Deformation Of Water Drops On Sheds Edge Of Large Diameter Composite Post Insulator And Optimization Of Sheds Parameters

The flashover of large diameter composite post insulator caused by heavy rainfall seriously threatens the safe and stable operation of UHV DC projects.At present,there are few related reports on flashover of large-diameter composite post insulators in rain conditions,and water drops deformation on sheds edge of insulator closely related to discharge.The influence mechanism of various factors on flashover voltage is not sufficient,and the structural parameters of the large diameter composite post insulator in heavy rainfall area need to be further optimized.Based on the National Engineering Laboratory of UHV Engineering Technology(Kunming),this paper takes the large diameter composite post insulator as the test sample to obtain the deformation characteristics of water drops on the sheds edge and optimize the parameters of sheds.A series of critical questions such as parameter characterization,test methods,simulation analysis,rain flashover characteristics,discharge theory analysis,sheds optimization,and protective measures of large diameter composite post insulators under rain are carried out systematically.The main contents are as follows:1)The characteristic parameters describing the water drops on sheds edge and the dynamic deformation of water drops under rain conditions,such as the initial diameter of water drops,the initial mass flow rate of water drops,and the maximum length of water drop deformation are defined,and the measurement method of the water drops characteristic parameters on sheds edge is proposed.Based on the characteristics of heavy rainfall,the methods of applying voltage and stain,salt ash and gelatin concentration,the repeatability and reproducibility of the artificial rain test results were studied,which formed a rain test method for the large diameter composite post insulator finally.2)The Navier-Stokes equation and the level set method are used to establish a coupling simulation model of the fluid-electric field to describe the water drops deformation.The difference between simulation calculation and artificial rain test is compared to prove the simulation method’s accuracy.The water drops parameters,such as initial diameter,initial mass flow rate,water drops’ conductivity,and electric field,are systematically studied.Besides,an analysis model of water drops’ internal and external pressure was established,revealing the water drops on the sheds edge deformation mechanism.3)Through the artificial rain test of large diameter composite post insulators,the influence of sheds structure parameters and environmental parameters on water drops parameters and dynamic deformation were systematically studied,and the influence rules of shed spacing,shed extension,rod diameter,shed structure,DC voltage,water drops’ conductivity and rain rate on water drops parameters and deformation parameters are obtained.The phenomena are explained,and the main factors determining the deformation length of water drops are found.4)The optimization of the shed parameters of composite post insulators was carried out by conducting a number of artificial rain flashover tests on more than 20 large diameter composite post insulators with different shed parameters under two typical umbrella-shaped combinations based on the controlled variable method.The influence of shed spacing,shed extension,shed extension difference,pole diameter,and shed structure on the rain flashover voltage of insulators are obtained.Based on the experimental results and theoretical analysis,the optimized shed parameters of a large diameter composite post insulator are proposed,which were applied in insulation design of converter stations for UHV DC projects such as Kunlulong and Lugaozhao.5)An artificial rain test was carried out on the composite post insulator with optimized parameters.The influence of various factors,such as rainfall intensity,surface pollution,rainfall angle,and booster shed on rain flashover was obtained.The optimized number and installation position of booster sheds were put forward.Combining theoretical analysis with the experimental phenomenon,the influence mechanisms of large diameter composite post insulators under shed structure parameters and environment parameters were discussed.The influences of the shed structure parameters on the rain flashover voltages were explained based on the deformation of water drops.