On Calculating the Phase-to-Phase CFO of Overhead Transmission Lines Based on the Spatial Minimum Electric Field

A spatial approach for calculating phase-to-phase switching impulse critical flashover voltage of overhead transmission lines is implemented using the Fourier enhanced charge simulation method (FEnCSM). Cathode-directed leader and streamer characteristics are used in an engineering model of pre-breakdown conditions. Rather than identifying breakdown based on complete bridging of the air gap, the proposed method identifies breakdown based on the ability of the leader-streamer system to survive the region of minimum electric field between phase conductors. Use of the minimum field as a basis for identifying breakdown allows anode-directed negative streamers to be reasonably neglected. Combined with FEnCSM, the proposed approach enables explicit representation of phase bundle subconductors and avoids the electrode-specific geometric constants or gap factors common in existing methods. Results obtained with the method compare well to four independent sets of experimental data for phase-to-phase flashover from the literature. The method was developed to facilitate ongoing research into practical use of the electric field as a basis for unifying electrical studies in the design of overhead transmission lines, including HSIL and other novel configurations.