Traditional and alternative grounding system's impedance and resistance measurements of a 138 kV transmission line tower

Abstract

One of the main causes of outages in transmission lines is lightning. To mitigate this occurrence, grounding electrodes are used at the base of the towers that make up the transmission lines. Since lightning is a phenomenon with components of low and relatively high-frequency energy (approximately up to 2 MHz), there is a certain complexity in accurately characterizing grounding systems. The primary parameter used to model a grounding system is the grounding impedance, which can be obtained through measurement. This paper presents measurements conducted on a 138 kV transmission line's traditional and alternative grounding system. The measured traditional grounding system consists of two horizontally buried copper grounding conductors and the alternative system comprises an electrode with four conductors encapsulated in concrete and buried vertically. The measurements were carried out using a 25 kHz earth resistance meter and impulse generators with waveform shapes of 1.2/50 μs, 1/70 μs, and 8/70 μs. Different measurement configurations are employed. The obtained measurements are compared with similar systems found in the literature, and the contributions of the concrete electrode to the grounding system are discussed.