In this paper, three methods, including dielectric barrier discharge (DBD) etching and deposition, and direct fluorination, were used for the surface modification of Al2O3-filled epoxy resin (Al2O3-ER) insulators to improve surface charge dissipation properties. The surface charge dissipation properties of the Al2O3-ER samples after these three treatments were compared. Firstly, the experimental results showed that DBD deposition reduced the most accumulated surface charges among the three treatments. The surface charge decay rates after DBD deposition and direct fluorination exceeded 98%. Then, the surface morphology, chemical components, and electrical parameters before and after the treatments were analyzed. Among the above three treatments, the surface roughness of the DBD deposited sample was the smallest, which facilitated the reduction of surface charge accumulation. The increase of the surface conductivity of the DBD deposited sample accelerated surface charge dissipation. Furthermore, the ageing effects of these three treatments were investigated. After five days of storage, it showed no significant difference between the dissipation properties of the DBD etched and the untreated samples due to the reorientation of polar groups towards the interface. However, there was only subtle changes in the surface charge decay rates of those DBD deposited and fluorinated samples, indicating that no obvious ageing effects were observed after DBD deposition and direct fluorination. The introduction of SiOx and C-Fn functional groups improved the anti-ageing properties of the DBD deposited and fluorinated samples, respectively. These comparative results can stimulate the development of eco-friendly plasma deposition techniques for the surface modification of Al2O3-ER insulators.

Atmospheric pressure plasmas and direct fluorination treatment of Al2O3-filled epoxy resin: A comparison of surface charge dissipation

Superhydrophobic and high-flashover-strength coating for HVDC insulating system

Space charges tend to accumulate on the surface and at the interface of ethylene–propylene–diene terpolymer (EPDM), serving as high voltage direct current (HVDC) cable accessory insulation, which likely induces electrical field distortion and dielectric breakdown. Direct fluorination is an effective method to modify the surface characteristics of the EPDM without altering the bulk properties too much. In this paper, the surface morphology, hydrophobic properties, relative permittivity, and DC conductivity of the EPDM before and after fluorination treatment were tested. Furthermore, the surface and interface charge behaviors in the HVDC cable accessory were investigated by the pulsed electroacoustic (PEA) method, and explained from the point of view of trap distribution. The results show that fluorination helps the EPDM polymer obtain lower surface energy and relative permittivity, which is beneficial to the interface match in composite insulation systems. The lowest degree of space charge accumulation occurs in EPDM with 30 min of fluorination. After analyzing the results of the 3D potentials and the density of states (DOS) behaviors in EPDM before and after fluorination, it can be found that fluorination treatment introduces shallower electron traps, and the special electrostatic potential after fluorination can significantly suppress the space charge accumulation at the interface in the HVDC cable accessory.

https://www.mdpi.com/2073-4360/10/5/500/pdf

Surface Layer Fluorination-Modulated Space Charge Behaviors in HVDC Cable Accessory.

Insulation failure and insufficient thermal management in electrical and electronic equipment threaten their safe and stable operation and restrict development toward high power and high integratio...

Oriented Boron Nitride Nanosheet Films for Thermal Management and Electrical Insulation in Electrical and Electronic Equipment

Review of interface tailoring techniques and applications to improve insulation performance

In order to prove the effectiveness of direct fluorination in improving dc flashover performance of epoxy insulators in SF6 gas and also to provide evidence for the importance of surface conductivity of solid insulators, sheet-shaped and truncated cone epoxy samples were prepared and were fluorinated in a laboratory stainless vessel using a F2/N2 mixture with 12.5% F2 by volume at 0.1 MPa and 85 °C for 30 min. Physicochemical characteristics of the fluorinated surface layer were evaluated by ATR-FTIR and SEM techniques, and the results showed substantial chemical modification of the surface layer, which has a thickness of 0.89 μm and a roughened surface. Further, as expected on the basis of previous studies, measurements of surface electrical properties of the surface fluorinated sample, compared to the unfluorinated one, revealed a four orders of magnitude higher surface conductivity and a much more rapid decay of surface potential after corona charging. Dc flashover tests were performed on the truncated cone samples in SF6 gas at 0.1 MPa with a stepwise increasing voltage before and after the fluorination. The flashover test results showed a definite improvement in dc flashover voltage. For example, the flashover voltage at 63.2% probability or the mean flashover voltage for 2 min duration of the voltage step increased by 13.8% or 13.6% after the fluorination. The performance improvement is mainly attributed to easy leakage and dispersion of the charge deposited on the surface fluorinated sample from the gas phase, due to high conductivity of the fluorinated layer. The flashover test results also showed the influences of the duration of the voltage step on the flashover voltage and on the increase rate of flashover voltage. This means that even the time constant of the fast gas phase charging should be larger than 2 min, and that there should be different influences of the inhomogeneous surface conduction between the virgin sample and the fluorinated sample.

Improved DC flashover performance of epoxy insulators in SF6 gas by direct fluorination

Highly hydrophobic materials are of interest in many scientific and technological areas. To improve surface properties of polydimethylsiloxane (PDMS), PDMS sheets were surface fluorinated in a laboratory vessel using a F2/N2 mixture with 12.5% F2 by volume at about 55 °C under 0.1 MPa for different times of 15, 30, and 60min. Surface wettability and surface energy were evaluated by contact angle measurements and surface energy calculations, and surface electrical properties were investigated by measurements of surface conductivity and surface potential decay. These results show that direct fluorination produced a highly hydrophobic and partially conductive PDMS surface with low surface energy, which had little correlation with fluorination time in the investigated range of 15 to 60 min. Moreover, annealing of the surface fluorinated PDMS sheets at 150 °C for 60 min caused a further increase in surface hydrophobicity, while reduced surface conduction of the fluorinated PDMS sheets. Attenuated total reflection infrared analyses and scanning electron microscope surface and cross-section observations reveal substantial changes in physicochemical characteristics of the sheet surface layers due to direct fluorination. The high hydrophobicity or low surface energy is attributed to the changes in chemical composition and structure of the surface layers and in their surface roughness. The partial conductivity of the fluorinated PDMS surfaces is a result of the competition between the compositional change and the structural change.

Highly hydrophobic and partially conductive polydimethylsiloxane surface produced by direct fluorination and subsequent annealing

The invention relates to a method for improving the discharge resistance of an epoxy insulator in a gas insulation system. According to the method, fluoridation is carried out on the epoxy insulator by using a gas mixture of fluorine gas and nitrogen gas or a gas mixture of fluorine gas and inert gas under the conditions of appropriate temperature and pressure in a closed reaction chamber, a fluoridation layer containing C-F bonds is formed on the surface of the epoxy insulator, so that the method is used for improving the discharge resistance of the epoxy insulator. Compared with the prior art, the method disclosed by the invention is simple in processing steps, good in controllability and low in economic cost, the epoxy insulators with arbitrary shapes and dimensions can be uniformly modified in batches, and the method is specially applicable for commercial application.

Zhenlian An

Papers

Improved DC flashover performance of epoxy insulators in SF6 gas by direct fluorination

Highly hydrophobic and partially conductive polydimethylsiloxane surface produced by direct fluorination and subsequent annealing

Method for improving discharge resistance of epoxy insulator in gas insulation system