Effect of Ageing and Moisture on Dielectric Properties of Natural Ester Impregnated Pressboard Insulation

Natural Ester is a promising liquid dielectric for power transformer applications. It has good dielectric properties and it is fully bio-degradable. However, the degradation of natural ester-based paper insulation needs to be studied in detail for understanding the consequences of long-term operation with natural ester-based power transformers. This paper presents the study of the degradation of natural ester-based pressboard insulation under the influence of thermal ageing and moisture is studied through dielectric response measurements, i.e., Frequency domain Spectroscopy (FDS) and Polarization-Depolarization Current (PDC) measurements. It was observed that both thermal ageing and moisture contribute to rapid decline into the resistivity of the insulation as well as increase in dielectric losses.