Influence of fluorination time on surface charge accumulation on epoxy resin insulation

Abstract

In order to suppress surface charge accumulation on the epoxy resin insulation and to investigate the influence of treatment time on the charge accumulation, epoxy samples are surface fluorinated for the different times of 10 min, 30 min and 60 min in a laboratory vessel using an F2/N2 mixture. Attenuated total reflection infrared analyses and the observations of the cross section and the surface of the samples by SEM indicate the increases in degree of fluorination, thickness and compactness of the fluorinated layer, and the decrease in surface roughness, with treatment time increasing. Compared with the deep surface charge traps and stable surface charge of the unfluorinated (original) sample, as indicated by the open-circuit thermally stimulated discharge current measurement, the fluorinated surface cannot store the charge. The corona charges deposited on the sample surfaces fluorinated for 10 min, 30 min or 60 min rapidly decay to zero in about 2 min, 10 min or 15 mi at room temperature respectively, showing a slowed-down release of charge with fluorination time. The measurements of surface conductivity and contact angle and the calculation of surface energy reveal that fluorination gives rise to dramatic increases in surface conductivity, surface wettability and polarity, while they decrease with treatment time. The significant increase in surface conductivity of the fluorinated sample is attributed to a very likely substantial decrease in trap depth and the adsorbed water on the fluorinated surfac. Surface charging current measurements further show that large steady state current flows along the fluorinated surface during corona charging, in comparison with the almost zero steady state current for the original sample. This implies that the fluorinated sample has much lower surface charge accumulation in the period of charging, than the original sample.

The impact of nano-coating on surface charge accumulation of epoxy resin insulator: characteristic and mechanism

“…M is the calibration coefficient, which must be obtained by system calibration tests. As shown in figure 2, the calibration curve of capacitance probe is measured, and fitting the calibration curve, the relationship of output voltage and surface charge density can be described as (5):…”

“…Fujinami changed the shape of insulator, making the outline substantially in parallel with the electric field line, and as a result of which, the surface charge accumulation was well suppressed [4]. Differing from the complex approaches to modify the structure, Liu studied the charge accumulation characteristics on the fluorinated surface of the epoxy resin insulator, finding that the surface modification for insulating material can increase the conductivity and suppress the charge accumulation but leads to a risk of decreasing the flashover voltage [5]. Wu investigated the effect of nanoparticles on the distribution of space charge in LDPE/SiO 2 composite material, indicating that the average deterioration rate of space charge could climb with the increased concentration of SiO 2 nanoparticles [6].…”

Microscopic degradation mechanism of polyimide film caused by surface discharge under bipolar continuous square impulse voltage

“…[9,10] The properties and structures of aged materials can be known through the modern material analysis method, such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), etc. Currently, in many professional papers the erosion effects of insulating materials caused by surface discharge are discussed, and the research objects mainly include epoxy and its composites, [11][12][13] silicon rubber and its composites, [14,15] polypropylene and its composites, [16,17] polyamide and its composites [18,19] and oil-impregnated insulation paper. [20,21] Therefore, there is also a great need for a better understanding of the microscopic aging mechanism of PI film material.…”