitalisation will definitely play an even more important role for Schubert in the future.“