Estimation of dielectric dissipation factor of cellulosic parts in oil-paper insulation by frequency domain spectroscopy

Abstract

This paper proposes a method for estimation of tanδ of cellulosic parts in oil-paper insulation from frequency domain spectroscopy based on equivalent circuit model of oil-paper insulation in real-life transformers. Existing literature shows that overall condition of oil-paper insulation in transformer can be assessed by conventional frequency domain spectroscopy. Also, the condition of oil can be separately and easily predicted through analyzing its dielectric properties by taking out the oil samples from transformer. However, it is quite difficult to assess the dielectric properties of cellulosic parts in oil-paper insulation as it cannot be directly accessed from outside for an operating transformer. Considering the aforesaid fact, this paper presents a segregated equivalent circuit model of composite oil-paper insulation that can separately estimate the tanδ profiles for oil as well as cellulosic parts. The tanδ profiles of cellulosic parts obtained from the equivalent circuit model have been validated experimentally. Results show that the tanδ profile obtained from experimental result holds good agreement with that of the proposed model.