Systematic Comprehensive Diagnostics of Transmission Line Tower Earthing in Czech Republic

Brochure 749). Grounding parameters change over time (due to corrosion and tower foundation aging) and therefore require continuous monitoring. The quantification of grounding parameters at regular time intervals helps to estimate the remaining lifetime of overhead lines and optimize maintenance planning. Therefore, the Czech transmission system operator (TSO) has established internal technical standard for regular measurements of grounding parameters

(i.e. tower footing resistance, earth impedance, soil resistivity, and tower voltage to earth under normal operation conditions – VE) of all overhead line towers. The data of grounding parameters are obtained through on-site diagnostic measurements from more than 13,800 transmission line towers. The standard measurement period is 12 years; however, the period is reduced to 4 years for specific cases including towers with a high value of the footing resistance, towers located in places with frequent public presence etc. The first overall measurement campaign took place between 2020 and 2025, during which time a large amount of data was collected and stored in a technical database. These data provide information on the technical condition and functionality of tower foundations using comprehensive statistical evaluation. Basic descriptive statistical parameters are used, and correlation coefficients serve to determine the relationship between the grounding parameters themselves and to link grounding parameters with geographical and geological conditions. The most important correlation is between soil resistivity and tower footing resistance. Each power line can thus be characterized by a specific

“fingerprint” based on the relationship between soil resistivity and tower footing resistance.

This fingerprint is graphically expressed using two-dimensional figures, such as a scatter map of grounding, and mathematically described using regression analysis parameters, such as linear and nonlinear regression coefficients and the coefficient of determination (R-squared, R2). The paper deals with a summary of the use of measured data, in particular statistical outputs derived from a large dataset on transmission line tower grounding.