Dravograd power plant: the first stage in the chain of Drava river power plants
This power plant is the first generating stage on the Drava River in the Slovenian territory and, at the start of its operation in 1944, it was the first pier-type power plant in Europe along with a similar plant in Lavamünd, Austria.
Construction began during the World War II in 1941 and was completed in 1944 with two units installed. In April 1945 however, allied air raids caused considerable damage to the power plant. After the war intensive renewal operations began so that as early as December of the same year one unit was again ready for operation and the second unit started up in February of the following year. With the launch of the third unit in 1955, construction of the power plant was completed.
A comprehensive refurbishment of the units was a part of the first phase of investments into the refurbishment of the Upper Drava power plants that commenced in 1994, increasing the net capacity to 26,2 MW. With the increased capacity and the use of the 8,94 m available head, the power plant can generate 142 million kWh of electricity annually.
The damming of the Drava River has created a reservoir 10,2 km long which stretches partly across the national border with Austria up to the higher power plant at Lavamünd. The reservoir contains 5,6 million m3 of water. The reinforced concrete dam structure is made up of three turbine piers placed among four spillways, as well as a left bank and a right bank building. A vertical Kaplan turbine is installed into each turbine pier with a generator located above it. Within each turbine pier, all the necessary equipment for the controlling of the reservoir is located. Four spillways, each 24 m wide, closed by the hook gates composed of two plates, have a total spilling capacity of up to 5400 m3/s of water. The gates, suspended on Gall's chains, are driven by electric hoists. A gantry crane is installed on the dam structure and is used for raising and lowering all heavy equipment and components.
The generators are connected by cables to the common busbars in the 6,3 kV indoor switchyard. A portion of the electric power generated is transformed to lower voltage for the plant’s auxiliary power supply, while the remaining portion is conveyed via overhead transmission lines to the main transformers.
The 110 kV outdoor switchyard, refurbished between 2010 and 2011, features double busbars to which two main transformers and six transmission line bays are connected for looping in the power plant to the grid and transmission of power in the direction of the Šaleška dolina, Mežiška dolina and Dravska dolina valleys.