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

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 to 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 rods 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. Computer 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.