History of Fala HPP
The Drava River originates in Toblaško polje in South Tyrol, Italy and flows into Slovenia near Dravograd; after a 133-kilometre journey, it leaves Slovenia at Ormož.
Flood on the Drava River in 1913 prior to Fala HPP construction
Until 1918, when the Fala HPP began operation, the river's flow along its entire length was unimpeded. From an area rich in forests, a lumber rafting transport route flowed down the river through Podravje and Podonavje and onwards towards the Black Sea. Prior to the construction of the railroad, the Drava River was the only (and later on, was the cheapest) transport route for lumber and other goods.
Musings on using the energy of the Drava River began at the end of the 19th century. Several locations for a power plant were available. Fala was chosen due to geological factors, for the valley is quite narrow, and damming wouldn't cause larger complications to cultivated surfaces and other buildings. The STEG company of Graz received a concession to build the power plant.
In 1913, construction of the first hydroelectric power plant on the Drava River commenced, which was, at the same time, the largest hydroelectric power plant in the eastern Alpine region. Its design was based on the concept that it would provide power to the network of industries in central Styria and Graz. The disintegration of the Austro-Hungarian countries and new state borders thwarted initial plans.
At the end of the World War I, the power plant was finished, but lacked some equipment and was without a sufficient amount of transmission lines to connect consumer centres, which in those days still used very little electric power.
Dam construction in 1916
The construction of such a facility was an extraordinary technical exploit. A Swiss firm with the greatest experience in hydroelectric power plant construction was chosen for the design and for supervision over construction. The necessary capital was acquired by STEG from Swiss banks. The installed equipment was for the most part manufactured in Switzerland as well.
According to initial plans, the Fala power plant would already begin operations at the end of 1916. The beginning of World War I, however, fundamentally changed these plans. The war caused a lack of labour and materials, so construction nearly came to a standstill in 1916. A factor in favour of the construction was that during this period, the military ministry in Vienna issued an order that among other areas, new industries for military purposes would be established also in the southeastern Alpine region.
Newly finished Fala HPP in 1918
In nearby Ruše, a factory for the production of carbide and nitrogen started being constructed, requiring immense electric power. This gave the Fala HPP priority in purchasing materials, also receiving war prisoners as labour, and construction once again proceeded. In May 1918, the first five of a foreseen seven units began operation, which was, however, under-utilised, for almost the only user of electric power was the factory in Ruše, which in those times used only approximately 5 MW of power. The factory was connected to the power plant via a 10 kV transmission line without any intermediary transformation, which caused a number of short-circuits of the insulation of the stator windings, for the atmospheric over-voltage without suppression was transferred from the transmission lines to the generators.
The main worry of power plant operators back then was how to increase the off-take of electric power, so transmission lines with various voltage levels were intensively constructed (80 kV, 35 kV, 10 kV) towards Maribor, Prekmurje, Varaždin and Zasavje. By 1926, the use of electric power had already increased so much that a sixth unit added, and in 1932, a seventh.
A look into the powerhouse in 1918
During this period the power plant had important national economic meaning, speeding up the industrialisation of Maribor and its surroundings. The supply of electricity reached all the way to Prekmurje and the Croatian Zagorje. In 1936, the electric power generation of Fala HPP represented a fifth of the entire generation of electricity in what was then Yugoslavia.
The power plant operated on a regular basis during World War II. Together with the network, Velenje and Trbovlje thermo power plants it was integral part of the company EVSÜD, which the occupation authorities established with its headquarters in Maribor. After liberation, the power plant was nationalised and connected to the emerging electric energy system of Slovenia, shaped by the construction of a 110 kV network voltage.
Old switchroom in use from 1918 to 1956
The Fala HPP was built in the Drava riverbed. It consisted of a powerhouse on the left embankment, five spillways and a navigation lock on the right embankment. A concession contract ordered the construction company to allow lumber rafts to travel via the power plant. At that time, from the spring until the first part of autumn, from ten to twenty lumber rafts of 90 to 100 m3 were floated on the Drava River.
Seven units were installed into the powerhouse, each comprising double horizontal Francis turbines and a synchronous generator, a rotating speed regulator and auxiliary equipment.
The spillways are still equipped with two gates suspended on Gall's chains, serving to spill water quantities exceeding the capacity of the turbines. The voltage on the generator's terminals was 10 kV. The total net capacity of all units amounted to 34 MW, with an installed flow of 350 m3/s. The average annual generation was 190,000,000 kWh.
Once the entire chain of power plants along the section from Dravograd to Maribor was constructed, the need for increased capacity of the turbines of Fala HPP became evident. The power plants lying upriver from Fala were designed for an installed flow of 460 m3/s. Due to the flow nature of the power plants in the chain, Fala represented a narrow throat. In order to remedy this, an additional unit was built between 1974 and 1977 so that the total turbine flow increased to more than 500 m3/s, and net capacity to 48 MW. The life of the old turbines and generators was slowly expiring, and thoughts about how the power plant could be renovated and modernised began. A number of variations regarding the replacement of the old units were entertained. The most logical and simplest solution was to replace the old units (turbine and generator) with new ones, but such renewal works would mean the giving up of several-percent use of the turbines. The original design of the turbines was such that the turbines were built over the lower water level and connected via a vacuum hose, which decreased their useful efficiency. Because of the vacuum effects, a vacuum arose in the turbines, resulting in an increased cavitation risk. In order to prevent this, the turbines would have to be installed beneath the lower water level, which would mean a change in the entire construction base of the powerhouse of the structure. As most favourable, a solution was approved in which the old and deteriorated units would be replaced with two new, vertical units with Kaplan turbines, which would be built into the right bank of the river.
The navigation lock was no longer needed, for with the construction of the remaining power plants along the Drava River, lumber rafting died out. In 1987 the renewal of Fala HPP began, encompassing the installation of the aforementioned two new units, each with an output of 20 MW, and replacement of the spillway gates, main transformers, equipment with a voltage of 0.4 V, and devices for voltage regulation as well as management and control of the power plant. Larger repair construction work was not necessary, for the facility had undergone fundamental renovation in 1967, when the foundations were laid through injection, and was still in very good condition. All repair work was concluded by the middle of 1991, when the new units were put into operation.
With the conclusion of the renovation work, the era of the old units had come to an end, bringing them to a standstill forever. Today they represent something of great value, a piece of the rich technical heritage of the first Slovenian hydroelectric power plant on the Drava River.