The environmental problems caused by greenhouse gases have received unprecedented attention. Sulfur hexafluoride (SF6), 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 SF6-alternative gases is presented in the paper. The review focuses on the application of the SF6-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.

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.

This paper investigates the dielectric breakdown properties of humid air, taking into account ion kinetics. Initially, an overall kinetic scheme that includes all the main reactions likely to happen in humid air is established for the first time. Then, the calculation method of dielectric properties is improved, based on more comprehensive avalanche model considering both spatial growth and temporal processes. Better consistency between present results and experimental values confirms the validity of the improved method and kinetic schemes. Finally, the effective ionization Townsend coefficients αeff in humid air at different humidity and gas pressures are calculated and analyzed considering ion kinetics. Reduced critical electric field strength (E/N)cr can be determined when αeff  =  0. The results show that (E/N)cr in humid air increases sharply in the beginning and then tends to be constant with the humidity rises. Besides, the mechanism of humidity’s effect on dielectric breakdown properties is well explained: at relatively low E/N, αeff decreases with the increase of humidity mainly due to more frequent three-body conversions, while at higher E/N, the main reason is the increased number of attachment reactions.

This paper focuses on the numerical investigation of low-voltage arc plasma behaviour with the contact opening process included. A flexible experimental setup with a rotating contact is designed to support this study. Based on the magnetohydrodynamic arc model, the elongation and the commutation behaviour of the arc plasma during the contact rotation progress are simulated. Under the given conditions of the external magnetic field and the contact rotating velocity, the arc motion is described in detail by the temperature distribution. The stagnation together with the following rapid jump of two arc roots is observed by both calculation and experiment. The rapid rise in the arc voltage is mainly caused by the increasing difference between the two arc roots displacement in the moving direction, and the jump instant of the arc root on the moving contact is according to the moment of the maximal voltage value.

In order to ensure the safety and economy of nuclear industry production, the analysis of nuclear materials and other materials used in nuclear industry environments are usually required before and during their installation and utilization, and after service. The advantages of laser-induced breakdown spectroscopy (LIBS), such as sample preparation not being required and in situ remote analysis, make it an efficient method for the analysis of hazardous samples and samples in remotely accessible or hazardous environments. The nuclear industry has become one of the fast-growing fields of LIBS application. In this review, the feasibility of LIBS in the nuclear industry is summarized from the aspects of the physical fundamentals of plasma, instrumentation, spectral analysis, and application progress. The radiation characteristics of LIBS and spectral lines of interest are discussed, along with the main influencing factors and spectral enhancement methods. LIBS instruments and spectral analysis methods used for identification are then presented, and qualitative and quantitative analysis. The various applications of LIBS in the nuclear industry and in fusion facilities are described, including the analysis of nuclear materials, isotopes, and steels and alloys. Finally, the challenges currently being encountered by LIBS applications and its potential development direction are considered.