Hydrodynamics-based Structure Research Of Composite Insulators Shed In Iced Area

The existing structures of composite insulator are easily bridged by icicles and its ice flashover performance is not obviously superior than that of the glass and porcelain insulators in iced area. Icing has become the important constraint of composite insulators'application in iced area. Icing is the hydrodynamics process of supercooled water droplets impingement on composite insulator. Therefore, the hydrodynamic-based analysis of water droplet impingement characteristics of composite insulators with different structures can achieve a purpose of reasonable design and selection of composite insulators'shed structure in iced area.Because of complexity of 3-D flow field and water droplets movement around the composite insulator, it is very difficult to solve the problem using analytic method, and making experiments to study the impact properties of composite insulators is not only long, more funding and resources consumption, but by the measurement accuracy restrictions. So using computer simulation techniques to study the flow field around composite insulators and then optimize the structure of composite insulators can greatly shorten the development cycle, with a great value of project application.In this paper, based on the basic principles of fluid dynamics and physical characteristics of gas-liquid two-phase flow around composite insulators in ice weather, a suitable numerical simulation model and method was established, using standard k-εmodel and the particle trajectory model respectively for the continuous phase of air flow and discrete phase of water droplets. On this basis air flow and supercooled water droplets impingement on the surface of composite insulators was numerical calculated using a CFD software FLUENT. At the same time, the numerical simulation was certificated by artificial icing experimental results. Then the water-droplet impingement characteristics including droplet collision coefficient of composite insulators in icing process were determined. In addition, the effects of free stream velocity(V), median volumetric diameter(MVD) of water droplets, inclination, distance, diameter and diameter ratio of shed on water-droplet impingement characteristics were investigated, the following main conclusions can be drawn:①Composite insulators with different shed structures have different water droplets collision coefficients. Thus structure optimization of shed helps prevent icing.②The median volumetric diameter of water droplets and free stream velocity impact the icing characteristics of composite insulators. Water droplet collision coefficient, water droplet impact area and local water droplet collision coefficient on shed surface increase with increasing of MVD and V. It would cause even more serious icing on surfaces of composite insulator.③Water droplet collision coefficient decreases with the increasing of top surface inclination, and increases with the increasing of bottom surface inclination.④Water droplet collision coefficient decreases with increasing of diameter or diameter ratio of shed, which increasing of diameter ratio is the first factor. Compared to the diameter and diameter ratio of shed, the influence of shed distance on water droplet collision coefficient can be neglected.According to the results, based on the icing properties and integrated the electrical characteristics of composite insulators, suggestions of the optimized shed structures of composite insulators used in iced area was put forward:①Top surface inclination is 15°and bottom surface inclination is 0°;②Diameters of sheds are different, there should be more than three small sheds between adjacent large sheds, diameter ratio of sheds should be increased;③Shed distance should be more than 30mm.Finally, according to the above proposals, a new structure of composite insulators used in iced area was designed.The results of the research have an important reference value on the further analysis of composite insulators'icing characteristics and the design or application of composite insulators'shed structures in iced area.