Influence of temperature and moisture content on frequency response analysis of transformer winding

Frequency Response Analysis (FRA) has been in use since the last decade as a sensitive method for detecting transformer internal defects. This study is focused on the influence of temperature and moisture migration on the FRA response of transformer winding. It also discusses the feasibility of FRA capability in moisture diffusion recognition in transformer paper insulation. To conduct this study, a single phase model transformer involving concentric LV and HV windings and a 20/0.4 kV, 1.6 MVA three-phase two windings transformer are taken as test objects. Experiments are carried out at different temperature and moisture conditions. FRA spectra are then recorded and analyzed. FRA spectra deviations as well as total capacitance variations due to the temperature and moisture changes in the test objects are calculated. Karl-Fischer Titration (KFT) is utilized to monitor the moisture migration within oil and paper insulations. Furthermore, a mathematical model is used to simulate one of the test object windings and verify the experimental result, and also clarify the main reason of FRA spectrum deviation in this circumstance. Finally, statistical indices in FRA evaluation are calculated to explore their capability in FRA spectrum interpretation once the moisture content of paper insulation is changed.