EuroWire November 2014

Technical article

Developments in green technologies for power cables – using clean materials in the production process By Sikora AG

Introduction Green technology is a topic which plays an increasingly important role worldwide, especially in light of greater shortages of resources and increasing environmental pollution. Industry has an obligation to develop products and processes that are sustainable, energy saving and environ- mentally compatible. At the same time, these products and processes have to be highly profitable. Crude oil is a basic irreplaceable resource. Oil is used in the form of plastic materials for cable insulation. Sikora’s understanding is to provide technical solutions for online quality assurance of materials and cables to enable economic and ecological production processes. By integrating measuring and control as well as inspection and sorting technologies in the production line, the scrap rate can be reduced and consequently material saved. Every litre of oil that can be saved due to lower rejection rates and less material consumption also conserves the less available resource. This article introduces a novel tech- nological solution that inspects the purity of XLPE pellets that are used at the insulation process of power cables. It is the first system on the market that inspects pellets to 100 per cent and automatically sorts out contaminated

pellets before they get into the extrusion process. By assuring absolute clean insulation material, the system supports the requirements of green technology within the process chain. The technology is the result of a development cooperation between Sikora and Maillefer.

Necessity of clean XLPE compound for power cables

▲ ▲ Metallic contamination inside the pellet (X-ray)

The purity of the XLPE compound that is used for the insulation of power cables plays a critical role. Perfectly pure compound reduces the risk of a breakdown. Metallic impurities of 50 μ m may cause damage to the end product with high follow up costs that can easily run into the millions. The repair of a defective submarine cable, for example, which has been damaged by contamination, can lead to weeks of downtime. It is for that reason that the Chinese Standard for high voltage cables, for example, demands the exclusion of contamination from 75 μ m in the processed materials. Accordingly, it is necessary to inspect the material to 100 per cent before it enters the end product. Sample tests are a first step but not sufficient to exclude all contamination reliably.

▲ ▲ “Black specs” on the pellet (big and small) (Optical)

Today, cable manufacturers use screens to catch impurities in the XLPE compound before they get into the cable. The screens are positioned directly in the melt flow after the extruder, before the crosshead. However, these screens can get clogged by scorches or excessive amounts of contaminants after a certain run time. Then the melt pressure in the extruder may increase significantly. Finally, the production has to be stopped in order to change the screens, which in turn means that later a joint is required at that position.

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November 2014