On the Wave Impedance for Power Lines

Expressions for the wave impedance of traveling wave current on a single wire power line for frequencies in the 100 Hz-l MHz range are derived. The wave impedance (Zz) is defined as the ratio of the vertical electric and the horizontal magnetic fields. A simple expression for Zz is given which is accurate to within 10%. A favorable comparison is made with experimental results. It is shown that Zz is usually significantly larger than the free space wave impedance (120¿). However, for measurements in the AM broadcast band, 10-20 meters from the wire, 120¿is a fair approximation to the wave impedance.