Surface flashover is a devastating electronic avalanche along the gas–solid interface when a high electric field is applied, which is a potential issue that threatens the safe operations of advanced power electronic, electrical, and spacecraft applications. However, the underlying physical mechanisms for surface flashover development are still under investigation owing to the complex charge transport processes through the gas phase, solid phase, and gas–solid interface. In this study, the history of surface flashover theory in the last 50 years is introduced, and several key questions are reviewed from the perspective of the competing mechanisms of charge transport: the role of each phase in a surface flashover, the origin of surface charging, and effects of traps in solid on surface flashover. Then, some suggestions involve charge transport processes in each phase, and their correlations are put forward, and a predictable ‘charge transport competitive flashover model’ is proposed by clarifying the competing mechanisms of charge transport processes through multiple phases. This study summarises the history and hot topics of physical mechanisms of surface flashover proposed based on classic and recent progress and offers promising routes for developing a more precise surface flashover theory and improving surface flashover performances.

In November 2017, the first ±1100 kV high-voltage direct-current power transformer in the world, which was made by Siemens in Nurnberg, passed its type test. Meanwhile, in early 2017, a ±1000 kV ultra-high voltage (UHV) substation was officially put into operation in Tianjin, China. These examples illustrate that the era of UHV power transmission is coming. With the rapid increase in power transmission voltage, the performance requirements for the insulation of power transformers are getting higher and higher. The traditional mineral oils used inside power transformers as insulating and cooling agents are thus facing a serious challenge to meet these requirements. In this review, the basic properties of traditional mineral insulating oil are first introduced. Then, the variation of electrical properties such as breakdown strength, permittivity, and conductivity during transformer operation and aging is summarized. Next, the modification of mineral insulating oil is investigated with a focus on the influence of nanoparticles on the electrical properties of nano-modified insulating oil. Recent studies on the performance of mineral oil at molecular and atomic levels by molecular dynamics simulations are then described. Finally, future research hotspots and notable research topics are discussed.

In the present work efforts have been made to investigate the influence of ac aging on space-charge dynamics in low-density polyethylene (LDPE). LDPE films with 200 μm were aged under various electric stress levels at 50 Hz for various times at ambient temperature. Space-charge dynamics in the samples after aging were monitored using the pulsed electroacoustic technique. It has been revealed that the space charge under ac aging conditions is related to the level of the applied field, duration of the voltage application, as well as the electrode materials. By comparing with the results of unaged sample the results from aged sample provide a direct evidence of changing trapping characteristics after ac aging. Negative space charge is present in the bulk of the material and the total amount of charge increases with the aging time. The amount of charge increases with the applied field. Charge decay test indicates that the charges are captured in deep traps. These deep traps are believed to form during the aging and related to change caused by injected charge. By using different electrode materials such as gold, brass alloy, and polyethylene loaded with carbon black, it was found that the electrode has an important role in the formation of charge, hence subsequent changes caused by charge. The charge dynamics of the aged samples under dc bias differ from the sample without ac aging, indicating changes brought in by ac aging. Chemical analysis by Fourier transform infrared spectroscope and Raman microscope reveals no detectable chemical changes taken place in the bulk of the material after ac aging. Finally, the consequence of the accumulation of space charge under ac conditions on the lifetime of the material has been discussed. The presence of deeply trapped space charge leads to an electric stress enhancement which may shorten the lifetime of the insulation system.

Surface flashover is a gas–solid interface insulation failure that significantly jeopardises the secure operation of advanced electronic, electrical, and spacecraft applications. Despite the widespread application of numerous material modification and structure optimisation technologies aimed at enhancing surface flashover performance, the influence mechanisms of the present technologies have yet to be systematically discussed and summarised. This review aims to introduce various material modification technologies while demonstrating their influence mechanisms on flashover performances by establishing relationships among ‘microscopic structure‐mesoscopic charge transport‐macroscopic insulation failure’. Moreover, it elucidates the effects of chemical structure on surface trap parameters and surface charge transport concerning flashover performance. The review categorises and presents structure optimisation technologies that govern electric field distribution. All identified technologies highlight that achieving a uniform tangential electric field and reducing the normal electric field can effectively enhance flashover performance. Finally, this review proposes recommendations encompassing mathematical, chemical, evaluation, and manufacturing technologies. This systematic summary of current technologies, their influence mechanisms, and associated advantages and disadvantages in improving surface insulation performance is anticipated to be a pivotal component in flashover and future dielectric theory.

Polyimide (PI) has excellent dielectric properties with superior thermal stability, and it is considered as a promising polymer dielectric for energy storage capacitors. Here, we studied the energy storage properties of PI composite films with BaTiO₃ (BT) nanoparticles in a wide content range. Benefiting from the high breakdown strength (520 kV/mm), the nanocomposite filled with 0.05 wt. % of BT exhibits an increased energy density of 4.51 J/cm³ at room temperature and keeps a good thermal stability (3.22 J/cm³ at 100 °C). Additionally, trap properties of the nanocomposites and their effect on breakdown strength were studied by thermally stimulated depolarization current. It was found that the dominant trap parameter on breakdown strength variation, with the increase in the BT content, is correlated with deep traps, deep and shallow traps especially their depths, and shallow trap density. Then, a physical quantity of average trap depth was introduced, the value of which decreases from 0.81 eV to 0.44 eV as the BT content increases to 50 wt. %, and a clear correspondence was discovered between the average trap depth and breakdown strength.

In this paper, we present the optimal strategy for public plug-in electric vehicle (PEV) charging services with multiple charging options: fast charging service and slow charging service. The PEV user make decisions by firstly considering the remaining energy, travel distance to charging station, then about the charging prices, charging rates and estimated charging time. To obtain insights of such a highly coupled system, we consider both monopoly and duopoly markets, where the two services are operated by a single service provider (SP) and two different SPs, respectively. For the monopoly market, we propose a three-stage Stackelberg game model. For the duopoly market, we propose a two-stage Bertrand competition and Cournot competition. We provided the SP’s optimal pricing strategies and decisions in the monopoly market, and the optimal pricing contract and quantity contract for SPs in the duopoly market with Bertrand competition and Cournot competition. Both the analytical and simulation results show that, in the monopoly market, offering two charging options can potentially improve the SP’s profit compared with offering one option only in the monopoly market; while in the duopoly market, it is optimal for SPs to offer the quantity contract rather than the price contract to maximize profits.