Customer case

Hydroelectric power station

Automated concrete removal used to increase capacity of hydroelectric power stations

As a part of the project to boost the electricity generating capacity of three hydroelectric power stations on the Drava River in Slovenia, Contractor Gradis needed to remove damaged concrete from vertical turbine draft tubes. They used a Conjet ACR™ robot to do the job. The operation made way for new reshaped steel linings with larger diameter for more efficient and greater capacity turbine generator sets.

Gradis worked on the contract for client and power station owner Dravske Elektrarne Maribor as part of the approximate DM 50 million second phase of refurbishing and upgrading three of Slovenia’s chain of eight hydroelectric power plants.

These power stations are strategically located along an approximate 100 km stretch of the Drava river, which falls about 120 m between the upper and lower power stations. The power plants provide about 13% of Slovenia’s electricity, but the aging electrical and mechanical equipment was so worn out that it needed to be gradually replaced over a period of several years.

The solution

One of Vuzenica’s three turbine generator sets had already been replaced when Gradis came in to remove concrete and increase the diameter of the power station’s second turbine draft tube. But before Gradis could put its Conjet ACR™ robot to work and get started on hydrodemolition, the power station’s overhead gantry crane had to lift out the old worn out generator and turbine. This operation was followed by another demolition contractor cutting out an approximate 5.25 m high section of the turbine’s cylindrical to rectangular stainless-steel draft tube casing liner, which was embedded in concrete.

Gradis, which adopted the same hydrodemolition technique for all nine turbines, placed the Conjet ACR™ robot on a moveable platform inside the confined 4.65 m diameter vertical turbine housing. About an 840 mm thickness of concrete had to be cut out round the entire periphery to increase the diameter to 6.33 m. This was done using the Conjet robot making three separate circumferential cuts from the working platform set at two different levels. About 65 m3 of concrete had to be removed from the draft tube, which the robot was able to achieve at about 1 m3/hour.

How it works

All of the Conjet ACR™ robot’s functions were remotely controlled by the operator working with a bird’s eye view high above the cutting area. High-pressure water was supplied by a Hammelmann power pack. This consisted of a heat and sound insulated ISO container housing a 750hp (550kW) Caterpillar diesel engine driving a pump operating at 1400 bar pressure and flow of 234 liters/minute.


Once Gradishad completed the concrete removal, a new and larger 4.85 m diameter stainless steel liner casing, reshaped to improve hydraulic efficiency, was positioned in the void. This was backfilled with fresh concrete. This was followed by installing a new four bladed, variable pitch turbine. The new turbine, just 200 mm larger than the old unit and operating at 125 rev/min with the same maximum gross head of 13.65 m, was able to accommodate an approximate 15% increase in water flow to just over 183 m3/second, raising rated power output of the replacement turbine generator set to 18.6MW.

Upon completion of three identical units, the refurbished and upgraded plant boosted total installed power output by nearly 43% to 64MW.

Customer case



MISSION:  Boosting electricity of
hydroelectric power stations

ROBOTS Used:  320-series

Robot 557 MPA

For restorations at powerstations, Conjet ACR™ hydrodemolition robot 557 MPA is recommended. The robot features the latest technology in hydrodemolition. Combining the reach of Robot 367, the flexibility of Robot 327 and the diesel engine of Robot 437, this robot has it all.

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