The effects of TiO2 nanoparticles on insulation and charge transport characteristics of aged transformer oil

The insulation property of transformer oil is prone to decreasing due to insulation aging caused by the heat, electricity and other factors under the long-term operation, which is vital to the safe operation of power equipment. It has been reported that nanoparticles can improve the insulation properties of transformer oil. However, there has been no evidence showing the effect of nanoparticles on insulation properties of aging transformer oil, and the modified mechanism of nanoparticles is not clear. To reveal the modified mechanism of nanoparticles on aging transformer oil, this paper presents the effects of TiO₂ nanoparticles on the insulating properties, space charge characteristics and trap characteristics of aged transformer oil. The results show that the insulation properties of transformer oil with different aging degree are improved by adding TiO₂ nanoparticles. The AC breakdown voltage of aged nanofluid is increased significantly to the one of non-aging transformer oil. The lightning impulse breakdown voltage is increased by 30%~40%. Besides, the partial discharge inception voltage is increased by 12%. Moreover, the space charge characteristics measuring by the pulse electro-acoustic technique show that the charge dissipation rate of the aged transformer oil is increased by 57% with the presence of TiO₂ nanoparticles, which reduces the accumulation of space charges. The thermally stimulation current shows that more traps with shallower energy level are induced by TiO₂ nanoparticles. The charge trapping and de-trapping process in shallow traps are beneficial to the rapid dissipation of charges and restrains the accumulation of space charges. Therefore, TiO₂ nanoparticles can effectively modify the charge accumulation and dissipation characteristics in aging transformer oil and significantly reduce the distortion of electric field, resulting in the improvement of the insulation property.

I. Introduction

The Oil-immersed power transformer is the core equipment for power transmission in power system, and its safety and reliability play an important role in ensuring the continuous and stable operation of the power system [1, 2]. Transformer oil is affected by the heat, electricity and other factors during long-term operation, causing insulation performance to deteriorate. Among them, thermal aging is the most important form of transformer oil aging. The thermal aging characteristics of transformer oil is a key factor affecting the safety, reliability and service life of transformers. It is also a hotspot in the research field of transformer oil-paper insulation system.