Assessing the impact of the Corona effect on the lightning response of transmission lines using the Time Domain Hybrid Electromagnetic Model (HEM-TD)

The impact of the Corona effect on the lightning response of transmission lines and respective backflashover probability were assessed by computational simulation, using the Time Domain Hybrid Electromagnetic Model and two different Corona models, the traditional increased-radius model by EPRI and the modified-electric -parameters model by Lee. The mechanisms influencing lightning overvoltages under Corona effect were clari-fied. Overvoltage waves across insulators of a 138 kV and a 230 kV transmission lines due to direct lightning strikes to the tower and to the shield wire(s) at midspan were calculated for different tower-footing conditions and the Disruptive Effect Method was applied for quantifying how the critical current was affected by the Corona effect. According to the Lee's model, this effect would significantly decrease the backflashover probability for strikes to the tower and to shield wires, reducing the outage rates of these transmission lines in about 30% and 45%, respectively, for a typical distribution of tower-footing impedances.