Measurements for Qualifying the Lightning Response of Tower-Footing Electrodes of Transmission Lines

The lightning response of tower-footing electrodes of transmission lines can be estimated from concise parameters, namely the low-frequency and 25-kHz grounding resistances (R
_T
and R
_25kHz
) and the impulse grounding impedance Z
_P
. Methodologies for measurement of these parameters are addressed and their constraints are discussed. Experimental and simulated results were developed for assessing the consistency of these methodologies and the errors of the results they provide. Measurements obtained in real transmission lines confirm the theoretical expectation that R
_T
> R
_25kHz
> Z
_P
. Procedures for reliable measurement of the three parameters are explained. The use of 25-kHz instruments is strongly disseminated, as it does not require disconnecting shield wires. As instruments dedicated to the measurement of the impulse grounding impedance are becoming available, the direct measurement of ZP is expected to become the most common practice in the near future, due to the superior results it provides for qualifying the lightning response of tower-footing electrodes.