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.

A new method of preparing the pseudo-pure state of a spin system for quantum computation in liquid nuclear magnetic resonance (NMR) was put forward and demonstrated experimentally. Applying appropriately connected line-selective pulses simultaneously and a field gradient pulse techniques we acquired straightforwardly all pseudo-pure states for two qubits in a single experiment much efficiently. The signal intensity with the pseudo-pure state prepared in this way is the same as that of temporal averaging. Our method is suitable for the system with arbitrary numbers of qubits. As an example of application, a highly structured search algorithm--Hogg's algorithm was also performed on the pseudo-pure state | 00 prepared by our method.

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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 10 O, C 6 F 12 O and C 4 F 7 N are some potential alternatives 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 calculation 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, microaerobic, micro-water and other impurities on the gas decomposition process.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.