Modernisation of a tandem crane system for lifting gigantic loads during inspection work

Lifting capacity Lifting capacity increase and tandem operation at the Jochenstein hydropower plant for lifting and transporting complete rotors accelerates inspection and maintenance of the generators.

The CraneKit from STAHL CraneSystems was awarded the contract for the modernisation of the crane system at the Jochenstein hydropower plant. Its partner, crane and plant manufacturer Haslinger, took on the complete planning, production, assembly and commissioning. In terms of mechanics and control technology, the new cranes are an absolutely special solution. Rotors weighing 220 tonnes can now be lifted without dismantling the poles.

Germany and Austria have a lot in common, and not just in terms of language and culture. The countries share Germany's highest mountain, the Zugspitze, but the small Jochenstein also deserves a mention for several reasons. This rocky island, which is around nine metres high, is located on the German side in the upper reaches of the Danube. There are many legends surrounding it. Among other things, it is said that the devil wanted to flood the Austrian market town of Engelhartszell through a wall in the Danube and therefore threw a large stone into the river. Whether this story is actually true remains to be seen. The fact is, however, that a run-of-river power station is located right here, which owes its name to the rocky island of Jochenstein.

The technical facilities of the Jochenstein hydropower plant are located both in Lower Bavaria (market town of Untergriesbach) and in Upper Austria (Engelhartszell). Pedestrians and cyclists have been able to cross the Danube on the weir all year round since around 1990. The construction of the power station was planned back in the early 1950s under the management of Donaukraftwerk Jochenstein AG (DKJ). The first three machine units were commissioned in 1955, followed shortly afterwards by two more machine units. In 2013, the shares of the German electricity group E.ON. were sold to Verbund AG, Vienna (Austria), which has operated the plant ever since.

The Jochenstein power plant has a head of just under 10 metres and, according to official figures, has an average annual capacity of 850 million kWh. The movable elements of the weir are located close to the Austrian bank. The ship lock and the switchgear are located on the Bavarian side. The powerhouse with the turbines is located in the centre of the river on the rocky island.

Regular inspections of the turbines and generators

The five machine sets have Kaplan turbines with diameters of 7.4 metres, all of which date back to the 1950s. These work together with five three-phase synchronous generators. Although the rotors in the generators are not directly exposed to the river water, they still have to be lifted out at certain intervals for inspection and maintenance work, for example to check bearings, windings and other components, correct imbalances and check thermally stressed insulation for damage and ageing. Cleaning work is also required, as dirt and oil residue can accumulate between the rotor and stator, which must be removed in order to achieve optimum performance.

A crane system with a lifting capacity of 75,000 kg was previously available for moving loads, especially when lifting the rotors out of the generators and for transporting them along the weir - 150,000 kg could therefore be lifted in tandem operation. However, as each individual rotor weighs 220 tonnes, all the poles on the rotor had to be dismantled each time for the excavation in order to reduce the weight. This took a lot of time and led to high costs during the overhaul. Verbund AG therefore looked for a solution to increase the lifting capacity of the crane system so that the entire rotor could be lifted out and transported to the interim storage facility without dismantling the poles.

STAHL CraneSystems played a decisive role in the development process of the new system and throughout the entire duration of the project. Its partner, Haslinger Metallbau + Krantechnik in Alderbach, was responsible for the complete planning, production and assembly and completed the commissioning on schedule in autumn 2024. The Haslinger Group has long been a top league player in welding technology. The company offers complete package solutions for crane construction from a single source - from planning and steel construction to assembly. As a certified partner, Haslinger can draw on the expertise of the STAHL CraneSystems engineering team for all tasks and questions as well as for PLC programming.

Unchanged crane runway due to load-dependent positioning

The challenge at the Jochenstein power plant was to increase the lifting capacity to 120,000 kg per crane while maintaining the same wheel loads. In addition, the approach dimensions specified by the old crane system had to be adhered to. In addition, the span of the crane runway changes when travelling from the straight runway section to the curved section. For this reason, the endcarriage, which connects the crane girder to the travelling gear, has a design with special wheels.

In the centre of the crane bridge, the trolley has a travel range of 5470 mm. The range was defined precisely so that it allows the rotor to be lifted out. The rope drum with a diameter of 800 mm is now made of sheet metal instead of the standard 610 mm round tube. Cross beams are used to distribute the load evenly. The wheel loads remain unchanged by limiting the maximum load to the centre of the crane bridge. A special operating mode was set up for this purpose, which only allows the crane to travel at 120,000 kg in this centre area via a safety circuit. This meant that the old crane runway could be used without extensive modifications, although the crane can now transport significantly higher loads. Instead of classic travel limit switches, safety encoders recognise the positions of the hoists. These also enabled to realise position-dependent overload detection, which made it possible to achieve performance level PLd.

Rotors weighing 220 tonnes can now be lifted out without dismantling the poles. This saves a considerable amount of time and reduces the cost of inspecting and maintaining the five machine sets. After excavation, the rotor is transported to the opposite side of the Danube and stored there for the duration of the inspection. The total crane runway length from the powerhouse to the Austrian bank is around 250 metres. The occasional outdoor operation required the system to be specified for an ambient temperature range of -10 °C to 40 °C.

Double load in tandem operation

In tandem operation, double the load can be lifted, i.e. now 240 tonnes - this is sufficient for the rotors including their poles. Tandem operation enables efficient handling of the rotors and their safe transport out of the powerhouse and over the weir. In the past, tandem operation required two experienced crane operators who had to work closely together to navigate the heavy or bulky loads safely and precisely. Today, radio control systems are increasingly being used for tandem operation to coordinate the movements of the cranes and trolleys, whereby various operating modes can be selected. The radio remote control is integrated into the crane's data bus. Both cranes communicate with each other via an industrial WLAN, thus enabling tandem operation.

The cranes have an auxiliary hoist unit with a lifting capacity of 16,000 kg, which is used in addition to the main hoist unit and is controlled together with it in tandem trolley operation. The main purpose of the auxiliary hoist is to move loads precisely during delicate lifting operations or assembly work in double-load operation. It enables flexible working, saves time and increases the efficiency of the entire crane system. As a so-called recovery hoist, it is also approved for passenger transport. The auxiliary hoist has two load measurement systems: one for regular loads and one for workman basket operation. Depending on the operating mode, the signals are processed in the control system (PLC).

Special mechanical and programming solution

The hoist is equipped with load and speed sensors, limit switches and actuators, all of which (apart from the speed sensor) are integrated into the crane's data bus. Instead of a hard-wired control system, a programmable KSK-S complete control system is used. The system is modularly expandable and there are options for partial automation. Monitoring when moving the crane or load handling attachment is improved. Error messages and operating statuses are output via a specially programmed user interface (Human Machine Interface) and shown graphically on the display.

Conclusion

The new crane system at the Jochenstein hydropower plant has been in operation since autumn 2024. The new crane is now used for many heavy-duty transports at the Jochenstein hydropower plant. In terms of mechanics and programming, it is a special solution that was customised for Verbund AG. A particular advantage of the STAHL CraneKit is its flexibility, which allows it to be easily adapted to the specific requirements of the respective application. The excavation of the entire rotor was successfully completed for the first time at the end of November 2024. Due to the excellent results, further projects are already planned with Verbund AG.

Authors

Heike Metzger is Senior Specialist Sales Enablement at STAHL CraneSystems
in Künzelsau in co-operation with Karl Haslinger, Managing Director of Haslinger GmbH Metallbau in Uttigkofen.

Images and captions:

Tandem crane system at the Jochenstein power plant for large loads.

The crane system transports various loads indoors and outdoors.

Special design: 800 mm cable drum made of sheet metal instead of standard round tube.

The auxiliary hoist for tandem trolley operation is approved for passenger transport.

Control cabinet (right) in the control panel for convenient selection of operating modes.

Powerhouse with five machine sets that have been in operation since the 1950s.

The generators in the powerhouse have a diameter of over 7 metres.

Removal of the rotor from the generator without removing individual poles.

Further transport of the rotor to the Austrian side.

Temporary storage of the rotor during inspection.