C ₅ F ₁₀ O has been widely studied as a great potential alternative gas to SF ₆ , a most potent industrial greenhouse gas that is predominantly used as an insulating medium in electrical equipment, due to its excellent insulation properties and environmental characteristics. Several experimental and theoretical attempts have been made and have obtained valuable results in the last five years. However, few researchers have thoroughly investigated the decomposition mechanism and the main decomposition pathways of the C ₅ F ₁₀ O/H ₂ O system, which are important for evaluating the insulating and environmental performance and providing guidance for engineering application. Herein, the decomposition characteristics and mechanism of C ₅ F ₁₀ O in the presence of moisture content was studied by density functional theory calculations. The main types of decomposition products with relatively high content have been summarized based on the evaluation of cleavage reactions and the influence of moisture. The electrical, environmental and safety performances of the primary products were analyzed. CF ₃ CFCF ₃ , CF ₃ CO, CF ₃ , OH and H radicals are the most primary particles formed by dissociation of C ₅ F ₁₀ O and H ₂ O. These particles may further convert into more than 20 kinds of relatively stable products, among which C ₄ F ₁₀ , C ₃ F ₈ , C ₆ F ₁₄ , C ₃ HF ₇ , C ₂ F ₆ and CO are primary ones. In addition, COF ₂ , CO ₂ , CO and C ₃ F ₆ can be used as components for estimating the degree of failures. The existence of H ₂ O has a negative impact on the insulation and environmental performance. In particular, trace water has a direct contribution to the production of highly toxic COF ₂ , CO and HF. Thus, it is necessary to strictly control the moisture and develop application standards before any industrial application of C ₅ F ₁₀ O in electrical equipment.

The reignition probability of switching overvoltage caused by vacuum circuit breaker (VCB) switching off shunt reactor (SR) in offshore wind farm (OWF) is studied. Firstly, a model of OWF is developed in the environment of electromagnetic transient program. According to the switching time of VCB, a current period is divided into non-reignition zone, reignition zone and current chopping zone. Based on the analysis of overvoltage mechanism, a method for calculating critical arcing time and reignition probability is proposed. Then, the effects of resistor-capacitor (RC) snubber on reignition probability are discussed. The capacitance of RC snubber is optimized based on switching dispersibility of VCB and critical arcing time, and a new structure of RC snubber is developed. Finally, the hybrid method of RC snubber with new structure and phase-controlled switching is presented to suppress the switching overvoltage. The results indicate that the method can eliminate the reignitions and weaken the impact of overvoltage on the insulation of power apparatus.

High-voltage insulated gate bipolar transistors (IGBTs), such as silicon carbide-based ones, are promising as wide bandgap power modules. However, current IGBT packaging methods are unsuitable for high-voltage applications due to excessive electric field stress, which increases the risk of partial discharge or electrical breakdown, compromising their insulating property; a new packaging solution is therefore needed. In this study, an integrated structure-material optimization strategy through the combination of the finite element method (FEM) and materials optimization is proposed to reduce the maximum electric field stress ( E _max ) at the triple junction, i.e., the interface of the ceramic substrate, the metal electrode, and the polymer-based encapsulation, of an IGBT. In epoxy resin encapsulation, it was determined that a symmetrical and chamfered electrode structure with a smooth transition at the triple junction reduces E _max from near 280 to 40 kV/mm at an operating voltage of 27.5 kV. Furthermore, when the permittivity of the substrate (AlN) and encapsulation materials (BaTiO ₃ -Resin composites) satisfy an optimal ratio, E _max can be further reduced to 34 kV/mm (a 15% decrease). These results indicate that the integrated structure-material optimization strategy effectively enhances the insulating property of high-voltage IGBTs.

Metal contamination in insulating oil is one of the main threats to the safe and reliable operation of oil-immersed equipment such as on-load tap changers. The mechanism analysis of metal ions’ influence on the discharge process of insulating oil is rarely involved in previous studies. Herein, the generation mechanism of metal ions and suspended particles is summarized first for subsequent modeling. Numerical models are constructed to simulate the streamer propagation in oil, considering the effect of two forms of metal contaminant. The dissociation source term of ionic compounds is introduced into the charge continuity equation to elucidate the impact of metal ions on streamer propagation. The results reveal that adding metal ions increases the overall speed of the streamer and decreases the maximum field intensity at the head of the steamer compared to pure oil conditions. Excessive ion concentration hinders the streamer’s development by creating the space charge shielding effect. Charge accumulation on the surface of suspended metal particles is the leading cause for the branching or turning of the streamer channel. The size, quantity of the metal particles, and the landing location will significantly affect the streamer propagation characteristics, e.g., the landing location on the surface of the metal particle will determine whether the subsequent branching streamer head can further develop. The results contribute to a better understanding of the influence of ionic and particulate metal contaminants on the microscopic discharge process in insulating oil.