Eco-Friendly Insulating Materials for Transformers in MVDC and HVDC Power Networks

This work investigates the viability of natural and synthetic ester liquids as potential alternatives to mineral oil in MVDC and HVDC transformer insulation systems. Finite Element Method simulations (FEM) were performed using the measured dielectric properties of the oils and their impregnated pressboards as input parameters to evaluate their influence on steady state electric field distribution. A comparison on the field distribution under AC and DC condition is performed for the different materials, identifying regions of maximum stress around the corona head and high voltage electrode. The temperature dependence of electrical conductivity values of the materials and their effect on the steady state DC electric field distribution is explored. The higher conductivity of ester liquids when compared to mineral oil provides a more uniform field redistribution between the oil and pressboard, also facilitating the shift of maximum electrical stress from the oil to pressboard. The results support the technical merits of using ester-based insulation material for field stress equalization in HVDC networks.