| The probability of encountering ice and snow disaster on the DC transmission line is very high in high altitude,snow and ice area.Composite insulators have been widely used in DC high voltage transmission system because of their advantages of light weight,high mechanism strength,excellent resistance to pollution flashover and less maintenance.However,a large number of test results and operation experience show that the anti-icing performance of composite insulators is not excellent.Hydrophobic coatings have effect on anti-icing in the early stage of icing.But anti-icing effect of coatings is no longer obvious with the increase of icing time.Therefore,it is of great academic significance and engineering application value to use electrothermal coatings to prevent icing.However,there is no research on the application of electrothermal coatings to composite insulators yet.And there is also no discussion about the layout method of electrothermal coatings for composite insulators,the anti-icing effect and pollution flashover characteristics after coating.The main work and achievements are as follows:(1)Based on the theory of heat transfer,the heat transfer balance model of short composite insulators was established.The threshold anti-icing power and current needed were calculated,and the influencing factors were summarized.The threshold anti-icing power of short composite insulators is between 0~136.84W,and the threshold anti-icing current is between 0~4.15mA.The ambient temperature and wind speed have a significant influence on the threshold anti-icing power and current,and MVD has little influence.And based on the circuit theory,the calculation method of the electric power of the composite insulators was proposed.The range of the volume resistivity of the electrothermal coating for anti-icing was calculated.The resistivity of the electrothermal coating is between 1.23×10~5Ω·cm and 2.07×10~6Ω·cm.(2)The effect of electrothermal coating on the potential and electric field of composite insulators was analyzed by the finite element software.The electric electric coating will distort the electric field along the surface.The degree of distortion is related to the number of the blanks and the thickness of the coating.The more the number of blank areas,the more distortion points along the surface electric field,but the smaller the maximum distortion,and the weaker the change degree of the potential distribution.The larger the thickness of the coating,the smaller the maximum distortion along the surface electric field.(3)The electrothermal coating was based on RTV silicone rubber.Graphite powder was as filler.KH550 was as coupling agent.TEOS was as crosslinking agent and DBTD was as catalyst.The electrothermal coating was prepared by mechanical mixing.The graphite content has little effect on the hydrophobicity and self cleaning property of the coating.With the increase of graphite mass percentage,the electrical conductivity of the coating presents three different stages.The first stage is a stable non-conductive stage,and the second stage is a rapid increase in electrical conductivity.The third stage is conductive and relatively stable.(4)There is a contradiction between anti-icing performance and insulation safety performance of composite insulators with electrothermal coating.The composite insulators coated with 20%,23%and 25%electrothermal coatings have anti-icing performance.The anti-icing effect increases with the decrease of the coating resistance.However,the DC flashover voltage of the composite insulators decreases significantly with the electrothermal coating on the surface of the composite insulators.The smaller the coating resistance,the better the anti-icing effect,but the worse the safety performance.Otherwise,the larger the coating resistance,the better the safety performance,but the worse the anti icing effect.Considering the insulation safety performance of insulators,it is difficult to achieve the method of using electric heating coating to anti-icing. |
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