Review of the decomposition characteristics of eco-friendly insulation gas

As one of the major concerns of climate change,identifying a proper eco‐friendly insulation gas for replacing sulphur hexafluoride(SF_(6))becomes a prominent research topic in recent years.c-C_(4)F_(8),CF_(3)I,C_(5)F_(10O),C_(6)F_(12O)and C4F7N are some potential al-ternatives that are proved to have excellent characteristics,including high insulation strengths and low Global Warming Potentials(GWPs).Beyond these key factors,the decomposition products of these alternatives are closely related to the gases'insulation performance,as well as the safety of operators and the compatibility with other materials.In addition,the type and content of decomposition products can be used for fault diagnosis.Therefore,a number of studies were carried out to reveal the decomposition mechanism of these alternative gases,and then to explore the gases'application feasibility and strategy.The recent advances obtained in these studies,including theoretical calcu-lation methods,detection of gas decomposition products,decomposition mechanism are reviewed,and some perspectives for future works are proposed.It is concluded that the phenomenon of solid matter precipitation in c-C_(4)F_(8)and CF_(3)I gas decomposition cannot be ignored and that more research is needed to reveal the influence of buffer gases,micro‐aerobic,micro‐water and other impurities on the gas decomposition process.

Influence of micro-water on AC breakdown characteristics of C_(4)F_(7)N/CO_(2)gas mixture under non-uniform electric field

The application of eco-friendly C_(4)F_(7)N/CO_(2)gas mixture has become a hot topic in the power industry.To obtain the influence law of micro-water on the AC insulation characteristics of C_(4)F_(7)N/CO_(2)gas mixture,breakdown tests were carried out under different non-uniform electric fields and micro-water volume fractions.With the gap distance of 1 mm and the electric field non-uniform coefficient less than 4.42,the breakdown voltage is positively correlated with gas pressure.With the gap distance of 6 mm and the electric field non-uniform coefficient of 9.28,the breakdown voltage shows a typical N-type change trend with the increase of gas pressure.With the gap distance of 9 mm and the electric field non-uniform coefficient up to 16.45,the breakdown voltage shows a typical N-type change trend with the increase of gas pressure.Micro-water has a negative effect on breakdown voltage under different electric fields,meanwhile the breakdown voltage of slightly non-uniform electric field is greatly affected by micro-water,and the influence of micro-water on breakdown voltage is different under different gas pressures.Therefore,the influence of operating gas pressure and slightly non-uniform electric field should be considered when the micro-water control index of C_(4)F_(7)N/CO_(2)gas mixture insulated equipment is formulated.

Research on key technologies in±1100 kV ultra-high voltage DC transmission

Based on completely mastering±800 kV transmission technologies,the first±1100 kV direct current(DC)transmission demonstration project is being constructed in China.Combining theoretical analysis and a large number of experiments,the margin of switching overvoltage in converter stations,the configuration scheme and performance of lightning arresters,the shielding angles of ground lines under different geographical conditions,and the maximum air gap of lines have been determined.The switching impulse flashover characteristics of equipotential sphere and typical rod-plane air gaps are also provided.The external insulation is designed differently for light,medium,and heavy pollution areas.For the±1100 kV project,if the 8×1250 mm^(2)conductors are applied,the pole gap is 26 m and the height of the line is 25 m,all the electromagnetic parameters will meet the requirement of international electromagnetic standards.The key design points of±1100 kV converter transformers,smoothing reactors,converter valves,and wall bushings are researched and the 75 mH smoothing reactors,±1100 kV/5000 A converter valves,and±1100 kV/5523 A wall bushings are successfully made.The optimised hierarchical connection modes and coordination control measure of the±1100 kV project are studied and the results can provide sufficient technical support for the demonstration project.