New approaches towards the investigation on defects and failure mechanisms of insulating composites used in high voltage applications

Stator insulations are critical to the reliability of high voltage rotating machines. Currently, state-of-the-art inspection systems mainly focus on electrical properties such as partial discharges to assess the performance of these composite materials. In the present work, non-destructive testing techniques and thermomechanical characterization methods are employed to characterize typical failures and defects of winding insulations and the resistance against delamination. X-ray computed (micro)tomography and ultrasonic measurements are performed to visualize defects in stator bar insulations. Both sample preparation as well as measurement set-up have been optimized to inspect defects in whole stator bars by means of X-ray CT. Additionally, the delamination resistance of insulation materials manufactured by resin rich and vacuum pressure technology are determined by TMA and DMA. The results give evidence that the evaluated inspection techniques provide a useful tool for the electrical industry regarding quality control, development of new materials or process optimization of stator windings.