Research On Property And Protection Measures Of Contaminated Station Insulator's Heavy Rain Flashover

Good external insulation is needed to guarantee safe operation of equipment in power system,especially in special climatic conditions such as heavy rain,icing,high altitude,etc.Recently,there are several heavy rain flashover accidents occurred on station insulators because of improper shape design.Only creepage distance is considered and sheds spacing is too short,which can't meet the demand of heavy rain flashover protection.Therefore,heavy rain flashover tests are necessary for designing shape of insulator with better performance in both pollution and heavy rain flashover.Besides,measurements for heavy rain flashover protection are needed for station insulators with short sheds spacing.Thus,heavy rain flashover tests method,property and measurements of protection are three main parts of this article.Firstly,heavy rain flashover accidents occurred on station insulators are counted.The result shows that heavy rain flashover is mainly happened on large conical bushings with pollution on the surface.The accidents are mostly happened in rain season,and ESDD on the surface is low.Heavy rain flashover happens rapidly in minutes after raining.According to the analysis of accidents,polluted specimen and clean water are determined to simulate heavy rain flashover.Rain is started after applying voltage.Rainwater drops on the surface slantingly.The angle between rain direction and horizon is about 45°.Secondly,three kinds of hollow porcelain insulators with different average diameter are selected for heavy rain flashover tests.The formula between average diameter and heavy rain flashover voltage is obtained.The influence of average diameter on rain process is analyzed in the aspect of water sheltering.Two hollow porcelain insulators and two composite insulators with different shed spacing are chosen for heavy rain flashover tests under three different rainfalls.The influence of rainfall,shed spacing and material on heavy rain flashover voltage is summarized.It is shown that local arcs crossing several sheds may decrease heavy rain flashover voltage significantly.Recommended value of shed parameter is given according to test results and standards at last.Thirdly,heavy rain flashover tests are carried out on hollow porcelain insulators and bushings with different water-cut sheds The test results indicate that water-cut sheds on hollow porcelain insulators have little effect on improving heavy rain flashover voltage.Water-sheds raise heavy rain flashover voltage of bushing significantly,but increasing water-cut shed overhang or reducing shed spacing may not raise flashover voltage further.The effect of water-cut shed on raining is analyzed:one is protecting the sheds below from being wetted,two is cutting polluted water curtain from top of bushing,three is making electric arcs more average.The changes pattern of leakage currents in heavy rain flashover of hollow porcelain insulators and bushings are introduced,as well as peak value,end value and frequency distribution of leakage currents under different conditions.Finally,recommended value of water-cut shed parameter is given.