Fluorinated nitrile (C 4 F 7 N) gas mixture has been introduced as the most promising candidate to replace sulfur hexafluoride using in gas-insulated equipment. In this study, the authors explored the influence of oxygen on the dielectric and decomposition properties of C 4 F 7 N-CO 2-O 2 gas mixture. The authors found that the dielectric strength of the C 4 F 7 N-CO 2-O 2 gas mixture with 2, 4, 6, 8 and 10% O 2 was increased by 4.85%, 6.49%, 7.70%, 3.21% and 2.74% compared with C 4 F 7 N-CO 2. The addition of 2-6% O 2 to the C 4 F 7 N-CO 2 gas mixture could effectively reduce the content of most of the decomposition byproducts such as CF 4 , CO, C 2 F 6 , C 3 F 6 , C 3 F 8 , CF 3 CN, C 2 F 5 CN, (CN) 2. While high content of oxygen (>6%) results in higher decomposition of C 4 F 7 N, which has a negative effect on the stability of C 4 F 7 N gas mixture. Generally, it is recommended to add 2-6% O 2 in the C 4 F 7 N-CO 2 gas mixture to improve its insulation properties as well as inhibit the decomposition of C 4 F 7 N in the discharge for medium-voltage engineering application.

Sulfur hexafluoride (SF 6 ), one of the most potent greenhouse gases with a global warming potential of 23 500 and an atmospheric lifetime of 3200 years, has been widely used as an insulating gas. The search for eco-friendly gas insulating medium to replace SF 6 has been a hot topic in the power industry over the past 5 years. The performance evaluation of eco-friendly gas insulating medium concentrates on several dimensions including stability and decomposition characteristics. This review focuses on recent advances in knowledge about the decomposition characteristics of eco-friendly gas insulating medium. The basic theoretical and experimental methods, discharge decomposition, thermal stability and gas-solid interface interaction properties of several potential eco-friendly gas insulating medium are summarized. The existing problems and future research directions are also discussed.

As the fossil energy crisis and environmental pollution become more and more serious, clean renewable energy becomes the inevitable choice of energy structure adjustment. The power system planning and operation has been greatly influenced by the instability of the power output of distributed renewable energy systems such as solar energy and wind energy. The hybrid energy storage system composed of accumulator and supercapacitor can solve the above problems. Based on the analysis of the energy storage requirements for the stable operation of the DC microgrid, battery–supercapacitor cascade approach is adopted to form hybrid energy storage system, in a single hybrid energy storage subsystem for battery and supercapacitor and in the microgrid system of different hybrid energy storage subsystem, respectively, and puts forward the corresponding power allocation method to realize the smooth control of the battery current, to reduce the battery charge and discharge times, to prolong the service life of battery and to improve the running stability of the microgrid.

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