ENGINEERING PERSPECTIVES ON SOIL PROPERTIES IMPORTANT TO THE DESIGN AND PERFORMANCE OF EARTH ELECTRODES AT LOW AND HIGH FREQUENCY

Earth electrode design for high voltage substations and tower foot electrodes for overhead power line towers are driven from both safety and lightning performance points of view. Conventionally, data obtained from tower footing resistance measurements are used in the design of tower foot electrodes. This data is representative of the low frequency behaviour of the electrode typically encountered under 50 Hz fault conditions. More modern equipment, however, allows for the measurement of the tower foot impedance, representative of the high frequency behaviour of the electrode typically encountered under lightning conditions. With only tower footing resistance requirements historically embedded in line design earthing specifications, the line design engineer now faces the dilemma whether to…