Above: HVDC links to renewable energy projects such as offshore wind farms present new opportunities for the cable sector

tions, a significant market for XLPE, there is a rise in use of DC cables and an increase of the nominal voltage of EHV cables in general (which presently exceeds 500kV). This puts increasing constraints on the cleanliness of the final compound. Current state-of-the-art technology for the production of insulation material for HV and EHV cables — com- monly known as the soaking or absorption process — is reaching its limits in terms of product quality and cleanliness.

Soaking developments The XLPE soaking process is performed in two steps because the peroxide used for the crosslink- ing of the insulation during extrusion of the cable cannot be added to the melt during compounding (typical compounding temperatures are in the range 200-240°C while the peroxide decomposes at a temperature below 140°C, which would result in crosslinking of the polymer). Instead, the peroxide is added to the compound in a second process step by solid state absorption, which can be both time and energy intensive and a potential source of potential contamination. Buss says it has developed an alternative and

more efficient process for production of XLPE, which it calls LSHC (linear short hyper clean process). As the name implies, this is said to allow production of hyper-clean XLPE compounds for medium through to extra-high voltage AC and DC applications. In its LSHC process, Buss says it has developed a one- step process for insulation production that avoids the need for the solid-state peroxide absorption (soaking) stage. As a result, CAPEX of an LSHC production line is said to be up to 40% lower, while OPEX can be reduced by about 30%. Cost and flexibility are also key in current cable compounding, Buss says. “There is presently a lot of pressure to reduce manufacturing costs by using more flexible and efficient compounding equip-


ment,” says François Loviat, Head of Process at the firm. “On the one hand this can be achieved by maximising the throughput of compounding lines, and on the other by reducing the costs of raw materials while maintaining outstanding quality. The latter also puts more pressure on the com- pounding equipment as cheaper raw materials often implies a compromise on stability or ease of processing of the raw materials.” A lot of effort is also invested in improving the

productivity of cable extrusion machinery. “This is mainly done by fine tuning the formulations in order to allow higher cable extrusion speeds. There is also a trend towards more flexible compounding lines, which can be used for different applications, such as PVC, polyolefin-based HFFR or TPU. This results from the need for compounders to produce a wide range of products and adapt quickly to changing demands,” Loviat says. “In addition, a consequence of this need for flexibility is that the use of underwater pelletisers is gaining in impor- tance over alternative pelletising technologies in cable compounding, despite the more significant investment required.” Buss says that its latest high performance com- pounding machine — the Compeo — is well suited to meet these flexibility demands. “Basically, this compounding extruder can be used for any applica- tion, from rubbers to engineering plastics, and from polyolefin based HFFR compounds to PVC,” says Andreas Niklaus, Senior Process Engineer. For example, the Compeo Kneader series can combine 2, 3 and 4-flight screw elements on the same machine. This allows uses to benefit from the benefits of traditional 3-flight kneader technology, such as smooth kneading conditions for sensitive products, as well as the advantage of the higher throughput of 4-flight kneader technology. For special applications, such as reactive extrusion, the Compeo line-up features novel 6-flight elements.


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