Study On The Flashover Performance Of Ice-covered Cylindrical Insulator And The Electric Field Calculation

The presence of atmospheric ice and snow accretion on overhead transmission lines is still a serious threat to the safe operation of a power transmission system. Despite the extensive investigations are carried out on icing flashover performance and characteristic, the flashover mechanism of ice-covered insulator is not well understood and most scholars only agree that ice is a particular type of contamination. Since the development of arc on an insulator covered with ice, including arc inception, propagation and final flashover, is closely related with the distributions of potential and electric field along the insulator, this thesis focuses on the study of icing flashover characteristics and mechanism on the base of a cylindrical insulator, without considering actual insulator configuration and icicles on the sheds caused by atmospheric ice and snow accretion.Major influencing factors of ice-covered insulator flashover voltage are investigated in the artificial climate chamber of low temperature and low pressure, based on a series of AC flashover experiments. The whole discharge process of ice-covered insulator is recorded by the camera technique at the same time, for the purpose of analyzing the formation and possible propagation of partial arc. In addition, arc propagation velocity during the flashover process is also obtained in this thesis. Electric field calculation model of cylindrical insulator is established using commercial FEM software, COMSOL Multiphysics? in order to investigate electric field distributions along the insulator before/after partial arc inception and analyze the interaction between partial arc development and electric field. Calculation results are compared with test results of AC flashover experiments, as well as measured results of insulator surface potential, to verify the reliability and accuracy of electric field calculation method.Through experimental investigation and simulation, the following conclusions are obtained in this thesis.AC flashover performance and discharge process of ice-covered insulator indicate that flashover voltage is linearly correlated with the length of ice free zone; flashover voltage is influenced by the position of ice free zone, whereas applied water conductivity plays a leading role in the flashover voltage with the aggravation of ice layer pollution degree; as applied water conductivity rises, the distortions of potential and electric field are more obvious; the highly conductive water film and the presence of ice free zone are key factors to change the potential distribution along the cylindrical insulator, which can lead to the different initial position of partial arc and the different discharge path; during various stage of the arc development, the propagation velocities and states of outer and inner arc are also different.According to the electric field calculation before partial arc inception, the characteristic of weak normal electric field component is changed by the ice layer. However, when ice free zone exists on the the surface of insulator, axial electric field component makes predominant contribution to the inception of partial arc.According to the electric field calculation after partial arc inception, electric field strength near arc root is greatest during the development of partial arc. At the first stage, electric field strength near arc root changes from high to slightly low, then low to high. At the second stage, when the length of partial arc reaches 60 % of insulator leakage distance, electric field strength in the front of arc root and along the residual ice layer both increase considerably.