Research on DC Breakdown Performance of Nanofluid-impregnated Pressboard Based on TiO2 Nanoparticles

UHVDC has been applied widely since it possesses technical advantages in transmission electric power in long distance and large capability, leading to the severe test for the insulation performance of converter transformer. Oil-impregnated pressboard (OP) is one of the key insulating components in converter transformer due to its high mechanical strength and dielectric property, and its electrical performance is strictly related to the phenomenon of space charge accumulation. Recent experiments have shown that the insulation nanofluid has attracted a great deal of attention due to its considerable dielectric performance. Meanwhile, TiO₂ semiconductor nanoparticles are considered to be the best choice owing to their low dielectric loss induced and considerable modification effect. However, the relation among particle sizes, DC breakdown voltages and space charge characteristics of nanofluid-impregnated pressboard (NP) based on TiO₂ nanoparticles remains largely uncertain, which limits the performance improvement of oil/pressboard insulating system. In this paper, the modification effect on DC breakdown strength of oil-impregnated pressboard based on TiO₂ nanoparticles with various sizes has been investigated. Moreover, the accumulation characteristics of OP and NPs were also studied by use of Pulsed Electro Acoustic Method (PEA). According to the experimental results and analysis, the relation among particle sizes, DC breakdown performance and accumulation characteristics of space charge was clarified and a possible modification mechanism has been proposed.

I. Introduction

Ultra high voltage direct current (UHVDC) has been applied widely and plays a important role in power transmission [1]. Oil-impregnated pressboard is one of the key insulating forms in converter transformer due to its high mechanical strength and dielectric property, and its electrical performance is strictly related to the phenomenon of space charge accumulation [2]. It has been reported that the space charge accumulation [3] – [4] can occur under DC stress, which can distort the local electric field and cause insulation failure easily. Therefore, it is of great significance to improve the insulation performance of OP under DC stress for the stable operation of converter transformer [5].