Study On Electrical Characteristics Of Ice-covered Insulators Based On Improved DC Discharge Model

The research of DC high-voltage long-distance transmission is very worthy since it can effectively reduce the transmission loss.As the weakest section in the high-voltage transmission lines,DC ice-covered insulators are more likely to have flashover accidents than AC ice-covered insulators.Therefore,the study of the electrical characteristics of DC ice-covered insulators is significantly meaningful of finding ways to prevent the insulators from ice flashover.The flashover voltage is an important parameter to reflect the performance of the insulator against ice-covered flashover.Circuit method used in the traditional algorithm to calculate the ice resistance for the flashover voltage calculating is rough,and is unable to consider the influence of the ice-covered structure on the flashover voltage of the insulators.In this article,based on the dynamic DC arc partial discharge model,a new improved DC algorithm is proposed.The field-path coupling method is adopted in the improved algorithm which uses the three-dimensional current field finite element algorithm for field calculation,then coupled local arc circuit calculation mathematical formula,the dynamic local arc development,and the flashover criterion.The voltage drop of the irregular ice structure can be calculated with high calculation efficiency and precision,so the method can be used for the calculation of the flashover voltage of the insulator under complex ice-covered structure condition.The comparison between case calculation and the experimental results proves that the algorithm has high accuracy.Based on this algorithm,the partial discharge characteristics of DC-covered insulators before flashover has been calculated,and an experimental platform is built.The effects of partial discharge before flashover on the flashover of ice-covered insulators have been verified from both experiments and simulations.Meanwhile,the effects of effective creepage distance on the flashover voltage of ice-covered insulator,the number of local arc roots,the relationship between conductivity of icing water and the polarity of the power supply,along with the flashover of the ice-covered insulator,are analyzed.The calculation results show that there are two main reasons for the change of insulator flashover voltage caused by ice coating.One is that the ice surface resistance is reduced due to the conductive effect of the water film on the surface of the insulator ice structure.The second is that the local arc is generated to shorten the length of the remaining ice structure.The combination of the two situations causes the residual resistance decreasing,and the leakage current generated by the partial discharge increaseing,thereby making the air on the surface of the ice structure to form a conductive path of the plasma state,and finally developing into a flashover.The effective creepage distance is basically proportional to the flashover voltage of the ice-covered insulator.When the arc length,structure and the water film conductivity does not change,the flashover voltage of the ice-covered insulator will increase with the increase of the local arc number;the relationship between the DC-transfer polarity and the flashover voltage is greatly affected by the creepage distance and the number of air gaps.According to the previous simulation and experimental conclusions,the shed structure of FXBW4 insulator is improved in this article to increase its anti-ice flash performance.The calculation of the flashover voltage of the improved structure and the unmodified structure under the same icing condition using an improved mathematical model shows that the improved structure can increase the flashover voltage of this type effectively.The improved calculation method proposed here to predict flashover voltage of ice covered insulator has a high accuracy and wide application.The anti-icing design concept of the insulator which has been proposed on the method can effectively improve the anti-ice performance of the insulator and has potential prospect of engineering application.