A case study on dielectric response measurement of high voltage generator insulation systems

Dielectric response measurements (DRMs) are a non-destructive method that has long been widely employed to state the insulation condition of many power system components. Such methods can reflect the deterioration problems that occur in the insulation system of rotating machines, such as conductive contamination on the end winding surface, moisture absorption, and stress grading system deterioration. In this paper, the investigation of the DRM of the stator winding insulation of an indirect hydrogen-cooled generator rate of 211.75 MVA, 15.75 kV is presented. The DRMs are carried out using polarization and depolarization current (PDC) as well as frequency domain spectroscopy (FDS) on the stator winding insulation system. The experiments are performed on both phase-to-ground and interphase insulation. Various dielectric characteristics, which are polarization current, depolarization current and a dissipation factor are recorded and analysed. The phase-to-ground PDC results show the natural characteristic of the stress grading system as a hump occurring in the current trace. In addition, the measured PDC results are converted into a frequency window so that calculated parameters can be compared with the measured FDS test results.