The high load that the electric cables in the open-cast coal mine is subjected to becomes clear immediately when you look at one of the powerful bucket-wheel excavators operating in the Rhine mining district. The operator of the open-cast mines, RWE Power AG, decided to include igus chainflex cables in the factory standard after extensive tests. Customised, optimised cables are used that are especially resistant to mechanical loads.
Motorists travelling on the A44 between Düsseldorf and Aachen can watch the gigantic mining equipment of the Garzweiler open-cast lignite mine at work as they drive past. On an area of currently about 3,100 hectares, seven bucket-wheel excavators mine 35 to 40 million tonnes of lignite each year. The mining equipment and the associated electrical components such as sensors and cables are subjected to extreme levels of mechanical stress during work. The resulting dust has an abrasive effect and is accompanied by moisture, temperature fluctuations and continuous movement. For this reason, RWE Power AG, as the operator, has defined extensive plant standards for technology and purchasing. As technology changes, standards must also be constantly advanced and adapted. This applies, for example, to the increasing use of bus technologies. Gunther Busch: "For example, there are many angle encoders installed on the bucket wheel excavators and spreaders that detect the position of equipment parts. We used shielded cables for these and other sensors, but their long-term functional reliability was not up to the task. " A major cause of this is the combination of high dust levels and, in some cases, laying of cables in bundles, which causes the cables to move against each other. This accelerates the abrasion considerably. For each of these cables, requirement profiles were drawn up with exactly 20 criteria such as UV-resistance, non-flammability, tear-resistance, resistance to oil, organic oil and lye as well as flexibility.
As RWE has already had good experience with the from igus since 2006, these cables were shortlisted. igus indicated its willingness to develop special cables for the special requirements of open-cast mining. The bus cables of the CFBUS series, which had been proving their worth for years in the face of extremely high dynamic loads and with very small bend radii, were used as the basis. Tests were able to confirm the resistance of the cables under the "heavy duty" conditions of open-cast mining. Among the modifications made to the cables in the course of customised development is the increased UV resistance of the outer jacket. With the Profibus cable, the special feature worth mentioning is that the supply cores have been integrated. This reduces the effort required in installation because one less cable has to be laid.
After the successful completion of the tests, the chainflex cables were included as special cables in the RWE power plant standards for electrical cables. Four of the five cable types were stored by RWE and a minimum stock quantity was defined.
The wide range of other cables for the energy chain enables a total solution of all cables for this application. Starting from the described bus cables up to medium voltage cables. While the igus employees undertook the harnessing of the cables and the filling, the trough and lining were also installed in the plant.
From the point of view of the cable specialists, it is interesting that the main characteristic of the chainflex types - their chain suitability - is not even needed in most cases. Rather, the focus is on typical heavy-duty specifications such as abrasion resistance and UV resistance. However, there are exceptions. In June/July 2013, one of the seven bucket-wheel excavators built in the 1970s underwent major maintenance. In the course of this work, the slip ring assembly in the excavator's massive slewing ring was replaced with a large, approximately one-metre-wide igus energy chain, which is of course also filled with the newly standardised bus cables.
RWE project engineer Jürgen Lenz: "The energy chain saves space and is less susceptible to wear. We also integrate additional elements, such as a water supply for the operation of the immission protection devices on the bucket wheel and conveyor path of the large-scale equipment, by which we avoid dust generation during dismantling. " The wide range of other cables for the energy chain enables a total solution to be found for all cables for this application. Starting from the described bus cables up to medium voltage cables. The trough and lining were installed by igus employees, who also took care of the assembly of the cables and the filling. In order to create access to the assembly site, a narrow access hatch first had to be cut through the thick steel structure at the connection between the crawler track and the superstructure.