EuroWire July 2015

Technologynews

▲ ▲ The UltraScreen system from Acuity Products

Flaw density in check

the cable maker does not need to know where each of the defects lie, just to know if their density has increased. Acuity Products has included flaw density measures in the UltraScreen system with an associated alarm threshold. From recent assessment of several long production runs in which the UltraScreen system has been employed, Acuity has established that there are small changes in the layers of the extrusion and their form which give rise to new indicators about the current effectiveness of production. Using a combination of time and frequency domain analysis, the data sets analysed support a proposition that the quality of the extrusion of the inner screen changes over the length of the run. These gradual changes can be considered as degradation as they increase the measured variability. Acuity Products – UK Website : www.acuityproducts.co.uk

over its entire length of production, since it is, of course, designed to be a continuous process lasting several days or weeks – you simply cannot cut into the cable to find out how good it is currently! So a non-contact ‘scanning’ method of monitoring the cable as it is being produced is required, and rapidly scanning ultrasonics is the only solution, according to Acuity Products. The UltraScreen system has feature detectors that automatically look for geometric anomalies at the inner and outer semicon interfaces with the insu- lation layer (typically linked to features like protrusions and fall-ins) and for the presence of unexpected artefacts within the insulation layer (typically linked to features like contaminants and voids). These features are automatically detected when their level of geometry anomaly and/or presence within the insulation layer exceeds certain predefined threshold values. But in looking for positive indication of a stopping point,

When expensive submarine length (XLPE) MV/HV power cables, it is important for good run economics to continuously be aware of the status of extrusion quality monitoring (EQM) systems, including the level of contaminants, protrusions and voids (CPV) which affect post-production electrical stress testing. A lot of work has already been under- taken into keeping process cleanliness factors high in an attempt to ensure that no contaminants find their way into the cable, or are formed during the molten process. This helps to keep the process running continuously for as long as possible without stopping to clean down and eliminate any build-up of excess product. But how do they know when to finally stop the extrusion before problems build up? At present, experiential factors are used as there are very few on-line methods to ensure the internal quality of the cable extruding highly

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July 2015

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