Monitoring of earthing system performanceat transmission line tower bases

摘要

The performance of earthing systems atrntransmission line tower bases has become important inrnrecent years. The main issue concerns electrical safetyrnaround the base of the tower under power frequencyrnfault or lightning conditions. Such events present arnsafety hazard, described in terms of step and touchrnpotentials. Previous published work has focussedrnmainly on the performance of substation earthingrnsystems. In this work, the performance of an operationalrn275kV tower base has been monitored over a period ofrntwo years. A series of a.c. and d.c. fall-of-potentialrnmeasurements have been carried out to determine thernearth impedance of the structure. Touch voltages havernalso been measured in the vicinity of the tower base. Inrnaddition, the soil resistivity in the locality was measuredrnperiodically and the effect of seasonal changes werernrecorded. This allowed the variation in tower earthrnimpedance to be correlated with measured soilrnresistivity changes.