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The paper reports a tooth profile modification method of spur gear. After establishing a standardized mathematical model for optimized tooth profile and simulating meshing process with ANSYS finite element analysis, we obtained 625 groups of gear models with different modification parameters. The group with minimum transmission errors owns the optimal parameters. Genetic algorithm was adopted in the entire process for the purpose of reducing the variation of transmission errors in meshing process. The arc and parabolic modification were doing the same processing. After comparing the transmission errors fluctuation produced by the meshing process of gear of nonmodification with arc modification and parabolic modification, we found that the best modification effects of arc modification and parabolic modification were both reduced by 90%. The modification method makes the gear drive process more stable and efficient, and it is also promising in general application for gear drive.

Abstract. Flexible DC cable has been more and more extensive research, compared to the AC cable, the effect of space charge on the insulation failure of DC cable is more significant. This paper summarized three methods to improve the space charge of insulating materials, namely: nanopartice modification, grafting special functional group modification and blending modification, the analysis shows that nano-particle modification and grafting special functional group modification method are better than the blending modification method in improving the electrical properties of insulating material. This paper has also discussed mechanism of the three modification methods, the modification of nano-particles and the modification of grafting special functional groups both can form traps in the insulation materials, limit the movement of space charge, but two methods will be affected by the grafting rate and dispersion and these in not good to control in the actual production process. The difference is that the special functional groups will also play the role of charge donor, to increase the space charge. The presence of nano-particle size effect, resulting in easy agglomeration of polymer, and the two modified methods will be further verified in the development process of DC 500kVcable. IntroductionThe DC electricity transmission has the advantages of low loss, easy to non-synchronous interconnection with the power grid and good economy efficiency when transmitting high voltage electricity power in long-distance and with the technical problem of pulse width modulation (PWM) and voltage source converter solved. In addition, with the rise of wind energy, solar energy and other new energy generation, flexible DC transmission technology receives more and more attention, especially when the international energy Internet construction more and more in depth [1], But the research on space charge of HVDC cable is less than HVAC cable, DC cable is easier to accumulate space charge and eventually lead to distortion of local electric field [2], this is also the main cause of cable damage. This paper mainly introduces the influence of space charge on insulation of DC cable, the research progress of DC insulation material and the inhibition mechanism of space charge.

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