# Accelerated Charge Dissipation by Gas-Phase Fluorination on Nomex Paper
## 1 Introduction  
Nomex paper has been recognized as an excellent insulation material due to its good thermal stability, stable mechanical and electrical properties and has been widely used in dry-type, converter and oil immersed transformers among others, in which the reliability of the oil-paper insulation system greatly influences the safety of the power transmission system [1; 2]. Previous researches indicate that the surface charge accumulated on the oil paper interface and the space charge accumulated in the oil impregnated paper may accelerate the degradation process of the oil paper insulation system, distort the electric field distribution and lead to insulation failures such as flashover and breakdown [3; 4]. Therefore, a series of studies on the charge dynamic of the oil paper insulating system has been carried out and various approaches have been conducted to modify surface charge and space charge characteristics of the oil paper insulation system. In recent years, various influence factors on the charge dynamics of the oil paper insulation system have been studied. [PERSON] et al. [5] investigate the space charge characteristic of multi-layer oil-paperinsulation under different DC voltages and temperatures using the PEA technique; [PERSON] et al. (2016) measured the space charge distribution in multilayer oil-paper insulation with different moisture content; [PERSON] et al. (2017) proposed a waveform recovery method to obtain accurate charge distribution in the oil-immersed-paper/oil insulations. [PERSON] et al. (2018) and [PERSON] et al. (2019) studied the influence of thermal aging and voltage reversal on the space charge characteristic of oil-impregnated paper insulation, respectively. Moreover, [PERSON] et al. (2018, 2019) investigated the surface charge accumulation and dissipation of oil impregnated paper under DC and pulse voltage. However, the increasing voltage level of a power transmission system calls for higher reliability of insulation materials. It is necessary to research and develop materials used in oil paper insulation with better electrical, mechanical, and thermal properties. Therefore, many approaches have been used to modify the performance of the insulation oil and the paper. Nanoparticles such as C\({}_{60}\), Fe\({}_{3}\)O\({}_{4}\), BN and TiO\({}_{2}\)([PERSON] et al., 2010; [PERSON] et al., 2011; [PERSON] et al., 2012) have been used to improve the dielectric strength of insulation oil. Recently, CdS and graphene quantum dots have also been added in the insulation oil to improve its breakdown voltage and thermal conductivity ([PERSON] et al., 2010; [PERSON] et al., 2012). Furthermore, [PERSON] et al. (2018) and [PERSON] et al. (2019) have synthesized nanoparticles modified insulation paper and investigated the influence of doped nanoparticles on the thermal and electrical properties of cellulose insulation paper. Surface modification is considered to be an effective method to improve the surface performance of materials without deteriorating the properties of matrix. For example, various kind of plasma treatments of cellulose paper have been utilized to enhance their hydrophobicity ([PERSON] et al., 2010; [PERSON] et al., 2018; [PERSON] et al., 2018). As one of the most commonly used surface modification method, gas-phase fluorination has already been used to modify the surface charge and space charge dynamics of polymer such as polyethylene, polypropylene, polyimide and epoxy resin ([PERSON] et al., 2010; [PERSON] et al., 2018; [PERSON] et al., 2018). Previous studies also show that the surface charge dissipation of oil-impregnated cellulose insulation paper under DC and pulse voltage could be accelerated by gas-phase fluorination ([PERSON] et al., 2010). Nomex paper is one kind of insulation paper with better performance compared with cellulose insulation paper. The high resistivity of Nomex paper would result in the slower decay rate of the accumulated charge, therefore it is necessary to find a proper method to modify the charge dynamics of Nomex paper.