Flexible epoxy based composites with enhanced delamination resistance

Abstract

This work highlights new strategies for the preparation of flexible epoxy-silicone rubber laminates, which promote high delamination resistance of stator bar insulations. Silicone rubber based damping layers are placed within rigid layered insulating composite materials to reduce thermo-mechanical stresses that particularly arise during on-off operation of rotating machines. To provide a good adhesion and covalent bonding between the elastomer layer and the epoxy based matrix, mercapto functional organosilanes are immobilized onto the silicone rubber surface by a two-step modification route. The surface characteristics of the damping layers prior to and after the functionalization process are characterized by means of contact angle measurements and XPS spectroscopy. Model insulations with the flexible damping layer are prepared by vacuum pressure impregnation process and the influence of the damping layer on the thermo-mechanical properties such as storage modulus, glass transition temperature and bending strength is determined. It can be obtained, that the flexibility of the new composite materials can be increased significantly, whilst the glass transition temperature is not affected by the elastomer layer. In a further step, stator bar prototypes with modified elastomeric damping layers are manufactured on-site to evaluate the electrical performance and the delamination resistance. The results reveal that both high-voltage endurance as well as delamination resistance can be improved considerably by the incorporated flexible layers. However, the electrical properties including loss factor or partial discharge magnitude are not influenced. From the results it can be concluded that the employment of flexible layers offers an innovative approach towards the manufacture of high-voltage generators with extended life-time, as reliability and longevity of high-voltage generators are directly related to the delamination resistance of the insulating composites.