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The non-uniform distribution of contamination on insulator surface has appreciable effects on flashover voltage, and corresponding researches are valuable for the better selection of outdoor insulation. In this paper, two typical types of porcelain and glass insulators which are widely used in ac lines were taken as the research subjects, and their corrections of AC flashover voltage under nonuniform pollution were studied. Besides, their flashover characteristics under different ratio (T/B) of top to bottom surface salt deposit density (SDD) were investigated, including the analysis of flashover voltage, surface pollution layer conductivity and critical leakage current. Test results gave the modified formulas for predicting flashover voltage of the two samples, which can be directly applied in the transmission line design. Also, the analysis delivered that, the basic reason why the flashover voltage increases with the decrease of T/B, is due to the decrease of equivalent surface conductivity of the whole surface and the decrease of critical leakage current. This research will be of certain value in providing references for outdoor insulation selection, as well as in proposing more information for revealing pollution flashover mechanism.

There are three systems and applications of fuel cells in China, namely transportation fuel cells, stationary systems and portable fuel cells. It is important for China to analyze the supply and the cost of fuel cells in the context of the energy crisis. After introducing the current situation of three systems, this article classified the existing policies, and made some analysis of the policy effects. Then a PEST–SWOT model was employed to summarize the strengths and weaknesses for fuel cells. Considering the own features of the three applications, different development strategies were put forward. Based on the above strategies, some conclusions were drawn about the development direction and framework of whole fuel cell systems in China. Finally, we proposed some prospects and suggestions on the fuel cell systems.

Pollution deposition of insulators may lead to flashover, and the factors affect it should be studied to better prevent the occurrence of pollution-induced flashover. In this paper, by taking XP-70 insulator as the sample, the software FLUENT was used to simulate the airflow field distribution as well as the particle collision coefficient (P) around insulator string. At the same time, a natural contamination test lasted for 20 months was carried out in the natural contamination site. The test results indicate that: wind velocity affects the air flow field near the surface of insulator; the particle collision coefficient (P) is affected by particle diameter and wind velocity; there is certain comparability between the simulation test and natural contamination test. Research results may not only give new thoughts for the establishment of insulator contamination model, but also provide references for the design of external insulation configuration.