Abstract
The horizontal electric field at the ground surface in the vicinity of structures hit by lightning flashes is relevant to the safety of human beings and livestock; it determines the touch and step voltages around the structure. This paper uses an approximate analytical formula for calculating the horizontal electric field, which was adapted to take into account the effect of the structure foundation. The input for the calculation is the current waveform at the base of the structure, and the results agree well with those obtained by other authors using the finite-difference time-domain (FDTD) method. The approximate formula is applied to calculate touch and step voltages in the vicinity of a structure and the results show that the use of the direct current (DC) approximation to calculate touch and step voltages may lead to significant errors; especially for fast-rising currents and relatively good-conducting soils. This means that DC approximation could be used for positive first stroke and poor-conducting ground (ρ ≥ 1000 Ω∙m), but cannot be used for subsequent strokes and good-conducting ground (ρ ≤ 100 Ω∙m). Moreover, step voltages differ more from the DC approximation than the touch voltages.
Highlights
The horizontal electric field at the ground surface in the vicinity of structures hit by lightning flashes is relevant to the safety of human beings and livestock, as it determines the touch and step voltages around the structure
Its application to the case of a structure hit by lightning faces two problems: (i) The expression was developed considering that the return stroke current starts at ground level, whereas in this case it starts at the top of the structure; (ii) The late time response was based on the assumption of symmetric current distribution from the bottom of the lightning channel, whereas in this case it is likely to be influenced by the structure foundation and its associated grounding system
The formula proposed by Barbosa and Paulino, complemented to take into account the effect of the structure foundation, was used to calculate the horizontal electric field at the ground surface in the vicinity of a structure hit by lightning
Summary
The horizontal electric field at the ground surface in the vicinity of structures hit by lightning flashes is relevant to the safety of human beings and livestock, as it determines the touch and step voltages around the structure. Its application to the case of a structure hit by lightning faces two problems: (i) The expression was developed considering that the return stroke current starts at ground level, whereas in this case it starts at the top of the structure; (ii) The late time response was based on the assumption of symmetric current distribution from the bottom of the lightning channel, whereas in this case it is likely to be influenced by the structure foundation and its associated grounding system This paper investigates these issues and proposes an amendment to the original expression in order to take into account the effect of the structure foundation in the nearby horizontal electric field.
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