Energy chain wrapped around the crane leg

New energy supply concept for heavy-duty ship cranes

The heavy-duty slewing cranes of the CAL series from Liebherr are used on so-called jack-up vessels that assemble offshore wind turbines. They can lift components weighing up to 1500 tons. Energy transmission through the slewing ring is ensured by an innovative concept in which two energy chains are connected to each other and enable a swivel range of the boom of up to 900 degrees.

Profile

What was needed: "multi-rotation module", also known as "RBR", consisting of two E4.1 energy chains, chainflex cables, steel construction
Requirements: Energy supply to the boom of the turbine, sensitive environmental conditions due to use on the high seas
Industry: Crane construction
Success for the customer: completely new energy supply system especially for this application, preliminary testing of the application in the laboratory, complete delivery including pre-assembly, assembly and delivery

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Problem

A "crane around the leg" is a completely new crane class from Liebherr-Werk Nenzing GmbH, a world-renowned specialist for ship cranes. It was developed for so-called installation vessels, such as the "Innovation", which assembles offshore wind turbines (WKA) at sea.
The "innovation" accommodates three tripods in the port, which serve as foundations for offshore wind turbines and weigh up to 850 tons each. It drives to the intended location and takes its position there with centimeter precision with the help of Azipod drives and bow thrusters – in such a way that it can set all three wind turbine foundations from this location. There, the jack-up vessel extends its four jack-up legs over a length of up to 50 meters to the seabed, so that it has a secure footing and is independent of the waves. A heavy-duty crane mounted on the ship with a lifting capacity of up to 1500 tons lifts the tripods from the ship and sets them down on the seabed. One of the design challenges with this new crane type was the energy supply to the boom. The most obvious solution – a conductor rail on the outer jacket of the lifting leg – is not practical under the environmental conditions of offshore use, because it can lead to malfunctions due to splashing water. The same effect is possible with an enclosed conductor rail, because condensation is created due to the temperature differences.

Solution

The Liebherr designers responsible for the implementation requested an energy supply system from igus. igus' answer: Two energy chains are laid around the lifting leg and connected via a carrier. The result is a very robust energy supply system that has proven itself under extreme conditions with a small footprint and a rotation radius of 900 degrees. Since this idea has not never been implemented in practice, Liebherr initially awarded igus the engineering contract to build and comprehensively test the system on a scale of 1:5. After successful completion, further tests in original size followed in the company's own test laboratory.
The final system, which igus calls a "multi-rotation module" or "RBR", consists of two E4.1 energy chains with a width, or in this case height, of 650 millimeters and a width of 108 millimeters. The lower chain is 33.90 m long, the upper 23 m. The chains work in opposite directions and are mounted on rollers, the upper one rotates freely. The two chains are connected by three drivers. Various variants from the chainflex range from igus are used as cables, which were developed from the ground up for mobile applications. In addition to the main power supply and the necessary signal lines, fiber optic cables for a camera were also integrated, which allow the ship's captain to see the crane's working area. The cables are 81 meters long, the complete energy supply system was pre-assembled, assembled and delivered as a ready-to-install system by igus – including the steel structure with an outer diameter of 14.40 meters.

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New concept prevails

The "Innovation" was put into service in August 2012 and immediately proved its worth in the construction of the "Global Tech I" wind farm in the North Sea, around 40 kilometers north of Juist. 80 turbines with a capacity of 5 MW each were built there. Based on the first "crane around the leg", Liebherr has developed a complete series called CAL. In the meantime, the "Vida" is already a second jack-up vessel in use, in which the crane was designed around the lifting leg. The energy chain system developed by igus-Engineering creates the prerequisite for energy and signals to be supplied reliably and flexibly to the boom of the heavy-duty crane – according to the principle of "energy around the leg".