Ultrasonic and Nuclear Magnetic Resonance for non-destructive diagnostics of cable systems

Due to mechanical, thermal and electrical stress non-reversible damages of the morphological texture can occur in polymeric materials used in cable systems (mainly polyethylene and silicone rubber). Reasons for the preceding damaging are for example included gas-filled microvoids and local inhomogeneities of the cross-linking-density. Considering the consequences of these processes, effective diagnostic methods are currently required, which have to fulfill certain demands (for example non-destructivity). Investigations carried out so far have shown that Ultrasonic and Nuclear Magnetic Resonance (NMR) meet these requirements. Ultrasonic diagnosis rest on the observation of the sound-propagation in materials. NMR is based on the recording of spin-dependent relaxation processes and its characteristics. Both diagnostic methods are well-known in materials science, whereas their use for monitoring equipment of cable systems has to be further developed. Therefore the current investigations focus on the detection, localization and characterization of defects. The analysis regarding the influence of mechanical stress (expansion of joints) shows a non-reversibility of this impact. Furthermore investigations relating to ageing phenomena are depicted. In addition first examinations using an automated ultrasonic measuring device, which has been developed with regard to industrial appliance, confirm the assumption of the ability to detect even small failures in insulation materials.