Examining the ageing of transformer insulation using FRA and FDS techniques

Frequency response analysis (FRA) is a widely accepted testing technique to assess the mechanical condition of a power transformer. However, it has been reported that FRA is also sensitive to non-mechanical parameters such as the temperature and moisture content of the insulation. Therefore, further studies are required to investigate the ability of FRA on examining the transformer insulation condition. In this paper a study based on an insulation degradation of a single phase 5 kVA model transformer is presented. Throughout the accelerated insulation degradation process, FRA and Frequency Domain Dielectric Spectroscopy (FDS) measurements are performed to analyze the degradation condition. Two methodologies are proposed to analyze the FRA results based on the relative change of capacitance and change of inter-winding capacitance. Results obtained from these approaches are verified with FDS analysis.