Transient ground impedance measurement using a very short current lead

This work describes a system for the measurement of the transient impedance of ground electrodes using a portable impulse generator and a new measuring arrangement. The innovation is the use of a very short current reaction lead, which is possible due to the use of transmission line with very low propagation velocity (3% of the velocity of light). The methodology for obtaining the transient impedance from the measurements is discussed and validated. The experimental results regarding transient impedance measurements for two ground electrodes arrangements are presented. The first arrangement consists of two vertical rods and the second one is an actual 138 kV transmission line tower leg, composed by a vertical electrode in parallel with a horizontal wire. A comparison with calculated values for both cases is also presented.