Gralla Run-of-River Power Plant

The Gralla run of river plant is a power plant on the river Mur and is located in the vicinity of Leibnitz in Southern Styria just bevor the Mur flows into Slovenia.

Machine Renovation after more than 40 Years in Operation 

Initial situation

Electrical wear

  • Deteriorated condition of the generator stator windings (insulation) and pole coils 
    Mechanical wear
  • Cast steel impeller blades, in some cases with anti-rust armour, cracks in the transition area between disk and blade 
  • Rotor discs: Low remaining wall strength and rusted Niro plating 

Cooling system

  • Partial obstruction of the cooling water pipers due to manganese deposits (increased pumping demands) 
  • Highly contaminated coolers and therefore poor heat transfer 

Project goals

As a result of the major overhaul and production of new electromechanical components of the two machine sets, the efficiency level of the plant was increased and the annual output increased by around 5 %. The renovated machines increase the performance reliability and reduce servicing time and costs. Not least thanks to the installation of a low-maintenance, closed cooling system. 

Renovation measures (2009-2012)

  • Dismantling of the two machine sets (approx. 88 to rotating mass) 
  • Production of new turbine impeller blades with optimised contours (verification with model test). 
  • Renewal of the turbine rotor discs including connection to the structure 
  • Supply of new generator stators and coolers. 
  • Replacement of pole coils and generator ventilators 
  • Renovation of the braking system 
  • Inspection and repair of portions remaining in use 
  • Complete renewal of corrosion protection 
  • Installation of a closed cooling system with a pipe coil cooler in the turbine inlets

Image from the Location

Owner VERBUND Hydro Power GmbH
Operator VERBUND Hydro Power GmbH
Commissioning 1964
Type Run-of-river power plant
Country Austria
Region Styria
Waters Mur
Output 15 MW
Annual output 71,884 MWh
Turbine Kaplan
Connectivity Fish bypass
Environmental protection at VERBUND

Ecology & environmental protection

The reservoir of the Gralla power plant has developed into a paradise for water birds. At the power plant’s own observation station, various species of ducks, swans and herons as well as widely travelled Nile geese from Africa can be watched. 
Since 2013, the Gralla power plant has also been equipped with a fish bypass. It was designed as a vertical slot pass and overcomes a height difference of 9.4 metres. The total length of the fish bypass is 354 metres. The dimensions of the fish bypass were chosen to suit the pike. The fish in the Mur can now swim around the power plant through 72 basins (12 of which are resting basins).
 
Responsible treatment of the environment

Technical Description 

The Gralla power plant was constructed from 1962 to 1964. After more than 40 years of operation, the turbines and generators in the power plant were dismounted and modernised. By doing this, the effectiveness of the power plant's machinery was improved and the electricity generation increased by around 5 percent. With the modernised turbines and generators, the Gralla power plant on the Mur River can cover the annual electricity needs of around 21,000 households. Two vertical Kaplan turbines with DC coupled three phase current synchronous generators generate an average yearly output of around 71 GWh. The Gralla power plant is also equipped with a fish ladder.