Dielectric response studies on insulating system of high voltage rotating machines

A significant method to characterize the electrical properties of materials and to evaluate the condition of the insulating systems is the dielectric response study which can be done in the time or frequency domain. The dielectric response measuring results can be affected by different parameters like measuring voltage, temperature, water content and aging condition of insulating system. In this work numerous measurements are presented, thus to understand, how the dielectric response measurement results at the insulating system of high voltage rotating machines can be affected by these parameters in the time and frequency domain. Because of the importance of the dielectric response application as a non-destructive diagnostic method the possibilities and limitations of this method to reflect the deterioration processes due to thermal and electrical stress were also investigated. In addition the possibility to transfer the measuring data from the time to frequency domain was investigated and the calculated and measured data were compared. For the test object actual stator bars were used that were manufactured with epoxy VPI technology.