Backflashover Analysis of Transmission Lines Considering Variation of Soil Electrical Parameters with Frequency and Water Content

This paper investigates the lightning performance of three soil models considering their electrical parameters dependent on the frequency and water content. These soil models are Smith-Longmire, Scott, and Messier models. First, the harmonic grounding impedance of a 30-m rod buried in stratified soil is analyzed using the full-wave electromagnetic software Altair FEKO for a frequency range of 100 Hz to 10MHz. Then, their impact on the ground potential rise (GPR) waveforms for different lightning currents is assessed. Finally, a backflashover analysis is carried out for a transmission line on stratified soil. Results indicated a notable variation in the harmonic impedance above 1 MHz. This variation has a pronounced impact on the GPR waveforms for different currents, especially in the peak values when the three soil models are used compared with the frequency-constant soil model. Finally, transient analysis for the transmission line demonstrates that depending on the lightning current waveform and soil model, a backflashover occurs and may lead to an outage in the power system.