Dynamic Deformation Of Pendant Water Drops At The Edge Of Hollow Procelain Insulator Sheds Under Extreme Rainfall And Its Effects On The Electric Field Between Sheds

For UHV/UHV AC/DC systems,insulators such as high voltage bushings in substations or converter stations are prone to confront flashover accidents under extreme rainfall,which brings great challenges to the safety of the power grid.Discharges of pendant water drops on the edge of high-voltage bushing play a key role in the process of rain flashovers.However,current researches ignore the influence of the dynamic deformation of pendant water drops on them.This paper takes a pendant water drop on the edge of a 500 kV hollow procelain insulator shed as the object.The dynamic deformation of the pendant water drop under different non-dimensional parameters and its effects on the electric field between the bushing sheds are studied by fluid-electric field coupling simulations.The main contents are as follows:(1)A fluid-electric field coupling simulation model was established.The fluid-electric field coupling simulation and the description of water droplet motion were realized by solving Navier-Stokes equations,electric field control equations,and level set equations.Comparing the simulation results under different maximum grid mesh sizes,the maximum grid mesh was determined.Based on this size,the interface thickness control parameter was determined by the sensitivity analysis.The reasonability of the simulation model was verified by comparing the results of the artificial rain experiment and the simulation.(2)In order to study the dynamic deformation of the pendant water drop,the fluid dimensionless numbers were introduced,and then the pendant water drop parameters and the electric field were nondimensionalized,respectively.Considering discharge phenomena between bushing sheds and a part of simulation results,the dynamic deformation parameters of pendant water drop were determined to be spatial parameters and temporal parameters,respectively.The variations of the spatial and temporal parameters under different dimensionless numbers were explored,and the influence of the breakup of pendant water drop on these parameters was revealed.(3)Based on the dynamic deformation of the pendant water drop,the influences of the variations of spatial and temporal parameters on the electric field between bushing sheds were explored.The influence of the spatial parameters and the dimensionless numbers on the maximum electric field between busing sheds at each moment is analyzed.The maximum length of the pendant water drop before breakup and the length of the pendant water drop corresponding to the global maximum electric field were compared,which provides a theoretical basis for the measurement of the length of the pendant water drop in the experiment.By establishing the maximum electric field model after the pendant water drop breaks up,the influence mechanism of the breakup of the pendant water drop and the dimensionless number were analyzed.The influence of the temporal parameters and the dimensionless numbers on the maximum electric field between bushing sheds was analyzed.The potential influence of the movement time of the separated water droplet on the direction of the global maximum electric field between bushing sheds was explored.(4)The influence of the dynamic deformation of the pendant water drop on the discharge between bushing sheds was explored.The remaining water drop and separated water droplet with positive and negative charges were approximately equivalent to a rod-plate electrode model,and then the breakdown of the air gap between the remaining water drop and the separated water droplet under different dimensionless numbers is analyzed.Three typical positions of discharges between bushing sheds are obtained through the experiment,which is consistent with the maximum electric field position.The relationship between the discharge induced by pendant water drops and rain flash was explored.Inhibiting the breakup of pendant water drops may provide a solution to discharges between hollow porcelain insulator sheds and rain flashovers.