With appr. 25 MW of installed capacity in the form of 4 high- and medium-pressure power stations, the 900-soul municipality of Ligonchio in the Tuscan-Emilian Apennines is one of the region's hydropower hotspots.
One of these power plants is the privately operated Ligonchio power station, commissioned in 1991. Last year, the plant underwent a comprehensive modernisation process including replacement of the electrical equipment, and the operators decided to use high-quality hydropower technology from Austria. While the turbines were supplied by Tyrolean hydropower specialist Geppert, the two new synchronous generators came from the well-known Upper Austrian manufacturer Hitzinger, which is leading the way with such machines in terms of new dimensions and sizes.
It is most noticeably northern Italy's city dwellers who are increasingly taking their holidays in the secluded Apennine region in the province of Emilia-Romagna. There they are looking for and finding the peace and quiet and natural beauty of the extensive beech forests of the Tuscan-Emilian Apennines National Park where the municipality of Ligonchio is located. The region relies on sustainable tourism which has been steadily increasing in recent years. Ligonchio oozes the pure charm of a mountain village, and located over 1,000 meters above sea level, it is the highest municipality in the Apennines. And yet there is something else that characterises its appearance: hydroelectric power. Electricity has been generated here in high-pressure power stations since the 1920s and the plants have long been part of the historic backdrop.
POWER PLANTS HAVE BEEN CHARACTERISING VILLAGE DEVELOPMENT
At the beginning of the 1920s, workers were drawn from the entire province of Emilia- Romagna to participate in the construction of the first hydroelectric power station at Ligonchio. The hydropower plant not only became a symbol of the spread of technology in the previously exclusively rural region, but also one of economic growth, which bought with it an increase in the population. This importance is reflected in the external appearance of the engine house. The building was designed in an Art Nouveau style and today is considered to be a successful example of early industrial architecture. On a technical note, this engine house contains the central two power plants which process the waters of the Ozola on the one hand and the waters of the Rosendola on the other. Overall, the three hydroelectric sets have a total installed capacity of around 11 MW. Today, the conventional Enel plant is in operation. As is the slightly further downstream power plant Ligonchio Ozola, which is the main usage point along the Ozola. An 11.9- MW vertical Francis turbine processes the water from a large reservoir which is fed by smaller side streams as well the Ozola. This power plant was built in 1928 and - just like the first plant - its striking, complex architecture blends into the Ligonchio landscape. Over the following decades, the two power plants have dominated the development of the small Apennine village. In the same way as they initially contributed to the growth of the local population, the increasing level of automation, particularly during the late 1960s, led to a decrease in employment and subsequently to increased emigration.
NEW POWER PLANT FROM PRIVATE INITIATIVE
It was then many years later before further investment was made in the rich hydro resources of the region. It took almost 70 years after the commissioning of the first power plant before another hydroelectric power plant was built in the Apennine community - the lower level power station to the Ligonchio-Ozola power station, which today is simply known as the Ligonchio power station. In contrast to the other three power plants, it is a privately operated plant belonging to P.E.I. AG with headquarters in Como. The power station, which has been in operation since 1991, was designed to take the processed water directly from the upstream plant and channel it via a gravity sewer to a stilling basin. The steel penstock runs from here in a direct fall line to the central building, which, in contrast to the other two large engine houses, is located in a remote area difficult to access. The works water covers just under 45 meters before it reaches the two turbines installed in the engine house. At the time of commissioning, the installed vertical axis Francis turbine had a rated capacity of 2,380 kW. Five years later, in 1996, a second, smaller turbine was installed. This 550-kW horizontal axis Francis turbine served as a "winter turbine" designed to meet periods of low water availability.
DOUBLE-SIZED WINTER TURBINE
Although after at least 20 years of operation the power plant could hardly be considered old, some parts of the electrical equipment no longer met today's standard of technology. For this reason, and to increase the profitability of the plant, the operator decided to replace the installed machines and the control and automation technology. The operators from northern Italy decided on the sophisticated machine technology from Austria. The two turbines were supplied by the Tyrolean company Geppert, which, in spite of the existing hydraulic and spatial conditions in the engine house, made use of a certain amount of leeway with regard to the type of turbines used. "The large machines could only be replaced by a vertical Francis turbine because of the structural conditions. With 2,300 kW, it is even slightly smaller in terms of performance than the previously installed model," explains Geppert's project manager Dipl. Ing. Christian Moriel. "The small horizontal axis Francis turbine has now been replaced by a diagonal turbine, which, thanks to its specific properties, covers a much larger scope than the previously installed set. With a rated capacity of 1,100 kW, it is twice as large and now allows a larger total quantity of water to be processed, namely up to 9,000 litres/sec. But where the diagonal turbine particularly excels, is that the power plant is also capable of operating with very small amounts of water, as is often the case in the winter. This turned out to be the right choice when it was commissioned in December, as the diagonal turbine operated with a turbine opening of just 3 percent during the first night of operation."
STARTING OPERATION WITH A THROTTLED TURBINE
The Geppert engineers faced a challenge even before construction began. It was necessary to ensure that the new turbines could be integrated without having to rework the engine house. According to Christian Moriel, even the dimensioning of the diagonal turbine required the use of every millimetre of space. The feedin of the larger "winter turbine" also required a larger cross-section, starting with the bifurcated pipe: DN1000 up from DN700. "Unfortunately, the owner was unable to obtain the necessary building permits in such a short period of time. So, as short-term measure, a pipe section was manufactured to make use of the existing DN700 butterfly valve in order to go into operation with the new turbine throttled," explains the Geppert expert. A further challenge faced by the Austrian machine suppliers was the delivery of the turbine and generator. This was not only due to the extremely steep and unpaved access route to the engine house, but also to the weight of the generator. The larger of the two weighed around 17.5 tonnes and therefore even required the overhead crane in the central building to be modified.
PUSH IN A NEW DIMENSION
This weight is by no means normal for a synchronous generator produced by the well-known manufacturer Hitzinger. Quite the contrary: the larger of the two Ligonchio generators (the BG136) is actually the first of this size that Hitzinger has constructed. It was produced as a result of the reaction of the long-established manufacturer from Linz to the demands of the hydropower market, which is increasingly demanding medium- capacity synchronous generators between 1.5 and 3 MVA. Up to now, the capacities offered by Hitzinger were lower than that and therefore designed for classic "low water" applications, but operators can now also count on the high quality of the Hitzinger generators in the medium-range class too. The manufacturer insists that no technological leap was required. It merely sought to transfer the high quality standards of the smaller machines to the larger ones. And in this they undoubtedly succeeded. These synchronous generators also score points in the medium- range class in terms of their robustness, operating smoothness, good reliability and high level of efficiency. They also transferred the patented control system for high continuous short circuit current, along with the additional complex isolation technology in order to make the turbines even more resistant to environmental influences. The larger of the two generators in the Ligonchio power plant has therefore become the first reference turbine in this performance category and has continued to prove itself for months.
MODERN CONTROL SYSTEM
In concrete terms, the larger generator is designed for 2,600 kVA and driven at 500 revolutions per minute by the vertical Francis turbine. The smaller synchronous generator, which is coupled to the shaft of the diagonal turbine, has a rated capacity of 1,400 kVA. The specified upgraded capacity of the turbines in the hydropower set is 1,119 kW. The total installed rated capacity of the turbines is around 3,350 kW. In place of a hydraulic oil system, the control device for both machines uses the tried-and-tested electric drives produced by the company enco. The electrical engineering company from Ratschings in South Tyrol managed the upgrade of the electrical equipment and modernisation of the control system. It was necessary to replace the transformers, the low and medium voltage equipment, and the substation. Specifically, as the lower-level power plant, the dual-generator operation requires state-of-the-art automatic control and a digital water level control system with feed-forward control. This level regulation system has now been exactly adjusted to the actual quantity of water in the turbines. The water is allocated to the machines precisely according to the respective efficiency curves to ensure that the power plant is always operated to optimum efficiency. The en-co electrical engineering specialists have now also implemented self-contained black-start capability of the power plant, for example after a power failure.
At the end of the thaw in June of last year, the two old machines were disconnected from the grid and the retrofit project got under way. The entire task took less than half a year and the new hydropower sets were commissioned in December. However, the entire project has not yet been completed. In the near future, conversion work is planned in the intake building, the surge chamber and raking device, and the supply pipe for the small machine will of course also be replaced. A lot of the electro technical and control detail is also soon to be implemented by enco. The new equipment has an additional total installed capacity of around 500 kW today compared to the old setup. That is remarkable, but still does not allow any precise conclusions to be drawn regarding the increase in the plants' standard capacity. The Ligonchio power plant currently generates around 5 million kWh in a standard year. Thanks to the higher efficiency of the new hydropwer set, the higher volume of water and more effective control system, it should certainly be possible to raise this by a couple of per cent. However, it is not possible to determine by exactly how much until operation starts. The operator is more concerned that the renovation has been successful, that the plant now meets all the current demands placed on hydropower plants, and that operational reliability has been ensured thanks to the high quality of the machines for many years to come. Finally, the high quality of the machines made in Austria is ensuring that red-white-red hydropower technology is making a name for itself in the mountains of the Apennines too.