Growth Mechanism And Experimental Study On Icicle Of Transmission Line

Transmission line icing is a highly hazardous natural phenomenon to power grid safety.The severe ice load,dynamic aspects(mechanical traveling waves),and insulation deterioration have provoked a number of serious problems,such as flashover,structural failure,and even breakdown of the electricity grid.As a special phenomenon of line icing,the growth of icicle increases the load of transmission lines,increases the probability of transmission line accidents,and greatly reduces the electrical gap between insulators,tower fittings,and other facilities,resulting in the decrease of insulation performance.Icicle growth model is the foundation of studying on its growth characteristics,which have important theoretical significance and engineering application value for improving the safety of transmission lines.The core content of icicle growth model is the supply of supercooled droplets and the calculation of icicle surface heat exchange.In this paper,the growth mechanism and characteristics of icicle are studied by numerical calculation and experimental method on the basis of the parameters of the supply of supercooled droplets and convection heat transfer on the surface of icicle.Firstly,the dimensionless expression of the growth of icicle in radial direction and longitudinal direction are obtained according to the principle of mass conservation and conservation of heat on the assumption that the supply of supercooled liquid drops at a unit time is a constant.Based on the mathematical model,the growth conditions and characteristics of ice edge icing in the early stage,middle period and critical length were analyzed.The calculation of heat exchange on the surface of icicle is an important parameter for icicle growth model.However,it is difficult to reflect the local thermal dissipation characteristics of icicle growth while most of the traditional empirical formulas replacing icicle with a single smooth cylinder,which can not express the influence of icing line and between the icicles when the real icicle is formatted.In this paper,the heat balance equation of icicle growth is established,and it is found that the convective heat transfer coefficient is the key factor to calculate the heat exchange.Then a hydrodynamics method for solving the convection heat transfer coefficient of icicle is proposed especially for the conical icicle structure under the influence of icing conductor and parallel icicle,which is difficult to calculate by traditional empirical formula.The convective heat transfer characteristics of the multi icicle structure at different icing line thickness and different growth conditions of icicle were obtainedFinally,an experimental platform of artificial climate chamber ice coating was set up,and an experimental measurement method of convection heat transfer coefficient on icicle surface was put forward.It is verified that the calculation of convective heat transfer coefficient on the icicle surface by using the fluid dynamics simulation method is more accurate.The experimental study on growth of icicle was carried out,and the results were as follows: in a certain range,the greater the wind speed,the higher the icicle growth efficiency.When the temperature of the environment is close to 0 degrees Celsius,the supercooled liquid drops are not easy to freeze,and the icicle is limited in the longitudinal and radial growth,forming a small ice edge.Icicle is not easy to form when the supply of supercooled liquid drops is insufficient.