Electro-Mechanical and Chemical Strength Analysis of Thermally Aged Nanofluid Impregnated Kraft Paper

The transformer is a long run device in a power system network. When transformer oil comes in contact with cellulosic insulation in the presence of heat, the solid insulation undergoes polymerization. As a result, dielectric, mechanical and chemical properties of the oil and kraft paper get affected. In this present study, electrical, mechanical and chemical degradation of the thermally aged nanofluid (NF), and mineral oil (MO) impregnated kraft papers are analysed. To understand the degradation of the aforementioned properties of the kraft paper, thermal ageing study has been performed. A comparative study of the aged kraft paper is carried out to study the electrical breakdown, tensile strength and the degree of polymerization. The thermal ageing experiment is performed for two different insulating oils, namely: MO and exfoliated hexagonal boron nitride (Eh-BN)/MO-NF impregnated kraft paper. 0.01wt.% of nanofiller concentration is chosen for the preparation of Eh-BN/MO-NF. Highly insulating, thermally conducting and superior physicochemical properties of the NF are suitably chosen for the thermal ageing. An ageing study of both MO and NF impregnated kraft paper is performed in two different ageing vessels at 160°C for different aging durations such as 100, 500, 1000 and 2000 hours respectively. It is observed from the experimental results that both modulus and tensile strength of Eh-BN/MO-NF aged kraft papers are superior than that of MO aged kraft papers. Electrical strength of the NF impregnated aged kraft paper has minimum decrement in the AC breakdown voltage. Early polymerization in MO impregnated kraft paper is the reason for drastic degradation of its mechanical strength. Eh-BN/MO-NF reduces the effect of early polymerization and minimum affinity towards polar contamination during thermal ageing and hence provides better electro-mechanical stability to the insulating NF impregnated kraft paper.