Experimental investigation on high-frequency and transient performance of a vertical earth electrode

The high-frequency performance of vertical earth rods is important for designing earthing systems and lightning protection systems. In this work, an experimental investigation on the high-frequency and impulse response of vertical earth rods is described. The rods of different lengths are installed at the Cardiff University outdoor earthing test facility. The tests were carried out for a range of frequencies between 50 Hz and 10 MHz using variable-frequency AC current sources. A low voltage impulse generator is used to inject impulse current of variable magnitude and shape into the electrode under test. The results show that for a short rod electrode, the earth impedance show a fall at frequencies higher than about 100 kHz. For the longer rod electrode, the fall in impedance starts at a higher frequency of about 1 MHz, followed by an increase in impedance at 3 MHz and above. The experimental results are compared with computation results using EMTP.