Investigation of carbon fillers modified electrically conductive concrete as grounding electrodes for transmission towers: Computational model and case study

The carbon fiber-carbon black composite electrically conductive concrete was employed as new grounding material, which has good grounding performance. As the mixing amounts of carbon fiber and carbon black were both 0.1%, the resistivity of concrete tended to be stable around 530 Ω·cm with the age growth. The resistivity fluctuation of the conductive concrete at different temperature from −40 °C to 50 °C was less than 5%. The compressive strength and flexural strength of the conductive concrete were 35.8 MPa and 6.3 MPa at 28 days, respectively. The rod grounding electrodes were made of the electrically conductive concrete and were laid in parallel on the bottom and side walls of the foundation ditch of transmission towers to build new type of stereo grounding grid. Considering parallel grounding effect, the computational model of grounding resistance of conductive concrete stereo grounding was established based on the calculation of grounding resistance of the metal electrodes. The ranges of grounding resistance amplification factor ψ and the utilization factor η were confirmed through experimental investigation. The laying scheme of electrically conductive concrete rod grounding electrodes in different soil types could be designed according to the model. Eventually, the validity of the model was verified through testing the grounding effect of the stereo grounding grid in practical grounding engineering of transmission towers.