Effect of Electric Field Along the Surface on the Flashover Voltage of GIS Insulators

To clarify the effects of field strength components on the insulators flashover voltage, 48 kinds of epoxy resin post insulators with different surface field strength distribution were cast as samples, and their flashover voltages under the standard lightning impulse were tested. According to the insulator surface electric field distribution results, which was calculated by finite element method, the relationships between maximum synthetic electric field (Emax), tangential electric field strength (Etmax) and normal electric field strength (Enmax) with flashover voltage Uf were obtained. The results show that the correlation coefficient between Emax, Etmax, and Enmax and Uf are -0.90, -0.84, and -0.73, respectively. According to the theoretical analysis of gas discharge, it is concluded that Emax is the most important factor affecting the initiation of flashover discharge along the insulator surface and the transition of discharge mode, while Etmax is the secondary factor affecting the development of flashover along the insulator surface. According to the analysis of the connection condition of the electrostatic field at the gas-solid interface, it can be seen that reducing the Enmax by changing the shape of the insulator and the electrode structure can effectively reduce the Emax along the surface, and can effectively restrain the accumulation of the surface charge of the insulator. Therefore, it is suggested that the synthetic electric field strength along the surface, its tangential and normal field strength should all be included in the design specification of the insulator electric field. © 2020, High Voltage Engineering Editorial Department of CEPRI. All right reserved.