Difficult-to-access geological terrain sometimes demands advanced technology to construct hydropower facilities. Cable cranes help to efficiently and safely deliver personnel and crucial material onsite.
By Christoph Vogelmann
Sites where new hydropower plants are being constructed are often quite inaccessible, perhaps being located in valleys and canyons in mountainous regions that may lack access roads. These sites also may involve environmental challenges, which can include extreme weather conditions.
For this set of circumstances, cable crane systems may provide an effective alternative to construct proper access roads only for the construction period. This article discusses what cable crane systems are, how they work, and locations where they have been employed.
Cable crane systems grant access to steep mountain ranges that have more than 70-degrees inclination and are capable of a line speed of up to 8 m per second (m/s) on a direct route to the construction site.
A cable crane system consists of a radio-controlled crane unit, a drive system and special ropeway equipment suitable for the transportation of heavy loads at the specific project site that includes particular ropeway towers for temporary systems, skyline supports, wire ropes and anchor systems.
|A 20-ton dump truck is being transported via a heavy crane system at the 360-MW Obervermuntwerk II project in Austria during heavy snows in the Alps.|
The crane unit is the centerpiece of the system. Depending on the need and construction site, the units are able to lift from 5 to 30 tons. Some models use two independently working lifting systems, which is useful when pipes are laid in steep terrain, for example.
The drive system moves loads along the track and normally consists of a diesel-hydraulic or electro-hydraulic winch. The winches, used to move a crane unit uphill or downhill, range in capacity from 205 kW to 1 MW.
Finally, the cable crane system is able to handle several types of construction equipment and material safely through the terrain and to the construction site. It is not only possible to transport machinery from point A to point B (e.g., from the valley to the mountain), but the loads can be unloaded at any point along the track – a crucial characteristic when penstocks are constructed.
Parallel cranes as an alternative
These crane systems are characterized by their high performance, efficiency and reliability, which help simplify complex construction at project sites. Using a parallel crane, it is possible to achieve a line speed of 6 m/s and a hoist speed of 3 m/s, for a payload of up to 28 tons. The span length and consequently the system’s reachable surface vary, but traverse paths of 280 m are realistic.
Parallel cranes are a similar construction to cable cranes, but operate basically in a flat area and cover a complete surface. They are mainly used, when dams are constructed in an area with limited space and accessibility (e.g., in canyons). Loads are then being handled precisely and quick on the entire construction site.
For parallel crane systems, two towers are installed on a rail system running on both sides of the construction site. By using winch driving systems, they are simultaneously maneuverable. This way the track ropes, always wire ropes, span the construction site and move horizontally. A carriage, positioned on those track ropes between the two movable towers, is driven by an additional winch and hauling cable. Consequently, the carriage which is holding the loads can be moved along two axes, right over the construction site: in one axis along rails and in the other along the track rope. Adding vertical lifting and lowering, the loads can be moved in three axes above the construction site and consequently cover a huge surface and at the same time offering a very efficient and precise material handling.
For technical, logistical and commercial contributions, cable crane systems have a high safety grade, avoiding common risks (i.e., safety is clearly visible due to no need to travel steep access roads).
Using a cable crane or material ropeway means heavy machinery can access steep and dangerous terrain without the need to travel on dangerous access roads. Also, using the cable cranes means operators are not exposed to over-the-road transport risks as all material is transported by mid-air to its final destination.
Use of a cable crane system avoids the construction of additional roads through the terrain to gain access to the construction site. For penstock construction, a track width of just 8 m is enough for an efficient and safe installation of pipes.
In most cases, cable cranes are completely deconstructed once a project is complete, but in some cases systems are built for permanent usage. Once systems are removed, the locations of the supports are returned as closely to pre-installation conditions as possible.
In the following paragraphs, some hydro power plant projects where cable crane systems have played a central role for an efficient and appropriate execution. In some cases, the cable crane even enabled the realization of the project.
Obervermuntwerk II pumped storage power plant
Vorarlberger Illwerke, Austria’s state-owned energy supplier, is partnering with Germany-based One EnBW to develop the 360-MW Obervermuntwerk II pumped storage power plant in Vorarlberg. This will be Austria’s second highest capacity pumped storage station upon completion, which is expected in 2018.
Construction of the €500 million (US$553 million) station began in May 2014, and the site is about 1,700 m above sea level. The site is not easily reachable and features steep inclines, inclement weather conditions, a remote location and environmental concerns such as avalanches during winter time.
Vorarlberg is one of the most-snowy areas of Europe. Some villages exceed 10 m of snow per year. During wintertime from November until June, the only access road to the site, the Silvretta-Hochalpenstrasse, is closed due to snow and avalanche risk. The utility’s development plan required the use of a cable crane system with a payload of 20 tons and that would allow personnel to work on the project year-round. Materials to be transported to the site (i.e., included personnel, machinery and construction material including pipes, cement and fuel).
|In 2016, construction of the headrace penstock at the 18-MW Krafthaus Obere Sill project in Austria necessitated 2.5-m-diameter pipe sections be installed on a 45-degree slope in the Alps. (View video at http://bcove.video/2oCOgV0)|
The cable crane system at the site, provided by LCS Cable Cranes, uses video to monitor the entire track (material-ropeway) and, when conditions force Silvretta-HochalpenstraàŸe closure, the cable crane system continually operates 24 hours a day.
This specific type of cable crane uses 60-mm-circumference stainless steel cable track ropes and a 34-mm hauling rope driven by an 800-kW electro-hydraulic drive. The crane system employed at Obervermuntwerk II, at its rated full load of 20 tons can travel the material-ropeway at about 6 m per second.
The cable crane system has now been operated by LCS for the third winter in a row and enables the complete logistics of the large construction site without any interferences. Fuel, cement, Construction machinery – even large trucks – are brought to the isolated construction site on a daily basis. After the termination of the project, in spring 2018, the cable crane will be dismantled and is available again for other potential projects
Obere Sill hydropower plant
A cable crane system was deployed to reconstruct the works of the surge chamber, shafts and penstock at the 18-MW Obere Sill hydropower project in Innsbruck, Tyrol, Austria. Obere Sill began operation in 1903 on the Sill River and is operated by the IKB.
The design of the cable crane system for Obere Sill needed to be adapted for unique site constraints: limited space to function under a bridge, overpassing the project’s surge chamber, crossing a city street and providing material to several shafts that run under ground.
Europabrà¼cke (Europa Bridge or Bridge of Europe) is a 777-m-long (2,549-feet) bridge that carries the A13 Brenner Autobahn over the 657-m-long (2,156-feet) Wipp Valley just south of Innsbruck. The bridge spans the Sill River and forms part of the main route across the Alps from western Austria to South Tyrol in Italy and also part of the main route between southeastern Germany and northern Italy.
The 420-m-long cable for this 15-ton system is in place beneath Europabrà¼cke Bridge. At the 210-m halfway point of the crane system, the track has a 12-degree curve situated directly above and exactly matching the bend of the penstock. This allows construction personnel to precisely install the new penstock pipes.
The crane system uses a double-track wire rope to transport construction material, machinery and pipes to the shafts and surge chamber as well as to install large pipes with a diameter of 2.5 m and 12 m in length on the over 45 degree steep slope.
The project was realized successfully from spring 2016 to early 2017.
Permanent system at Kwoiek Creek hydroelectric plant
Machinery manufacturer Litostroj Hydro Inc. needed to install four 14.775-MW horizontal Pelton turbines and related equipment for operation of the 49.9-MW Kwoiek Creek hydroelectric plant in British Columbia, Canada.
The project, developed through a joint venture of Innergex II Power Trust and the Kanaka Bar Indian Band called Kwoiek Creek Resources L.P., is a run-of-river plant on a tributary to the Fraser River.
Construction began in late 2011 in a completely inaccessible area of the Rocky Mountains in British Columbia, Canada, after 18 years of planning and preparation. The developer obtained more than 50 approvals, permits and licenses from 14 government regulatory bodies.
|A parallel crane (green) was installed at the 42-MW Lesce hydroelectric project in Croatia, which due to its location in mountainous terrain was difficult to access.|
The construction site has no separate access road for material or personnel. Everything was transported using a 600-m-long, 20-ton payload capacity material ropeway that crossed the Fraser River tributary.
The ropeway is licensed for passenger transportation under the British Columbia Securities Act (BCSA) for construction purposes and employs a fixed, installed gondola. For this purpose, separate rescue systems such as extra brake systems as well as an additional evacuation system provided by GANTNER Seilbahnbau were installed to meet BCSA regulations.
After the completion of the construction works, this cable crane system was modified into a permanent system, which is still operating to provide access to the hydropower plant for maintenance.
Cable cane systems brings workers into the slope at Bear Creek hydro power plant
Another cable crane system, used for a penstock construction in British Columbia, Canada was licensed for manpower transportation for construction purposes. This system used two separately working crane units. The main crane unit was used for transporting construction equipment and material, while the smaller crane unit carried the gondola mentioned above.
The two-crane units allowed for lowering the gondola directly onto the slope, where operators could control the other crane unit during installation of a more than 1,000-m-long penstock. The workers who installed the pipes did not have to overcome challenging mountain ranges and were not exposed to unnecessary risks. This enabled safe and efficient penstock installation on a steep slope in a forested area of the Rocky Mountains that has more than a 41- degree inclination.
The site is nearly twice as steep as one of the three-steepest vehicular roads in the world, Baldwin St. in Dunedin, New Zealand. The street has a 35% grade (19-degree inclination) overall and disputed 38% grade (21-degree inclination) at its steepest section.
These cable crane systems are used at very diverse hydro power projects with different characteristics and varying challenges such as limited accessibility and space, lack of access roads and environmental circumstances that impede the conventional use of trucks for logistics.
At first impression, the installation effort may seem huge but the final advantages and efficiency gained by this unconventional transportation solution speaks for itself. The decisive key is definitely to find the appropriate design and abilities for each project, as the potentials of a cable crane system are larger than expected.
Christoph Vogelmann is project manager for LCS Cable Cranes.