Recently, Maillefer has successfully commissioned several of the fastest and technologically most advanced high-voltage VCV lines. These lines are equipped with a groundbreaking curing technology, Round Value Package Premium, which enables high-speed curing without the problems normally found with increased line speed.
Challenges to overcome
The insulation process for high-voltage submarine cables is, in many ways, a very complicated process. It requires balancing between many limiting factors such as, production length, production time and production speed. Higher speeds are of course beneficial to achieve longer lengths in shorter time.
Production speed, on the other hand, is limited by cable core geometry, curing power and extruder performance. With typical technology, cable core ovality starts to increase dramatically when increasing speed and the related curing power. Technological innovations designed into Round curing remove these challenges. Thanks to a special heat impulse, the curing process begins by forming a crosslinked layer on the outside of the core in a very efficient manner. This outer crosslinked layer maintains a very round cable core during heat expansion and shrinking, specifically at the curing and cooling sections of the CV line.
Thanks to Round technology, it is now possible to also increase the curing power of the CV tube without any issues. In other words, we can now start the curing very efficiently, while increasing the total curing power without any negative side effects. More curing power naturally leads to higher production speed. Typical speeds for a standard VCV line and a VCV line with Round are shown in the graph below. Our CV lines are now producing multiple submarine cable campaigns at a record-breaking speed of 1.55 m/min for a 220 kV 400 mm2 copper conductor cable core.
Premium Curing Tube
Curing and extrusion go hand in hand
High-speed alone is nothing without exceptional quality as well. Round technology provides the best results in terms of cable core ovality. Typically, thick insulation layers with small conductor are demanding constructions when trying for perfection. The Round technology enables production of cores with 0.995 roundness and at record speeds.
Continuous improvement on the extrusion screw design and crossheads are also pivotal to success. Maillefer’s screw development aims towards higher extrusion outputs without any areas of low flow or stagnation points. Streamlined designs are very successful in realising long production campaigns necessary for submarine cable production.
The addition of Round technology has also made it possible to utilise the full output available from our insulation extruder. Now that constrains based on curing power and cable core roundness have been lifted, we are able use higher screw speed and further reduce the residence time of insulation material inside the extruder and crosshead.
Figure 1. Typical production speed for HV cables on a VCV line with Round technology in comparison to a standard VCV line of the same length. Cable constructions are based on Chinese standards. Actual speeds will vary depending on the actual VCV line layout.
Long deliveries, even longer in the horizon
Thanks to the speed increase of Round technology, long campaigns can be realised in a shorter time. Projects consisting of 120 tons of insulation material are realised in less than 12 days. Examination of breaker plate and fine mesh filters after such a long campaign have shown absolutely no signs of XLPE material stagnation or scorch. Several very successful production campaigns confirm that we are nowhere near reaching the maximum lengths possible with this technology. The new VCV lines are unique chances to showcase how all of our recent developments and innovations have come together and enabled Maillefer to push the boundaries of cable insulation technology one step further, together.
Image source: Courtesy of Maillefer
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