Failure Characteristics and Mechanism of Nano-Modified Oil-Impregnated Paper Subjected to Repeated Impulse Voltage

Abstract

Nano-modification is a prospective method for improving the electrical properties of transformer oil. In most situations, transformer oil combined with cellulose paper is used to construct an insulation system for power equipment, such as power transformers. However, the influence of nanoparticles on the electrical performance of oil-impregnated paper is still unclear. Therefore, in this paper, we identify the failure characteristics of both fresh and nano-modified oil/paper. Specifically, the accumulative failure characteristics of nano-oil-impregnated paper (NOIP) are experimentally determined. The space charge distribution and trap characteristics of fresh paper and NOIP were measured, and the effect of nanoparticles on the space charge behavior are then analyzed. Finally, we measure the microstructure of fresh paper and NOIP subjected to repeated impulses. The test results indicate that nano-titanium oxide (TiO2) particles have a limited effect on the breakdown voltage of NOIP. However, the particles can dramatically improve the resistant ability of NOIP against repeated impulses. For the NOIP with a nano-concentration of 0.25 g/L, the improvement reaches 62.5% compared with fresh paper. Under repeated applications of impulse voltages, the space charge density of NOIP is much lower than that of fresh paper. The deep trap density of NOIP is much higher than that of fresh OIP, whereas shallow trap density is relatively lower. Micropores are generated in paper insulation subjected to repeated impulses. The amount of the generated micropores in NOIP is lower than that in fresh paper. Nano-TiO2 particles suppress the accumulation of space charge in the oil paper insulation, which weakens the electric field distortion in the dielectric. However, nanoparticles reduce the accumulative damage caused by repeated impulses. The above two points are considered the main reasons to improve the resistant ability against repeated impulses.

A Promising Nano-Insulating-Oil for Industrial Application: Electrical Properties and Modification Mechanism

“…The activation energy (trap level) E can be calculated by the half-width formula [41]:E=2.47Tm2kΔT where Δ T is the temperature difference corresponding to the half-peak in K, and k is the Boltzmann constant in eV/K.…”

“…Given that the temperature is approximately proportional to time, the integration of the current with temperature can be used in the calculation of the amount of charge released by the trap [41], as shown in the following equation:Q=true∫t0t1I(t)dt=1δtrue∫T0T1I(T)dT where Q is total charge of the trap in C, δ is the heating rate in K/min, T 0 is the experimental starting temperature, and T 1 is the temperature at which the current drops to zero.…”

Research on Creeping Flashover Characteristics of Nanofluid-Impregnated Pressboard Modified Based on Fe3O4 Nanoparticles under Lightning Impulse Voltages

“…The creeping discharge at the interface between oil and pressboard is tightly related to the electric field distribution, wherein the stronger the local tangential electric field at the interface, the more easily the creeping flashover occurs [23]. Since the lightning impulse voltage is mainly composed of high-frequency alternating components [24], the process of analyzing electric field distribution along the interface between oil and pressboard is similar to that under AC stress.…”

Review of accumulative failure of winding insulation subjected to repetitive impulse voltages

“…An attempt has been made to improve the ability of OIP to resist repetitive impulse voltages by suspending nanoparticles in the paper pulp and impregnating the paper using nanomodified oil. Both these methods have produced good results [84,[153][154][155][156][157][158][159][160]. However, more attention needs to be given to the comprehensive improvement of the insulating dielectric rather than the electrical performance; e.g.…”