Excellent Vacuum Pulsed Flashover Characteristics Achieved in Dielectric Insulators Functionalized by Electronegative Halogen–Phenyl and Naphthyl Groups

Abstract

Designing electrical insulation materials with excellent surface flashover strength in a vacuum environment is crucial for highpower equipment and aerospace devices. In the present paper, the effect of two types of electronegative groups, the halogen−phenyl groups and the aromatic π-conjugated naphthyl groups, is used to greatly improve the vacuum flashover characteristics of polystyrene (PS), a commonly used polymer dielectric material in high-power devices. By polymerization of the monomers containing these electronegative groups, the bulk insulation material as a whole is modified expediently. In comparison to the base polymer PS, the electron affinity of the structures containing strong electronegative groups is studied with first-principles calculations based on the density functional theory. The nanosecond pulsed vacuum flashover testing results show that the vacuum flashover strength is increased by 10% after replacing the PS pendant phenyl groups with fluorophenyl groups and increased by 44% when replaced with the naphthyl groups. Furthermore, the thermally stimulated current and secondary electron emission yield spectroscopies are measured, to study the influence of strong electronegative groups on the trapping characteristics and further the electron-emitting features of the polymer dielectrics, which are closely related to the charged particle multiplication process during the vacuum flashover. The results prove that introducing strong electronegative groups can inhibit the triggering of vacuum flashover, suppress the electron emission, delay the flashover process, and thus greatly increase the vacuum flashover voltage. The study of this paper not only puts forward two groups of easily processable polymers with excellent vacuum flashover strength but also paves ways for the future material design of special insulation polymers.

Design and 3D printing of porous cavity insulation structure for ultra‐high electrical withstanding capability

“…It is worth noting that the voltage waveforms and electrode types used in flashover voltage testing in representative literatures selected for comparison are the same or similar to those in this study. Clearly, the cavity insulation structures exhibit ultra‐high surface insulation improvement ratio in both the cases of DC [26, 27, 46, 50–54] and impulse [24, 28, 35–38, 46, 55–59] flashover, which far outperform the other flashover mitigation strategies.…”

“…Comparatively, multipactor suppression is the more direct, effective, and frequently used strategy, which is based on the design principle to reduce the secondary electron yield (SEY) of the insulators and reduce the number of electrons available for SEEA. The SEY reduction approaches, including bulk insulation modification (e.g., chemical grafting [24,25], doping of functional fillers [26,27]) and surface treatment (e.g., fluorination [28,29], composite coating [30][31][32][33], plasma treatment [34][35][36], and thin film deposition [37,38]) have shown the ability of multipactor suppression to some extent. Nevertheless, most of these methods are collectively cumbersome and have poor mechanical stability.…”

Largely Enhanced Surface Flashover Voltage of Poly(ether Imide) by Scalable and Durable ZnO Coating: A Gift from In Situ Growth

“…The occurrence of flashover mainly depends on the surface state of the dielectric, such as surface morphology, surface trap, surface charge migration, outgassing from surface, and accompanying gas ionization. − Researchers have put forward various methods to modify the properties of the interface to improve the flashover voltage. Typical methods include − introducing micro-nanostructures on the dielectric surface for morphology modification by 3D printing; modulating the interfacial charge migration behavior by cross-linking or fluorination; changing the surface traps by graphene, Cr 2 O 3 , and other nanoparticles; and regulating the outgassing rate and gas ionization by polythiourea-assisted coating. Although different modification strategies focus on modifying the interface properties from different perspectives, the ultimate goal is to improve the flashover voltage by suppressing surface charge accumulation and mitigate electric field distortion, which can suppress electron multiplication. , …”

An alternative simulation approach for surface flashover in a vacuum using a 1D2V continuum and kinetic model

“…Surface flashover is found in * Author to whom any correspondence should be addressed. high voltage transmission apparatus, spacecraft, pulsed-power devices and particle accelerators, etc [1][2][3][4][5][6][7][8][9][10][11]. Depending on the background pressure and gas species, plasma discharge during surface breakdown varies from streamer discharge and corona discharge, to Townsend-like discharge, etc [8,12,13].…”