Experimental investigation of the impulse characteristics of practical ground electrode systems

In this work, the results of an experimental study of the impulse characteristic of practical ground electrodes consisting of horizontal conductors of various lengths, a grounding grid and full-scale tower footings are reported. These electrodes are installed at an outdoor test site having nonuniform soil, with equipment facilities for generating low- and high-magnitude impulse currents. The tests on the horizontal electrode were used to determine the effective length and the voltage and current distribution over the electrode length. For the grounding grid, the impulse resistance was determined and compared with the low-frequency resistance. The tests on the tower footings were intended to determine impulse resistance and demonstrate its non-linear variations with current magnitude. Isolated tower footings showed large reductions in impulse resistance due to soil ionisation compared with the full tower base, which showed only a small reduction. Computer simulations of the test electrodes using the electromagnetic field method showed good agreement with the measured results.