Transient resistivity measurements on 345-kV transmission towers

A transient injection method was used to simultaneously measure the time variation of footing impedance and soil resistivity on a series of 345-kV steel pole towers. For each tower, the ratio of transient resistivity to impedance, giving an effective tower perimeter, reached an asymptote by 500 ns. The soil resistivity estimates were log-normally distributed with natural log standard deviation of 0.63 for this locale. These time-evolved resistivity values are compared with observations based on frequency domain modeling.