Study On Flashover Characteristics Of Suspension Insulators

The insulation degradation is an important factor leading to grid fault under icing or snow weather conditions.Although a large body of researches have been done on icing insulators,on the snow-covered insulators have been hardly considered.As for the researches on the flashover voltage of snow-covered insulators,lots of attentions are focused on the influence of snow parameters,only a few studies can be found on the contaminated surface of snow-covered insulators.However,the contamination of insulators is heavy at autumn and winter,and which would significantly affect the flashover performance.Therefore,deep researches on snow-covered insulator performance with contamination surface are necessary.In this paper,experiments on the contaminated suspension insulators under different snow conditions have been done based on the domestic and overseas researches.Our experiments are carried out in the large-scale multi-functional artificial climate chamber and Xuefengshan natural icing test station respectively.And combining the electric field simulation calculation and the snow flashover process to analyze the flashover performance.According to the experiments,it is found that the trend in the AC and DC flashover voltage of the snow-covered insulator is similar to icing and contaminated insulators,power-function declining with the increasing of salt deposit density(SDD).As for the insulators with the same degree of contamination covered by 10 mm snow,the flashover voltage of insulators covered by uneven snow is lower than that covered by even snow.In addition,with the increasing of contamination level,the gap between the two flashover voltages narrows and tends to zero.Under the same snow-covered conditions,the flashover voltages of unit creepage distances of insulators is different due to the different structure of the umbrella skirt,while the measured values under the DC negative voltages are lower than that under the AC ones.It is worthy of noticing that the flashover voltage declining rate under AC/DC voltage of composite insulators FXBW-35/70 is much higher than other five types of insulators,averagely up to 20%.Under the uneven snow condition,the flashover voltage of glass insulator LXY-70 decrease first and then increase with the snow thickness(snow thickness range: 5 to 30mm).However,things are different for the composite insulators FXBW-35/70,the flashover voltage decreases with the increasing of snow thickness.For glass insulator LXY-70 and LXAY-70,whether in the artificial snow or natural snow conditions,the flashover voltage of snow-covered increases with the snow thickness increasing when the snow thickness range from 10 mm to30mm.And the flashover voltage of natural snow-covered insulators is higher than that of simulated snow-covered insulators,but all the difference is less than 10%.Therefore the artificial snow-capping test method described in the paper can be used to simulate natural snow-capping test in laboratory.Through the analysis of the simulation results,it is showed that the surface electric field distribution of the insulator is related to the snow thickness and the relative permittivity of the snow accretion on the insulator surface.When the snow thickness range from 5mm to 10 mm,the surface electric field strength of the insulators increases with the increasing of the relative permittivity of snow accretion,but the appreciation is small.When the snow thickness reaches 20 mm and above,the surface electric field strength also increases along the relative permittivity increases,and the appreciation is greater.Furthermore,with the increasing of snow thickness,the appreciation is increasing.By observing the flashover process of composite insulator FXBW-35/70 under different thickness of snow,it is found that the snow thickness has a great influence on the snow flashover process,and with different thicknesses of snow the difference of the flashover process is obvious.When the snow correction is thin,the arc is mainly develops and forms flashover along the leeward side surface of snow-covered insulators.When the snow correction is thick,it is mainly through the upwind and the gaps between snow accretion.Based on the analysis of the simulation and the flashover process,the snow accretion affects the flashover process not only by affecting the distribution of the electric field along the surface of the insulator,but also by affecting the surface resistance of insulator through the capillary effect affect liquid water content.In summary,the insulator surface contamination,thickness of snow accretion,snow shape,insulator umbrella skirt structure,the voltage type affect the flashover voltage of the snow-covered insulator.The artificial snow-capping test method used in this paper can be used in laboratory simulation of natural snow flashover test.And the impact of snow accretion on the voltage gradient distribution of the insulator along the surface and its capillary effect on the surface resistance of the insulator have an important effect on the flashover performance of insulators.