Study On AC Flashover Model Based On Arc Performances Of Ice Cylinder And AC Ice Flashover Performances Of Insulators

Icing has a serious influence on the electrical external insulation performances of insulator strings.For this reason,the scholars at home and abroad have conducted a lot of research on the AC arc performances of ice surface,mathematical models and AC flashover performances of artificial iced insulators.However,the arc length they studied is relatively short,and the study of AC flashover performances of natural iced insulators is not systematic.With the support of the National Natural Science Foundation of China and combined with the construction requirements of the national ultra-high voltage transmission project,this paper systematically carried out the study of AC arc performances with different arc lengths(10～60 cm)in a large multi-functional artificial climate chamber.Research on the AC discharge process of natural iced suspension insulators(porcelain,glass and composite insulators)and post insulators was carried out at the Xuefeng mountain Observatory for power equipment safety of Education Ministry.Based on the test results of AC arc volt-ampere performances and reignition performances on ice surface and the AC flashover test phenomenon of natural iced insulators,an AC flashover model of iced insulators was established.Combined with the test results of AC flashover performances of natural iced insulators,the flashover model is tested and verified.The main work of the paper is as follows:(1)The AC discharge process of a natural iced insulator(LXY-210)was photographed by a high-speed camera,which can be divided into an unstable development stage and a stable development stage.The phenomenon of arc drift and arc connecting together with different points during the arc development process is analyzed.The relationship between the length of the AC arc in the stable development stage of the AC arc of the iced insulator,the upward development speed of partial arc on the low-voltage end,the downward development speed of partial arc on the high-voltage end and the time are studied.It is found that the critical length of arc is between 62.6%*H～64.6%*H.When it is less than the critical arc length,the speed is basically less than 4.8 m/s.When the critical arc length is reached,the speed increases sharply to 70.67 m/s and above.(2)In this paper,a physical model of rectangular plate ice and ice cylinder is designed,the rectangular plate ice and ice cylinder samples are compared through experiments.The results show that ice cylinders are ideal samples for the arc performance test of ice surface.At the same time,this paper analyzes the alternating light and dark changes of the AC arc on the ice surface,the arc foot distribution on the ice surface and the multi-arc foot phenomenon of a single arc.It was found that the arc foot bifurcation always exists on the ice surface,and the multi-arc foot phenomenon of a single arc is a transitional state.(3)An ice cylinder(length 200 cm,diameter 40 cm)AC arc performances test platform was built,and the AC arc volt-ampere performances and reignition performances of ice surfaces with different lengths(10,20,30,40,50 and 60 cm)were experimentally studied.The result reveals how the volt-ampere performances and reignition performances of the AC arc on the ice surface changes with the length of partial arc.(4)An ice surface AC arc spectroscopy test platform was built to test the spectrum performance of the ice surface AC arc.In this paper,the excitation temperature has been calculated by the relative intensity method,the relationship between the intensity ratio of the two peaks of the OH group and the rotation temperature is used to obtain the rotation temperature of ice surface AC arc,and the Hα(656 nm)spectrum is used to calculate the electron density of the ice surface AC arc plasma.The relationship between the excitation temperature,rotation temperature,electron density of the AC arc on the ice surface and the peak value of the leakage current are found.(5)Based on the natural ice AC flashover test and the performances test of rectangular plate ice arc,it is found that there is a melted water-film on the surface of ice layer in contact with the insulator during the discharge process of the iced insulator.The calculation methods of the residual resistance of ice layer in contact with the insulator and the residual resistance of ice layer in contact with air are respectively given.A residual resistance model of ice layer for iced insulators has been proposed,and the residual resistance of ice layer of lightly iced and semi-cylindrical iced insulators have been analyzed.Based on the volt-ampere performance constants and reignition performance constants obtained by the tests,a mathematical model of AC flashover of iced insulators has been established,the critical flashover criterion of AC arc of iced insulators and AC arc development criteria have also been proposed.(6)A systematic experimental study on the AC ice flashover performances of 11 natural iced insulators was carried out at the Xuefeng mountain Observatory for power equipment safety of Education Ministry.The AC ice flashover voltage of insulators with string lengths up to 13 pieces is obtained with the change of SDD,ice thickness,ice amount and ISP.It is proved theoretically and experimentally that the ice flashover voltage has a power function relationship with SDD.The AC flashover voltage test results of natural ice and artificial ice insulators are compared,and the ratio of AC flashover voltage of natural and artificial iced insulators is in the range of 1.07～1.27.Based on the AC flashover test results of 7 and 13 semi-cylindrical iced insulators,the model has been tested and verified.The research results showed that the maximum relative errors between the test results and calculation results of the model are 12.6%and 8.3%,respectively.