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Sensitive partial discharge (PD) measurements on HV/EHV cable systems are usually based on electrical or electromagnetic PD detection. Unfortunately, interferences may significantly reduce sensitivity, especially in on-site after-installation testing and, even more, in on-line PD monitoring. This paper deals with optical PD detection, which is absolutely immune to any kind of electromagnetic interference. Optical PD detection necessarily requires transparent or translucent insulation systems to be applicable. Stress cone elements for HV/EHV cable accessories meet the requirements for optical PD detection, if made from transparent silicone elastomers.
Partial discharges may cause damage to electrical insulation of high voltage equipment. They initiate elastic waves in the insulating material, e.g. in the stress cone of an outdoor termination. Localisation of the origin of such elastic waves can help to predict serious damaging processes in the electrical insulation. In order to measure and evaluate the wave propagation effects in typical multilayered elastomeric structures, knowledge of the material properties is required. The propagating velocity and the attenuation of longitudinal waves are important parameters. Values for these quantities found in the literature were not appropriate. Therefore, for cross-linked polyethylene (XLPE) and cured liquid silicone rubber (LSR), the longitudinal wave velocity and the attenuation were evaluated in the temperature interval from -20°C to 50°C and in the frequency range from 200 kHz to 600 kHz using a two-sample ultrasound technique. The loss factor was determined from these measured quantities. Additionally, low frequency Dynamic Mechanical Thermal Analysis (DMTA) was applied to investigate LSR and XLPE in a temperature interval between -100 and 50°C and to check qualitatively the ultrasound data.
Steife Faser-Bragg-Gitter-Sensoren und bewegliche Faser-Mikrodistometer (extrinsische Fabry-Pérot-Interferometer-Sensoren) bieten der Baustoff-Forschung und der baubegleitenden Qualitätssicherung einzigartige Möglichkeiten, Mikroverformungen in der Zementsteinmatrix nahezu rückwirkungsfrei bereits zum Beginn der Erstarrung und ebenso nach der Erhärtung zu messen. Zuverlässige Meßaussagen im Zementsteingefüge erfordern jedoch eine gezielte Dimensionierung sowie ausreichende Haftung in der Matrix. Die Arbeit beschreibt die physikalischen Grundlagen der Sensoren und definiert Dimensionierungskriterien. Der Einfluss der betonchemischen Beanspruchung auf Festigkeit und Langzeitstabilität der eingebetteten Sensorfasern (Glas, Coating) wird untersucht.