FREQUENCY-DEPENDENT IMPEDANCE OF VERTICAL CONDUCTORS AND A MULTICONDUCTOR TOWER MODEL

The paper proposes a frequency-dependent characteristic impedance of a vertical multiconductor system above an imperfectly conducting earth and a multiconductor multistair model with a number of legs between to wer arms to represent an actual tower for a lightning surge analysis. Surge impedances calculated by the proposed formula and model show a s atisfactory accuracy compared with a number of experimental and field test results of vertical conductors and actual towers. It is observed that an imperfectly conducting earth causes no significant effect on t he characteristic impedance of a tower, and the wave propagation veloc ity is nearly the light velocity in free space in the entire frequency range.