The environmental problems caused by greenhouse gases have received unprecedented attention. Sulfur hexafluoride (SF ₆ ), which is the preferred gas for use in gas-insulated switchgear (circuit breakers, disconnect switches, etc. for high-voltage electrical circuits), has a very high global warming potential, and there is a large international effort to find alternative gases. Recently, this effort has made important progress, with promising alternative gases being identified and tested. An overview, in particular the current state of the art, of the study of SF ₆ -alternative gases is presented in the paper. The review focuses on the application of the SF ₆ -alternative gases in gas-insulated switchgear, with detailed analysis of calculations and measurements of their basic physical properties, dielectric strengths, and arc-quenching capabilities. Finally, a discussion of and perspectives on current research and future research directions are presented.

Environmental considerations are increasingly taking a front seat in all arenas of our daily lives. Among the major concerns are greenhouse gases and the resulting global warming problem. Although sulfur hexafluoride (SF ₆ ) is the most widely used insulation and arc-interruption medium in electrical power equipment, it is an extremely potent greenhouse gas with a very high global warming potential (GWP). Hence, the global power industry has been actively seeking SF ₆ -alternative gases for decades. In recent years, much progress has been made in developing promising new gases that have dielectric properties similar to, or even better than, SF ₆ but with much lower GWPs. Many engineering-oriented tests have been performed on the technical performance of these gases and some manufacturers have announced their application in pilot projects. However, their large-scale application still seems premature, in particular because of the lack of some critical fundamental physicochemical information for these relatively novel compounds. To provide a better understanding of these SF ₆ -alternative gases, this paper reviews the recent advances in obtaining their fundamental physicochemical properties, emphasizing basic data calculations and fundamental experiments. The most important properties are analyzed comprehensively. These include the basic physical properties of arc plasmas formed from the gases, decomposition characteristics, materials compatibilities, swarm parameters, cross-sections and some dielectric properties. Finally, perspectives on current research and future research directions are presented.

Wide bandgap (WBG) semiconductor devices are developing rapidly due to their superior performance compared to traditional silicon-based devices. However, the packaging technology of traditional devices has limited the application of WBG semiconductor devices because of the challenges in electrical insulation. The complex environment of high blocking voltage, high frequency, and high temperature is the major reason for insulation failure of encapsulation structure. Therefore, in this article, an epoxy resin composite with nonlinear conductivity is proposed to be used as a coating to improve the electric field distribution of high-voltage high-power IGBT modules. First, an electrical field simulation model was built considering the thermal stress. It was found that the electric field in high temperature was improved compared with that in room temperature due to the temperature-dependent conductivity of silicone gel. Nevertheless, the risk of insulation failure still exists. After the application of nonlinear conductivity materials (NCMs) coating, the maximum electric field at the triple junctions and the ratio of electric field distortion in high field areas were significantly decreased. Further analysis showed that the optimization ratio of electric field increased with the increase of the blocking voltages or power losses in the IGBT chip. The results have demonstrated that the NCMs can reduce the maximum electric field in the IGBT encapsulation structure by 73% under the operating conditions of 120 W 10 kV. Partial discharge (PD) tests show that the partial discharge initial voltage (PDIV) of the substrates with NCM coating is increased by 33% compared with the normal encapsulation structure and the coating significantly inhibits the growth of electric trees. The presented results indicate that the NCMs have the potential to improve the insulation performance of high-voltage high-power IGBT modules.

Recently, the C₄F₇N/CO₂ mixture has been highly considered as a promising SF₆ alternative due to its low greenhouse effect and excellent electrical performance. Apart from its dielectric strength and arc-quenching capability, the decomposition characteristics of C₄F₇N/CO₂ also play an important role in its future applications in gas-insulated electrical equipment. Therefore, decomposition experiments of the C₄F₇N/CO₂ mixture were carried out under multiple AC discharge breakdowns by using a needle-to-plate electrode configuration. The compositions of the gas mixture before and after breakdowns were detected by using a gas chromatography-mass spectrometer. The results show that a trace amount of C₃HF₇ exists in the C₄F₇N product; the decomposition of the C₄F₇N/CO₂ mixture mainly produces CO, CF₄, CO₂, C₂F₄, C₂F₆, C₃F₈, CF₃CN, C₃F₆, C₄F₆, C₄F₁₀, C₂F₅CN, C₂N₂, HCN, C₂F₃CN, and HF. As the number of breakdowns increases, the content of most decomposition products increases significantly, while the content of C₃HF₇ decreases. The possible formation pathways of the decomposition products were determined, and the corresponding reaction enthalpies were calculated by quantum chemistry calculation. Relevant results not only reveal the decomposition characteristics of C₄F₇N/CO₂ under AC breakdowns but also help us to better understand the corresponding physicochemical mechanisms, which will provide a good reference for stable operation and safe maintenance in applications.

The perfluoronitrile C₄F₇N is considered a promising SF₆-alternative in high-voltage gas-insulated apparatus, thanks to its high dielectric strength and low global warming potential. However, a complete and consistent set of electron-neutral collision cross-sections of C₄F₇N is still lacking, which hinders relevant plasma modeling. In this contribution, the available electron-neutral collision cross-sections of C₄F₇N are first compiled and assessed. The initial cross-sections are adjusted iteratively by the electron swarm method to determine a complete and self-consistent cross-section set of C₄F₇N for the first time. The set is validated by a systematic comparison of electron swarm parameters between Boltzmann equation analysis and experimental measurements in pure C₄F₇N as well as C₄F₇N/N₂ and C₄F₇N/Ar mixtures. The proposed cross-section set of C₄F₇N will be made available to the community in the LXCat database. It will be of particular importance for applications with an emphasis on the discharge mechanisms of this novel gas.

A model is proposed to simulate the generation and propagation of the shock wave (SW) produced by underwater electrical wire explosion in microsecond timescale, with the assumption that the exploding wire instantly turns into uniform discharge plasma channel (DPC) after the onset of explosion. To describe the interaction between the DPC and the surrounding water medium, the initial temperature of DPC is obtained by fitting calculated pressures with experimental data, and the injected energy of DPC is provided by the measured discharge current after wire explosion. To attenuate the high frequency oscillations generated by the discretization, the method with the double artificial viscosity parameters is proposed to calculate the SW propagation characteristics, and the input parameter is the above-calculated DPC boundary trajectory. Based on the proposed model, the DPC and SW properties of an underwater copper wire explosion are analyzed. The results show that the estimated initial temperature of DPC is about 15 000 K, the attenuation of peak pressure can be characterized by a law of the radial propagation distance r to the power of −0.74, and the efficiency transferred from stored electrical energy to the exploding wire and the generated water flow are ∼71.5% and ∼10%, respectively.