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Site

Moste, Slovenia

Size or capacity

Installed discharge: 3 x 9,5 m3/s, 1 x 6 m3/s, nominal power of generators: 3 x 7,5 MVA, 1 x 11 MVA, power output: 21 MW

Investor / Client

SAVSKE ELEKTRARNE LJUBLJANA D.O.O.

Description of Facility and Services

Ideas on the upper Sava Dolinka River head exploitation emerged already before the World War II. To some extent, the Kavčke gorge was then established as a natural point for construction of a dam. Immediately after the War and based on these ideas preparations for a “general design” started. In 1947, the design in the scope of the nowadays Moste HPP, i.e. with the Kavčke dam, a headrace (tunnel) and a half-buried powerhouse on the left Sava River bank was developed. It was made by a design engineering institute of Projektni zavod LRS – Department of hydro power plants, Ljubljana which was a direct predecessor of later Hidroelektroprojekt (former Elektroprojekt, now IBE) established in 1949 by merging of some design engineering groups. The main Design Engineer was Mr. Kleindinst.

The Moste HPP was designed and constructed as a diversion canal plant with three 7.5 MVA aggregates (the Sava River water behind the Kavčke dam) and a fourth one which shall replace the already old Završnica HPP (the Završnica River water intake) with a powerhouse constructed already in the far 1914 in the immediate vicinity of the new Moste HPP. From its toe to the crest, the dam was 50 m high and the storage reservoir had an active storage capacity of 6.000.000 m3. In 1956, the dam was provisionally raised and in 2004, it was finally raised by 1.5 m with installation of special gates. This resulted in additional 1.000.000 m3 of active storage capacity. “Francis” turbines exploiting a head of 70,5 m with a discharge of 9,5 m3/s were used. The aggregates started to operate in 1952 and in 1954, respectively. The fourth aggregate, intended to substitute the old units of the Završnica power plant, was installed only in 1977. It was supposed to operate as a prototype reversible pumping unit using the upper basin of the Završnica River and the lower basin of the Sava River water taken from the penstock. In order to provide switching from the turbine into pumping regime a special overlapping flap was designed. At a discharge of 6m3/s and with a head of 154 to 161 meters the turbine generator unit reached the electric power of 11.000 kVA. Unfortunately, during operation it became obvious that pumping of relatively dirty Sava River water in a clean Završnica basin was an ecologically disputable issue. This is why the pumping regime was quickly abandoned and the fourth aggregate operated only as a substitute of the Završnica HPP. Later on it was even so re-modelled that the elements serving for pumping regime were eliminated (overlapping flap).

During construction as well as later on during operation it became clear that the powerhouse was constructed in a geologically demanding terrain (deficient geological research and poor condition of construction machinery in the time of construction) causing ousting and inclination of the powerhouse. It resulted in the powerhouse cracking and leaning of the aggregates axes. Several reconstruction works including soft rock anchoring, injections and refurbishment of the machines bearing support were performed. Finally, the aggregate 3 faced another design of a shortened axis (during replacement of the worn-out generator 3). The reconstruction works did not completely meet the expectations. So, the solution came in form of construction of a new powerhouse at a new location (slightly in the downstream direction) in better geological conditions and with a new tunnel and a new penstock. Regarding the existing dam and considering the fact that in Slovenia there are no possibilities of hydropower plants construction with head storage reservoirs, exploitation of the existing storage reservoir with an even increased installed discharge was a necessity. This shall be realised by construction of the Moste II HPP. It shall require also a downstream compensating basin with a smaller dam where the head shall be exploited by a smaller Moste III HPP. The studies and preliminary designs were made in 2000 and later on. Unfortunately, the project was temporarily stopped due to environmental issues.

Since it has been urgent to do something in order to extend the life cycle of the unsuitable powerhouse and due to an extensive damage which would occur in case of the power plant standing still by the already constructed dam and an interesting weekly storage, in 2004 and in 2005 possibilities of a more radical reconstruction of the powerhouse were studied. Therefore, it was agreed to install only two bigger aggregates instead of the existing three, which exploit the Sava River water potential. Their total power shall be something smaller than the existing total power of the three aggregates. The room gained in the powerhouse by elimination of one aggregate shall be used for stiff connection and the powerhouse reconstruction. In 2005, the Moste HPP refurbishment project was so revived. The works shall start in 2008, and they shall be accomplished in 2011. Besides, the existing 110 kV switchyard shall be reconstructed as well; it shall be replaced by a new GIS type switchyard (jointly by the distribution company and the Transmission System Operator).

Throughout the historical development of all parts of these demanding works the design engineering of the structure was implemented by IBE and its predecessors.

IBE d.d., Hajdrihova ulica 4, SI-1001 Ljubljana, Slovenia
Telephone: +386 1 4776 100
Fax: +386 1 2510 527
E-mail: info@ibe.si

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