Alternative study to reduce backflashovers using tower-footing grounding systems with multiple inclined rods

Abstract

This paper investigates the influence of the inclination angle on the harmonic grounding impedance (HGI) of three arrangements with multiple rods. Then, Ground Potential Rise (GPR) and the lightning performance (backflashover prediction) on transmission towers using these grounding systems are studied. A full-wave electromagnetic software FEKO using Method of Moments (MoM) is utilized to compute the HGI in a frequency range of 100 Hz to 10 MHz, assuming the soil with low-frequency resistivity of 1,000 Ω m and modeled considering the frequency effect on the ground parameters. The analysis is carried out for grounding systems of multiple rods composed of 2, 3, and 4 inclined electrodes considering inclination angles of 0°, 15°, 30°, 45° and 60°. The transient GPR developed for the first and subsequent return strokes are evaluated. The calculated HGI showed expressive differences for each topology and also for various inclination angles. Consequently, transient GPR waveforms present expressive mitigation for each grounding system whose difference can be obtained only by varying the inclination angle of the rods. Finally, the backflashover probability is reduced when these arrangements with multiple rods combined with highly inclined electrodes are used as tower-footing grounding systems, improving the lightning performance of power systems. • Harmonic impedance of inclined rods is computed for frequency-dependent soil. • GPR is significantly influenced for arrangements with multiple electrodes and angle. • Backflashover is reduced when multiple rods are used as a grounding system. • These arrangements are an alternative for lines located in limited urban areas.