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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.
The diffuse field assumption employed in basic statistical energy analysis (SEA) and in statistical room acoustics is violated for source and receiver positions close to boundaries or discontinuities. A simple approach is proposed to include the correction initially suggested by Waterhouse based on spherical Bessel functions in SEA predictions for rectangular rooms. With this modification the SEA results will be augmented by a position dependence and an additional frequency dependence. The approach is applied and demonstrated also for plate-like structures with different boundary conditions. An analytical solution is shown for the corner position on a simply supported plate and for edge positions on plates with more complex boundary conditions. The validity of the approach is confirmed by means of comparisons with modal analysis and finite element calculations.