| The rain flashover of outdoor insulators under extreme rainfall has become one of the serious hazards affecting the safe and stable operation of UHV and EHV transmission projects.Previous studies have shown that the rain flashover in substations mostly occurred in the insulators with dense sheds and large diameter,however,whose electrical insulation performances under extreme rainfall have not been comprehensively investigated.In this dissertation,the hollow porcelain insulators were taken as the test specimens.Through the artificial rain tests,the influences of different rain conditions and shed parameters on surface rainwater characteristics and flashover characteristics of the specimens were studied.The relationship was discussed thoroughly between the water droplets deformation and flashover characteristics.This work can provide technical supports for the insulator shed parameters design and the prevention of the rain flashover in extreme rainfall areas.Firstly,on the base of the existing research,the artificial rain tests method for the hollow porcelain insulator under extreme rainfall was formulated and the meaning of surface rainwater characteristics was defined.The parameters of water drops representing surface rainwater characteristics were proposed,including the initial diameter of water droplets,the initial velocity of water droplets and the deformation length of water droplets.Moreover,the specific measurement methods of the three parameters were also given.Secondly,surface rainwater characteristics tests were carried out under different rain conditions and shed parameters,and the photos of the surface raining of the hollow porcelain insulator under different conditions were taken.Then,through a lot of measurement and analysis work,the laws of characterization parameters of surface rainwater characteristics were obtained.The test results show that rainfall rate,shed spacing and shed overhang have significant influences on the characterization parameters,while the influences of rainwater conductivity is relatively slight.Thirdly,the rain flashover tests under extreme rainfall were conducted to study the influences of rain conditions and different shed parameters on flashover characteristics.The laws of rain flashover voltage with the rainfall rate,rainwater conductivity,pollution degree and shed parameters were obtained.Moreover,based on the results for surface rainwater characteristics tests,the influences of the water droplets deformation on the inter-shed discharge,discharge model and rain flashover voltage were especially analyzed.Finally,the influences of booster sheds on surface rainwater characteristics and flashover characteristics of the hollow porcelain insulator were studied through experiments under extreme rainfall,and the influence of water droplets on the electric field strength on the hollow porcelain insulator surface was studied through the electric field simulation.Then the reasons why booster sheds changed rain flashover voltage were analyzed.The test results show that rain flashover voltage can be significantly increased by booster sheds.Rain flashover voltage increases nonlinearly with the increase of the number of the booster sheds,which is related to the surface rainwater and arc characteristics changed by booster sheds. |
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