Electric Field-Dependent XY Equivalent Structure Modelling of Oil-paper Insulation Systems in Power Transformers: Improvement and Verification

XY equivalent structure model plays a crucial role in characterizing insulation states of oil-paper insulation system (OPIS) in power transformers based on frequency domain spectroscopy (FDS). However, the conventional modeling method of OPIS only considers simplified calculation of complex permittivity for insulating mineral oil (IMO) under low field. This could cause large deviations and cannot meet high-field reality. Therefore, this paper develops a new XY equivalent structure model to characterize insulation dielectric performance of OPIS including IMO and oil-impregnated paperboard (OIP) based on high-field FDS. Firstly, the modeling processes of XY model of OPIS are investigated as a function of electric field. Then, the complex permittivity behaviors of IMO, OIP and OPIS subject to diverse electric fields are discussed, respectively. Subsequently, according to high-field dielectric behaviors, a new calculation approach of complex permittivity of IMO is proposed introducing two field-related parameters and an electric field enhancement factor τ(E). Finally, the effectiveness of new field-dependent XY model for OPIS is validated using high-field complex permittivity of IMO. Compared to traditional model, this work can accurately characterize field-dependent dielectric behaviors of OPIS in power transformers. This article will provide a solid foundation for health management and prognostics of OPIS in power transformers.