Study On AC Flashover Performance Of Iced Insulators Connected With Alternately Large And Small Diameter Sheds

In recent years, many accidents caused by iced insulators flashover bring serious threat to the safe operation of electric power system. Although there are many researches on flashover characteristic of iced insulators at home and abroad, the study on anti-icing flashover measurement is less. People want to use"V"type string, PRTV-coated insulators and varied-size series connected string etc to improve the flashover voltage of iced insulator strings in practice. Because it does not change the tower structure of the transmission line, the string connected with alternately large and small diameter sheds(CALSDS) is suitable for the anti-icing reform of the lines which have already been build. So it has an important engineering application prospect.Based on the researching results carried at home and abroad, this paper focuses on following aspects in the large scale artificial climate chamber:â‘ The influence of the large insulators'assembled position on the iced-flashover voltage of CALSDS strings; The relationship between the flashover voltage of iced insulators and string length,SDD of insulators; The influence of potential distribution on the flashover voltage of CALSDS insulators; Analyzing the e-field distribution of the insulators by the e-field emulation;â‘¡The relationship between flashover voltage of the anti-icing composite insulators and SDD; Analyzing the e-field distribution of the anti-icing composite insulators by the e-field emulation;â‘¢Analyzing the difference of flashover procedure between normal insulators and CALSDS insulators; Discussing ice-flashover mechanics of the CALSDS insulators and the factor influence on its ice-flashover characteristic;â‘£Comparing the creepage gradient of the CALSDS strings with that of anti-icing composite insulators and analyzing the reasons caused the difference between them;Based on the test results and analysis, the main conclusions in the paper are as following:â‘ The diametrical difference between large and small shed and the space length of the adjacent large sheds are the important keys to improve the ice-flashover voltage of the CALSDS strings. With appropriate layout structure, the small sheds of insulators aren't liable to be bridged by icicles and the e-field strength of icicles will be reduced, then the possibility of arc along icicles'surface is be decreased. The large sheds aren't liable to be bridged by icicles too, and the air gaps between large sheds'icicles and small sheds aren't liable be broken down, so the leakage distance will be utilized sufficiently;â‘¡The relationship between the flashover voltage of CALSDS strings and its length is non-linearity and its ice-flashover voltage and creepage gradient always exceed the normal insulators in severe icing. The relationship between SDD and the flashover voltage of CALSDS insulators appears negative power function and its influence extent to CALSDS insulators is lower than to normal ones;â‘¢The arc of normal insulator extend along icicles'surface and it is only related with the arc distance of insulator. The arc of CALSDS insulators extend along its leakage distance. When the voltage reach to a certain degree, the air gaps between large sheds'icicles and small sheds are broken down, the arc path is altered and become the main discharge path along the air gap. Finally, with voltage raising the flashover will form.â‘£The creepage flashover gradient of anti-icing composite insulators is greater than that of glass CALSDS strings in slightly contaminative condition, but lower than that of glass CALSDS strings in moderate and severe contamination condition.