Redmond Gary Australia has designed and delivered two special hydraulic cable pushers that were purpose built for German contractor ea.R Energieanlagen Ramonat GmbH for installation of cables for the Verbund Hydro Power AG extension project in the south of Austria. Cables had to be installed at a maximum altitude of 1772 metres located in ReijBeck and Kreuzeck Mountains in the northern part of the Malta Valley. The extended capacity will increase the power generation to 430 Megawatt. The location of the site, the altitude and extremely steep conditions created challenges for the cable installation contractor.

In ReijBeck, cables are being installed between termination 1 and termination 2 this year and between termination 2 and termination 3 next year. The cable length being installed is 3000 metres (system length), so in single phase 11,400 metres. The cable sections are divided as follows:
Cavern to termination 1: 1250m
Termination 1 to termination 2: 1250m
Termination 2 to termination 3: 650m
Termination 3 to transformer station: 650m

The cable drums weighed 30 tonnes and in combination with the cable carrier and prime mover, the total weight exceeded 100 tonnes. Due to the steep inclines of the site and slippery conditions on the roads, the prime mover was unable to pull the trailer to the top of the mountain. Two heavy duty articulated tip trucks were setup in tandem in front of the trailer to haul the cable to the elevated worksite, roughly 18 km to the top of the hill then 2km into a mountain into the cavern to the main station where the turbine and transformer are located. As the road was quite narrow with no possibility to turn the truck and trailer around at the top of the hill a second truck from behind was used to pull the big cable trailer back down the mountain. The cable installation itself was not that difficult since the slope was only 14%.

After the truck was finally positioned at the worksite, due to the extremely steep terrain, the Redmond Gary cable pushers had to be lifted onto the newly built cable cavern with the aid of a cable system and flying fox.

Cable was fed through a cutaway in the road and into the open cavern. The cable pushers were specially designed to have dual purpose. Firstly, they could be used as a pusher with each cable pusher developing 20kN push force from a standing start and at the same time when cable pushers were used as a brake, they could provide 35kN braking force. In this installation, due to the weight of the cable being 20kg per metre and with an outside diameter of 120mm, there was a considerable technical challenge to be met by ea.R Energieanlagen Ramonat.

The current section installing cables between termination 1 and termination 2 – 450 metres. This installation has a downhill slope starting at 14% then dropping sharply into a 50% decline. The calculated brake force for these sections is around 60kN. The cable weight is 24 tonnes and 800 metres of cable in the steep slope means 16 tonnes of cable weight in 50% slope. That’s approximately 80kN and another 10kN on the 14% slope. These are only theoretical values because we cannot calculate the effects of corners and bends. To install these cables on such steep declines, the required brake force was divided into three sections – the cable drum drive takes 20kN and each pusher takes 20kN. Theoretically, the cable drum trailer can hold the whole lot but the radial forces on the cable at the entrance guide and the following corner guides and the bottom layer of the drum would be so high that the cable would be destroyed. The challenge of this type of installation was the absolute synchronisation of all the machinery components. This job was made easier as the two Redmond Gary Australia pushers were both radio controlled and electronically synchronized.

The cable winch only plays a minor role in this case. It only ensures the cable is under tension and runs smoothly over the cable guide. The cable trailer winds the cable off at the rate of 5 metres/second and keeps the cable under tension. After going through the first pusher, the contractors had to ensure there was a bit of slack in the cable otherwise the force when going through the entrance guide rollers would have been too high. The first pusher was located 600 metres from the cable trailer. The second pusher was located 300 metres from the first pusher. Therefore, pusher number one brakes with 20kN before pusher number 2 contributes to the project. Under this situation, the pushers were used to their absolute braking capacity. It was calculated that the braking force exerted by the cable trailer brake was approx. 30kN.

So far, two sets of cables have been installed using the pushers as cable brakes. The cables were installed successfully and the customer is extremely happy with the performance of this new equipment. Redmond Gary Australia is pleased to be a part of this project and has gone to great lengths to make sure the engineering design is world class. There were a number of difficulties that had to be addressed by our design office. These difficulties are not normally considered for Australian conditions. Some of the design hurdles were to manufacture suitable cable shoes to be able to withstand the high load when exerting a braking force of 35kN. In addition to this, the equipment had to be manufactured to work in altitudes up to 3000 metres above sea level. At this height, the air is much thinner and the diesel engine would not meet the power output requirements compared with equipment manufactured for the Australian market. In addition, the pushers were manufactured with radial piston motors to give the maximum efficiency for the caterpillar system. The caterpillars were increased in length by 30% in comparison with our standard range to give additional grip on the cable increasing its braking ability.

Also, these pushers were the first items we have manufactured with CE Compliance. This is a requirement for all equipment exported into European Union countries. This proved to be more difficult than first thought. Redmond Gary Australia enlisted the assistance of Pilz who are specialist safety engineers. Through their sister company, Pilz Ireland, the equipment was tested and certified to meet Australian Standards and CE Compliance.

Video of pump storage power plant: