Approximate Formulas for Terminal Voltages on the Grounding Conductor

This paper proposes approximate formulas to estimate voltages on a horizontal grounding conductor. The formulas are derived in the time domain using Bewley´s lattice diagram method based on transmission and reflection coefficients. The expression of the approximate formulas is simple, and the formulas are useful for engineers to carry out grounding system design for lightning protection. This paper concerns a voltage source with step waveform. A formula for an arbitrary voltage waveform can be calculated by using Duhamel´s integral. Surge characteristics of voltages and an effective length of a grounding conductor are discussed using the proposed formulas. It is easy to understand experimental and simulation results of a grounding system using the approximate formulas.