To Study The Characterization And Evaluation Of Cellulosic Based Solid Insulation Having Low Permittivity

Abstract

The oil impregnated paper (OIP) insulation system is critical in the power transformer because the life of transformer is generally governed by life of insulation system. OIP is the basic insulation system used in transformers. Generally liquid insulation is mineral oil and solid insulation can be made of paper, pressboard, epoxy, and wood. Among them, kraft paper and pressboard is widely used as solid insulation in the transformer, which is made from unbleached softwood pulp through sulphate process. In service period of transformer these insulation system undergoes various stresses like thermal, mechanical, chemical and electrical. Due to the difference in the permittivity (dielectric constant) of oil (DC is 2.2) and pressboard (DC is 4.4 – 4.6), electric stress is generated between them which causes the degradation of insulation. The good life of insulation requires reducing the electrical stress between cellulose as much as possible. The various methods are developed to reduce the permittivity of solid insulation with the help of filler and additives such as fibers, resins, inorganic insulating materials etc but it also alter the properties of OIP which is undesirable. So the characterization and evaluation of these modified pressboards are very important to decide their usability in transformer as solid insulation. Detailed discussion on the characterization and evaluation is included in this thesis report titled as: “To study the characterization and evaluation of cellulosic based solid insulation having low permittivity”