Experimental investigation of high frequency and transient performance of earth rod systems

• Tests were carried out on rod electrodes of different lengths under dc, variable frequency ac and impulse energization.
• The effect of enhancing the rod electrodes with ‘cross’ and ‘star’ configuration horizontal electrodes was examined.
• Such enhancements to the rod electrode demonstrate that significant benefit is obtained across the entire frequency spectrum and also under impulse energization.
• Computer simulations of the electrodes show close agreement with measured values.

The high-frequency performance of vertical earth rods is important for designing earthing systems and lightning protection systems. In this work, experimental investigations on the high-frequency and impulse response of vertical earth rods with horizontal electrode enhancements are described. The rod electrode systems are installed at the Cardiff University outdoor earthing test facility and variable frequency tests were carried over the range 50 Hz–10 MHz. In addition, a low voltage impulse generator was used to inject impulse current of variable magnitude and shape into the electrode under test. The application of ‘4-point cross’ and ‘8-point star’ enhancements to single-rod electrodes have not only demonstrated the expected reduction of low frequency earth resistance but have also helped with a reduction in impedance at higher frequencies. Such enhancements may produce a greater overall benefit compared with extending the length of the rod only. Numerical simulations of the experimental setups agree quite well with test results over a low frequency range but more significant differences are seen at higher frequencies.