Application of polarization based measurement techniques for diagnosis of field transformers

This paper presents both quantitative and qualitative analysis of several polarization based measurements, which include frequency domain spectroscopy (FDS) and polarization depolarization current (PDC) measurements on four different field transformers. The X-Y model and the RC circuit model are mainly used in the analyses. In this study sequential FDS/PDC measurements on the same unit are used to identify the progressive change of the insulation condition. Influence of oil conductivity and geometrical parameters on the estimates from FDS response is shown in detail. Based on this study a simple technique to improve the reliability from FDS measurement is discussed. Influence of the oil refurbishment process on polarization based measurements is also presented and discussed.